Investigation Of Damage Evolution And Failure Of The Three-dimensional Woven Composites

Three-Dimensional(3D) woven composites are a type of structure composites, which are used in the fields of aviation, aerospace, constructional engineering, medical devices and so on. The fiber yarns in 3D woven composites can form a spatial network, which results in good mechanical properties, impact resistance and oneness. As a result, the usage amount of 3D woven composites is increasing in each industry sector. Because of the complicated structural of 3D woven composites, there are several interactional failure modes. The basis of the application is to sufficiently investigate the 3D woven composites. In this paper, we aim to learn and discuss the processes of the damage and failure of 3D woven composites, and propose several available analytical models for 3D woven composites.In Chapter 1, the research background is reviewed and the research purposes are introduced. The main content contains the experimental research, mechanical analysis mode, damage evolution research and the waviness in the fiber yarns under the quasistatic load, and contain the experimental and numerical research under impact load. On the basis of the review, the main research content of this paper is introduced. Proposing numerical method to study the 3D woven composites is the core purpose of this paper.In Chapter 2, the quasi-static tensile and compressive experiments of the 3D woven composites are carried out. The stiffness and strengths are obtained. The fracture appearance is observed in macroscopic and microscopic view. The damage failure modes and failure process are studied. The ballistic impact experiments of the 3D woven composites are carried out. The impact damage resistance and the damage failure process are studied. All the experiments will be the basis of the numerical researches in the next chapters.In Chapter 3, a continuum damage model for predicting the damage initiation and development in 3D woven composites is proposed, in which the fiber fracture, inter-fiber fracture and matrix fracture are considered in the level of the fiber yarn and the matrix. A set of damage variables is presented to characterize all the failure modes of the fiber yarn and matrix. The damage initiation and propagation criteria are based on the Puck criteria for the fiber yarn and the paraboloidal yield criterion for the matrix. This continuum damage model is implemented by combining with the finite element method(FEM). The representative volume element(RVE) of the 3D woven composites and its sub-unit cells——interior and surface cells are extracted. The finite element models of the two types of sub-unit cells are built. And the modulus and strengths are predicted under quasistatic tensile and compressive loads. The damage evolution and failure processes are studied.In Chapter 4, a random sinusoidal waviness model is proposed which considers the fiber yarns’ random waviness to investigate the stiffness and strength of 3D woven composites. An important phenomenon should be noted that the fiber yarns usually deviate from their designed positions during the manufacturing process, which results in the random waviness of the fiber yarns. In some cases, these waviness phenomena may affect the mechanical responses significantly. Based on the actual statistics of the fiber yarns’ random waviness, the amplitude and half-wavelength are assumed as random variables and the random sinusoidal waviness model of the 3D woven composites is built. The moduli and strengths of the 3D woven composites are predicted under quasi-static tensile and compressive loads. The variations of the modulus and the strength with the random characteristics of the fiber yarns’ waviness are discussed.In Chapter 5, a ballistic impact damage evolution model for ballistic impact is established. The strain rates are introduced in the constitutive functions of the fiber yarns and matrix. Combined with the inhomogeneous finite element method, the macroscopic finite element model is built in which the mesoscopic fiber yarns and matrix are considered. The dynamic response and damage process of the 3D woven composites are predicted under ballistic impact load. The influences by the impact velocities on the failure process of the 3D woven composites are discussed.