This paper discusses the application of acousto-ultrasonic (AU) techniques for the evaluation of the strength and degradation of an adhesive bond of a composite repair patch. Both symmetric and asymmetric composite patch specimens were studied. Asymmetric specimens were divided into four groups with different bonding conditions. Results indicate that the AU parameters (AUP and correlation factor) are correlated with the interfacial bond strength. There is almost a linear relation between them, the higher the AU parameter, the higher the bond strength. For the symmetric specimen, the inter-facial shear load-strain property was also obtained during destructive tests. The curve indicates typically three stages of inter-facial deformation, initial linear deformation, non-linear deformation and a final linear deformation with reduced slope. Adhesive yielding causes non-linear behavior. It was found that there is a good correlation between AU parameters and the length of yield zone. Both symmetric and asymmetric specimens were tested under tension-tension fatigue. For asymmetric specimens, AU waveforms were recorded and ultrasonic C-Scanning was also used to check bond integrity at different numbers of fatigue cycles, Results show good correlation between the AU parameters and the inter-facial damage. KEY WORDS: Acousto-ultrasonics, composite repair patch, bond joint

Authors: Shiguo Rao and Isaac M. Daniel Robert McCormick School of Engineering and Applied Science Northwestern University, Evanston, IL 60208

Conference: 31st ISTC - Chicago IL - Oct 26-30 / 1999

SKU/Code: 31T-03

Pages: 12

In structural design there are practical cases where the compressive stress on a plate varies parabolically. The objectives of this study are to furnish a systematic procedure for investigating stability problem of anisotropic rectangular plates, and to provide analysis results for some typical buckling problems of anisotropic plates. A close-form solution for buckling analysis is obtained based on classical plate theory and Rayleigh-Ritz method. It is found that the effect of material anisotropy and geometry of plates on buckling load is coupled. The order of magnitude of that effect is obtained. The laminated plates of AS4 graphite fibers and 3501-6 epoxy resin, [O/~~Js, under two loading conditions are analyzed. These loading conditions are (a) a load that varies parabolically in the longitudinal direction of the plate and (b) a load that varies parabolically in the transverse direction of the plate. The buckling loads and modes with respect to different values of 0 and different aspect ratios of the plate are presented. The analysis results presented in this study may be used for engineering design. KEY WORDS: Buckling, Material Anisotropy, Analysis

Authors: Hurang Hu*, Ayo Abatan, and Ashraf Badir Department of Engineering, Clark Atlanta University, Atlanta, GA 303 14

Conference: 31st ISTC - Chicago IL - Oct 26-30 / 1999

SKU/Code: 31T-20

Pages: 12

LaRCTM MPEI-5 (Langley Research Center Tkf Modified Phenylcthynyl lrnide -5), a _ phenylethynyl containing aromatic polyimide which is a mixture of linear, branched and star shaped phenylethynyl containing imides, was evaluated as a matrix for high performance composites. Three molecular weight versions of the poly(amide acid) solution of LaRCTM MPEI-5 (theoretical number average molecular weights of 5500 g/mole, 7500 g/mole, and 9500 g/mole) in N-methypyrrolidinone were synthesized at 35% solids. Unidirectional prepreg was fabricated from these solutions and Hercules IM7 carbon fiber utilizing NASA-Langley’s multipurpose prepreg machine. A composite molding cycle was developed which yielded well consolidated void-free laminates. Composite mechanical properties such as short beam shear strength, longitudinal and transverse flexural strength and flexural modulus, longitudinal tensile strength and notched and un-notched compression strengths were measured at room temperature (RT) and elevated temperatures. These mechanical properties were compared to determine the effect of molecular weight on the composite laminates. These properties were also compared to those of a similar material, LaRCTM MPEI-1, and to the linear, phenylethynyl containing polyimide, LaRCTM PET15. KEY WORDS: Composites, Polyimides, Prepreg, and Processing

Authors: Roberto J. Cano Jill E. Bennett2 Harry L. Belvin Brian J. Jensen NASA Langley Research Center Hampton, Virginia 23681-0001

Conference: 31st ISTC - Chicago IL - Oct 26-30 / 1999

SKU/Code: 31T-21

Pages: 14

Reusable launch vehicles (RLV’s) require lightweight durable structure to meet stringent mass fraction requirements and to achieve reduced operating costs. Titanium honeycomb, with its high specific strength and stiffness and inherent insulative properties is a viable option for RLV liquid hydrogen (LH2) propellant tanks. In order to evaluate the potential use of titanium honeycomb, room temperature flat wise tension (FWT) tests were conducted on conditioned and unconditioned specimens with two types of core-to-facesheet bonding methods: liquid interface diffusion (LID) bonding and aluminum brazing. Conditioned specimens were thermally cycled from -253°C to 315°C for 100 cycles representing one life time of a RLV LH2 main propellant tank. Results indicated that only a slight reduction (~7%) in FWT strength occurred due to thermal conditioning for both LID-bonded and Al- brazed specimens. Microscopic examination of conditioned specimen bond lines did not indicate appreciable thermal-induced microcracking. KEY WORDS: Titanium, Honeycomb/Sandwich, Aluminum Brazing, LID Bonding, Structure, Thermal Mechanical Cycling, Reusable Launch Vehicle

Authors: Patrick B. Stickler, P.E. Boeing Phantom Works, Structures Technology Kent, Washington 98 124

Conference: 31st ISTC - Chicago IL - Oct 26-30 / 1999

SKU/Code: 31T-24

Pages: 8

In this paper, fabrication of bio-decomposable composites using natural fibers and their strength properties are presented. Bio-decomposable composites (NfBC: Natural Fiber Bio-decompos- able Composites) were fabricated using bamboo and jute fibers in conjunction with biodegrad- able thermoplastics. Bamboo fiber reinforced plastics (BfRP) and jute fiber reinforced plastics (JfRP) were fabricated by hot pressing. Their tensile and bending strengths were examined as well as the tensile strength of bamboo and jute fibers. The experimental results showed that the specific strength of well prepared by bamboo fibers was as high as that of glass fibers, which was promising that the bamboo fibers were applicable as the reinforcement of biodegradable plastics. It was also found that the tensile and bending strengths of BfRP and JRP composites increased about 200-300% of the matrix, due to inclusion of bamboo and jute fibers, respectively. The SEM (scanning electron microscope) photographs of failed surface of specimens showed that the resin impregnation into reinforcements was poor, for the bamboo and jute fiber composites. How- ever, the BfRP have a potential in strength to be used as materials for semi-structural or even for structural elements supporting relatively severe loads. KEY WORDS : Bio-decomposable Composites, Natural Fibers, Strength Properties

Authors: Jianye JIANG, Kazuya OKUBO, Toru FUJI1 Department of Mechanical Engineering and Systems, Doshisha University Kyo-tanabe, 6 1 O-032 1, Japan

Conference: 31st ISTC - Chicago IL - Oct 26-30 / 1999

SKU/Code: 31T-26

Pages: 12

This study primarily investigates the high strain rate impact response of Vinyl Ester resin (VE350) system and their composites made with S2-Glass fiber reinforcement using compression Split Hopkinson Pressure Bar (SHPB). Three different thicknesses of 3.175, 6.35, 12.7 mm were studied at different strain rates. The laminates were fabricated using affordable vacuum assisted resin transfer molding (VARTM). Laminates of thickness 12.7 mm fabricated using three different resin systems (VE350, Si-AN and Epon) were also investigated to study the influence of the resin system at different strain rates. In the case of neat resin samples, the dynamic modulus, which is the slope of rising portion of the stress- strain plot, increases with the increase in the thickness. This is attributed to the higher cross-linking of polymer chains, which is proportional to the thickness. For S2-glass/Vinyl Ester samples the dynamic modulus as well as the peak stress increase with the strain rate as well as the thickness. However, once the failure is initiated, the peak stress decreases with further increase in the strain rate. Laminates with Epon resin system exhibit lower peak stress and dynamic modulus a compared to those with Vinyl Ester and Si-An resin systems, while the laminates with Si-An resin system were found to be brittle. KEY WORDS: Vacuum Assisted Resin Transfer Molding (VARTM), High Strain Rate Testing, Dynamic Modulus.

