Research On Fatigue Life Prediction And Damage Analysis Of 2.5D Wovencomposites

2.5D woven composites is a new kind of structural material, researches on fatigue property of 2.5D woven composites are extremely limited. Theorical and experimental researches on 2.5D woven composites’ fatigue properties and failure mechanism are carried out in this thesis. Fatigue residual stiffness and residual strength degradation model of unidirectional composites,Meso-geometrical model, strength predicted model, fatigue life prediction model and progressive damage analysis method for 2.5D woven composites are researched especially. The main work done in this dissertation includes:(1) Experimental research on mechanical properties and fatigue characteristics of 2.5D woven composites. The experimental research on tensile strength and tension-tension fatigue behavior for 2.5D woven composites in warp and weft directions is conducted. The tensile strength and tension-tension fatigue characteristics of 2.5D woven composites are obtained, the damage mechanism and failure modes are investigated comparatively.(2) Modeling research on residual stiffness and residual strength degradation of unidirectional composites considering fiber volume fraction. The residual stiffness and residual strength model for unidirectional laminas subjected to fatigue loadings are deduced and established, considering different fiber volume fraction and stress level. The effective of the residual stiffness and residual strength models are proved by numerical experiments.(3) Research on meso-model and stiffness prediction model of 2.5D woven composites. By adopting the hypothesis of rectangle section shape for warp, hexagon section shape for weft, and broken lines for the simplified orientation of warp, a new geometric model for 2.5D woven composites is established.Based on the geometric model, coupled with the volume average method, the stiffness prediction model is established. The calculated geometric parameters and elastic modulus of 2.5D woven composites agree well with the test values. The comparison results indicate the rationality of the meso-model.(4) The strength prediction modeling is developed based on meso-structure of 2.5D woven composites. The unit-cell model is established deriving from the new geometricmodel. Based on the unit-cell model, a strength prediction model is developed, in which the modified Hashin and Mises failure criterionsare adoptedto detect damage of the yarns and matrix separately, different stiffness degradation coefficients are used in different failure modes.A parametric progressive damage analysis program is developed by FEA software, which can predict the progressive damage process of 2.5D woven composite in meso-structure. The predicted strength and failure modes agree well with the test results. Comparison results verify the strength prediction model and analysis method.(5) Fatigue life prediction model and analysis method for 2.5D woven composites are developed. On the bases of the unit-cell model, introducing the residual stiffness and residual strength degradation model of unidirectional composites, adopting fatigue failure criterions and stiffness sudden degradation model to identify and establish failure of the yarns or matrix, a fatigue life prediction model is established. The ANSYS FEA software is used to develop the program of fatigue life prediction and progressive damage analysis. The fatigue progressive damage process of 2.5D woven composite in meso-structure is simulated. The experimental verification showed that the fatigue life and failure modes can predict accurately by fatigue life prediction and damage analysis method.