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

The dynamic delamination in woven glass fiber reinforced plastic (GRP) comp osite is studied with a 3D finite deformation anisotropic viscoplastic mode l in conjunction with contact/cohesive laws. Thr large deformation of the m aterial during impact loading is described through an anisotropic plasticit y model in total Lagrangian co-ordinates whose coefficients are determined experimentally. The interaction between lamina is analyzed through a contac t/interface model. The tensile and shear tractions in zero thickness interf ace elements, embedded between lamina, are calculated from interface cohesi ve law. The interface cohesive law describes the evolution of these tractio ns in terms of normal and tangential displacement jumps and other interface parameters. The compressive traction at the interface is calculated throug h the impenetrability condition employed in the contact module. Once the ef fective dis placement jump exceeds a specified critical value, the interfac e elements are assumed to have failed, i.e., delamination is said to have t aken place. Three interface cohesive laws are proposed to describe the dela mination process. It is assumed that loading of interface takes place rever sibly up to a specified value of the displacement jump Followed by irrevers ible 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 experim ents. The heterogeneity of composite materials leading to wave dispersion a nd scattering is modeled by considering a layered composition of the GRP pl ate. Each lamina is assumed to be made of three layers of materials. The mi ddle 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 u nder 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 Aat as well as two types of wavy structures are analyzed. A nalyses are carried out to establish the effect of critical displacement ju mp, mixed mode coupling parameter employed in interface laws, interface wav iness and the effect of interface laws. The response of GRP composite durin g impact is characterized in terms of the free surface velocity, delaminati on event vs, time and interface normal and shear stresses, The interface no rmal and shear stresses are obtained directly from the interface cohesive l aws, as well as, by extrapolating continuum stresses From integration point s of the neighboring triangular elements to the interface.:It is shown that the finite element model predicts the response of the material in confirma tion with the available experimental results. The wave dispersion and scatt ering effects are obtained in the form of attenuation of shock stress and f ree surface velocity. The model predicts partial delamination during compre ssive shock loading above a certain threshold due to local shear and mode c oupling. (C) 2000 Elsevier Science SA. All rights reserved.