The flexure response of novel thermoplastic (Elium^®) 3D fibre-reinforced composites (FRC) was evaluated and compared with a conventional thermoset (Epolam^®)-based 3D-FRC. Ten different types of sample 3D-FRC were prepared by varying fibre orientations, i.e., 0°, 30°, 45°, 60° and 90°, and resin system, i.e., thermoplastic and thermoset. The bending characteristics and failure mechanisms were determined by conducting a three-point bend test. Results elucidate that the on-axis specimens show linear response and brittle failure; in contrast, the off-axis specimens depicted highly nonlinear response and ductile failure. The thermoplastic on-axis specimen exhibited almost similar flexure strength; in comparison, the off-axis specimens show ~17% lower flexure strength compared to thermoset 3D-FRC. Thermoplastic 3D-FRC shows ~40% higher energy absorption, ~23% lower flexure modulus and ~27% higher flexure strains as compared to its thermoset counterpart.

This paper presents a multi-scale-homogenization based on a two-step methodology (micro-meso and meso-macro homogenization) to predict the elastic constants of 3D fiber-reinforced composites (FRC). At each level, the elastic constants were predicted through both analytical and numerical methods to ascertain the accuracy of predicted elastic constants. The predicted elastic constants were compared with experimental data. Both methods predicted the in-plane elastic constants “ $E_x$ ” and “ $E_y$ ” with good accuracy; however, the analytical method under predicts the shear modulus “ $G_{xy}$ ”. The elastic constants predicted through a multiscale homogenization approach can be used to predict the behavior of 3D-FRC under different loading conditions at the macro-level.

The effect of tightening torque and washer size on the performance of basalt natural fiber composite joints was investigated experimentally. It was found that washer size is the main design driver in controlling the out-of-plane behavior of the joint. Specifically, there was a 36.5% increase in the 0.2% offset strength when the torque was increased for small washer configurations, whereas a 42% increase was observed when the torque was increased for large washer configurations. Moreover, the ultimate bearing strength also showed an improvement under the combined effect of washer size and tightening torque. Additionally, damage onset and failure mechanisms of the bolted joint were investigated using optical microscopy. The morphological observations indicated excessive crushing for large washer configurations. It is postulated that bearing performance could be improved by choosing appropriate washer size and tightening torque.