Reliability Analysis Of C/SiC Composite Bolted Joints

Carbon fiber reinforced silicon carbide ceramic matrix composite is widely used in new aircraft due to its high specific strength and modulus.Compared with traditional metal materials,the preparation process of C/SiC composites is complex,and the mechanical properties have great dispersion.Mechanical connection is usually the weak part of C/SiC composite structure,which is easy to failure under complex environmental load.Therefore,C/SiC composite bolted joints are taken as the research object,and the reliability of bolted joints under static load and dynamic load is analyzed.Firstly,this paper establishes a progressive damage modal of C/SiC composite bolted joints,and estimates the ultimate failure load of the bolted joints through simulation analysis.The progressive damage analysis modal uses an improved three-dimensional Hashin failure criterion to determine whether the structure unit has failed.According to the respective characteristics of composite fiber and matrix,the stiffness drop-off degradation model is used for the failure mode related to fiber,and the exponential stiffness degradation model is used for the failure mode related to matrix.The ABAQUS software and the UMAT program were used to conduct progressive damage analysis on C/SiC composite perforated plates.The ultimate failure load of the structure is basically consistent with the test results,and the structure failure mode is basically the same,which verifies the effectiveness of the modal.Then,the progressive damage model is used to analyze the reliability of C/SiC composite bolted joints under static load.Establish a finite element model of C/SiC composite bolted joints,and the C/SiC composite performance parameters as random variables.Through the Bucher method selected sample points,and substitute them into the progressive damage model for finite element analysis to obtain the ultimate load of the sample point.Then the quadratic response surface function without cross term is used to fit the structural function,and the failure probability of the structure under tensile load is obtained by the checkpoint method.The tensile strength test of C/SiC composite bolted joints at normal temperature is carried out.Comparing the load-displacement curve,structural ultimate load and failure mode of the bolted joints under tensile load,the test results are basically consistent with the simulation results.Finally,the fatigue reliability of C/SiC composite bolted joints under random vibration load is studies.First,the three-point bending fatigue test data of C/SiC composites is analysis.The P-S-N curve of C/SiC composites in the case of small samples is obtained by heteroscedasticity regression analysis.Then,taking the typical C/SiC composite bolted joints as the research object,a finite element model is established,and the effectiveness of the model is proved by the modal test,and the boundary conditions of the model are corrected by the frequency response test.Then,the random vibration analysis of bolted joints is carried out by applying basic excitation,and the stress response of the dangerous position of the structure is obtained.Combined with the material's P-S-N curve and fatigue cumulative damage criterion,the fatigue reliability of the structure is evaluated based on the frequency domain method.Finally,the random vibration fatigue test of C/SiC composite bolted joints is carried out.The failure location of the structure is consistent with the simulation results.The failure mode of the structure is that the bolts are loose,which makes the structure lose its original load-bearing capacity.The results of the structural fatigue reliability analysis are verified.