Impact Response and Failure Prediction of Marine Composite Structures

摘要

Well-designed composite sandwich structures and joints are crucial in achieving satisfactory service life and survivability for naval ships. Damage in composite sandwich and joint structures subjected to an impact is characterized by the coexistence of discrete (delamination and debonding) and continuum damage (matrix cracking and intralaminar damage). Either a fracture mechanics-based or a continuum damage mechanics-based tool cannot effectively characterize the interaction between the discrete and continuum damage and their compounding effect that leads to the final rupture. Because of the constituent driven failure progression, the stress and strain at the element level cannot be directly used to predict the constituent damage and the resulting stiffness degradation.In this paper, a hybrid model based on the discrete and continuum damage progression is developed and numerically implemented within the LS-DYNA environment via a user-defined material subroutine. The continuum damage progression and its resulting stiffness degradation are predicted based on the constituent stress/strain and their associated failure criteria while the delamination damage is numerically captured via a cohesive interface model. To extract the constituent stress/strain from the corresponding stress/strain at the element level, the new micromechanics model (CELLMAT) described in this paper is used to bridge the material response from one length scale to another. Given the constituent stress/strain, the mechanism-driven constituent failure criteria are used to predict the failure mode and damage progression. The micro-damage resulting from the fiber/tow/matrixfailure is described by a set of internal variables that characterize the degradation of the orthotropic material stiffness. Both the initiation and propagation of an interface debonding is numerically simulated using the interface cohesive element with a user-defined cohesive law. To prevent the penetration of the upper and lower surface of a cracked element, an eroding single surface contact is used within LSDYNA-3D. Both the validity and applicability of the hybrid model are demonstrated via numerical examples.