An Optimal Design Method for Off-Axis Tensile Test Specimens of Unidirectional Ceramic Matrix Composites

Abstract

The invention discloses a method for optimizing the design of an off-axis tensile test piece of a unidirectional ceramic matrix composite material, comprising: establishing a parametric model of a traditional ceramic matrix composite material off-axis tensile test piece based on the finite element method; Calculate the elastic properties of composite materials by the degree average method; establish the off-axis local coordinate system; solve the model loading, extract the maximum axial stress and maximum internal shear stress of the test section, and the axial stress field of each node; construct stress comparison parameters Process the obtained stress; set optimization constraints and optimization goals, bring them into the optimization program for calculation, and output the optimization results; verify and analyze the optimization results. The invention effectively reduces the deformation of the test piece caused by the additional bending moment in the off-axis stretching process, and ensures that the test piece will not fail due to in-plane shear stress. Therefore, the success rate of the test is improved, and effective test data can be obtained, which provides a test basis for the study of its mechanical properties.

Description

technical field [0001] The invention relates to a method for optimizing the design of a unidirectional ceramic matrix composite material off-axis tension test piece, which is mainly used to solve the deformation of the test piece caused by the additional bending moment in the off-axis tension, the uneven stress distribution, and the Failure due to shear force and fracture not in the test section. Background technique [0002] Ceramic matrix composite materials have advantages such as high specific strength, good high temperature resistance, and low density. They are important hot-end parts materials for advanced aero-engines in the future. They have been initially successfully applied in foreign military and civilian aero-engines, and my country is also actively Carry out corresponding research work. In engineering applications, braided ceramic matrix composites are more widely used. However, in actual work, due to the complex stress environment of ceramic matrix composites...

AI Technical Summary

Problems solved by technology

[0003] However, due to the brittleness of ceramic matrix composites, there are problems in the off-axis tensile test of traditional test pieces (1) how to ensure that there are complete load-bearing fibers on the test piece; (2) how to reduce the deformation caused by the additional bending moment; (3) How to ensure that the specimen will not fail due to in-plane shear stress; (4) How to ensure that the stress in the test section is uniform and the fracture occurs in the test section, etc.

As a result, the success rate during the test is very low, and it is difficult to obtain valid test data

Due to the lack of corresponding test support, most of the current literature does not consider the change of the failure mode of the fiber bundle under off-axis loading when studying the off-axis tension of ceramic matrix composites, and ignores the unidirectional ceramic matrix when the off-axis angle increases. The transformation of the failure model of composite materials has made the research on the deformation and failure behavior of unidirectional ceramic matrix composites under off-axis tensile loads insufficient, and has not fully revealed the matrix cracking and failure of ceramic matrix composites under off-axis tensile loads. Evolution law of three failure mechanisms of interface debonding and fiber failure

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