Analysis Of Component Material In-situ Properties And Effect On Shear Properties Of Carbon/Carbon Material

C/C composites have been used in aerospace,national defense and other fields for their superior mechanical properties at high temperatures.However,in the process of C/C composite material preparation,cracks or other defects,has an important influence on the performance of materials finally;high temperature treatment process in the preparation process will lead to changes in modulus and strength of carbon fiber;in addition,the microstructure of the component materials is complicated,the in-situ propertity of the component material can be significantly different from the original property.Therefore,it is important to get the in-situ property of component materials accurately for evaluating the performance of C/C composite structures.In this paper,the in-situ properties of the component materials composites were studied,and its effect on the shear properties of the composites was investigated.The mesostructure and microstructure of 4D C/C composites were observed and characterized by various microscopic observation methods.4D axial weave C/C composite has periodic characteristics,and Z direction fiber bundle is more compact than XY plane fiber bundle,and random pores are distributed in the matrix.There is interface between the fiber bundle and matrix,and microcracks exist at the interface.The shape,size and position distribution in Z direction fiber bundle in the cross section are statistical characterized,section shape of fibers are similar to cashew shape,sizes and location are non uniform distributed,showing the stochastic characteristic.Taking the distribution of the cross section of Z direction fiber bundle getting from the real structure into account,based on two-dimensional geometry model of fiber bundles in random distribution established with same volume fraction,and the size,shape and position parameter are confirmed using the spatial statistics function,The 3D modle(RVE)are extended from the two dimensional geometric model along the Z extension.The effective elastic constants and transverse compressive strength of the fiber bundle are calculated by using the finite element method and the periodic boundary condition.The model is compared with that of the regular filament in the cross section.The transverse compression,transverse shear and shear interface of fiber bundle / matrix interface in-situ properties were experimented,and the distribution of the test results was tested by statistical analysis method.The results show that the transverse compressive strength preferentially coincides with the lognormal distribution,the transverse shear strength is preferentially coincides with the normal distribution,and the shear strength of the fiber bundle / matrix interface is preferentially coincides with the Weibull distribution.The effect of shear properties of Z direction fiber bundle and test temperature on the shear properties of 4D axial bonded C/C material was investigated.Z to the fiber bundle push out specimen and full shear specimens respectively by XY shear test,results shows that with XY shear load,Z direction fiber bundles have a enormous improvement for XY layer interlaminar shear modulus and shear strength.The double notched specimens are used for the test of shear properties of 4D C/C material at room temperature and high temperature,the results show that with the increasing of temperature,shear strength increased and then decreased,reached a maximum value at around 2000 ?,the shear modulus is nonlinear.