Creep Mechanics Behavior And Mesoscopic Mechanics Simulation Of CMCs

CMCs are widely used in hot end parts of aeroengine because of their light weight,high temperature resistance and high strength.SiC/SiC composites which belong to CMCs have excellent oxidation resistance.The use of CMCs in long-term high temperature and high stress will result in creeping of the material,which will cause two effects:(1)The creeping material may touch or even squeeze other parts.(2)Long-term creep may weaken the material properties and finally lead to fracture.Therefore,the study of CMCs creep properties and prediction of CMCs creep curve provide a basis for the future use of CMCs.In this paper,the creep behavior of SiC/SiC composites was studied.This paper manufactured special fixture in consider of the small size and brittle characteristics of mini-composites.The creep tests in aerobic and anaerobic conditions were carried out at 900℃ and 1000℃ with load of 108MPa-232 MPa.The fracture surface of the material was analyzed by SEM.The results showed that the composites have better creep resistance,smaller strain and longer service life under anaerobic conditions.The probability model of the fiber strength distribution was established,and the fracture strength of the monofilament in the mini-composite material was obtained.The mesoscopic mechanical model of mini-composites was established to simulate the distribution of fiber stress at different oxidation degree.The strength probability model was used to judge the material failure.This method explains the failure mechanism of mini-composites under aerobic conditions from the meso-perspective.The creep curves of mini-compostes were fitted by Curtin-McLean model.The creep model of 2D weaved materials was predicted by the second development function of ANSYS.The method is effective for predicting the creep of complex weaved composites.