Investigation and modelling of size effects in Ni/PU hybrid foams — A new model to predict size-effected properties in foams

For the design and development of new products, the properties of new, multifunctional materials are an important instance for engineers. Therefore, for material testing and simulations a representative volume element (RVE) needs to be found to gain the bulk properties. In the present work, Ni/PU hybrid foams with pore sizes from 10 to 30 ppi (pores per inch) are investigated under quasi static compression in order to determine the RVE for the main characteristics stiffness, plastic collapse stress and plateau stress. In addition a new model to calculate the bulk properties as function of pore geometry including anisotropy is developed and validated against the experimental investigation. It could also be shown, that RVE size is dependant on the investigated mechanical property as well as pore size. Also the mass increase for the coating process is non-linear and mass normalization of all investigated characteristics is indispensable. The model is validated on 20 ppi open cell aluminium foams, where the importance of mass normalization also becomes apparent again. Thus, the model is capable of capturing the behaviour of mechanical characteristics for foam materials in general. • New model to predict bulk properties of hybrid foams. • RVE size for Ni/PU hybrid foams. • Mass normalization is crucial when investigating hybrid materials.