Stress Field Analysis Near Crack Tip Buried In The Rosette Carbon-Carbon Nozzle Of SRM

This paper is based on the fund project concerning stress field analysis near crack tip buried in the rosette carbon-carbon nozzle of SRM supported by the China Aerospace Science & Technology Corporation (CASC). Flexible nozzle is one of the most important components used in SRM. The nozzle is subjected to the cautery and concussion of the hot gas and complex mechanical loads in the process of working. The existence of cracks in the rosette carbon-carbon nozzle is undoubtedly making great influence in the security of the nozzle. Under the requirements of the fund project, the main works are as following: Firstly, according to the material properties characteristics of the expanded segment of the carbon-carbon nozzle, the general solution of equal-parameter orthotropic plane crack problem is found, and is used as the interpolation functions in fractal two level finite element method (F2LFEM). Next, on the basis of the actual characteristics of the outspread segment of the carbon-carbon nozzle, one of the forty-eight sections located in the circumferential of the small head of the outspread segment, is taken as the analysis object from the whole nozzle model. According to the geometry characteristics of the analysis object, the FEA model is set up. Based on the characteristic of the exported data of the FEA model, a program is written by combining FEM with F2LFEM. Considering the structure and thermal-structure coupling as the loads of the model, the stress intensity factors (SIFs) are calculated with different crack angles. Thirdly, different isotropic interpolation elements are adopted in the crack tip field, which is discretized by fractal finite element method. The influence to the precision and convergence of the results with different element types is considered. At last, in the force of structure loads, the stress fields of the crack tip with a crack and without a crack are compared. In the existence of the crack, the stress fields near the crack tip under the structure loads are compared to that under the thermal-structure couple loads.