The Mechanical Behavior of Air Textured Aramid Yarns in Thermoset Composites.

Abstract

The purpose of this study was to investigate the properties of air-textured aramid yarn (ATAY), in a single yarn composite (SYC), in a 3D woven fabric preform, and in a 3D preform composite. Yarn tensile tests demonstrated textured yarn was 70-77% lower in tensile strength, 82-85% lower in tensile modulus, and 60-190% higher in breaking strain than those of the control yarn. The results of SYC testing illustrated that the control yarn composite had only a 5% higher tensile strength, a 27% higher modulus, and 11% lower energy to break than the textured single yarn composite. Fabric tensile tests demonstrated a low initial modulus and a much larger secondary modulus for all 3D woven preforms. The ATAY fabric had a similar initial modulus and a much lower secondary modulus in the weft direction compared to the control fabric. The ATAY fabric had a significantly higher yield shear stress and strain, primary and secondary shear moduli, energy to yield point, and total energy absorbed to 4° than those of the control. With the same fiber volume fraction, the ATAY composite had a slightly lower tensile strength and modulus, but a 120% higher shear modulus, than the regular aramid yarn (RAY) composite. Unlike the RAY composite brittle failure behavior, the ATAY composite failed in a ductile manner with multiple diverting cracks propagating during failure. The ATAY composite had a much higher yield point in the 45° direction tensile test, a much higher softening point in the warp direction tensile test, and increased the interlaminar shear strength of a laminated composite by 37% as compared with the control.