Authors: UKVaidya, N.Jadhav, M.V.Hosur, A.Haque, H.Mahfuz, S. Jeelani Center for Advanced Materials Tuskegee University, Tuskegee, AL 36088

Conference: 31st ISTC - Chicago IL - Oct 26-30 / 1999

SKU/Code: 31T-30

Pages: 12

It is well known that adhesive joints have their optimum strength for thin bondline thicknesses (0.1 - 0.5 mm). The most common analytical methods used for adhesive joint analysis show improved strength at increasing bondline thicknesses. This erroneous trend in prediction is investigated in this article. It is found that the through the thickness stress distribution is the main cause of the errors. The stresses, both peel and shear at the interface between adhesive and adherend are found to increase, after an initial decrease in the low bondline thickness range, with increasing bondline thickness while the average stresses decrease. This trend explains the trends found in experiments. Further, as experimental results have shown, a theoretical optimum adhesive thickness is found. KEY WORDS: interface stresses, stress singularity, peel stresses

Authors: D.M. Gleich, M.J.L. van Tooren and A. Beukers Delft University of Technology, Faculty of Aerospace Engineering, Kluyverweg 3,2629 HS Delft, The Netherlands

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-137

Pages: 13

Thermoplastic composites based on commodity polymers like polypropylene (PP) are being used in an ever-expanding range of applications, many of which require the addition of a compatibilizer to ensure good interfacial properties. It is important to understand the effects of such additives on processing and performance. In this work, the non-isothermal crystallization kinetics of different mixtures of acrylic-acid-grafted polypropylene (AAgPP) and PP has been studied at different cooling rates by means of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and polarized light optical microscopy (PLOM). FTIR detected the existence of poly(acrylic acid) (PAA), a by-product of the grafting process, in the AAgPP while PLOM confirmed the nucleation role of PAA. To minimize degradation of AAgPP at high temperature, especially for low cooling rates, antioxidant was used. It was observed by PLOM that the antioxidant crystallizes earlier than the polymers and then plays a role as nucleating agent for the crystallization of PP and AAgPP. DSC also confirmed the higher crystallization temperature and degree of crystallinity for samples containing antioxidant. Ozawa’s equation and Chee’s approach have been used to determine the Avrami exponent, n, which is related to the primary crystallization regime. The results indicate good agreement between the two approaches. No significant differences in the tensile strength were observed among the blend mixtures, whereas the modulus showed some variation. The AAgPPs show higher water uptake and diffusion coefficients compared to the raw PP. KEY WORDS: Acrylic Acid, Grafted Polypropylene, Crystallization, Diffusion

Authors: M.-T. Ton-That, K. C. Cole, and J. Denault Industrial Materials Institute, National Research Council Canada 75 De Mortagne Blvd., Boucherville, QC, Canada J4B 6Y4

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-028

Pages: 11

In order to understand membrane transport and thereby develop suitable membranes for protection and separation, there are a few characteristics of the membrane and the diffusing constituents that must be known. These include the molecular states of the diffusing components, their diffusion coefficients, permeabilities and the membrane selectivity. In general, the fundamental physical property required to design and optimize polymers used as barrier and membranes is the mutual diffusion coefficient. The FT-IR-ATR (Fourier Transform Infrared Attenuated Total Reflectance) technique offers the advantage of allowing polymer-penetrant interactions to be identified as well as allowing the transport two or more diffusing species to be monitored. The basic FT-IR-ATR Fickian diffusion model developed by Barbari and Fieldson was applied to the resultant data. In this paper, FTIR-ATR spectroscopy was used to measure the effective diffusion coefficients of acetonitrile in an aliphatic polyurethane and sulfonated triblock co-polymer films. For the polyurethane elastomer, the effect of varying isomer content at a fixed hard segment content on the diffusion of acetonitrile was examined with FTIR-ATR spectroscopy. The results show a clear dependence on the chemical structure of the hard segment. In the case of the sulfonated triblock co-polymer, the increasing the sulfonation level leads to the ability of the membrane to transport water and other polar molecules through the film. KEY WORDS: Elastomers, FT-IR, Diffusion

Authors: James M. Sloan, D. Crawford, E. Napadensky and N. Beck Tan U.S. Army Research Laboratory Weapons & Materials Research Directorate Polymers Research Branch APG, MD 21005

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-127

Pages: 11

A 3D finite element model of human spine and its mechanical behaviour have been simulated. In particular, the mechanical behaviour of the last three lumbar vertebras with intervertebral discs (L3-L5 system) has been pointed out. The performance of a new class of prosthetic material used in intervertebral disc sobstituition treatment has been investigated. This material is a composite made by a matrix of PHEMA poly(2-hydroxyethyl methacrylate) and PCL poly(caprolactone) reinforced with PET poly(ethyl terephthalate) fibers. To perform the comparative analysis, a 3D nonlinear Finite Element analysis has been implemented. The stress-strain curve of a natural disc and of PHEMA-PCT-PET have been experimentally characterized to obtain the material properties used in the simulations. The results of simulations show that, although PHEMA-PCT-PET is stiffer than human disc material, the global behaviour of the two model, in terms of maximum vertical displacement and von Mises stress distribution, is similar. The stresses induced in the discs are higher than the prosthesis but the differences are localized in cortical region. The different stress distribution induced in the L4 vertebral shows that the vertebral body, after the intervetebral disc substitution, is less stressed of about 19%. KEY WORDS: Biomaterials, Finite Element Analysis, Mechanical properties

Authors: Marco Bellucci, Luigi Di Palma, Luigi Ambrosio, Antonio Apicella Department of Material Engineering and Production University “Federico II”, Naples-Italy

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-118

Pages: 8

Construction of large superconducting magnets coils for fusion reactor applications includes resin transfer molding impregnation ofthe composite electrical insulation. This composite insulation acts as the primary electrical isolation between the individual magnet turns, and bonds the coils together to form a monolithic structure. Resin processing characteristics, radiation resistance, and cryogenic mechanical properties arc the primary issues for selection of these materials. The epoxy matrix must exhibit low viscosity and long working life for impregnation of these large structures. Service conditions include neutron and gamma radiation at cryogenic temperature. The processing and properties of a series of epoxy resins and hardeners were screened, and one formulation selected for refinement. This formulation was optimized by addition of radiation resistant modifiers. Enhancement of all processing, mechanical properties, and radiation performance was demonstrated. KEY WORDS: Resin Transfer Molding (RTM), Insulation, Fusion, Cryogenic

Authors: James B. Schutz Eltron Research, Inc Boulder CO 80301

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-040

Pages: 15

Elastomers play a role in the development of composite integral armor for future Army vehicle systems. Ethylene-propylene diene (EPDM) rubber, conforming to MIL-G-22050, was chosen as the primary candidate to enhance the anti-ballistic properties of the integral armor. The design of these vehicle systems must be capable of enduring temperatures between –40.0°C and 71.1°C. To understand the temperature effects on this rubber, quasi-static and dynamic loading conditions were investigated at strain rates of approximately 1.7e10-2 s-1 and 180 s-1, respectively. Although the elastomer is conformed to the military specifications, three different grades of hardness are stated under MIL-G-22050. KEY WORDS: ethylene-propylene diene (EPDM), elastomer, dynamic properties

Authors: Paul Moy, Gumersindo Rodriguez, and Linda Ghiorse U.S. Army Research Laboratory Weapons and Materials Research Directorate Aberdeen Proving Ground, MD 21005-5069

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-053

Pages: 9

Significant opportunities exist for the processing of polymers (homopolymers and blends) using electric fields. Specific attention is given here to electrospinning, but we note that electroaerosol formation and field-modulated film casting represent additional processing options. Of particular interest is the ability to generate polymer fibers of sub-micron dimensions using electrospinning, down to about 0.05 microns (50 nm), a size range that has been traditionally difficult to access. In our work, poly(lactic-co-glycolic acid), PLA/PGA, poly(lactic acid) PLA, and poly(ethylene-co-vinylacetate) (PEVA) have been deposited from solutions in methylene chloride or chloroform by electrospraying or electrospinning to afford morphologically tailored materials for tissue engineering and related applications. Low solution concentrations tend to favor electrostatic spraying ('electro-aerosolization') while higher concentrations lead to spinning on fibrous mats. Preliminary observations of muscle cell growth on PLA electrospun mats are reported. KEY WORDS: Biomaterials, Applications-Medical, Fibers

Authors: Joel D. Stitzel,1 Gary L. Bowlin,1 Kevin Mansfield,1 Gary E. Wnek2, David G. Simpson3 Departments of Biomedical Engineering,1 Chemical Engineering,2 and Anatomy3 Virginia Commonwealth University Richmond, Virginia 23284

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-076

Pages: 7

The use of mechanical fasteners is an efficient and accepted method for the attachment of necessary outfitting to traditional shipboard structures. As the use of polymeric composites for shipboard structures becomes more prevalent, however, an examination of the effectiveness of the use of mechanical fasteners to attach outfitting to the new composite structures is necessitated. In this study, an experimental examination of the use of self-tapping screws for mechanical attachments to polymeric composite materials has been examined. The major focus of the study was the use of self-tapping screws for mechanical attachments to SCRIMP’ed FRP sandwich panels with a balsa core. The FRP laminates of these sandwich panels were reinforced with woven glass fabric in ply layup of multiples of 0/90/45. Evaluation of the self-tapping screw attachments was conducted under static uniaxial loading, static shear loading, and combined shear and axial static loading. Discussion of both failure loads and failure mechanisms seen for the self-tapping screw attachments is presented. KEY WORDS: Sandwich Composites, Glass Laminates, Mechanical Fasteners

Authors: Ellen Lackey, James G. Vaughan, and Michael Frazier Department of Mechanical Engineering The University of Mississippi University, MS 38677

Conference: 32nd ISTC - Boston MA - Nov 5-9 / 2000

SKU/Code: 32ndT-035

Pages: 14

Authors: M. V. Kireytsev, V. L. Baser, M. Istomin, National Academy of Sciences of Belarus

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-079

Pages: 13

This paper describes the development of a low VOC, water-borne primer, 3M Scotch- Weldä EC-3963, that is designed for 250°F service structural adhesive bonding. The effect of resin and curing agents on primer performance was discussed. Due to the interdependence of multiple components on the final performance, neural networks analysis approach was adopted. This approach accelerated the development process. A primer formula was developed to meet the major critical aerospace adhesive structural bonding requirements. Such performance includes high primer thickness tolerance for metal-to-metal peel, and low primer thickness threshold for MEK resistance. The primer also delivers good crack resistance after being exposed to 100% humidity and 140°F condition.

