Meso-scale Modeling Of Damage Development And Failure Of Composite Laminates

ii Composite laminates have been widely used in the field of aviation and aerospace because of their high specific strength,high specific stiffness,and designable characteristic.Since the failure mechanism of composite laminates is very complicated,finite element method has becoming the most wildly used method for modelling their failure and for analyzing the underling mechanism.In the current study,a better meso-scale finite element modelling method for composite laminates has been proposed by combining and improving cohesive element method,phantom node method,and continuum damage model method for modelling delamination,matrix cracking,and fiber direction damage respectively.The main contents are summarized as follows:(1)A fatigue cohesive model based on double-linear static cohesive model has been developed,based on which a zero-thickness fatigue cohesive element has been established.In order to solve twodimensional fatigue delamination problems with irregular meshes by using the proposed cohesive element,a delamination front tracking method,as well as suited delamination propagation algorithms,has been proposed based on status of mesh nodes.Upon that,a fatigue delamination propagation modelling method based on cohesive elements has been proposed.By using the method to study different one-and two-dimensional fatigue delamination propagation problems,its validity has been proved,and influences of mesh density and model parameters on modelling results have been investigated.(2)Based on the fatigue cohesive model,a fatigue phantom node method has been established.After improving its static cracking algorithm and after developing suited fatigue cracking algorithms,a modelling method for matrix cracking of composites laminates has been proposed considering both quasi-static and fatigue loading conditions.Via problem analyzing,validity of the new method has been proved and influences of mesh density and model parameters on modelling results have been studied.(3)Models for fiber-direction damage and nonlinear in-plane shear have been introduced into phantom node elements and,in order to suit that element,a three-dimensional phantom node cohesive element has been developed by following the rationale of phantom node method.Based on that,a new method for modelling quasi-static failure of composite laminates is established.Then,tension of openhole quasi-isotropic laminates has been studied to investigate the validity of the new method.Based on modelling,influences of structure sizes on load bearing capacity have been discussed,while the underling reasons for the variation of predicted failure load of structures with different sizes have also been investigated.Meanwhile,the importance of matrix cracks on failure of composite laminates under tension has been pointed out.Whereafter,influence of mesh density has been discussed thoroughly and availability of using reduced cohesive strength when modeling delamination and matrix cracking has been investigated.(4)By introducing fatigue cohesive model into phantom node cohesive elements and by simplifying fatigue delamination propagation algorithms,a modelling method for damage propagation and failure of composite laminates under fatigue loading bas been developed based on that for quasistatic situations.Also,damage developing algorithms has been adjusted in consideration of the characteristic of fatigue models.By using the proposed method to model failure of open-hole quasiisotropic laminates under tension-tension fatigue loading,its validity has been discussed and mesh dependence of the current method has been studied.In the meantime,influence of model parameters has been investigated.