Modeling impact induced delamination of woven fiber reinforced composites with contact/cohesive laws

The dynamic delamination in woven glass fiber reinforced plastic (GRP) composite is studied with a 3D finite deformation anisotropic viscoplastic model in conjunction with contact/cohesive laws. The large deformation of the material during impact loading is described through an anisotropic plasticity model in total Lagrangian co-ordinates whose coefficients are determined experimentally. The interaction between lamina is analyzed through a contact/interface model. The tensile and shear tractions in zero thickness interface elements, embedded between lamina, are calculated from interface cohesive law. The interface cohesive law describes the evolution of these tractions in terms of normal and tangential displacement jumps and other interface parameters. The compressive traction at the interface is calculated through the impenetrability conditions employed in the contact module. Once the effective displacement jump exceeds a specified critical value, the interface elements are assumed to have failed, i.e., delamination is said to have taken place. Three interface cohesive laws are proposed to describe the delamination process. It is assumed that loading of interface takes place reversibly up to a specified value of the displacement jump followed by irreversible loading beyond this value. This feature represents a partial damage of the interface in the event of unloading. Dynamic delamination in the woven GRP composite is studied through analyses of plate-on-plate impact experiments. The heterogeneity of composite materials leading to wave dispersion and scattering is modeled by considering a layered composition of the GRP plate. Each lamina is assumed to be made of three layers of materials. The middle layer of half the thickness of lamina is considered as GRP and the two end layers of equal thicknesses are considered to be of matrix material, i.e., polyester resin. The possible delamination of the composite material under compressive shock loading is shown to occur due to local shear effects. This is modeled by considering waviness of the interface between lamina. Interfaces with flat as well as two types of wavy structures are analyzed. Analyses are carried out to establish the effect of critical displacement jump, mixed mode coupling parameter employed in interface laws, interface waviness and the effect of interface laws. The response of GRP composite during impact is characterized in terms of the free surface velocity, delamination event vs. time and interface normal and shear stresses. The interface normal and shear stresses are obtained directly from the interface cohesive laws, as well as, by extrapolating continuum stresses from integration points of the neighboring triangular elements to the interface. It is shown that the finite element model predicts the response of the material in confirmation with available experimental results. The wave dispersion and scattering effects are obtained in the form of attenuation of shock stress and free surface velocity. The model predicts partial delamination during compressive shock loading above a certain threshold due to local shear and mode coupling. (C) 2000 Elsevier Science S.A. All rights reserved.