Authors: Yong K. Wu*, Jim A. Handy and Clarke J. Hall 3M Aerospace Labs, 3M Center, Maplewood, MN 55144

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-113

Pages: 1

carbon fibre fabrics, and some typical results are described. Examples of numerical simulation of forming processes using the PAM-FORM modeling software are given. A short discussion of parts that have been formed using double diaphragm forming is included.

The Air Force requires development of environmentally compliant aircraft coating systems that perform adequately in terms of corrosion protection. Current Air Force corrosion inhibitor paint chemistry relies heavily on the use of Cr(VI) compounds in the form of strontium or barium chromate, which are incorporated into both the surface pretreatment and the primers. These corrosion inhibitor systems are very effective, but are known carcinogens and therefore must be eliminated. To address this problem, sol-gel based surface treatments are being investigated as a potential replacement for the current chromate-based approach. Surface modifications based on the conventional epoxy-zirconate sol-gel and the newly developed self-assembled nanophase particle (SNAP) silicon sol-gel coatings have been investigated. The formation of SNAP sol-gel relies on aqueous solution processes to generate nanoscale particles with an inorganic core and an organic exterior. SNAP coatings provide functionality for bonding to appropriate substrates and tailorable chemistry for interaction with subsequent polymer layers. Adhesion and barrier properties of the SNAP sol-gel surface treatment have been compared to the corrosion protection afforded by conventional coating systems. It has been demonstrated in a 2000 hr salt spray test that coating systems with SNAP surface treatment perform as well as systems with Alodine™ pretreatment and a chromated primer. Superior adhesion and corrosion protection characteristics make SNAP surface treatment a promising environmentally benign alternative to chromate pretreatments. 1

Authors: N.N. Voevodin1, V.N. Balbyshev2, A.J. Vreugdenhil1, J.A. Johnson, and M.S. Donley Air Force Research Laboratory, Materials & Manufacturing Directorate, Nonstructural Materials Branch, Bldg 654, Wright-Patterson Air Force Base, OH 45433-7750, USA 1 University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0168, USA 2 Universal Technology Corp., 1270 N. Fairfield Rd., Dayton, OH 45432-2600, USA

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-102

Pages: 15

EVALUATION OF MICROCRACKING IN AEROSPACE COMPOSITES EXPOSED TO THERMAL CYCLING: EFFECT OF COMPOSITE LAY-UP, LAMINATE THICKNESS AND THERMAL RAMP RATE

A series of carbon fiber epoxy based laminates with the same thickness were prepared to study the dependence of lay-up schedule on the microcracking performance of a commercial prepreg system. The laminates were exposed to a previously established thermal cycle for Kevlar materials and inspected for microcracking at fixed intervals of thermal cycles. This initial assessment was used to identify the lay-up resulting in the greatest level of microcracking that

was then used to evaluate the effect of thermal ramp rates and thickness of composite materials on the microcracking performance of the chosen prepreg system.

EXPERIMENTAL EXAMINATION OF FATIGUE PROPERTIES USING SELF TAPPING SCREWS FOR MECHANICAL ATTACHMENT TO SANDWICH COMPOSITE MATERIALS

An increase in the use of advanced composite materials to construct structures has highlighted the need for effective outfitting attachment methods. One such method uses mechanical fasteners, which provide an efficient means of mounting various types of equipment onto the composite structure. Data concerning the static and hygrothermal effects of a self- tapping screw/sandwich composite attachment method have been presented; however, fatigue data for this attachment method has not been discussed. Test specimens examined in this report consisted of a sandwich composite of two vinyl ester-glass laminate facesheets with a balsa core. Representative outfitting brackets were attached to the upper facesheet with four self- tapping screws. These brackets were then connected to a test fixture, and a hydraulically operated testing machine was used to subject the samples to fatigue loading conditions. The fatigue samples were subjected to a minimum of 1,000,000 cycles at various loads in an attempt to cause failure. If the sample did not exhibit a fatigue failure prior to completion of at least 1,000,000 cycles, the fatigue test was stopped and a load-displacement plot was generated using a uniaxial static test to determine the effects of fatigue on the sample’s properties. Results demonstrated a general decrease in panel stiffness throughout the test and that panels subjected to greater than 60% of the baseline uniaxial tension screw pullout load were more likely to fail than those at lower mean load levels.

Authors:  Michael Frazier NASA Marshall Space Flight Center, MSFC, AL James G. Vaughan and Ellen Lackey University of Mississippi, University, MS

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-094

Pages: 14

The Horsetail Creek Bridge (HCB), constructed in 1912 was rated 50 percent deficient in flexure and 94

percent deficient in shear, mainly due to the traffic loads increase. Analysis of the alternative retrofitting

designs indicated that glass FRP (GFRP) laminates would be most suitable for shear strengthening,

while carbon FRP (CFRP) laminates would be best for flexural capacity enhancement. Upon completion

of the bridge strengthening, four full size beams were constructed to simulate the retrofit of the bridge.

One of the beams served as a control, while the other three were reinforced with various configurations

of FRP composites. Third point bending tests were conducted. Load, deflection and strain data were

collected. All beams were instrumented with fiber optic sensor and conventional strain gauges. Results

revealed that addition of either GFRP or CFRP composites strengthening provided static capacity

increase of 45 percent compared to the control beam. The beam strengthened with CFRP for flexure and

GFRP for shear, which simulated the HCB cross beams after the retrofit, exhibited near 100 percent of

moment capacity increase. Post cracking stiffness of all beams was increase, primarily due to the

flexural CFRP laminates. The addition of GFRP for shear alone was sufficient to offset the lack of steel

stirrups in the actual bridge, allowing for a conventionally reinforced concrete beam with significant

shear deficiency to fail in flexural mode. The resulting ultimate deflections of the shear GFRP reinforced

beam were nearly twice those of the control beam. A design method for flexure and shear was proposed

before the onset of this experimental study and used on the HCB. The design procedure for flexure was

refined and allowed for predicting the response of the beam at any applied moment. The flexural design

procedure includes provisions for non-crushing failure modes, and was shown to be slightly

conservative using the design material properties.

Authors: Damian I. Kachlakev, Ph.D., P.E. Civil and Environmental Engineering Department California Polytechnic State University- San Luis Obispo

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-124

Pages: 16

Authors: Marco Bellucci, Luigi Di Palma, Antonio Apicella Department of Material Engineering and Production University —Federico II“, Naples-Italy

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-051

Pages: 11

PLASTIC EXTRUSIONS SUBJECTED TO CREEP TESTING AT ELEVATED TEMPERATURE

Experimental results on fiber micro buckling of continuous glass fiber reinforced hollow-cored recycled plastic extrusions under creep tests are introduced in the paper. The full size specimens with dimensions in 2.5 x 3.5 x 42 cubic inches were submerged in warm water at a temperature of 125 o F when they were under a four-point bending creep test. The results show that the micro buckling of the embedded glass fiber roving occurs along 90% the length of the specimen on the upper inner surface (compressive side) and mainly during the time between 5 and 100 hours from the initial loading moment. The micro buckling causes the steady state apparent flexural modulus of the composite drop faster, and it also causes the plastic matrix local crackling which subsequently leads to the structural failure of the composite. The stress level has little effect on the steady state creep rate. The results also show some evidence that the plastic matrix becomes more brittle when it is submerged in warm water for certain long time. From the results, it is indicated that the pattern or distribution of the micro buckling is significantly different from that of short-term four-point bending test for the same composite materials, for which the fiber micro buckling occurs locally only on the middle section of the specimen.

Authors: Zhiyin Zheng John J. Engblom Department of Mechanical and Aerospace Engineering Florida Institute of Technology Melbourne, FL 32901

