Title:          A Dynamic Mechanical Analysis Approach to Quality Evaluation of Additively Manufactured Continuous Fiber Reinforced Thermoplastics

Authors:  Patrick A. Rodriguez and Donald W. Radford

Abstract:        Additive manufacture of continuous fiber reinforced thermoplastics (CFRTP) exhibits the potential to relieve many of the constraints placed on the current design and manufacture of continuous fiber reinforced structures.  At present, the additive manufacture of CFRTP has been demonstrated to varying extents; however, comprehensive dialogue regarding manufacturing defects and the quality of the processed continuous fiber reinforced thermoplastics, especially those of high fiber volume fraction, has been missing from the field.  Considering the preliminary nature of additive manufacture of CFRTP, exemplary processed composites are typically subject to various manufacturing defects, namely excessive void content in the thermoplastic matrix.  Generally, quality evaluation of processed composites in the literature is limited to test methods that are largely influenced by the properties of the continuous fiber reinforcement, and as such, defects in the thermoplastic matrix are usually less impactful on the results and often overlooked. 
Hardware to facilitate the additive manufacture of CFRTP was developed and continuous fiber reinforced specimens, with high fiber volume fractions (~ 50 %), were successfully processed with intentionally varied void content in the thermoplastic matrix.  The quality of the additively manufactured specimens was then evaluated by means of Dynamic Mechanical Analysis (DMA).  DMA allows for thermomechanical (i.e. highly matrix sensitive) evaluation of the composite specimens, specifically in terms of the measured elastic storage modulus, viscous loss modulus, damping factor and the glass transition temperature.  The results of this work have demonstrated that DMA exhibits multi-faceted sensitivity to the presence of void content in the additively manufactured CFRTP specimens.  Within the relevant range of void content, non-destructive specimen evaluation by DMA resulted in a measured negative trend in both the maximum measured storage moduli and maximum measured loss moduli with respect to increasing void content in the printed composites.  Effects of void content were also measured in the glass transition temperature, where an approximate 1.2 °C drop in Tg was recorded over the relevant range of void content.

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Conference:  CAMX 2019 | Anaheim, CA

Publication Date:  September 23, 2019

SKU/Code:  TP19-0758

Pages:  15