Effects of void content on flexural properties of additively manufactured polymer composites

Mechanical characterizations are inevitable to the research and development in additive manufacturing (AM). Most mechanical tests for composite materials are relatively expensive, time-consuming, and challenging. Therefore, three-point flexural testing is widely adopted as it offers an easy and fast method to assess AM composite's performance. The correlations between the flexural and other mechanical properties in AM composites are, however, not understood. In this work, multiscale modeling is utilized to connect micro-scale composite properties to macro-scale flexural simulations and experiments. Two AM composite samples of continuous carbon fiber-reinforced polyetheretherketone (PEEK) are considered. The void volume fractions in these samples are similar to 10 and 5%, typical of the composite's AM process. First, elastic constants for the two samples, considering their porosity, are predicted via micro-mechanical finite element analysis (FEA). A test model is then constructed to carry out detailed macro-scale FEA stress analysis in flexural tests. Specifically, flexural strength of AM composites is correlated to their tensile and compressive strengths. The findings of this study can pave the way for rapid characterization, process optimization, and new materials development in AM composites.