Investigation On Fatigue Performance Of T800 Carbon Fiber Composite Material And Structure

In the field of aeronautics and astronautics,there are more and more cases under alternating load.The conventional fatigue life model s and prediction methods can not be directly applied to composite materials.Under different loads and stacking sequences,the fatigue performance of composite materials is significantly different.The combination of fatigue test and theoretical analysis is the main method to determine the fatigue life of composite material structures in aerospace and other fields.It is of great scientific value and practical engineering significance to study the fatigue damage evolution,failure mechanism and life prediction of composites.In this paper,based on the building block approach,the fat igue properties of carbon fiber/epoxy resin composites are studied by experiment and numerical simulation,and the fatigue properties of specimens with embedded delamination damage and composite structural component are analyzed.Firstly,the research progress of fatigue properties of carbon fiber composites is introduced,and the development status of fatigue test research and fatigue model is summarized.The fatigue properties and failure modes of composites under different fatigue loads are studied,and the detection methods in the process of fatigue test are introduced.The fatigue models of composite materials are mainly summarized,including fatigue life model,residual strength model,residual stiffness model and progressive damage model.This paper introduces the development o f building block approach,and applies building block approach to the fatigue performance research of composite structures.Secondly,quasi-static tensile test,tension-tension fatigue test,quasi-static compression test and compression-compression fatigue test are carried out for [0]16and [90]16 unidirectional plates respectively,and quasi-static off-axis tensile test and fatigue test are carried out for [±45]8 laminated plates.The failure modes of unidirectional plates with different stacking sequences are analyzed,and the difference between quasi-static and fatigue failure is compared.The residual stiffness model and residual strength model of unidirectional plate s are obtained by fitting the test results.The constant equal life models and key parameters of T800 carbon fiber epoxy resin typical unidirectional plates are given,which provide basic fatigue performance parameters for finite element simulation.Quasi-static tensile test and fatigue test under different load levels are carried out for laminates with specific stacking sequence.Based on the three-dimensional Hashin criterion,the maximum stress criterion and the Ye delamination criterion,the fatigue failure criterion applicable to composite laminates is summarized,and the sudden degradation rule of material properties under fatigue load is proposed.On this foundation,the fatigue progressive damage analysis model of T800 laminates is established,and the fatigue life and fatigue damage failure process of T800 laminates are predicted.The simulation results are consistent with the experimental results.The interlaminar properties of composites are weak,and the interlaminar properties directly affect the compressive load of materials.Therefore,different types of specimens with embedded circular and rectangular delaminations are designed and manufactured,and compression tests and numerical simulation are carried out.The progressive damage model of T800 carbon fiber twill fabric laminates with typical embedded delaminations is established,and the variation of compressive strength with delamination area and location is revealed.Compression fatigue tests are carried out on the specimens with non-delamination and embedded delaminations,and the influence of embedded delamination on the compr ession fatigue performance of the specimens is analyzed.Finally,the fatigue properties of composite structural component are studied.The fatigue performance test system of T800 composite I-beam structure is built,and the typical damage failure mode and fatigue life of the structure are obtained.By comparing the results of visible damage and strain,the causes of damage occurrence and propagation are analyzed.The fatigue life analysis model of the structure is established,and the prediction results are in good agreement with the test results.