Effect of rotary ultrasonic machining on surface structure and ablation resistance of C/C composite

Abstract

C/C composite is widely used in aerospace due to excellent high temperature mechanical properties. Improving its ablation resistance has become the focus of attention. Due to anisotropy of composite materials, the difference of thermal conductivity and thermal expansion coefficient between fiber and matrix, surface morphologies affect ablation performance greatly. In particular, fiber exposed length (FEL) and crack had a significant impact on its ablation resistance. Therefore, this paper constructed a FEL theoretical model based on machining damage, and verified that the error of the modified model was within 12 % through experiments. Meanwhile, improvement effect of rotary ultrasonic machining (RUM) was clarified. It is found that RUM reduced FEL by 15%∼38% in all fiber angles and decreased the crack pores on machined surface. Then, oxyacetylene ablation experiments on C/C composite surface under conventional machining (CM) and RUM were carried out. The results showed that RUM surface had better ablation resistance, and interface ablation and porosity decreased significantly.