Finite element modeling and durability evaluation for rubber pad forming process

Abstract

Elastomer (or rubber pad) forming is a dieless forming process. The forming process has several advantages compared to general press forming process in terms of tool cost and scratch problem. However, when the elastomer is subjected to severe deformation during forming process, it can result in an expensive cost for the replacements of elastomer. Therefore, it is necessary to evaluate accurate tool life. In this study, the FE analysis was conducted for the rubber pad forming process and the fatigue life evaluation of the elastomer tool was investigated numerically using the reference experimental data. For the FE analysis, uniaxial and equibiaxial tension tests of natural rubber 50 were carried out in order to obtain the mechanical material properties of the elastomer. The hyperelastic behavior of the elastomer was characterized using Ogden model. The elastomer forming process was modeled using a commercial software LS-DYNA 3D. Two important factors of FE modeling were to calibrate the simulation conditions and to obtain the target product shape with a preformed elastomer. With the result of FE analysis, a durability of the elastomer was conducted focusing on fatigue life, because the elastomer is applied for repeated loadings during the forming process. Unlike general fatigue analysis, the fatigue life of the elastomer is predicted with respect to the strain measures due to Mullins effect. Furthermore, the Polar Effective Plastic Strain (PEPS) diagram [6] considering the strain path changes was used to check the failure of the blank during the forming process.