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-033

Pages: 13

Vacuum assisted resin transfer molding (VARTM) is targeted as a replacement for many prepreg systems in the manufacture of advanced polymeric composites due to the lower manufacturing costs. The requisite of homogeneous and low viscosity resin systems in order to perform ambient injection limits the use of conventional toughening techniques in VARTM applications. Therefore, preformed particle modified tackifiers were developed for VARTM applications so as to create interlayer toughened composites. In the present study, four different tackifier materials were developed and sprayed onto 3K-70 plain weave carbon fabric. The tackified laminates showed increased fracture toughness with no significant change in thermal properties. * Author to whom correspondence should be addressed KEYWORDS:Vacuum assisted resin transfer molding (VARTM), tackifiers, high performance composites. 1. INTRODUCTION In the last decade more attention has been given to liquid molding manufacturing techniques for fiber reinforced polymer composites in an effort to replace traditional high-cost autoclave/prepreg systems. Vacuum assisted resin transfer molding (VARTM) is targeted as one of the most promising candidates. VARTM is a resin infusion process in which dry fiber reinforcements are sandwiched between a metal tool and a vacuum bag. The fiber preform is then infused using vacuum pressure with a low viscosity resin until the preform is completely saturated. This technique offers numerous cost advantages over prepreg systems such as lower equipment cost, room temperature and atmospheric pressure processing conditions, scalability to large complex shaped structures (1), and flexibility in the fiber reinforcement selection (2). The level of mechanical performance for VARTM processed composite systems has yet to reach that of prepreg systems. When this obstacle is overcome, the result will most likely be a more extensive utilization of VARTM processing. Improving toughness without significantly changing thermal properties in VARTM systems has been targeted in this study. The need of low viscosity resin systems to allow ambient infusion limits considerably the use of traditional toughening techniques (3). Stitched woven carbon fiber composites has shown excellent impact properties when processed with infusion techniques, but cracks were found in the stitching regions of the laminates due to heterogeneity and different thermal expansion properties of the fibrous preform structure (4, 5). Matrix modification using epoxy-rubber adducts has also been previously studied in order to improve the impact properties of VARTM systems (6), and significant increases in toughness without sacrificing processing characteristics were realized. Seferis and coworkers (7, 8, 9, 10) successfully demonstrated the effectiveness of interlayer toughening of RTM systems using preformed elastomeric particles with increases in mode I and mode II fracture toughness without significantly affecting the interlaminar shear strength. In this study, a tackifier toughening technique previously developed for RTM was implemented for VARTM systems. Traditionally a tackifier is a material that is applied to dry fabric reinforcement that allows the plies to retain their integrity during the manufacturing processes. However, adding preformed particles to the tackifier resin the interlaminar fracture toughness can be increased by modifying the interlaminar regions of the composite part. The goal of this study was to develop different toughened tackifier systems for VARTM applications, analyze the thermal and mechanical behavior of these systems in comparison with an untackified system, and to evaluate the compatibility of this toughening technique with the processing requirements of VARTM composites. 2. EXPERIMENTAL 2.1 Materials Four different tackifiers for spray application were developed in this study. Each tackifier system consisted of preformed elastomeric particles and an epoxy resin present in equal amounts by weight. The elastomeric particles contained in all four tackifiers were based on butadiene/acrilonitrile and carboxyl functionilized. The particle size averaged 50 µm with a glass transition temperature of œ6°C. The compositions of the four different epoxy-based tackifier resins are summarized in Table 1. The tackifiers were produced by dissolving the tackifier resin components in acetone with a low shear mixer for 10 minutes. The elastomeric particles were mixed separately in acetone before being added to the epoxy/acetone solution. The resulting tackifier/acetone solution was high shear mixed for 20 minutes. Extra acetone was then added to obtain a 10-15 wt.% solution of tackifier in order to improve its spraying characteristics. The tackifiers are labeled T1 through T4. The textile reinforcement used to manufacture the tackified VARTM panels was T300-3K/70 plain weave fabric from Toray Industries Inc. with a yarn density of 12.5/25mm and an areal weight of 198g/m2. An experimental epoxy based VARTM resin was used as the matrix for all composites. The resin has a viscosity of 800 cps and a potlife of 6 hours. 2.2 Tackifing Processing The 10-15 wt.% solution of tackifier in acetone was sprayed onto the fabric with a spray gun operated at 0.1-0.14 MPa (15-20 psi) using a 1.2 mm nozzle. The gun was not pointed perpendicularly to the fabric to avoid the formation of tackifier composition gradients along the panel. Instead, the gun was pointed parallel to the fabric so that the tackifier particles were uniformly deposited. Only one side of the fabric was sprayed, after which it was placed in a convection oven at 70°C for ten minutes to let the acetone evaporate. The spraying and drying cycles were repeated until the fabric was loaded with 4 wt.% tackifier. Table 1: General properties and compositions of VARTM tackifier systems used. T1 T2 T3 T4 Resin High molecular Low molecular Epoxy Thermoplastic characteristics weight DGEBA* weight DGEBA* combination modified epoxy and composition (wt.%) * Diglycidyl ether of bisphenol A 2.3 VARTM Laminate Processing Five laminates were manufactured, four tackified panels and a control panel with no tackifier. The laminates were fabricated from 16 plies of woven fabric and the experimental VARTM resin system. All the manufacturing conditions used were the same for all the laminates and the only variable was the tackifier type. A 50.8 mm (2 in) wide Kapton® tape crack initiator was applied to the middle ply to facilitate fracture toughness testing. Figure 1 shows the apparatus used for fabricating the VARTM panels. The fabric plies were placed onto an aluminum plate, covered with a peel ply and three layers of Teflon®distribution mesh. A vacuum bag was placed on top of the plies and secured to the aluminum tool with vacuum tape. The inlet and outlet for the resin infusion were made of a 9.525 mm (3/8 in) diameter Teflon® tube, which was connected to a Teflon® Helitube® to facilitate resin distribution across the fabric. The outlet tube was connected to a vacuum pump and 0.095 MPa (28 inHg) was pulled in the vacuum bag for about 20 minutes to consolidate the preform and evacuate air. Then the inlet line was opened to let the resin infuse. After the resin reached the outlet line, the inlet was shut to remove air bubbles from the laminate. The outlet line was then closed and the panel was put into a convection oven for the curing cycle. Panels were ramped at 2.78 °C/min (5 °F/min) to 80°C, held at this temperature for 7 hours, ramped at 1.11°C/min (2 °F/min) to 177°C, held at this temperature for 2 hours and then allowed to cool to room temperature in the oven. Figure 1: Top view of VARTM setup. 2.4 VARTM Laminate Analysis Each laminate was machined in order to obtain samples for thermal and mechanical testing. 2.4.1 Dynamic Mechanical Testing Dynamic mechanical analysis (DMA) experiments were performed on the VARTM laminates using a TA Instruments Inc. DMA 2980. The experiments were carried out in nitrogen with a heating rate of 5°C/min to 300°C, a frequency of 1Hz and amplitude of 50µm. For each experimental condition, two samples were cut, one close to the resin inlet and one close to the resin outlet in order to verify if any particle migration occurred. 2.4.2 Mode I fracture toughness Mode I interlaminar fracture toughness was measured using the double cantilever beam (DCB) method (11). For each laminate, six samples, 330.2 mm (13 in) long and 12.7 mm (0.5 in) wide were tested; a sharp crack tip was created before testing by pre-cracking the sample. The specimens were pulled apart at a rate of 25.4 mm/min (1 in/min). 2.4.3 Mode II fracture toughness Mode II interlaminar fracture toughness was also tested using the end notch flexure method (ENF). For each laminate, ten samples were used having the same dimensions as the ones used for Mode I tests. A three point bend apparatus was used with stationary posts 101.6 mm apart. The crack tip was positioned 25.4 mm from the post and the loading point was 50.8 mm from the post. The displacement rate was 2.54 mm/min (0.1 in/min) and the load was recorded until failure occurred. 2.4.4 Interlaminar Shear Strength (ILSS) Apparent interlaminar shear strength (ILSS) tests were also performed in a three point bend apparatus according to ASTM D 2344 (12). For each laminate, ten samples, 25.4 mm (1 in) long and 12.7 mm (0.5 in) wide were tested. The support span length was such that the span to specimen thickness ratio was equal to 4. The cross-head rate was set at 1.3mm/min (0.05 in/min), and samples were taken from adjacent locations along the length of the laminates in order to verify if any difference in mechanical performance occurred due to tackifier migration upon resin infusion. 2.4.5 Optical Microscopy The fractured specimens were analyzed using optical microscopy and different magnification photomicrographs were taken to verify tackifier migration and distribution. 3. RESULTS & DISCUSSION 3.1 Tackifier Migration Analysis Tackifier washout resulting in thermal and mechanical property gradients in the direction of resin infusion has been previously reported for RTM laminates (13). Therefore, particular attention was given to testing for any tackifier migration in the laminates. Both DMA and optical microscopy were used to determine if tackifier migration occurred in this work. Figure 2 shows cross sections of tackified and untackified laminates. Optical microscopy was performed along the length of the laminate in the resin infusion direction to analyze the uniformity and distribution of the rubber particles. No apparent tackifier composition gradient was found for any of the systems, and the distribution of the rubber particles was even and uniform. In addition, processing infusion times were not affected by the Figure 2: Cross section of laminates showing A) an untackified laminate‘s interlayer (100X) B) a uniform interlayer of rubber particles (100X). Dynamic mechanical analysis (DMA) was also used to measure how the glass transition temperature (Tg), measured as the peak in loss modulus, changed along the infusion direction. (Table 2). The untackified panel was labeled C. Table 2: Glass transition temperatures (Tg) at the inlet and outlet of the tackified VARTM laminates. C T1 T2 T3 T4 Tg inlet (°C) 202 198 198 204 201 Tg outlet (°C) 202 196 195 204 200 Glass transition temperatures did change along the length of the laminate but the extent of the variation was within the error of DMA measurements. Therefore no significant tackifier migration was revealed by this analysis. 3.2 VARTM Laminate Mechanical Analysis Mode I and Mode II interlaminar fracture toughness tests were performed on the composite systems to determine if tackifier chemistry had a significant effect on the fracture properties. Results from mode I interlaminar fracture toughness, measured as GIC using the area method (11), are shown in Figure 3. 1000 800 ) 600 2 m J(/ C I G400 200 0 C T1T2T3T4 Figure 3: Mode I interlaminar fracture toughness energy (calculated as GIC) for the untackified laminate (C) and the four laminates containing different spray tackifiers (T1 - T4). The results display an increase in GIC values when a spray tackifier was used, ranging from 26% for system T4 to 76% for system T3 when compared to the value obtained from the untackified laminate. Previous work has shown that this behavior was found to result from a more tortuous crack path created when elastomeric particles are present in the interlayer (9). Figure 4 shows cross-sections of a tackified composite after mode I testing. It is interesting to notice how the crack propagates around the tackifier particle in Figure 4 A. Mode I samples were viewed using optical microscopy and showed that the cracks deflected out of the plane where the crack initiator was placed. Two separate parallel cracks were often formed and extensive bifurcation of the crack front was observed. Figure 4: Photomicrographs showing the tortuosity of a A) side crack (200X) B) main crack (50X) in tackified laminate T3 subjected to Mode I experiments. The results from mode II interlaminar fracture toughness experiments of all the laminates were calculated as GIIC, the critical strain energy release rate (11) and the results are summarized in Figure 5. 3000 2500 2000 ) 2 m J(/ 1500 C I G 1000 500 0 C T1T2T3T4 Figure 5: Mode II interlaminar fracture toughness energy (calculated as GIIC) for the untackified laminate (C) and the four laminates containing different spray tackifiers (T1 - T4). The results show a trend similar to GIC but the toughness increase was statistically significant only for laminates T1 and T3, for which the toughness gain with respect to the control panel is 44% and 73%, respectively. The GIIC values are related to compression after impact behavior (13, 14 15) and constitute an important variable for the design of composite structures. Apparent interlaminar shear strength tests (ILSS) were also performed on the laminates and the results are summarized in Figure 6. The results show that the introduction of a spray tackifier caused a slight decrease in the interlaminar shear strength of the laminates. The decrease in ILSS values was greatest for system T4 (13.5%) and lowest for system T2 (4%). Since the samples were machined along the resin infusion direction and the standard deviations are consistently small and comparable to the standard deviation of the control panel, there was no shear strength gradient along the laminates due to tackifier migration. This is in agreement with the previous findings on DMA tests and optical microscopy. In general, all the mechanical testing performed showed a noticeable increase in fracture toughness for the laminates in which the tackifier resin was epoxy based (T1; T2; T3), but for the laminate containing a thermoplastic fraction (T4) the increase in properties was statistically insignificant. In addition, the results show how the chemistry of the tackifier resin drastically influences the effectiveness of the tackifier in increasing the fracture toughness of the laminates. An inadequate choice of the tackifier resin, even if its weight percent is only 2 wt.% of the dry fiber reinforcement, can nullify the ability of the tackifier to perform as a toughening agent. C T1 T2 T3 T4 Figure 6: Apparent interlaminar shear strength for the untackified laminate (C) and the four laminates containing different spray tackifiers (T1 - T4). 4. CONCLUSIONS Four toughened tackifiers were developed for use in VARTM applications. These epoxy based tackifiers were modified with preformed rubber particles and sprayed onto carbon fabric. The different tackifier resins were selected based on differences in molecular weight, composition, and functionality. Processing of the VARTM laminates was not affected by the presence of toughened tackifiers. It was shown that by using tackifiers, an increase in GIC by 76% and a corresponding increase in GIIC by 73% of the same laminate were found when compared to the untackified system. Glass transition temperature (Tg) was not affected by the tackifier. ILSS decreased only slightly. In conclusion, toughened tackifiers can be used to increase the toughness of VARTM systems without loss of mechanical performance. 5. REFERENCES 1. D. Heider, C. Hoffmann and J. W. Gillespie, 45th International SAMPE Symposium, 45, 1567 (2000). 2. T. Pike, M. McArthur and D. Schade, 28th International SAMPE Technical Conference, 374 (1996). 3. P. K. Mallick, Fiber Reinforced Composites: Materials, Manufacturing and Design, Marcel Dekker, Inc., New York, 1993. 4. M. B. Dow and D. L. Smith, 21th International SAMPE Technical Conference, 595 (1989). 5. S. B. Shim, K. J. Ahn, J. C. Seferis, A. J. Berg and W. Hudson, Journal of Advanced Materials, 26, 48 (1995). 6. B. S. Hayes, E. N. Gilbert, J. C. Seferis, R. Moulton and D. Dixon, 32th International SAMPE Technical Conference, 294 (2000). 7. R. W. Hillermeier, B. S. Hayes and J. C. Seferis, 44th International SAMPE Symposium, 44, 660 (1999). 8. R. W. Hillermeier, B. S. Hayes and J. C. Seferis, Journal of Advanced Materials, 31, 52 (1999). 9. R. W. Hillermeier, B. S. Hayes and J. C. Seferis, Composites Part A, 32 (5), 721 (2001). 10. R. W. Hillermeier, B. S. Hayes and J. C. Seferis, Polymer Composites, 20 (1), 155 (1999). 11. N. J. Pagano, ed. Interlaminar Response of Composite Materials. Composite Materials Series, ed. R. B. Pipes. Vol. 5. 1989, Elsevier: New York. Ch. 4. 12 Standard Test Method for Apparent Interlaminar Shear Strength of Parallel Fiber Composites by Short-Beam Method, ASTM D 2344 œ 84, (1984). 13. J. L. Kittelson and S. C. Hackett, 39th International SAMPE Symposium, 83 (1994). 14 M. A. Hoisington, Process/Property Interrelations of Layered Structured Composites, Doctorate Dissertation, University of Washington (1992). 15 H. G. Recker, V. Alstadt, W. Heckmann, H. Tesch and T. Weber, 23rd International SAMPE Technical Conference, 934 (1991). 16 W. L. Bradley, The Role of Matrix Toughness of Thermoplastic Composites, R. B. Pipes, ed. Elsevier Applied Science, New York, 1993.

