Impact Damage Analysis with Stress Continuity Constraints Fulfilment at Damaged-Undamaged Regions and at Layer Interfaces

Abstract

Low-velocity impacts have a relevant importance for safety of laminated and sandwich composite structures, because they are highly susceptible to damage. In this paper, a 3D cost effective zig-zag model is developed in order to efficiently simulate such impacts. It a priori fulfills the continuity of out-of-plane stresses at layer interfaces, the continuity of stresses under in-plane variation of properties across undamaged and damaged regions and it is suitable for general boundary conditions. Its main advantage is its capability to accurately predict stresses from constitutive equations at a low cost, along with being refined across the thickness keeping fixed the number of unknowns. A modified Hertzian contact law that forces the target to conform to the shape of the impactor and the Newmark's implicit time integration scheme are used for computing the contact force time history. The progressive damage analysis is carried out using stress-based criteria. Non-classical feature, a continuum damage mesomechanic model is employed that accounts for the effects of local failures in homogenized form by modifying the strain energy expression. Fiber, matrix and delamination failures are predicted using stress-based criteria, and then the modified strain energy expression is employed for computing stresses. Such modeling options enable to account for the residual properties as they are in the reality, as shown by the comparison with the damage experimentally detected. As shown by the comparison with experiments, a closed-form solution by the Galerkin's method, obtained as a series expansion of trial displacement functions, accurately simulates the contact force and the damage progressively accumulated. The results show the importance of in-plane stress continuity for obtaining accurate predictions.Keywords Impact-induced damage; 3D variable-kinematics zig-zag model; undamaged/damaged stress continuity; interlayer stress continuity; fixed d.o.f; mesomechanic damage model.