Reliability Research And Sensitivity Analysis For Carbon/Carbon Exit Cone’s Material Parameters

The service environment of solid rocket nozzle is very complexity, during the operation of the nozzle,it suffer high temperature and high pressure. Carbon/Carbon exit cone,which has a series of excellent performances of light weight,high strength,low ablativity,good thermal shock resistance and so on,were applied in the nozzle widely. But the nozzle involves various material systems, the structure is very complicated. The harsh service environment of solid rocket nozzle, especially the discrete material parameters of composites,makes the exit cone may have several kinds of primary invalidation modes. In this paper,we use the solid rocket motor nozzle C/C exit cone as the research object.Using different quantization models to describe the uncertain parameters. A high precision finite element model of nozzle structure was built based on the interface data of exit cone which was obtained by three experiments.And based on the finite element model, the reliability analysis and sensitivity analysis of the exit cone under the different quantization models was studied.The main research work of this paper is as follows:(1) A normal atmospheric temperature shear experiment was designed to verify the interfacial glue layer has a good reproducibility before its damage,and obtained the shear strength of the glue layer; A high temperatur e shear experiment was designed to obtain the critical temperature of the interfacial glue layer; Through the design of the one-dimensional heat transfer model experiment, and combined with the numerical simulation, the correctness of the heat transfer mod el is verified. According to actual material performance, load and heat boundary condition, A high precision finite element model of nozzle structure was built.(2) Based on the well-established nozzle thermal structure model, The mean value of the material parameters was used as the numerical simulation input data, and the first strength theory was used as the failure criteria,At last,the finite element analysis results shows that the exit cone has three primary invalidation modes: interlaminar shear invalidation, axis compress invalidation, and hoop compress invalidation.(3) The input material parameters matrix was generated by the Latin hypercube sampling.Then the corresponding response was obtained by the finite element analysis.The response surfaces of the three invalidation modes were obtained by a higher order fit. Using probabilistic model and non-probabilistic model to quantify the material uncertainty parameters, determine the range of the material parameters.(4) Based on the response surface, the reliability index of different quantization characterization under different failure modes was calculated. And the reliability index of different quantization characterization was compared with each other.At last, the sensitivity of different characterization methods under different failure modes was calculated.And the result showed that the thermal expansion was the most.important factor of the interlaminar shear stress, axis compress stress, and hoop compress stress.