Dominik Schueler

Simulation of High Velocity Impact on Composite Structures - Model Implementation and Validation

High velocity impact on composite aircraft structures leads to the formation of flexural waves that can cause severe damage to the structure. Damage and failure can occur within the plies and/or in the resin rich interface layers between adjacent plies. In the present paper a modelling methodology is documented that captures intra- and inter-laminar damage and their interrelations by use of shell element layers representing sub-laminates that are connected with cohesive interface layers to simulate delamination. This approach allows the simulation of large structures while still capturing the governing damage mechanisms and their interactions. The paper describes numerical algorithms for the implementation of a Ladevèze continuum damage model for the ply and methods to derive input parameters for the cohesive zone model. By comparison with experimental results from gas gun impact tests the potential and limitations of the modelling approach are discussed.

Numerical modelling of impact and damage tolerance in aerospace composite structures

This chapter discusses numerical methods that are used for predicting impact damage in advanced composite structures. To support the acceptance by industry for design and certification of composite aircraft structures, composites damage models are required for implementation in commercial finite element (FE) codes and validation at specimen and substructure level. DLR experience on modelling damage progression and failure in composite structures under impact is reviewed based on meso-scale composites ply damage models and an energy-based delamination failure criteria in explicit FE codes. The numerical methods are applied to predict impact damage and damage tolerance in stiffened and unstiffened aircraft panels from hard and soft body impacts, including pre-stressed panels subjected to impact loads. Issues concerned with validation of computational methods for certification by analysis are discussed.

Crash concepts for CFRP transport aircraft – comparison of the traditional bend frame concept versus the developments in a tension absorbers concept

ABSTRACT Due to their inherently brittle behaviour, carbon fibre reinforced plastics (CFRP) structures demand for a specific design to achieve appropriate crash energy absorption compared to classical metallic fuselage designs. In this paper, experimental as well as numerical studies on two different crashworthy designs are presented. The first concept aims to absorb the crash energy by crushing of CFRP components below a reinforced cargo cross beam in combination with further energy absorbing devices in the lower side shell. The feasibility of this concept was in the meantime proven by tests at the coupon and structural element level. An alternative crash concept making use of energy absorption in so-called tension absorbers in the passenger and cargo floor structure was developed and assessed with the focus on a reduction of structural mass in combination with improved concept robustness. This paper provides a summary of the performed research work and discusses the context of the concept development. Details on the individual research tasks can be found in further publications which are given in the references.