Z-pin effect on interlaminar mechanical and ablation performance of quartz-phenolic composites

When a spacecraft flies at a high speed through a high-heat flow, the ablative composites suffer from severe delamination and bulging due to their weak interlaminar performance. This will interfere normal operations of spacecraft. To improve the interlaminar performance of ablative composites is of great significance to the ablative structures. This study investigated Z-pin reinforced quartz-phenolic composites and reinforcement mechanism. First, a thermogravimetry (TG) test was used to analyze the thermal decomposition process of the phenolic. Second, a series of tests, including a single Z-pin pull-out, a single-lap joint tensile and an oxyacetylene ablation test, were conducted to investigate composites' ablation performance. We also deployed a 3D morphometer and an infrared thermography to reveal the function of Z-pins. The results demonstrated that Z-pins can improve composites' ablation performance in both structure and function. In the structure, Z-pins suppress the interlaminar delamination of composites by enhancing the interlaminar strength. As the ablation time increases, interface bridging between the Z-pin and laminates contributes increasingly to the interlaminar shear strength of laminates. After 60 s of ablation in a flame of 920 degrees C, the interlaminar shear strength of Z-pin specimens is 84.66% stronger than that of the normal composites. In the function, the Z-pins suppress large areas of bulges by providing escape channels for pyrolysis gas, and reduce bulging areas by 60%. Z-pin technology can effectively suppress mechanical erosion of the ablative surface due to the delamination and bulging. It is an important way to improve ablation performance of ablative structures.