Experimental investigation and validation of strength-based topology and fiber path optimization in additively manufactured continuous fiber reinforced composites

Abstract

Material extrusion-based fused filament fabrication (FFF) is a widely used additive manufacturing (AM) technology that offers design freedom to fabricate intricate, robust, and lightweight parts when used with continuous carbon fiber (CCF) reinforced filaments. FFF is well-suited for optimization methods, as designers can specifically tailor the positioning of CCF filaments, albeit within certain manufacturing limitations. This study integrates experiments and finite element analysis (FEA) to investigate strength-based optimization methods applied to two benchmark structural domains and loading scenarios. Two methods were used to concurrently design the shape or topology and fiber paths: shape optimization using the level-set method, and topology optimization using both density-based solid orthotropic material with penalization (SOMP) and level-set methods. CCF filaments were printed to follow the optimized fiber paths, and a discontinuous fiber reinforced filament was used to fill in the remaining gaps. The parts were then compression molded for full consolidation, followed by testing for their stiffness and failure loads. FEA predicted locations and magnitudes of failure with reasonable accuracy, even in regions with complex stress states and fiber paths. X-ray micro-computed tomography (µCT) examination of failed coupons showed that fiber flow (deviations) during compression molding occurred and impacted parts’ performance. Finally, comparing designs optimized for stiffness versus strength showed premature failures due to stress concentrations in stiffness-optimized designs. This study underscores the critical need for integrating proper optimization strategies with realistic AM constraints and processing-induced defects to enhance the performance and reliability of CCF reinforced AM parts.