Authors: Edoardo P. Depase, Brian S. Hayes and James C. Seferis* Polymeric Composites Laboratory Dept. of Chemical Engineering University of Washington Box 351750 Seattle, Washington 98195-1750

Conference: 33rd ISTC - Seattle WA - Nov 5-8 / 2001

SKU/Code: 33ISTC-035

Pages: 9

Authors: Marc DEMERS, Kenneth W. NEALE and Pierre LABOSSIÈRE Department of Civil Engineering University of Sherbrooke Sherbrooke, Quebec, Canada

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-008

Pages: 14

The aim of this research was to optimize the rehabilitation of industrial buildings without effective structural steel reinforcement due to corrosion by aggressive natural and industrial agents. This paper presents the experimental results of research into the mechanical behavior under bending of small concrete beams without internal steel reinforcement. The type of specimen used in the research project was a 100x100x700mm beam reinforced externally with unidirectional carbon fiber fabric applied at the intrados using the wet lay-up system technique. A four-point bending test with a 600mm support span was carried out The area strengthened measured 590x95mm. Four types of strengthening were considered and, for comparison, specimens without strengthening were also tested. Only one concrete strength was used. The specimens were instrumented and tested to failure. The structural performance in terms of load carrying capacity and deformation around the zone under tensile and compression strain was compared. The results obtained showed varying behavior in the bonded plate-concrete joint depending on the type of strengthening applied as well as different failure mechanisms.

Authors: Prof. G. Bilotti. Dr. A. Pantuso – IUAV (Venice University Institute of Architecture)

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-019

Pages: 9

Rubber mechanical seals are an important part of the Blown Optical Fiber (BOF) cable plants aboard ships because they provide a barrier against water if compartments are flooded. Age performance of these rubber seals, residing inside couplers joining tubes carrying the optical fibers, is of critical importance because the system is anticipated to have a lifetime of 30 years. New seals are capable of meeting the pressure holding requirements. However, performance of the seals is expected to degrade with time because of changes in their material characteristics. It is important, therefore, to be able to model and predict this performance over time. A study was undertaken to model pressure holding and aging effects of rubber seals analytically. Closed-form solutions and Finite Element Modeling (FEM) were shown to be effective in modeling contact pressures along the circumference of the seals due to preloading and hydraulic loading, especially for simple seal geometries. It was also shown that pressure holding ability is highly dependent on seal constraints, dimensions and tolerances of the mechanical parts, the elastic modulus of the seals, and compression set that occurs in the rubber with aging. Simple analytical methods can provide a good initial estimate of seal performance under new and aged conditions. Within the constraints and uncertainties of this study, it was concluded the seals considered meet the requirements over a 30-year lifetime.

Authors: Keith S. Caruso, Thomas C. Magee, Richard R. Talbott, Michael Rooney, and Andrew M. Lennon The Johns Hopkins University Applied Physics Laboratory Laurel, Maryland 20723-6099

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-078

Pages: 15

Trace degradation of fluorocarbon or halocarbon materials must be addressed in their application in sensitive systems. As the dimensions and/or tolerances of components in a system decrease, the sensitivity of the system to trace fluorocarbon or halocarbon degradation products increases. Trace quantities of highly reactive degradation products from fluorocarbons have caused a number of failures of flight hardware. It is of utmost importance that the risk of system failure, resulting from trace amounts of reactive fluorocarbon degradation products be addressed in designs containing fluorocarbon or halocarbon materials. Thermal, electrical, and mechanical energy input into the system can multiply the risk of failure.

Authors: OPTO-ELECTRONIC SYSTEMS Roamer E. Predmore1 NASA Goddard Space Flight Center Materials Engineering Branch Greenbelt, MD 20771 John S. Canham, Ph.D. Swales Aerospace Inc. NASA Goddard Space Flight Center Materials Engineering Branch Greenbelt, MD 207712

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-097

Pages: 14

Vasco X2M steel is being utilized in the production of critical US. Army components. The material is heat treated and shot peened for the purpose of inducing compressive residual stresses on the component su$ace. Grinding is pe$ormed aper heat treatment in order to achieve the dimensional tolerances required for the precision components. This paper describes the use of Barkhausen Noise Analysis (BNA) techniques to qualifi the heat treatment and shot peening processes and to detect thermal damage due to abusive grinding. 

