Damage And Failure Analysis Of Carbon Fiber Reinforced Composites Across Macro-Meso-Micro Scales

The carbon fiber reinforced composites have been widely used in aerospace engineering,civil engineering,automotive engineering and so on due to the advantages of the excellent mechanical properties and its designability.Thus,the mechanical property characterization of composite materials and mechanical behavior prediction of composite structures have become the hot-pot of research of composites.Compared with the experimental methods,the numerical methods are more efficient,more economical and more suitable for material design.Besides,the composites are heterogeneous in nature,so there are important theoretical significance and application value for the development of the multiscale methods and the analysis of influence factors of composite properties.To conduct damage analysis of carbon fiber reinforced composites from the microscale to the macroscale,this study focuses on the generation of representative volume element(RVE)model,the prediction of equivalent mechanical properties and the development of multiscale methods across three scales.The emphasis is on revealing the damage evolution process of carbon fiber reinforced composites under tensile loading,which provides basis and method for material structure design and failure assessment of carbon fiber reinforced composites.The specific research work includes:1.The random perturbation method is modified to establish the fiber random distribution RVE.Based on the finite element model of the RVE,a void generation method with void shape considered is developed.With the finite element analysis method,the elastic analyses are conducted based on these models to reveal the effects of microstructures on the elastic properties of unidirectional composites,including fiber distribution patterns,fiber shapes and voids.The predicted results show that the fiber distribution patterns and fiber shapes have little influences on the longitudinal elastic parameters and great influences on the transverse elastic parameters.The voids have little effects on the longitudinal elastic modulus.However,they have great effects on the other elastic parameters.2.Based on the two-dimensional fiber random distribution models,the effects of fiber shape,void shape and thermal residual stress on the damage evolution process and transverse tensile properties are revealed.The predicted results illustrate that as the interface debonding is inhibited by the complicated fiber shape,the RVEs with gear fibers have larger tensile strength values.After the voids are considered in the RVEs,the matrix plasticity and damage make more contribution to the crack initiation.After the thermal residual stress is taken into account,the matrix damage is the main cause to the crack initiation and the strength values of the RVEs with different fiber shapes become very close.3.With the hierarchical multiscale method,the tensile properties of a kind of twill woven composites are preidicted and the effects of fiber arrangement on the predicted responses are revealed.The results indicate that the initial damage is induced in the weft tows under transverse tensile loading.It can also be found that different fiber distribution patterns result in different elastic parameters and strength values of tows,which contributes to the differences in the tensile properties of woven composites.Then the multiscale method based on the micro-mechanics failure(MMF)theory is modified with the clustering method so that the fiber random distribution pattern can be considered.With the modified multiscale method based on MMF,the tensile properties of the twill woven composites are predicted once again and the damage evolution process at the microscale can be obtained.It can be found that due to the less inter-fiber distances in the fiber random distribution model,the loading strain for the damage initiation of the mesoscale model based on the fiber random distribution model is much smaller than that of the mesoscale model based on the fiber hexagonal distribution model.4.An analytical method for the elastic property prediction of woven composites is developed.Then based on the MMF theory,a multiscale method across three scales is developed so that the damage analysis of woven composite structures at macroscale,mesoscale and microscale can be achieved simultaneously.The progressive damage analyses of the woven fabric laminates with a hole under tensile loading and the woven fabric laminates under impact loading are conducted.It can be found that the developed multiscale method can be used to not only predict the mechnnical behavior of woven composite structures,but also reveal the damage situations at the microscale and mesoscale,which demonstrates the effectiveness of the method.