Impact Tests and Simulations of Crashworthy Composite Structures Using Variable Load Concept

Composite materials are used extensively in modern helicopter structures to reduce weight. Applications include energy absorption components necessary to meet crashworthiness requirements, where composite material can offer higher Specific Energy Absorption (SEA) than traditional metallic materials. However, the constant force energy absorbers that are currently used exhibit some limitations, such as under-utilisation of the crushing stroke leading to inefficient material usage and therefore higher than necessary decelerations to the occupants in some crash scenarios. This paper describes the results of a project to develop an improved system for crashworthiness. As part of this project, a novel Variable Load Concept (VLC) has been introduced to improve the performance of the energy absorption components. The crushing force can be controlled through the radius size of trigger mechanism and the use of pressurised composite tubes. The concept and the system were developed and further validated by crush testing at speeds of quasi-static, 2 m/s and 8 m/s. The results established that the VLC with pressurised composite tube system can be used in crashworthiness applications, and that the significant improvement in energy absorption characteristics is possible. Finally, an explicit finite element study was carried out using software PAM-CRASH, where very good agreement with experiment was demonstrated.