Authors: Patrick Sincebaugh, Victor Champagne, Marc Pepi, Daniel Snoha

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-067

Pages: 8

The vacuum assisted resin transfer molding (VARTM) process was successfully developed to enable infusion of thermoplastic pre-polymers into a fiber preform at temperatures up to 180 0C. A flat heated mold with a heated delivery system for transporting the molten resin from the melting unit to the mold was used. The fiber preform was bagged with a high temperature plastic film and sealing tape. A 1-D heat transfer analysis predicted a 25 0C temperature gradient from the mold surface to the top surface, of a 5 mm thick glass fiber preform. An insulating layer placed on top of the preform reduced the temperature drop across the preform to an acceptable value of 10 0C. The pre-polymer used was a cyclic butylene teraphthalate oligomer (supplied by Cyclics Corporation), which was melted by heating to 165 0C. A catalyst was added just prior to infusion of the catalyzed pre-polymer into the fiber bed. The viscosity-time characteristics for this material, which polymerized within the mold to form polybutylene terephthalate (PBT), were measured to establish the VARTM processing window. Viscosity values for this material at 160 0C varied from 0.1 Pa.s at introduction of the catalyst to 0.5 Pa.s after approximately 60 minutes. This time was reduced to 16 minutes when the temperature was raised to 167.5 0C. Flat panels were successfully molded, using S2 glass fabric and S2 glass mat, with fiber volume fraction values over 45% achieved. DMA tests on the molded panels showed that the flexural storage modulus varied from approximately 18 GPa at room temperature to 9 GPa at 150 0C for the S2 glass fabric/PBT composite.

Authors:  A. Chatterjee1, P. J. Mallon1, 3, M. A. Dweib1, S. Ziaee1, J. W. Gillespie Jr.*1, 2 and D. Heider1 1Center for Composite Materials 2Department of Material Science and Engineering & Department of Civil and Environmental Engineering University of Delaware, Newark, DE 19716, USA 3Present Address: University of Limerick, Limerick, Ireland

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-086

Pages: 15

The use of carbon / epoxy composites in aircraft, marine, and automotive structural applications is steadily increasing. Robust composite structures processed using low-cost techniques with the purpose of sustaining high velocity impact loads from various threats are of great interest. An example of a low-cost process is the out-of-autoclave, vacuum assisted resin transfer molding (VARTM) technique. The present study evaluates the perforation and damage evolution created by various projectile geometries in carbon / epoxy laminates. The laminates were produced from eight-harness satin weave carbon fabric with an epoxy matrix processed using VARTM. A series of ballistic impact tests have been performed on satin weave carbon / epoxy laminates of different thickness with projectile geometries representing hemispherical, conical, fragment simulating, and flat tip. A gas-gun with a sabot stripper mechanism was employed to impact the samples with 50-caliber projectiles. The perforation mechanism, ballistic limit, and damage evolution of each laminate has been studied.

Authors: C. Ulven and U.K.Vaidya Department of Materials and Mechanical Engineering University of Alabama at Birmingham Birmingham, AL 35294 M.V. Hosur Center for Advanced Materials Tuskegee University, Tuskegee, AL 36088

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-024

Pages: 9

 Due to increasingly stringent environmental constraints, alternate methods for paint removal of military hardware, such as aircraft, are being investigated and developed. DOD studies have shown that 20% of the hazardous waste produced by DOD are due to paint removal operations. FLASHJET® is a particularly promising alternative that has been shown to not only give significant reductions in generated hazardous waste, but also reductions in cost and improvements in process control. However, the most important issue for these alternative processes is that there is no degradation of the material, such as mechanical properties in any way. The FLASHJET® process inputs heat into a material through high but short duration energy pulses. In this study, the influence of FLASHJET® processing on the fatigue behavior of two aluminum alloys; (1) Al 2024-T3 and (2) Al 7075-T6 was determined. No degradation in fatigue behavior based on fatigue lifetimes was observed under the conditions tested, and this is in concurrence with a small number of other studies using similar testing methods. More importantly, it was also shown in the present study that almost half of testing conditions gave statistically significant improvement in fatigue lifetimes, and this may be due to the thermal energy affecting stresses at the crack tip of a fatigue crack while being insufficient in magnitude to degrade the strength-related microstructural features of the alloys.

Authors: FATIGUE PROPERTIES OF Al 7075-T6 AND Al 2024-T3 Victor K. Champagne, James Campbell Scott M. Grendahl, Wayne W. Ziegler, U. S. Army Research Laboratory Weapons and Materials Directorate AMSRL-WM-MD, Building 4600 Aberdeen Proving Ground, Maryland 21005-5069

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-068

Pages: 11

In this paper, a conventional test method of a three-point bending beam (3PBB) specimen based on cohesive crack model is adapted to characterize Mode-I fracture of concrete-composite bonded interfaces. Two types of fiber fabrics: E-glass and Carbon are used, and a common epoxy resin is applied to bond the concrete-composite interfaces. Mode-I fracture tests of the 3PBB specimens for concrete-CFRP and concrete-GFRP bonded interfaces are performed to determine the applied loads and load point displacements, from which the interface fracture energy is obtained. The effect of loading rates on fracture toughness of concrete-CFRP (in displacement control rates of 0.002 mm/sec, 0.01 mm/sec, and 0.05 mm/sec) is studied and discussed. It is expected that the proposed experimental method can be effectively used to obtain fracture toughness data useful for delamination studies under various environmental exposures and service loading.

Authors: BASED ON COHESIVE CRACK MODEL Yingwu Xu and Pizhong Qiao Department of Civil Engineering, College of Engineering, The University of Akron, Akron, Ohio 44325-3905, USA

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-026

Pages: 1

Authors: P. George, J. Griffith and G. Orient, The Boeing Company J. Madsen and C. Teng, Northrop Grumman Corporation R. Courdji, Convergent Manufacturing Technologies

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-027

Pages: 15

COMPOSITES

Symmetric cross-ply carbon fiber/epoxy laminates containing fibers with different surface treatments were thermally cycled at cryogenic temperatures to investigate the impact of fiber/matrix adhesion on transverse microcracking. Three fiber surfaces were used: Unsized but exposed to an oxidative surface treatment, epoxy sized, and surfactant sized. It was found that the adhesion of the matrix to the fibers as determined by interlaminar shear strength and dynamic mechanical analysis changed as the surfaces of the fibers were altered. The extent of microcracking in the laminates exhibited a dependence on fiber/matrix adhesion, with high levels of adhesion corresponding to decreased microcracking. * Indicates author to whom correspondence should be sent

Authors: John F. Timmerman, Brian S. Hayes, and James C. Seferis* University of Washington Department of Chemical Engineering Polymeric Composites Laboratory Seattle, Washington 98195

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-028

Pages: 1

A finite element model of the human thorax complete with musculoskeletal structure (ribs, sternum, vertebral column, intercostal muscle and skin) and internal organs (heart, liver, lungs, stomach and kidneys) has been developed. The NURBS surfaces of each of these components (heart, liver, lungs, etc) were created with Geomagic. These entities were then exported, individually from Geomagic into the finite element code IDEAS. For each of the entities (heart, liver, lungs, skeleton, etc) the surfaces and volumes were meshed with shell, membrane or solid linear tetrahedral elements. Solid elements were used for the interior portion of the organs. Solid elements were also used for the interior (trabecular) bone of the ribs and shells elements used for the outer (cortical) bone. Membrane elements were used for muscle and skin because they cannot take compressive loads. In this initial model the organs were attached to one another and to bone at the nodes. The model consisted of a total of 261,000 elements. The model was only exercised under static load. The current model will be further developed in LS-DYNA where all interfaces between organs and themselves or bone will be modeled using sliding elements and plate elements will be used to represent soft body armor.

Authors: Emily E. Ward1, Michael Kleinberger2 and Jack C. Roberts3 The Johns Hopkins University, Applied Physics Laboratory Laurel, Maryland 20723-6099 and The Johns Hopkins University Mechanical and Biomedical Engineering Departments Baltimore, MD

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-064

Pages: 14

The electrical and electronic equipment (EEE) marketplace continues to go through tremendous growth. With improvements in technology constantly taking place, this growth is expected to continue. End-of-life issues, such as reuse-reduce-recovery-recycle, safety, and compliance with regulatory matters are all of major concern and are being addressed. The shear volume of old EEE to be disposed of is tremendous. Efforts are ongoing to address the reuse-reduce-recycle aspects of EEE. Safety is being addressed in much of today’s EEE by the use of flame retardants, which significantly reduce fire risks. This in turn saves lives and the destruction of property. Compliance with regulatory matters greatly impacts the selection criteria of flame retardants that are used in EEE. This will be impacted by the proposed European directives regarding waste electrical and electronic equipment (WEEE) and the restriction on the use of certain hazardous substances in electrical and electronic equipment (RoHS). This paper will explore these end-of-life issues for EEE. It will examine the effect that particular flame retardants can make toward meeting various demands placed on electrical and electronic equipment.

