Characterisation of nonlinear material parameters of foams based on indentation tests

Abstract

Closed cell polymeric foams, for example EVA foams, are widely used in engineering, sport and biomedical fields. The mechanical behaviours of foam is highly nonlinear, and the foams are often under complex loading conditions in service over different spectrums of strain. Foam testing and determination of the nonlinear foam constitutive parameters are important to predict their performance in service and to aid materials development and product design. Current testing approaches normally involve the use of conventional compression or shear tests, which require well defined sample shapes and sizes. In this work, the use of continuous indentation test and inverse FE modelling method to determine the nonlinear material parameters was systematically investigated. This potentially could provide a much more simple testing approach with the capacity for in situ situation where standard testing specimens are not attainable. The results were directly compared to conventional compression test and combined compression–shear tests of EVA foams. The accuracy and validity of each method were comparatively studied and discussed. Results showed that the indentation approach produced comparable results to the combined compression–shear tests, while uniaxial compression test could not provide accurate material data to simulate complex loading conditions.