Adapting an in situ X-ray CT compression stage for pull-out testing: Methodological development and characterization of failure evolution in Ni/PU hybrid foams

The integration of metallic fasteners into cellular hybrid materials presents significant challenges regarding interface integrity and localized load transfer. This study is exploratory in nature, focusing on the methodological development and evaluation of a custom-engineered in situ pull-out system designed for X-ray micro-computed tomography (micro-CT). By successfully adapting an existing compression stage for pull-out configurations, this research enables the three-dimensional visualization of internal failure sequences that remain inaccessible via conventional testing methods.The investigation of Nickel-coated polyurethane (PU) hybrid foams demonstrated a matrix collapse stress of 7.1 MPa in compression mode and a pull-out resistance of 4 MPa. In situ analysis revealed that compression failure is driven by localized deformation bands oriented at 10° to 15°, likely attributable to structural inhomogeneities. During pull-out, interfacial bonding remains intact beyond initial matrix failure, forming an annular damage zone characterized by progressive strut buckling and lateral sliding. Based on these findings, we propose design guidelines that a larger major diameter and coarser thread pitch enhance load-bearing capacity and preserve structural integrity. These insights underscore the potential of Ni/PU hybrids as tunable, high-performance materials for sustainable infrastructure.