Investigation Of High Temperature Mechanical Properties Of C/C Composites Based On Digital Image Correlation Technology

C/C composites is a kind of material which has the function of thermal protection and load bearing,it has high specific strength,high specific modulus and good thermal stability,and it is widely used in hypersonic vehicle fuselage,leading edge,head cone and hot parts of aero-engine,it is a key strategic material to support thermal structure technology.C/C composites need to serve in high temperature and even ultra-high temperature environment,the mechanical properties of C/C composites at high temperature are very important to structural design and evaluation,and the lack of performance parameters often becomes the bottleneck factor to limit the development of key structural components,improvement of the structure efficiency and reliability.C/C composites are composed of fiber preform and carbon matrix,it is often regarded as anisotropy material,and the mechanical properties show obvious temperature correlation,so it often needs multiple datas to support accurately grasp the properties of the material.The traditional experimental method of mechanical properties adopts simple test to construct uniform distance region.The mechanical property parameters obtained by a single experiment are limited and the test efficiency is relatively low.In view of the above shortcomings,a non-contact measurement technique was proposed to obtain the surface strain field of the sample,and the objective function was constructed by using the difference between simulation and test.A high throughput mechanical properties test method for identifying multiple elastic properties parameters was constructed by inverse method.Through the design of complex specimen shape to make the objective function is sensitive to several elastic properties parameters.The traditional mechanical properties test and room temperature parameter inverse identification method were used to test the mechanical properties of needled C/C composites at room temperature,then the feasibility of parameter inverse method in testing the mechanical properties of C/C composites at room temperature was verified.The high temperature experiment in vacuum environment was carried out to analysis the temperature correlation of mechanical properties of C/C materials,the high flux high temperature mechanical properties test method was developed,then a high temperature parameter inversion compression experiment was carried out.Several mechanical property parameters of needled C/C composites were obtained.The digital image correlation technique was used to test the surface strain field of the sample,and the objective function was constructed by using the difference between the simulated strain field and the experimental strain field,and the inverse method of material performance parameters based on the optimization problem was proposed.In order to meet the requirements of parameter inverse method for sample shape,referring to the sample configuration used in parameter inversion at home and abroad,a kind of excellent sample shape was selected by using electric / thermal / force multi-field coupling calculation.According to that sample,a parameter inversion compression sample form considering both uniform temperature field and uneven strain field was designed and optimized.The compression properties of two kinds of C/C composites were tested by traditional room temperature compression experiment,and the mechanical properties of the materials at room temperature were obtained,and the failure laws of the two materials were analyzed.The shear properties of two kinds of C/C materials were tested by two-V notch in-plane shear test.The shear modulus and strength of the two materials were obtained,and the failure mechanism of the two materials was analyzed.The virtual strain field method was used to verify the accuracy of the inversion identification program by taking the simulated strain field as the real strain field.The mechanical property parameters of C/C composites at room temperature were identified by using the completed inverse method of room temperature parameters,and the four in-plane mechanical property parameters of C/C composites were obtained,which were compared with the real mechanical properties parameters measured by the traditional method.The feasibility of parameter inversion method in testing the mechanical properties of composites at room temperature was verified.The high temperature experiments(compression,shear)of C/C composites at 1600 ? were carried out.The temperature dependence of the properties of C/C composites was analyzed.It was found that high temperature had different degrees of strengthening effect on the mechanical properties of C/C composites.The high temperature mechanical property test system was built,the high temperature mechanical property test method was developed,and the high temperature parameter inversion compression experiment of needled C/C composites at 1600? was carried out.The synchronous measurement of temperature field and strain field is completed by using thermal imager and non-contact whole field measurement method,and the temperature field data of material surface are obtained by image processing method.The finite element model with the same temperature environment and boundary condition as the high temperature parameter inversion experiment was established,and the optimization objective function was constructed by using the difference between the simulated strain field and the experimental strain field.The material parameters at high temperature were used as design variables,and the input parameters were adjusted by using the Isight optimization software,the optimized convergence value was regarded as a mechanical property parameter inversion value to obtain the mechanical property parameters of the needled C/C composite material at the temperature of 1600?.