Validation method for thickness variation of thermoplastic microcellular foams using punch tests

Abstract This paper is concerned with a punch-test based experimental validation method and the investigation of thickness variation in forming process of a thermoplastic material. One of the key factors that characterize the final geometry of thermoformed parts is thickness variation. The material characterization process is usually based on uniaxial measurements performed at different temperature levels being relevant for the thermoforming process. Consequently, the material model can be inaccurate in biaxial stress state, which is dominant in thermoforming process. In this contribution a punch-test based validation method is presented via the case-study of a thermoplastic microcellular polyethylene-terephthalate (MC-PET) foam material. In the proposed method the thickness variation is investigated both experimentally and numerically, by means of laser scanning method and FE simulations. Finally, the utilization of the proposed method as a validation tool for the evaluation of material models that are fitted to uniaxial test data is also demonstrated.