Matthew David

Failure mechanisms in energy-absorbing composite structures

Quasi-static tests are described for determination of the energy-absorption properties of composite crash energy-absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens were used to identify local compression crush failure mechanisms at the crush front. These mechanisms are important for selecting composite materials for energy-absorbing structures, such as helicopter and aircraft sub-floors. Finite element models of the failure processes are described that could be the basis for materials selection and future design procedures for crashworthy structures.

Analysis of Crushing Response of Composite Crashworthy Structures

The paper describes quasi-static and dynamic tests to characterise the energy absorption properties of polymer composite crash energy absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens are used to identify local compression crush failure mechanisms at the crush front. The varied crushing morphology between the compression strain rates identified in this paper is observed to be due to the differences in the response modes and mechanical properties of the strain dependent epoxy matrix. The importance of understanding the role of strain rate effects in composite crash energy absorbing structures is highlighted in this paper.

Failure Mechanisms and Energy Absorption in Composite Elements under Axial Crush

Test methods are presented to determine failure modes and energy absorption properties of composite crash structural elements from quasi-static tests on chamfered carbon fabric/epoxy tube segment specimens under axial compression loads. High speed film and CT scans of failed specimens are used to identify trigger mechanisms, failure mode evolution at the crush front and failure processes during steady crushing. FE models of failure were developed which could be the basis for materials selection and design procedures for crashworthy composite structures. These are based on meso-scale composites ply damage models combined with cohesive interfaces to represent delamination failures, which damage and fail when the interface fracture energy is reached. The models are implemented in an explicit FE code and parameters for the ply damage and delamination models were obtained from related materials test programmes. The FE models were applied to simulate axial crushing in tube segments and C-channels, showing good predictions of measured peak forces at failure initiation, steady crush forces and total energy absorption.

Design and testing of crashworthy aerospace composite components

The chapter presents the current state of the art in design, analysis and test of crashworthy composite aircraft structures. It describes a methodology based on the test/simulation pyramid adopted for aircraft structures in which test and analysis methods for crashworthy structures are developed and validated on structural elements and aircraft subfloor structures. Special attention is given to design, manufacture and crash test of a helicopter frame concept structure in advanced composite materials having high specific energy absorption where design rules are still under development.