Title: Fatigue Characterization of Extrusion-Based Additively Manufactured Thermoplastic Composites: A Repeatable CouponPrinting Protocol and Case Study on PA6-GF and PA12-CF

Authors: Mohammad Amjadi , Peter Woytowitz, Minh Tran, Reza Molaei

DOI:

Abstract: Additive manufacturing (AM) of thermoplastics is gaining rapid adoption in biomedical, aerospace, and automotive applications due to their ability to produce complex geometries, reduce material waste, and enable lightweighting. Among AM techniques, material extrusion (MEX/FFF) is the most widely used because of its relatively low cost and accessibility. However, parts produced by MEX often suffer from process-induced anisotropy, voids, and weak interlayer bonding, all of which degrade long term mechanical performance and make fatigue characterization particularly challenging. The lack of standardization has hindered researchers and engineers from generating consistent fatigue data and establishing reliable design allowable for AM thermoplastics and their composites in structural applications. To address this gap, we propose a practical and repeatable coupon-printing protocol designed specifically for MEX composites. The protocol enables the generation of low-scatter fatigue data by minimizing variability introduced by print settings and specimen geometry. It is demonstrated using nylon (PA6) reinforced with short glass and carbon fibers (PA6-GF and PA12-CF), two widely used engineering materials with growing relevance in AM. The experimental plans include varying infill density, infill pattern, layer height, raster angle, and build orientation to capture the effect of key process parameters on fatigue performance. Resulting S–N relationships and observed failure modes are analyzed to quantify parameter sensitivity and life-prediction modeling. The proposed protocol improves repeatability across builds and enables a clearer separation of intrinsic material behavior from structural effects associated with infill pattern or wall loops. This makes it possible to establish more reliable data sets that can ultimately inform the creation of ASTM- or ISO-like standards for AM thermoplastics and composites. Standardization of such methods will be a critical step toward developing repeatable design allowables and ensuring confidence in fatigue life assessments of functional AM parts where long-term durability under cyclic loading is essential. In parallel with the experimental effort, we extend modeling work by formulating and evaluating a critical-plane damage parameter for life prediction. This parameter, previously validated for injection-molded short-fiber thermoplastics, has shown strong correlation with experimental data. Its applicability to additively manufactured short-fiber thermoplastic composites is evaluated and discussed, with the goal of integrating both experimental and modeling insights into a unified framework for fatigue life assessment of AM materials.

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Conference: SAMPE 2026

Publication Date: 2026/04/27

SKU: 80

Pages: 15

Price: $30.00