Authors: Flame Retardant Electrical and Electronic Equipment Raymond B. Dawson and Susan D. Landry Albemarle Corporation 8000 GSRI Ave. Baton Rouge, LA 70820 Phone: Ray - (225) 388-7888, Susan - (225) 768-5745 FAX: (225) 768-5607 ray_dawson@albemarle.com susan_landry@albemarle.com

Conference: 34th ISTC - Baltimore MD - Nov 4-7 / 2002

SKU/Code: 34ISTC-058

Pages: 12

Studies were conducted with six different candidate high-temperature neat matrix resin specimens of varied geometric shapes to investigate the mechanisms involved in the thermal degradation of polyimides like PMR–15. The metrics for assessing the quality of these candidates were chosen to be glass transition temperature (Tg), thermo-oxidative stability, dynamic mechanical properties, microstructural changes, and dimensional stability. The processing and mechanical properties were not investigated in the study reported herein. The dimensional changes and surface layer growth were measured and recorded. The data were in agreement with earlier published data. An initial weight increase reaction was observed to be dominating at the lower temperatures. However, at the more elevated temperatures, the weight loss reactions were prevalent and probably masked the weight gain reaction. These data confirmed the findings of the existence of an initial weight gain reaction previously reported (refs. 1 to 10). Surface- and core-dependent weight losses were shown to control the polymer degradation at the higher temperatures.

Authors: Kenneth J. Bowles and Ojars V. Klans NASA Glenn Research Center Cleveland, Ohio 44135 Demetrios S. Papadopoulos University of Akron Akron, Ohio 44325 Daniel A. Scheiman QSS Group, Inc. Cleveland, Ohio 44135 Linda L. Inghram and Linda S. McCorkle Ohio Aerospace Institute Brook Park, Ohio 44142

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-003

Pages: 15

This paper assesses impacts to heat release and flame performance when electric cables are conditioned at their temperature rating in lieu of normal ambient temperatures, and determines that enhanced flame performance predictions for electric cables can be made when cable materials are subject to increased conditioning temperatures corresponding to cables‘ temperature rating. The fire load presented by electric power and signal cables running in overheads, walls, and in raised floors has grown considerably within the last twenty years. Increased electric power demand, owing to greater use of computing and other productivity-enhancing equipment, now represents sizeable load profiles to utilities. Command, control, and communication systems have also tracked the increasing demand for building electric power, and the power and signal cables serving automation systems, telephone, intercom systems, broadband, cable television, CCTV, and security services occupy significant space in building voids and utility-routing channels. However, despite the sizeable flame load presented by building electric cables, commercial and regulatory flame-testing criteria are less rigid than the test requirements invoked for building outfit and furnishings œ serving to understate the heat-release performance of electric cables. Material conditioning criteria imposed on building outfit and furnishing age specimens to simulate mimic normal material denigration in response to the expected environment œ providing improved predictive accuracy of flame performance. However, pre-test conditioning requirements for electric cables are rarely invoked, and when invoked, apply thermal aging criteria reflecting comfortable room temperature environments, while overlooking realistic cable operating temperatures.

Authors: James Angelo Ruggieri, P.E. Rupert P. Chandler, P.E.

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-000

Pages: 14

Complex permittivity, permeability and microwave reflectivity of carbon nanotubes, Ni-coated carbon nanotube / polymer composites have been studied at frequency ranges of 8.2~12.4GHz and 2~18GHz. The real part (e') of complex permittivity of the carbon nanotube / epoxy resin composites ranges from 14.87 to 13.86, and the imaginary part (e.), from 6.42 to 5.87, the loss tangent tgd (e./e'), from 0.42 to 0.45. The real part (µ') of complex permeability of this composites ranges from 1.02 to 1.14, and the imaginary part (µ.), from 0.08 to 0.11, the loss tangent tgd (µ./µ'), from 0.06 to 0.11. The nickel was plated on the surfaces of carbon nanotubes by electroless plating technique. Compared with the epoxy resin matrix composites containing pure carbon nanotubes, the absorbing peak of composites containing Ni-P coated carbon nanotubes moves to the higher frequency, and those of composites containing Ni-P and Ni-N coated carbon nanotubes after heat-treatment move to lower frequency. The carbon nanotubes are used as dipoles to absorb the microwave. The coercive forces for the Ni-P coated carbon nanotubes, Ni-P and Ni-N coated carbon nanotubes after heat-treatment, are 304.34Oe, 81.65Oe, 183.85Oe respectively. It is notable that the microwave absorbing peaks of the three composites move to the high frequency with the increasing of the coercive force.

Authors: Donglin Zhao and Zengmin Shen The Key Laboratory of Science and Technology of Controllable Chemical Reactions BUCT, Ministry of Education, China; Institute of Carbon Fiber and Composites, Beijing University of Chemical Technology, Beijing 100029, China

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-099

Pages: 1

The impact due to the advancement of polymer composite structure can be seen in the usage of polymer composite in civil transportation, especially in the aerospace industry. A significant percentage of the aircraft structures are made up of polymer composites. Since aircraft are prone to light object impacts in space like birds and hails, it is of importance to perform periodic damage checks on the structures, especially on polymer composite structures. This is because, unlike conventional metals, polymer composite material may not exhibit any signs of damage on the outer surface of the structure, but may have a significant amount of internal damage. Therefore it is crucial to determine this internal damage and to commence immediate repairs. One of the easiest and cheapest means of polymer composite repair is by hand lay up. In the hand lay up method, there are two choices one can choose, namely using a wet lay up method where the matrix is applied onto the fiber or by using prepreg composite material, where the matrix has already been pre impregnated into along with the fibers. Therefore, the objective of this study is to determine which repair method would yield better mechanical tensile strength. From the testing conducted, it was found that, as expected, the prepreg repair had better mechanical performance compared to the wet lay up method.

Authors: Faris Tarlochan, Wan Mazlina and Julaidi Rasidi Universiti Tenaga Nasional, Jln 7 km Kajang Puchong 43009, Kajang, Malaysia

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-034

Pages: 4

PYROGRAF carbon nanofibers have a low diameter and good electrical conductivity, so that in carefully fabricated thermoplastic composites they are very effective additives for lowering electrical resistivity. This paper describes a method for further reducing this resistivity by as much as a factor of 20 by adding chopped glass fibers to the polymer melt containing heattreated carbon nanofibers. This surprising effect is because the nanofibers preferentially deposit at the interfacial region between the polymer and the glass fiber. Effectively, the nanofibers coat the glass fibers to make them conducting, converting them into a scaffolding conductor much longer than the nanofibers themselves. The resistivity decrease is much more significant at low nanofiber concentrations. Furthermore, the resistivity decrease due to the glass fiber component is more pronounced for longer or lower diameter glass fibers. Moreover, this improved glass fiber-containing material is more robust during high shear mixing and compounding. These hybrid glass/carbon fiber composites thus promise to significantly increase the breadth of applications for fiberglass composites to encompass those requiring electrical conductivity as well as enhanced mechanical properties.

Authors: G. G. Tibbetts*1, C. Kwag1, D. G. Glasgow2, , and M. L. Lake2 1 General Motors R&D Center, Warren, MI, 48090 2 Applied Sciences, Inc., Cedarville, OH, 45314

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-087

Pages: 9

In this paper, a test method using notched three-point bending beam (3PBB) specimen is presented to characterize the thermal effects on the mode-I fracture of composite-concrete bonded interfaces. A common epoxy resin system is used to impregnate carbon fiber fabrics and then bond the carbon fiber-reinforced polymer (CFRP) composite to the concrete. Mode-I fracture tests of the 3PBB specimens for CFRP-concrete bonded interfaces are performed to determine the applied load and load point displacement relationship, from which the interface fracture energy is computed. A temperature range from –34.4°C (-30°F) to 71.1°C (160°F) with increments of about 16.67°C (30°F) is applied to the fracture tests, and the effect of temperature on the fracture energy of CFRP-concrete bonded interfaces is studied and discussed. The results indicate that the temperature plays an influential role on the properties (e.g., the interface fracture energy, critical load, and fractured surface) of adhesively bonded composite-concrete interfaces. The test data presented are useful for design of concrete structures externally reinforced with FRP composites, and the test protocol of modified 3PBB specimen can be used as a qualification method to test new hybrid material interface bond and to study durability-related effects on the interface.

Authors: Yingwu Xu and Pizhong Qiao Department of Civil Engineering, The University of Akron Akron, Ohio 44325-3905, USA

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-035

Pages: 13

The use of through-thickness reinforcement in the form of stitches or short rods has been proposed to improve the interlaminar property of laminated composites for several years. In stitched composites, the bending resistance of a stitch has been often ignored due to the splitting of fibers in a single stitch. For the metallic short rods, the bending resistance has also been not taken into account when investigating their influence on delamination toughness of composite laminates because it is generally regarded that the rod diameter is very small. This paper investigates the influence of bending stiffness on delamination toughness of composite laminates. Typical DCB and ENF specimens will be considered. The present numerical results show that bending stiffness can have a significant effect on the delamination resistance for laminated composites.

Authors: Liyong Tong and Xiannian Sun School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney New South Wales 2006, Australia

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-065

Pages: 11

A micromechanical analysis of the representative volume element (RVE) of a plain weave textile composite has been performed using the finite element method. Assuming that failure criteria for the yarn and matrix are known, the failure envelope for a plain-weave textile composite has been constructed using microstresses from the finite element analysis. This method is referred to as the Direct Micromechanics Method (DMM). The predicted values of stiffness and strength compare well to expectable magnitudes. The DMM failure envelope compared relatively closely to the Maximum Stress Criterion, but was less conservative than the Tsai-Wu failure theory when compressive applied stresses were present. Failure of the matrix was the dominant mode of initial failure, but the particular criterion chosen to determine matrix failure did not have a large effect on the results.

