Stable and Accurate LS-DYNA Simulations with Foam Material Models: Optimization of Finite Element Model Parameters 2017-01-1338

Cellular foams have found a predominant application in automotive industry for efficient energy absorption so as to meet stringent and continuously improving vehicle crashworthiness and occupant protection criteria. The recent inclusion of pedestrian protection regulations mandate the use of foams of different densities for impact energy absorption at identified impact locations; this has paved the way for significant advancements in foam molding techniques such as dual density and tri-density molding. With increased emphasis on light-weighting, solutions involving the use of polymeric or metallic foams as fillers in hollow structures - foam encapsulated metal structures - are being explored. Another major automotive application of foams is in the seat comfort area, which again involves foams of intricate shapes and sizes. In addition, a few recently developed foams are anisotropic, adding on to the existing complexities. Complexities associated with controlled/ uncontrolled spatial variation in density and the geometry of molded parts and use of foams in sandwich composites offer several challenges for the CAE community in modeling the foam components.

As a first step to capture these complexities, optimal settings of available LS-DYNA modeling features have to be determined to enable effective Finite Element Analysis (FEA) of foam components. This paper aims to investigate the various underlying parameters such as element formulations and size, contact stiffness and hourglass control, governing stability and accuracy of foam material models and to identify the optimal settings of these parameters. The optimal settings for the identified parameters are elucidated in the context of the rate dependent foam model in LS-DYNA (Fu-Chang Foam).