Modeling the initiation and growth of delaminations in composite structures

Abstract

A method for modeling the initiation and growth of discrete delaminations in shell-like composite structures is presented, The laminate is divided into two or more sublaminates, with each sublaminate modeled with four-noded quadrilateral shell elements. A special, eight-noded hex constraint element connects opposing sublaminate shell elements. It supplies the nodal forces and moments needed to make the two opposing shell elements act as a single shell element until a prescribed failure criterion is satisfied. Once the failure criterion is attained, the connection is broken, creating or growing a discrete delamination. This approach has been implemented in a threedimensional finite element code. This code uses explicit time integration, and can analyze shelllike structures subjected to large deformations and complex contact conditions. The shell elements can use existing composite material models that include in-plane laminate failure modes. This analysis capability was developed to perform crashworthiness studies of composite structures, and is useful whenever there is a need to estimate peak loads, energy absorption, or the final shape of a highly deformed composite structure. This paper describes the eight-noded hex constraint element used to model the initiation and growth of a delamination, and discusses associated implementation issues. Particular attention is focused on the delamination growth criterion, and it is verified that calculated results do not depend on element size. In addition, results for double cantilever beam and end notched flexure specimens are presented and compared to measured data to assess the ability of the present approach to model a growing delamination.

A damage model for the simulation of delamination in advanced composites under variable-mode loading

“…The law proposed here is a bilinear relation between the tractions and the displacement jumps [21], [24], [45]. The bilinear law is the most commonly used cohesive law due to its simplicity.…”

Nanomanufacturing : nano-structured materials made layer-by-layer.

“…Instead, one could replace the solid elements by shell elements. An analysis similar to that previously used to model discrete delaminations within thin composite structures could be used (Reedy, Mello et al 1997). In that analysis a DLAM element constrains two stacked shell elements to act as a single shell element until the stacked elements separate (delaminate) with separation defined by a T-U relationship.…”

Finite element simulation of delamination growth in composite materials using LS-DYNA

“…Two different values of viscosity parameter are used in the simulations; g = 0.01 and 1.0 N s/mm 3 , respectively. Note that g is a material parameter depending on deformation rate, which appears in Eqs.…”

“…Note that g is a material parameter depending on deformation rate, which appears in Eqs. (1) 3 corresponds to a viscosity stress of 6.5 MPa, which is around 13% of the interface strength, and denotes a higher rate dependence. In addition, two sets of simulations are performed here.…”

“…It can cause a significant reduction in the compressive load-carrying capacity of a structure. Cohesive elements are widely used, in both forms of continuous interface elements and point cohesive elements [1][2][3][4][5][6][7], at the interface between solid finite elements to predict and to understand the damage behaviour in the interfaces of different layers in composite laminates. Many models have been introduced including: perfectly plastic, linear softening, progressive softening, and regressive softening [8].…”