Study on single-lap joints tensile properties under fire and thermal conductivity of Z-pin reinforced thermal protection composites

AbstractQuartz fiber reinforced phenolic (QFRP) resin composites were often used in thermal protection structures such as the engines and tip of missiles or rockets, but its anti-erosion performance needs to be further optimized. Z-pin technology can improve the anti-erosion performance because Z-pin effectively improved the inter-laminar shear strength of composite materials. However, it will increase the through-thickness thermal conductivity (TC), resulting in a decrease of its thermal protection performance. This paper successfully established the equation about through-thickness TC of Z-pin reinforced composites based on theoretical analysis and experimental results and tested the single-lap joints tensile strength of the samples compared with the blank and Z-pin samples under fire which characterized the interlayer performance of Z-pin reinforced thermal protection composites at high temperatures. Research showed that the through-thickness TC of the composite increases regularly with the TC and content of Z-pin, and this is because the pins act as a thermally conductive pathway. The TC increases by 13.19%, 12.34% and 12.13% when the Z-pin implantation volume fraction is 2.18%, 0.785% and 0.401%, respectively. Z-pin samples have an increase in shear strength of 63.85%, 78.97% and 88.31% compared with blank samples when the ablation time is 20s, 40s and 60s, respectively, indicating that Z-pin technology effectively could reduce the shear strength of single-lap joint with the increase of ablation time. These results prove the controllability of the through-thickness TC enhancement and effectiveness of interlayer strength by Z-pin, and guide the structural design of Z-pin reinforced thermal protection composites.