Impact Response Prediction of Expanded Polypropylene Foam Energy Absorbers

Expanded polypropylene (EPP) foam has been the most widely used material for energy absorption in low speed bumper impacts for its low cost, lightweight, and ease of prototyping. An accurate finite element prediction of such bumper system impacts further enhances these advantages and reduces design cycle time, weight, and cost. These Optimized multi-density EPP foam absorbers, which meet performance, weight, and cost targets can then be designed and prototyped very quickly. This paper describes a finite element procedure and material model that can be used to accurately predict the impact performance of a bumper system consisting of an EPP foam absorber coupled with a bumper beam which can be made of steel, aluminum or any composite material or plastic.

Key characteristics of EPP foam such as strain rate sensitivity, shear and tensile response, and rebound properties have been incorporated into the finite element models. Additionally, importance has been given to the accurate modeling and representation of the bumper beam and various boundary and interface conditions. Consistency of measuring devices in impact testing and its effects on the correlation between computer simulation and real impact tests will be examined. Response prediction of cumulative and isolated impact tests such as the tests followed in Federal Motor Vehicle Safety Standard (FMVSS) 581, Canadian Motor Vehicle Safety Standard (CMVSS) 215, and Insurance Institute for Highway Safety (IIHS) procedures will be demonstrated. The accuracy of the finite element prediction techniques will be demonstrated by comparing actual data from analysis and impact tests and showing a validation of loads and deflections.