Crashworthiness Investigation and Optimization of Empty and Foam Filled Composite Crash Box

Abstract

Metallic and composite columns are used in a broad range of automotive and aerospace applications and especially as crash absorber elements. In automotive application, crashworthy structures absorb impact energy in a controlled manner. Thereby, they bring the passenger compartment to rest without subjecting the occupant to high decelerations. Energy absorption in metallic crash absorbers normally takes place by progressive buckling and local bending collapse of columns wall. A distinctive feature of such a deformation mechanism is that the rate of energy dissipation is concentrated over relatively narrow zones, while the other part of the structure undergoes a rigid body motion. In comparison to metals, most composite columns crush in a brittle manner and they fail through a sequence of fracture mechanism involving fiber fracture, matrix crazing and cracking, fiber-matrix debonding, delamination and internal ply separation. The high strength to weight and stiffness to weight ratios of composite materials motivated the automobile industry to gradual replacement of the metallic structures by composite ones. The implementation of composite materials in the vehicles not only increases the energy absorption per unit of weight (Ramakrishna, 1997) but also reduces the noise and vibrations, in comparison with steel or aluminum structures (Shin et al., 2002). The crashworthiness of a crash box is expressed in terms of its energy absorption E and specific energy absorption SEA. The energy absorption performance of a composite crash box can be tailored by controlling various parameters like fiber type, matrix type, fiber architecture, specimen geometry, process condition, fiber volume fraction and impact velocity. A comprehensive review of the various research activities have been conducted by Jacob et al. (Jacob et al., 2002) to understand the effect of particular parameter on energy absorption capability of composite crash boxes. The response of composite tubes under axial compression has been investigated by Hull (Hull, 1982). He tried to achieve optimum deceleration under crush conditions. He showed that the fiber arrangement appeared to have the greatest effect on the specific energy absorption. Farley (Farley, 1983 and 1991) conducted quasi-static compression and impact tests to investigate the energy absorption characteristics of the composite tubes. Through his