Three Parameter Yield Criteria And Failure Research Of Composites Laminates

With the development of computer science and technology, progressive failure analysis has been used in simulating the strength of composite materials. The definition of a building-block virtual test drives the formulation to a top-down and bottom-up model, which involves an accurate simulation of physical tests using multi-scale progressive failure analysis(PFA). Virtual test can be used to reduce necessary physical tests both for certification and for determining allowables. Moreover, virtual test can predict the failure mode and the region where the traditional test can not monitor. It also can simulate the various combined load conditions freely, which is difficult to realize for normal test. Virtual test provides assistance to planning and reduction of experimental testing at coupon and large component levels by obtaining the failure process and strength envelope of the composite materials.Based on the mechanical behavior and failure mode of uniaxial tension, compression, shear strengths, this paper presents a three-parameter generalized failure criteria. This failure criterion is validated by the multi-axial experimental test and proved to be more suitable for predicting the strengths and failure envelop of such material compared with the uniaxial and biaxial tests of the Polymethacrylimide(PMI) foam material.The thermalsetting epoxy and thermalplastic Polyether ether ketone(PEEK) are tested under tension, compression and shear load. The linear elasticity of epoxy and nonlinear plasticity phonomina with loading and unloading of PEEK are invesgated. A computational plasticity model based on the there-parameter failure criteria for hydrostatic pressure dependent materials is presented. A new semi-associated flow rule is proposed for the initial yield criterion. Different from other well- known flow rules which depends on the plastic Poisson ratio, this flow rule uses the standard uniaxial strength values for plasticity flow and is more convenient to be used. An implicit integration method by return mapping algorithm is carried out and the consistent tangent Jacobian matrix is also presented for the implicit integration.By applicating this plasiticy model into the thermalplastic PEEK material, the mechanical behavior and failure envelops of the AS4/PEEK composites under uniaxial and biaxial load are carried out. The mulit-scale nonlinear failure analysis procedure of thick composite laminates is established at the micro-scale of fiber and matrix. The virtual test is validated by the unidirectional lay-up composite laminates.The multi-scale virtual test approach is proposed form the fiber/matrix to laminae, then to laminate for the plain weave fabric(PWF) composites. The uniaxial tension, compression and shear tests are carried out for the unidirectional and multiaxial laminates of PWF composites. The mechanical and failure behavior are investigated and the complete stress-strain test data are obtained. The domain superposition technique based on the multi-point costriant(MPC) is presented to establish the reprensented volume element(RVE) model of the PWF. Due to avoid eastablishing the matrix elements in the resin rich regions of the cross area of the fiber tows, this approach is proved that it is an efficient way for numerical simulation of complex composites materials and structures by modeling the textile composite model quickly and easily by less model number. The simulating results of stiffness and the failure behaviors of the PWF composites are validated comparing to the test results.The open-hole tests of three different lay-up composite laminates are performed. The traditional strain gauge method and the digital image correlation(DIC) system are used to measure the strain distribution and failure process. The mechanical behavior and failure mechanisms of the open-hole composite laminates are investigated. The application of the s-version finite element method(SFEM) in the progressive failure analysis of open-hole composite plates is investigated. Compared with the experimental and DIC results, good agreements are obtained in the strength prediction and the strain filed during the failure process. The virtual test of the open-hole composites is validated. Besides, compared with the conventional FEM, the easy meshing technique is proved to be an efficient way for simulating the composites with less model elements and fine mesh quality in the discontinued areas such as open-hole.