Numerical Analysis Of Residual Stresses And Fracture Forms In C/SiC Composite Joints

Carbon fiber reinforced silicon carbide matrix composite(C/SiC) has many excellent mechanical, physical and chemical properties at high temperature, so it's used among the candidate material in the fields of spaceflight, aerial, weapon and nuclear energy. But it's difficult to fabricate complex, multicomponent structures for the limitation of woven methods of C/SiC components. As a result, the joining of the components in the applications must be solved. However, the stress concentration appears during joining and loaded will decrease the mechanical properties, so it's important to research the residual stresses and fracture forms for the design of the C/SiC composites joint.The residual stresses appear during the joining process with On-Line Liquid Infiltration Joining of C/SiC composite and stress concentration in riveting joints when loaded are stimulated by FEM method. In order to make the result more reliable, experiments are carried out to examine the stimulation results. The main contents and conclusions are as follows:(1) The effect of the porosities in the textile composites on the stress in the joints by on-line liquid infiltration process has been studied. Different porosities have little effect on the residual stresses distribution, but it influences greatly the maximum of the stress. It is shown that the maxima of residual stresses decrease with the porosities increasing, however, the residual stresses decreasing speed becomes slow after the porosities reaching to 17%.(2) The relation between the cone angle and the stress concentration in the riveting C/SiC joints when load is in the axial orientation has been investigated. The stress concentration will be the minimum when the cone angle is in the range of 2° to 10° . As a result, a formula describing certain relation between the geometrical structure parameters and fracture forms of joints was obtained, if the parameters satisfy this formula, rivet will break, otherwise, the rivet will be pulled out of SiC.(3) The fracture forms of the C/SiC composites riveting joints have been analyzed, based on the result, the optimal design was obtained. The joints will be damaged from shear fracture in the rivet when component size given. When the joints under 1200N shear load, it will be lightest with radius of rivet being 2.2mm and the thickness of the joining component being 3.0mm.(4) Experiment was carried out to validate the numerical stimulation analyses. It is testified by the experimental results that the established FEM-models to analyze the stress concentration and fracture forms are rational and the stimulation results are right.