Narrow Results

Foam–metal composites are being increasingly used in a variety of applications. One important aspect in the structural integrity of foam–metal interface is the ability to resist failure around the interface whilst ensuring required load bearing capacity. This study investigated the mechanical and failure behavior at the interface region at micro-scale. The foam–metal composite consisted of polyurethane (PU) foam directly adhered to a galvanized steel face sheet. Optical, scanning electron and atomic force microscopies were used to examine the interface geometry and to obtain a realistic surface profile for use in a finite element (FE) model. Finite element analysis (FEA) was used to study the effects of different interfacial roughness profiles on the mechanical interlocking and modes of failure, which are directly related to the interfacial strength. A set of FE models of idealized surface pairs of different geometries and dimensions were developed based on the microscopic observations at the foam–metal interface. The FE modeling results show that the micro-scale roughness profile at the foam–metal interface causes mechanical interlocking and affects the stress field at the scale of the interface surface roughness, which consequently governs the specific failure mode and the relative proportion of the cohesive to adhesive failure in the interface region for a given foam–metal interface. It was found that the aspect ratio (relative width and height) and width ratio (relative spacing) of roughness elements have a significant effect on the stresses and deformations produced at the interface and consequently influence the modes (cohesive or adhesive) of failure.

We investigate the cohesive response of biointerfaces mediated by noncovalent receptor–ligand bonding under monotonic, cyclic or other types of loading. By examining the spatiotemporal evolution of the state probability distribution that describes the collective association and dissociation kinetics of interfacial bonds, we show that such interfaces resist the imposed surface separation in a strongly rate-dependent manner. Remarkable hysteresis is exhibited when the interfaces are exposed to single stretching and relaxation cycles at high loading rates, and this hysteretic response shifts in consecutive multiple cycles. There generally exists an optimal ramping velocity that gives rise to the maximum energy dissipation at the interfaces. These results should be useful in understanding the cell-matrix adhesion and de-adhesion phenomena under dynamic and repetitive forces, as well as the adhesion-mediated cellular behaviors such as migration and reorientation.

In this paper, selective laser sintering (SLS) was applied to join two materials by printing Ti–6Al–4V powder on a Ti substrate without any support parts. The characteristics of the interface between the as-built Ti–6Al–4V sample and the substrate were investigated. The analysis indicates that a heat-affected zone (HAZ) and the fish-scale type were formed at the joining area. The combination of smaller grains, acicular α′ martensite, and lamellar (α + β) structures was observed inside the interface zone. The hardness value at the interface area was measured by about 320 HV which is higher than 280 HV of the substrate and smaller than 369 HV of the as-built sample. The results predict that the SLS process is a promising method for manufacturing of hybrid materials.