Damage Evolution Of 3D Braided Composite Shaft Based On Acoustic Emission And 3D-DIC

The fiber reinforcement has a spatial network structure in the three-dimensional braided composite material,which has the advantage of impact resistance and fatigue resistance,and overcomes the conventional laminated composite material.Due to its good mechanical properties and integrity,the three-dimensional braided composite shaft has great potential in the fields of aerospace,wind turbines and automotive.The structural parameters of 3D braided composites have an important influence on its mechanical properties,so studying the damage evolution process of materials under different structural parameters can help optimize the design of 3D braided composite shaft structure and improve safety.The composite damage failure process is complicated,and multiple damage modes are difficult to distinguish.In this paper,Acoustic Emission(AE)and 3D Digital Image Correlation Method(3D-DIC)are used to monitor the static load torsion process of three-dimensional braided composite shafts with different braid angles.The damage signal and the surface deformation of the specimen were studied for the material failure process,and the damage mechanism was further discussed by the finite element analysis using the mesoscopic cell model.main tasks as follows:1.Design and prepare three-dimensional braided composite shaft test pieces,build a torsion experimental platform,acoustic emission monitoring and three-dimensional digital image acquisition systems.The experimental method was used to test the static load torsion performance of the threedimensional braided composite shaft,and the angle-load curve was obtained.The influence of the braiding angle(25°,35° and 45°)on the mechanical response was discussed.The experimental results show that with the increase of the braiding angle,the bearing capacity of the three-dimensional braided composite shaft is improved.The fracture characteristics are studied by electron microscopy and the crack propagates inward along the fiber weaving direction.2.The AE signal is collected by the acoustic emission synchronous monitoring system.Firstly,based on the three characteristic parameters of event counting,energy and peak frequency of AE signal,the damage trend of the damage process is described.The results show that the damage process of the three-dimensional braided composite shaft is divided into three.Stage,initial stress stage,damage accumulation stage,and concentrated damage stage.Then,multiple feature parameters are selected and simplified by principal component analysis.According to the clustering performance index,the fuzzy clustering analysis of the simplified results is used to achieve the purpose of damage pattern recognition.The results show that the simplified results cluster analysis is mainly divided into three categories,according to the three-dimensional braided composite damage form corresponding to matrix damage,fiber / matrix debonding damage and fiber breakage.The matrix failure type has a low frequency and the number runs through the entire loading process.The fiber/matrix debonding and fiber breakage types are distinguished from the time domain waveform characteristics.Finally,the characteristic waveforms of different damage stages are selected for wavelet transform,and it is found that the energy migrates from the low frequency band to the high frequency band with the accumulation of damage.As the braiding angle increases,the test piece is broken by the matrix damage accumulation and the fiber/matrix debonding and fiber breakage damage accumulation.3.The three-dimensional digital image is processed to obtain the strain field of the threedimensional braided composite transmission shaft.Combined with the comprehensive analysis results of the AE signal characteristic parameters,the strain field energy of the specimen can accurately predict the location of the damage failure.The damage accumulation is local,mainly concentrated on the damage.Near the fracture area of the test piece.4.In the finite element simulation of three-dimensional braided composite material shaft,the microcell model based on periodic braided structure was adopted,and Hashin failure criterion and maximum stress failure criterion were set respectively for fiber and matrix for damage determination.The simulation results show that the damage of the model first appears at the interface between the fiber and the matrix,and the matrix damage expands and connects with the increase of the load,and finally leads to the failure of the specimen.And with the increases of the braiding Angle,specimens bearing capacity enhancement and fiber damage increases,45 ° model carrying capacity of the largest and fiber damage is serious.The results are consistent with the experimental results.