Using indentation to identify the parameters of a numerical third-body model: Application to a rubber-like material

This paper proposes a reverse analysis procedure to identify the constitutive parameters of a rubber-like material, as input for an upcoming friction model. For this purpose, several indentations were experimentally performed and numerically duplicated. The aim is to develop an elasto-plastic indentation model to be consistent with the future friction model, which describes an elasto-plastic flow. The material, representative of a third body, is modeled as a collection of deformable and cohesive bodies using a soft multibody meshfree approach. Two parameters will be identified, which are the Young modulus of each body and the cohesion coefficient between each body. The model is able to simulate a wide range of behaviors, from elasto-plastic to purely elastic indentations. The resulting kinematics is consistent with velocity field measurements from the literature. Moreover, indentation curves could also be extracted. Results show that hardness depends on the elastic and the plastic contributions. The elastic contribution is governed by the Young modulus of each body, while the plastic contribution is driven by the ratio of cohesion coefficient over Young modulus. Two reverse analysis methods are proposed, one for elasto-plastic materials, the other for visco-elasto-plastic materials, both suited to modeling third-body mechanics. Unicity of the solution is ensured for a cohesion coefficient less than 0.2-0.4 times the Young modulus. Several tests were carried out on a rubber-like material and showed that hardness depends on strain rate according to a power law. Using reverse analysis, the values of Young modulus and cohesion coefficient as a function of strain rate were determined.