Modelling Impact Damage in Sandwich Concept Structures

Abstract

To reduce development and certification costs for composite aircraft structures, efficient computational methods are required by the industry to predict structural integrity and failure under dynamic loads, such as crash and impact. By using meso-scale models based on continuum damage mechanics (CDM), proposed by Ladeveze and co-workers [1], [2], it is possible to define materials models for FE codes at the structural macro level which embody the salient micromechanics failure behaviour. CDM provides a framework within which in-ply and delamination failures may be modelled. In previous work [1], [3] ply failure models were developed for unidirectional (UD) fibre and fabric reinforced plies with three scalar damage parameters representing in ply microdamage and damage evolution equations introduced relating the damage parameters to strain energy release rates in the ply. Delamination models for interply failure were obtained by applying the CDM framework to the ply interface, as described in [2]. Failure at the interface is modelled by degrading stresses using two interface damage parameters corresponding to interfacial tension and shear failures, whilst fracture mechanics concepts are introduced by relating the total energy absorbed in the damaging process to the interfacial fracture energy. The ply CDM and delamination models have been implemented into a commercial explicit FE crash and impact code [3], which uses a numerical approach for delamination modelling based on stacked shell elements with contact interface conditions, which may separate when the interface failure condition is reached.