Numerical Study On Elastoplastic Fracture Process And Low-Velocity Impact Damage Of Laminated Composites

This thesis contains two relatively independent parts. In part one, a novel finite elementsub-partition strategy was developed to simulate crack extension in elastoplastic material. Its validitywas estimated by numerical simulations. In part two, two delaminational failure criteria weremodified to predict delamination growth in laminated composites under low-velocity impact.Part one:1. Under the framework of a sub-partition and substructure strategy, an elastoplastic extendedfinite element method (XFEM) was developed which combining with the Newton-Raphsonalgorithms forJ2elastoplasticity and the elastoplastic failure-propagation criterion. It has beenrealized based on the ABAQUS/Standard user subroutine UEL. By use of it, crack moving alongarbitrary path in elastoplastic material was numerically simulated by XFEM in first time. Themethodology developed here can represent other non-linear fracture process by directly employingnonlinear elements. It avoids constructing the crack tip asymptotic singular function for the traditionalXFEM, which would be a great challenge for nonlinear crack problem.2. Firstly, the elastoplastic XFEM developed in this thesis were employed to predict the crackinitiation angles of the central crack in infinite size plate with various original inclinations. Then thestress intensity factors for cracks in finite size plate are obtained in the condition of small scaleyielding. Finally, the ductile crack expanding in finite plate and three point bending beam weresimulated respectively. The accuracy and adaptability of simulating elastoplastic complex fracturehave been proven.Part two:1. Two interfacial damage models, Choi-chang criterion and cohesive zone model, were modifiedbased on the of damage mechanism of laminated composites under low velocity impact. They havebeen implemented via ABAQUS/Explicit user subroutine VUMAT.2. These two to modified interfacial damage models were employed to predict the delaminationgrowth in laminated composites under low-velocity impact. The results are in fair agreement withexperimental phenomena in previous literatures, so the modifications are valuable.