PERFORMANCE OF SUPERPLASTIC TIN - LEAD MATERIAL AS ENERGY ABSORBING SYSTEM
Different systems and materials have been used to protect occupants during car accidents. Most of the reported work is directed towards the use of structural members made of engineering materials subjected to quasi-static loading conditions. It is well established that the behavior of materials under dynamic loading conditions is somewhat different from their behavior under quasi-static loading.
In this work, a superplastic Tin- Lead alloy which is sensitive to strain rate in the quasi-static range from 10-2 /s to 100 /s was used to simulate the behavior of ordinary engineering materials. These materials are only sensitive to strain rate in the range of 1 to 104 /s which is not possible to obtain on available testing machines and needs special design of equipment.
Furthermore, other systems based on utilizing the plastic energy consumed in deforming the material as means for protection of occupants in the car collision were investigated.
Two different methods were investigated. One utilizing the extrusion process to a high extrusion ratio by extruding a cylindrical pellet of 26 mm diameter into 21 cylinders of 3 mm diameter each. The other method utilized the plastic work consumed in the inversion of a hollow cylinder around a die profile radius. Both methods were investigated on the superplastic Tin- Lead alloy at three different strain rates. The first in the rate sensitive region, the second below it and the third exceeds it, namely at
3x10-4, 5x10-3 and 1x10-1 respectively.
It was found that the use of superplastic Tin- Lead alloy in the quasi-static loading condition is very successful to simulate the behavior of engineering materials when subjected to dynamic loading. It was also found that the utilization of the concept of plastic work consumed in deformation represented by extrusion and tube inversion is a successful method to be used against any collision problems in general and automobile accidents in particular to protect the car and occupants.
Finally, it was found that during the rate sensitive region, the effectiveness of the system based on extrusion was 2.3 times that in the region below that region whereas the effectiveness was 6.07 times in the case of the tube inversion method, in the same strain rate region.