The effect of resin-rich layers on mechanical properties of 3D printed woven fiber-reinforced composites

Composites for aerospace and automotive industries trend towards maximizing fiber volume fraction. In such applications, the design criteria typically maximize material stiffness with little concern for strength, and elongation at break. However, several fiber-composite applications would benefit from improved strength, and elongation at break. Given typical manufacturing constraints, limited success has been reported on maximizing composite properties imparted by the matrix, such as strength and toughness. Select studies have shown that inclusion of neat resin layer spacing between composite layers, referred to as resin-rich layers (RRL), lead to significant improvements in Mode II interlaminar toughness. Additive manufacturing offers a useful platform for manufacturing parts with controlled RRL and composite layer placement. In this study, we present a novel method for the fabrication of woven glass fiber reinforced composites with controlled RRLs using a 3D vat polymerization technique. We utilize a plain woven glass fiber mats and a novel methacrylated resin (DA-2) that allows for fiber mat incorporation during printing. The goal of this study is to determine the effects of RRL thickness on mechanical properties. Laminated composites are produced with controlled RRL thickness in the range of 0–200 µm. The printed laminates are tested for tensile, flexure, short beam shear, Mode I, and Mode II interlaminar properties. Overall, RRL does not show improved in-plane or out-of-plane performance for the chosen materials. However, the observed trends in interlaminar toughness are shown to strongly depend on the resin properties, namely the resin's plastic zone size. We conclude that the resin plastic zone size is a key resin property that determines whether improved toughness and strength are achieved with the presence of RRLs.