The Study Of Phase Field Models Of Failure In Fiber Reinforced Composites

Fiber reinforced composites have been widely used in aviation,aerospace,automobile and energy industries because of the outstanding properties,such as high strength,high modulus,low density and tailor ability.However,on the other hand the sophisticated micro structures of composites usually result in concurrent failure behaviors in fiber,matrix and interface.Therefore,investigations of failure mechanisms are of vital importance in estimating the safety and stability of composite materials and structures.Over the past decade,phase field model offered an elegant,convincing and convenient way to deal with crack initiation and evolution and were widely used in various fracture mechanics modellings.In this dissertation different kinds of phase field models for failure in fiber reinforced composite microstructure,single ply and laminate are proposed for achieving optimal accuracy and efficiency.The main works are arranged as follows.(1)In composite microstructures,the topologies are usually very complicated and the fiber/matrix interface is very thin.In order to model the complicated failure mechanisms,the dissertation proposes a new phase field model,in which an auxiliary interface phase field is introduced and used to smear the interfacial properties.Moreover,the influence of energy split scheme on the modelling is investigated,and then two new split schemes are proposed.Therefore,complicated failure mechanisms in composite microstructures can be modelled accurately within a unified phase field framework.(2)For modelling failure in single composite ply,a modified anisotropic phase field model is proposed.In the model,the anisotropy of fracture properties is considered by a new structural tensor.Then,the effect of penalty parameter on the critical energy release rates along different directions is investigated.Accordingly,a new phase field driving force is constructed for accurately considering different failure mechanisms.(3)For the failure in composite laminates,a new explicit phase field model is proposed.In the model,four different degradations functions are introduced to characterize the influence of different failure modes on the material.Then,a new phase field driving force is constructed,that different failure mechanisms,i.e.intralaminar failure and interlaminar failure,can be captured simultaneously by the new model.(4)To further improve the modelling efficiency for composite laminates,the dissertation proposes a new phase field model that can couple with cohesive element.The intralaminar failure and interlaminar failure are modelled by the new phase field model and cohesive element,respectively.The key point is that the interlaminar failure mechanism is removed from the new model.Then cohesive element is modified,such that different failure models can be combined accurately.This new method can significantly reduce the quantity of grids and improve the capacity of modelling large scale problems.