Assessment Of Structural Reliability Based On Strength Distribution Of Composite Material

As a kind of material with high performance,C/C composite material has the advantages of high temperature resistance,low density,high specific strength and good toughness.It has been widely used in many fields.However,due to the fiber types and processing technology,the mechanical properties of C/C composites are relatively discrete,which seriously restricts the design of engineering structures with high reliability.With the increasing requirement of structural safety performance in engineering,the structure designed by the conventional safety coefficient method can no longer meet the requirement of structural reliability in practical engineering.At present,most researches in the domestic and abroad focus on the strength and reliability evaluation of structures under static load,and are lack of studies that consider the reliability of the whole structure system and the reliability analysis of structures under dynamic conditions.Therefore,based on the method of statistical analysis and considering the dynamic response prediction of the structure under random conditions,the comprehensive reliability evaluation of the structure has important theoretical value and engineering significance.In this paper,C/C composite materials are taken as the research object,and their strength distribution and strength reliability,as well as the structural comprehensive reliability assessment method,are studied.The specific work is as follows:Firstly,the experiment test to obatian the strength of C/C composites was carried out to obtain the random distribution rule of its strength properties.To determine the number of test samples that can guarantee the accuracy of the results,a set of shear strength data which is more discrete is used for analysis,and the number of samples used in subsequent tests is determined by residual analysis.It is believed that the sample number determined by this method is applicable to both the tensile strength test and the compressive strength test.The results show that the number of samples used to obtain the strength distribution of C/C composites should be at least 30.Furthermore,the C/C composite specimens were subjected to in-plane tensile tests,in-plane compression tests,in-plane shear tests,inter-layer tensile tests,out-of-plane compression tests and out-of-plane shear tests under quasi-static conditions using the MTS electronic universal testing machine.Then,the strength distribution of C/C composites is explored according to the strength data of the materials obtained from the experiment.Weibull distribution,normal distribution and logarithmic normal distribution are used to fit the strength law of C/C composite materials.In order to correspond with residual analysis,linear regression analysis method is used to solve the parameters in the distribution model.In addition,in order to compare the fitting accuracy of the three distribution models,the goodness-of-fit test of the three strength distribution models mentioned is conducted by using different test criteria,and the strength reliability of C/C composite materials is evaluated according to the obtained optimal fitting distribution model.The results show that Weibull distribution could characterize the strength distribution of C/C composites well.Finally,by considering the randomness of structural dynamic response and structural strength performance,structural safety performance analysis is conducted based on the Tsai-Wu failure criterion.Then,the reliability of the structure under dynamic random load is evaluated.The intensity variation rule of the structure is simulated by the optimal fitting model,and the sturctural dynamic response is predicted by the mean value.When calculating the dynamic response prediction of the structure,the orthogonal anisotropy of the material is taken into account.The Latin hypercubic sampling method is used to calculate the mean value and variance of the response by considering the uncertainty of the structural parameters.Numerical simulations on a rudder structure is carried out,and the comprehensive reliability of the structure is given.