Authors:  Bhavani Sankar, Bokwon Lee, and Ryan Karkkainen University of Florida Department of Mechanical and Aerospace Engineering Gainesville, Florida 32611

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-045

Pages: 11

Four types of carbon-fiber-pultruded-composite (CFPC) sucker rod materials, which have good heat-resistance and can be applied to wells where the long-service temperatures are above 60, were manufactured by continuous pultrusion process using vinyl ester or epoxy resins as matrices. Meanwhile, a safe and reliable proprietary connector of the CFPC sucker rod to steel was developed to resolve load limitation problem. The quasi-static mechanical properties and dynamic fatigue properties of the composites were investigated. Dynamic Mechanical Thermal Analysis (DMTA) was performed in dual cantilever bending mode to measure the glass transition temperatures (Tg) of the composites. Results show that the CFPC sucker rods have many advantages such as lightweight, high strength, good fatigue and heat resistance, etc. The CFPC sucker rod with a tensile strength of 1950 MPa can maintain 90% of its original strength after 10 million cycles at a frequency of 90Hz and a stress ratio of 0.375. A database containing more than 10 field trials shows that compared with steel sucker rods, the CFPC sucker rods can reduce the load added at polish rods and save energy, showing a good prospect in oil field application in China.

Authors: Xiaoping Yang1*, Chengjin Xue2, Yunhua YU1, Chengzhong Wang1, Xuelin Gu3 1.Institute of Carbon Fiber and Composites, Beijing University of Chemical Technology, Beijing 100029, P.R. China 2.Department of Science & Technology, China Petroleum & Chemical Corporation, Beijing 100029, P.R. China 3.General Engineering Machinery Factory of Shengli Petroleum Administration, Shandong 257061, P.R. China

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-066

Pages: 9

In the current study, the frequency and temperature dependent axial damping behavior of filament wound carbon/polyurethane tubes is examined. Axial and torsional damping test stands capable of conducting measurements for a temperature range of room temperature to 80°C, and a frequency range of 1 Hz to 100 Hz have been built. A damping model for orthotropic composite tubes in axial tension is proposed. The predicted and measured results are in good agreement with each other, within the precision of the test equipment. The viability of carbon/polyurethane composite for application in flexible driveshafts is discussed in the context of internal heat generation and misalignment.

Authors: Y. Shan and Charles E. Bakis NRTC Rotorcraft Center of Excellence Department of Engineering Science and Mechanics The Pennsylvania State University University Park, Pennsylvania 16802

Conference: 35th ISTC - Dayton OH - Sep 28-Oct 2 / 2003

SKU/Code: 35ISTC-100

Pages: 14

The need for materials that have superior structural bonding performance for aerospace assemblies that cure at low temperature and short process times have not been satisfied by current industry product portfolios. This work examines current state-of-the-art approaches to satisfy the need for cost reduction with processes that provide equivalent mechanical performance to those cured in classical autoclave conditions. Film adhesives curing at uncharacteristically low temperatures, low pressure bonding and state-of-the-art development efforts have been examined.

Authors: David S. LeGrand Henkel Technologies - Aerospace 2850 Willow Pass Road, Bay Point California 94565 United States

Conference: 36th ISTC - San Diego CA - Nov 15-18 / 2004

SKU/Code: 36ISTC-075

Pages: 8

The free vibration of sandwich plates has been widely studied. Unlike most approaches, which assume an incompressible core, Frosting’s Higher-order Sandwich Panel Theory (HSAPT) takes into account the compressibility of the core and gives good approximate predictions for the free vibration of the soft-core sandwich. Recently, however, Sokolinsky pointed out an inconsistency in Frostig’s higher order approach, and proposed a consistent higher-order approach to analyze soft-core sandwich beams. In the current work, Sokolinsky’s one-dimensional beam formulation has been further refined and extended to the case of a two-dimensional sandwich plate with composite skins and honeycomb core. The natural frequencies for a simple-supported composite sandwich plate with aluminum faces and aluminum honeycomb core were calculated by this model. The results were compared with previous predictions and with experimental data in the literature, showing good agreement.

Authors: Tongan Wang, Shankar Rajaram and Steven R. Nutt University of Southern California Los Angeles, CA 90089

Conference: 36th ISTC - San Diego CA - Nov 15-18 / 2004

SKU/Code: 36ISTC-083

Pages: 8

Silicone impregnated reusable ceramic ablator (SIRCA) was used as the thermal protection system (TPS) for the backshell interface plate (BIP) and the transverse impulse rocket system (TIRS) covers on the Mars Exploration Rover (MER) aeroshell. The SIRCA tiles were bonded with RTV 560 to both metallic and graphite/polycyanate substrates, each of which provided its own challenges. Unlike most structural components and due to the relative fragility of SIRCA tiles, it is difficult to nondestructively test the bonded SIRCA directly to assess workmanship; witness coupons were used instead. When some of the witness test results showed poor failures, rather than assume that the flight hardware, by comparison, had acceptable bonds, the tiles were removed, details of the standard process were reevaluated, and process updates were made. Subsequent witness coupons showed uniformly cohesive failures and strengths well above required values. More recently, testing has been undertaken to better refine the process in preparation for the next application to flight hardware. Results and discussion of process changes will be addressed.

Authors: TILES Stephanie E. Buck Flight Materials and Processes Engineering Group Mechanical Engineering Section Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109

Conference: 36th ISTC - San Diego CA - Nov 15-18 / 2004

SKU/Code: 36ISTC-006

Pages: 1

A new, affordable, thermally stable resin system suitable for liquid molding prcoesses (e.g. resin transfer molding (RTM), compression molding, vacuum assisted RTM, resin infusion, etc.) has been developed in our laboratory. Initial characterization of the physical, thermal, rheological, crosslinking, durability, and mechanical properties are presented for neat resin and reinforced composite laminates (S-2 glass and T650-35 carbon fiber). The described resin system, P2SI 635LM, exhibits a good balance of performance, processability, and affordability.

Authors: Jason E. Lincoln, David B. Curliss, Christin M. Grabinski, and Paul Titas Performance Polymer Solutions Inc., 91 Westpark Road, Centerville, OH 45459

Conference: 36th ISTC - San Diego CA - Nov 15-18 / 2004

SKU/Code: 36ISTC-057

Pages: 13

Lightweight composite structures for high-technology applications increasingly have to fulfill high demands not only on low constructive weight and adequate stiffness but also on reduced vibrations and sound radiation. These good vibro-acoustic qualities are needed to meet the rising comfort and environmental requirements. Here, especially anisotropic and shear-elastic composites offer a high vibro-acoustic lightweight potential. The specific combination of different materials and the large variety of design variables give the possibility to synergetically achieve the pretentious demands on coupled dynamic and acoustic properties. In order to fully exploit this high vibro-acoustic potential a detailed knowledge of the structural- dynamic and acoustic phenomena and coherences of the different anisotropic composites is necessary. Thus, the specific anisotropic vibration and damping characteristics of shear-elastic composite structures have to be coupled with the acoustic behaviour by physically based simulation models. For this purpose advanced analytical and numerical methods have been developed at the ILK in order to include not only stiffness and strength but also the sound radiation in the design process. The performed parameter studies reveal the coupling of the manifold dynamic and acoustic design variables. The knowledge of these coupled dependencies allows the development of vibro-acoustically tailored composite structures for high-technology lightweight applications.

Authors: Prof. Dr.-Ing. habil. W. Hufenbach, Dr.-Ing. L. Kroll, Dr.-Ing. O. Täger, Dr.-Ing. B. Zhou Dresden University of Technology Institute of Lightweight Structures and Polymer Technology (ILK), D-01062 Dresden, Germany Tel.: +49/351/463-38134, Fax: +49/351/463-38143, e-mail: ot@ilk.mw.tu-dresden.de

Conference: 36th ISTC - San Diego CA - Nov 15-18 / 2004

SKU/Code: 36ISTC-014

Pages: 14

Models are presented for determination of thermal conductivity of a composite lamina manufactured with woven fiber mats. In analyzing the cure cycle of a composite part, the common practice has been to use weight-averaged thermal properties. The limitation of this approach is apparent when one finds that thermal conductivity calculated for fiberglass/epoxy composite is very close to thermal conductivity of carbon/epoxy composite. This happens when composite parts with the same fiber volume fraction are considered. The reason for this is that in employing weight-average formulations the effect of fiber thermal conductivity is overshadowed by the density of the constituents. To overcome this problem, one needs to take another approach. In this investigation finite element analysis is performed on a unit cell representing the weave pattern of the lamina to determine thermal conductivities of fiberglass/epoxy and carbon/epoxy composite lamina. The resulting thermal conductivities are very different for the two composite types. These results make more physical sense since thermal conductivity of carbon fibers is many times larger than that of fiberglass fibers.

Authors: Hossein Golestanian Mechanical Engineering Department University of Shahrekord Shahrekord, Iran

Conference: 36th ISTC - San Diego CA - Nov 15-18 / 2004

SKU/Code: 36ISTC-041

Pages: 14