Numerical Simulation Of Tensile Behavior Of Unidirectional Ceramic Matrix Composite Under Off-axial Loading And Its Application

Ceramic Matrix Composites(CMCs)are important thermal component materials in furture advanced aircraft-engines because of their advantages,such as: high specific strength,high temperature resistance and low density.CMCs have been applied to forgein military and civilian aircraft-engines for initial successful application.And similar research works are also carrying out actively.Generally,woven CMCs(such as 2.5Dimension CMCs and 3Dimension-4direction CMCs)are widely used in engineering application.In woven CMCs,fiber bundle can be regarded as unidirectional CMCs,Due to the angle between the axial direction of the fiber bundle and the main direction of the composite,the fiber bundle is usually under an off-axis tensile load.At the same time,the interlacing and extruding between the fiber bundles at the intersection introduces transverse compressive load to fiber bundle.In order to investigate the deformation and failure behavior of woven CMCs accurately,it is necessary to study the deformation and failure behavior of unidirectional CMCs under off-axis tensile loading and complex loading conditions.An optimized design method for the off-axis tensile test piece of unidirectional ceramic matrix composites is proposed to obtain the shape of the optimal test piece under different off-axis angles.The off-axis tensile tests of unidirectional CMCs with three different material systems were carried out,and the tensile stress-strain curves were obtained under different off-axis angles.The similarities and differences of failure modes under different off-axis angles were compared and analyzed.The concept of critical off-axis angle was proposed.A new method for testing fiber characteristic strength and Weibull modulus was proposed,and the characteristic strength and Weibull modulus of T300 and T700 fiber were measured.Fiber shear experiments were carried out to measure the shear strength of T300 and T700 fiber.Tensile tests of 2.5D CMCs and 3D-4d CMCs were carried out,and the fractures were analyzed by microscopic observation.The failure analysis models under complex stress condition of different component in CMCs have been established.Based on the continuum damage mechanics model of brittle materials proposed by Benjamin Richard,the anisotropic damage caused by crack initiation in brittle materials is further considered,and combined with the probabilistic failure analysis method,a numerical model can be obtained for deformation and failure analysis of brittle materials under complex stress condition.On the basis of interface cohesive zone model(CZM),a numerical model has been build to analysis the failure behavior of interface in CMCs under complex loading condition.The proposed model has been compared with the cohesive model in ABAQUS.Combining the fiber probability failure model with fracture mechanics theory,the random distribution of the initial cracks of the fibers can be derived,and the distribution of the axial tensile strength of the fibers at different positions of the fibers can be further derived,and the transverse compressive strength and dispersion of the fibers are combined according to the strength criterion.Finally,substitute the random distribution model of fiber strength into the Tsi-Wu strength criterion to analyze the failure behavior of the fiber under complex load conditions.Unidirectional CMCs with random distribution of fibers was established,and the failure modes of matrix,interface and fiber under complex load were introduced to simulate the failure behavior of unidirectional CMCs under axial and off-aixal tensile loading.The predicted stress-strain curve agrees well with the experimental results.The variation of the cracking stress of the matrix with the off-axis angle is analyzed,and the influence factors of the critical off-axis angle are discussed.The RVE model of 2.5D CMCs and 3D-4d CMCs were established,and the failure analysis database of unidirectional CMCs under complex load conditions was established.The analysis model for complex woven CMCs considering the loading state of fiber bundles were established to predict the stress-strain curve,compared to the model without considering the loading state of fiber bundles,the result of model considering the complex loading state of fiber bundles find better agreement with the experimental results.