4D local investigation of mechanical behavior of open-cell foams by enhanced morphological analysis and microstructure-adapted digital volume correlation for tribology applications

In ex-poro-hydrodynamic (XPHD) lubrication, fluid impregnated, open-cell elastomer foams constitute a composite material aiming to improve the load carrying and damping capacity of lubricated systems and to provide more environmentally sustainable solutions. The performance of XPHD-based devices depends on the interactions between solid and fluid phases, occurring and evolving simultaneously during dynamic compression of an imbibed foam. Even at normal regimes, the foam microstructure undergoes large deformations and is prone to strain concentrations which modify its local porosity and influence the mechanical behavior of the composite. In this context, this work focuses on the development of a systematic and accurate characterization technique for describing the main morphological changes happening under uniaxial compression of a high porosity dry open-cell polyurethane foam, by in-situ X-ray microtomography (μCT) testing. A combination of 3D image analysis and digital volume correlation (DVC) is considered to identify and trace the spatial and temporal location of key microstructural features at every loaded state. In this way, the detailed transformations of cells and pores obtained by this method are presented here to give further insight into the deformation mechanisms involved. Then, the advantages and the limits of the overall methodology in analyzing high porosity open-cell foams are regarded in terms of feature segmentation and measurement precision. Both a classic and a microstructure-adapted DVC are compared at their respective scales, and finally their sensibility to emphasize local strain heterogeneities is discussed.