Application Of Cohesive Element In Modeling Fiber Reinforced Composite Structures Under Impact Loadings

The dynamic response of fiber reinforced composite structures under impact loading is numerically simulated in this dissertation. On the basis of previous work,a delamination damage model considering strain rate effect is proposed. The main results obtained are as follows:1. A new numerical model is suggested for fiber reinforced plastic composites.The model considers that FRP laminates has been constituted by single FRP laminated plates and cohesive layers. Hence, the constitutive models also consist of two parts, namely, continuum damage mechanics model for FRP laminate plates and damage model for adhesive layers. The damage model for adhesive layers include of three parts: (1) a linear elastic response in which the traction force is linear relation to the corresponding displacement, and adhesive layers can be completely restored after unloading; (2) damage initiation, once the initial damage criterion is satisfied,there is irreversible damage to the adhesive layers; (3) damage evolution, with further loading, adhesive layer's stiffness begins to degrade until eventually destroyed. The damage model of the adhesive layer takes into account the strain rate effect in the unified framework with continuum damage model. The continuum damage model for FRP laminate plates and the adhesive layer damage model are incorporated into the ABAQUS / EXPLICIT finite element program by the user-defined material subroutine VUMAT.2. The numerical simulations of fiber reinforced plastic laminates were carried out by using the proposed FEM model, two typical numerical examples were presented, namely low velocity impact and high speed perforation. It is demonstrated that the present numerical results are in good agreement with the experimental observations in term of residual velocity and failure pattern in the case of high velocity perforation. It is also demonstrated that both the present numerically predicted load-displacement curve and failure pattern are in agreement with the experimental results for low speed impact.3. A numerical model is proposed for fiber metal laminates (FML). The model considers FML to be composed of FRP laminates and metal sheets and intermediate adhesive layers. The numerical simulations of fiber metal laminates were performed by using the proposed numerical model. The results show that the present model can predict well the ballistic limits and damage patterns in the care of high speed perforation, and that the effect of the FRP laying method of FRP on the ballistic limit is very small. The results also show that in the case of low velocity impact, the present model can also predict well the load-displacement curve and the damage pattern well, and that the mechanical properties of the aluminum plate have greater influence on the response of FML.