Methodology for Impact Behaviour and Residual Strength

Abstract

In co-operation with different national, European and international partners in national and European projects an analytical approach for modelling and calculation of the transient impact behaviour and the residual strength of composite materials, elements and sub-structures was developed during the past years in the Institute of Structural Mechanics. The main features of the approach are an independent damage characterisation method; a new failure criterion for delamination damage; a simple model for the prediction of impact damage (incl. matrix cracking, delamination and fibre breakage), based on the bending strain energy density; and an algorithm for the residual strength analysis of single and/or multiple delaminations, either introduced by impact or pre-implanted. The approach led to the development of a Windows and NT compatible computer program - called "COmposite Damage Tolerance Analysis Code" (CODAC) - which enables the calculation of the impact transient response, the impact damage area (incl. the through-the-thickness location) and consequently the residual static compressive strength of composite laminates, and, in an extended version, of stringer-stiffened composite panels for mid-bay impact; recently a first step was successfully undertaken for impact below stringers. The comparison between calculated and experimentally evaluated impact damage zones as well as of the residual compressive strengths showed a good agreement of the results. In future work the extension of the analysis code to the damage growth simulation under fatigue loading and the prediction of the residual strength after fatigue will be performed.