Polyurethane Foam and Steel-Foam Interface Characterisation: An experimental Study

Abstract

It is known that metal-foam composite beams exceed the structural properties of metal only beams. However, the interface failure mechanisms of metal-foam composites are not well understood. To address this issue, our research investigates the failure behaviour of zinc-coated steel - polyurethane (PU) foam composite beams. The primary aims are to characterise the mechanical properties of PU foam including its failure envelope, and to quantify the steel-foam interface strength of composite beams with the cohesive laws. A yield surface model that describes the failure behaviour of low density PU foam is developed here. The required data are experimentally measured with quasi static uniaxial and triaxial tests on PU foam samples in different loading modes. Furthermore, the strong anisotropy of ultimate stresses, yield stresses and elastic moduli of PU foam is characterised. A test method to quantify the interface strength of composite (steel-foam) beams is employed. Stiffened double cantilever beams, with a crack placed in the steel-foam interface, are used as test specimens. The propagation of the crack tip is recorded using the Digital Image Correlation (DIC) technique. The strain energy release rate is analytically determined using the J-integral, based on the dimensions and properties of the composite beam and the applied loads. The analytical determination of the strain energy release rate is mathematically extended by including a variable width beam. The cohesive laws for mode I and mode II failure of the steel-foam interface are derived using the test method employed. The developed testing equipment and analysis process of the recorded data provides the basis for further interface characterisation at the University of Auckland. The experimentally acquired results of the steel-foam interface and the yield surface model of the PU foam can be directly used as inputs for finite element simulations to predict failure of composite structures, thus improving their design process.