Research On The Composite Damage Mechanisms Based On 3D Structure Evolution Characterization

Both the artificial composites and the composites in nature have been widely concerned by the materials scientist and the design engineer due to their excellent mechanical properties.The excellent mechanical properties of composites were closely related to the microstructure morphology and the interaction between micro structures of composites.So it has important theoretical significance and engineering application value to research on the three dimensional(3D)micro structure evolution and the interaction mechanism of microstructure-applied load for a deep understanding of composite damage mechanisms,mechanical properties and for the further structure optimization design.In this paper,the relevant research work has been conducted on single fiber composites with simple micro structure,the shell of the Strombus gigas with the crossed lamellar micro structure and short fiber-reinforced composites with 3D randomly oriented micro structure.The 3D internal morphology evolution images such as pore formation,crack initiation and propagation were obtained through synchrotron radiation X-ray computed tomography at sub-micrometer resolution and the mechanics parameters associated with material mechanics performance were obtained through quantitative extraction of the real micro structure morphology and deformation evolution information.By combing the mechanics parameters with the corresponding mechanical model,the interaction mechanism of different 3D microstructures was analyzed and the damage initiation,propagation and evolution mechanisms of pore and crack etc.were revealed.The main content and the innovation of this paper are:Firstly,the strain concentration accumulation induced microcracks initiation mechanism and the remote damage mechanism of fiber interface deformation localization caused by crack tip were proposed.1.The experimental study on the single fiber composites damage evolution was carried out through synchrotron radiation X-ray computed tomography.The microstructure morphology and deformation evolution images during the process of microcracks initiation,propagation and material failure were obtained and local large deformation of matrix in single fiber composites before crack initiation was observed.The strain concentration accumulation induced microcracks initiation mechanism was proposed accordingly.2.The nonlinear deformation of fiber interface appeared during the crack propagation through the fiber in single fiber composites and the remote damage mechanism of fiber interface deformation localization caused by crack tip were proposed.Secondly,the toughening mechanisms of crack deflection in the crossed lamellar microstructure were revealed.1.The 3D microcracks morphology evolution in the shell of the Strombus gigas was obtained from the experiment and the special damage evolution of the reverse C type crack morphology was observed.The toughening mechanisms of weak layer multiple cracking in the first level aragonite fiber structure were proposed.2.The crack bridging toughening mechanisms of the second level aragonite fiber structure were proposed based on the net crack morphology observed in Strombus gigas loading experiment.Thirdly,the key mechanisms of micro-damage processes of randomly oriented short fiber-reinforced composites were investigated.The 'fiber-end aggregation-induced pore connection' mode of crack initiation was proposed.1 The pore formation mechanisms caused by shear stress concentration were proposed on the basis of the contact relationship between pore formation and fiber ends obtained from the SR-CT experiment.Two key micro structure parameters fiber length and orientation angle could determine whether the pore appeared by determining the value of shear stress at the fiber ends.2 The 'fiber-end aggregation-induced pore connection' mode of crack initiation was proposed based on the fiber-end aggregation features of the real internal microstructure surrounding the sheet crack.Two key micro structure parameters,particularly,the distance between neighboring fiber ends and the number of neighboring fiber ends,were decisive factors in the proposed mode.Finally,a summary of the full text was given,and the main contents and results were shown,and the research ideas and direction for the future work was raised.