Investigation On Out-of-Plane Shear Fatigue Properties Of 3D Woven Composite Materials

Composite materials have the advantages of high specific strength,specific stiffness and good fatigue resistance,which have important application value in aviation,aerospace and other fields.Especially with the development of aerospace field,higher requirements for materials are put forward,and three-dimensional woven composites are invented.Due to the complex microstructure,macro anisotropy and micro heterogeneity of 3D woven composites,there are still many unsolved problems in the study of mechanical properties and damage evolution mechanism.At present,a lot of achievements have been made in the study of tensile and compressive properties of 3D woven composites,but there are few reports on the shear,especially the out of plane shear fatigue of 3D woven composites,which is a lack of fatigue life assessment of 3D woven composites.In order to solve these problems,this paper will deeply study the out of plane shear fatigue test method,damage failure mechanism and performance prediction method.The research status of 3D woven composites at home and abroad is summarized and reviewed through the investigation of relevant literature.The research progress of out-of-plane shear fatigue of 3D woven composites at home and abroad is introduced and analyzed in detail The damage criteria and fatigue damage evolution simulation of woven composites are reviewed.This investigation mainly analyzes the achievements and limitations of shear fatigue test of 3D woven composites,reviews the existing research methods of composite damage mechanism,and summarizes and analyzes the structure of composite equal life curve and life prediction.At the same time,this investigation reviews the damage criteria and fatigue damage evolution simulation of woven composites,summarizes the achievements and limitations,and finally clarifies the purpose,significance and main research contents.A set of test methods for out-of-plane shear fatigue properties of 3D woven composites is proposed,and a special fixture for loading out-of-plane shear fatigue properties of 3D woven composites is designed.The out-of-plane shear static and fatigue mechanical properties of 3D woven composites were studied;Combined with 3D DIC(three dimensional digital image correlation)technology,a test and analysis system of 3D woven composites was built.The mechanical properties of3 D woven composites,such as out-of-plane shear stiffness,strength and fatigue life under specific loading conditions,were obtained,and the failure process and mechanical response were recorded.The results show that the test method proposed is stable and reliable,which can promote the study of static and fatigue mechanical properties of 3D woven composites.The out-of-plane shear fatigue damage mechanism of 3D woven composites is studied.Based on the experimental method proposed,the out-of-plane shear fatigue properties of 3D woven composites were systematically studied by means of 3D DIC strain measurement system,non-contact full field temperature measurement thermal imager,optical microscope and micro CT technology.The S-N curves of two stress ratios(R = 0.1 and R =-1)were obtained.Next,through a variety of means,the typical fracture morphology was observed by optical microscope,the internal cracks of 3D woven composites in out-of-plane shear fatigue were observed by micro CT,and the temperature during the fatigue test was monitored by thermal imager in real time to reveal the damage mechanism of 3D woven composites in out-of-plane shear fatigue.The out-of-plane shear fatigue life criterion of 3D woven composites is proposed,and the suitable fatigue life criterion is established according to different material service conditions.In order to meet the requirements of materials under different working conditions,the concept of S-N curve cluster is proposed,and the S-N curve cluster of three-dimensional woven composites under out-of-plane shear fatigue is established.Then,the model of nonlinear DSR CLD(dual stress ratio constant life diagram)for out-of-plane shear fatigue of 3D woven composites is established,and the equal life curves of the materials under different fatigue life criteria are given.Based on the equal life model,a fatigue life prediction model is established,and a method to obtain S-N curve under arbitrary stress ratio is proposed.A progressive damage failure model of 3D woven composites under out-of-plane shear fatigue is established.Based on the multiphase finite element method,a full-scale out-of-plane shear finite element model of 3D woven composites is established.In this model,the strain discordance effect between fiber and matrix,the nonlinear effect of fiber compression twist band,fiber transverse failure fracture angle and fiber shear failure are introduced,and the nonlinear damage process of epoxy matrix is considered.Then,the stiffness and strength degradation model of fiber bundle and matrix under fatigue load is combined,The stiffness degradation,life and S-N curve of 3D woven composites are predicted.The predicted results are in good agreement with the experimental results.Finally,this investigation analyzes the out-of-plane shear fatigue failure process of 3D woven composites,reveals its failure mechanism,and provides reference for out-of-plane shear fatigue design of 3D woven composites.