航空刹车用C/C复合材料断口分析

Fractographic analysis of C/C composite for aircraft brakes

利用SEM断口形貌分析了现役航空刹车用C/C复合材料的结构和界面结合状况,探讨了其断裂机理,分析了化学气相沉积炭的沉积机理.结果表明:C/C复合材料的断裂以"弱界面断裂"为主.裂纹优先在基体炭、炭布层间或长纤维束和短纤维间的弱界面等薄弱环节处产生.当裂纹尖端扩展到基体炭中的微裂纹处时,裂纹扩展转向;当裂纹扩展到纤维时,取道纤维与基体炭间弱界面层向前扩展,纤维经历与基体炭脱粘、弯曲、拔出、断裂等过程,导致整个材料断裂.航空刹车用C/C复合材料中的CVD炭以粗糙层状结构为主,CVD过程包括碳氢气体热解、成核、炭化、沉积生长等过程,其中,成核以物理成核为主.图2,表1,参16.

The structure and interface of carboncarbon(C/C) composites for aircraft brakes has been studied by SEM. The fracture and chemical vapor deposition mechanism have been investigated. Results show that (a) the fracture of the C/C composites is weakinterface fracture. Cracks take place preferentially at the interface between carbon cloth laminates or between long bundled fibers and web shortcut fibers. When cracks propagate to the matrix, the matrix carbon fractures brittlely and cracks go forth along the weak interface between carbon fibers and matrix, during which carbon fibers go through debonding with carbon matrix, flexure, pullingout and rupture. (b) Chemical vapor deposition is the main densification method for preparing C/C composites using for aircraft brakes, while liquid impregnation and mixed processes (CVD+liquid impregnation) are also adopted. Rough laminar pyrolytic carbon is more suitable for C/C composites in aircraft brakes. The CVD process mainly includes pyrolysis of hydrocarbon gas, nucleation (mainly physical nucleation), carbonization, deposition and growth.2figs.,1tab.,16refs. 