Crack Propagation Of Lip-shaped Matrix Crack Of Ceramic Matrix Composites And Effect On Damage Evolution

Ceramic Matrix Composites(CMCs)have become one of the most popular materials for high temperature components in aero-engines due to their high strength,low density,high temperature resistance,good wear resistance,and high oxidation resistance.However,CMCs are brittle due to their poor plastic deformability and cracks are easy to appear in the matrix under load.In particular,there are a lot of defects in the matrix itself,such as cracks and voids.The further expansion of matrix cracks will seriously affect its performance.Therefore,it is important to explore the influence of matrix cracks on the damage evolution process of CMCs.Firstly,the matrix crack of CMCs was abstracted as a lip-shaped crack,and a mathematical model of the lip-shaped crack was established.The complex potential function of the lip-shaped crack under arbitrary tensile load was derived using the complex function and conformal mapping methods.The stress field and displacement field were obtained according to the fracture mechanics theory.The expressions of Ⅰ mode stress intensity factor and Ⅰ mode energy release rate at the tip of the lip-shaped crack were given,as well as the expressions of Ⅰ-Ⅱ mixed mode stress intensity factor and energy release rate were given.The I mode failure criterion and the Ⅰ-Ⅱ mixed mode failure criterion were established,respectively.Secondly,off-axis tensile experiments on unidirectional fibre-reinforced C/SiC ceramic matrix composites were carried out.The off-axis tensile stress-strain curves and full-field strain clouds on the surface of the specimens were obtained.The failure rules of matrix crack were investigated.Finally,a numerical model of CMCs contained randomly distributed lip-shaped cracks was developed to simulate the failure process with I mode lip-shaped matrix cracks and Ⅰ-Ⅱ mixed mode lip-shaped cracks under tensile loading.The influence of matrix crack on the damage evolution of CMCs was investigated,and the influence of several factors,such as the size,the distribution of lip-shaped cracks,and the interfacial strength on the results was also analyzed.The simulation results were in good agreement with the experimental results.