Tensile Deformation and Failure Behavior of Open Cell Nickel and Copper Foams

Abstract

Tensile deformation and failure behavior at room temperature of the open cell nickel and copper foams with high porosity (≈96%) fabricated with the slurry foaming process at Mitsubishi Materials Corporation, Japan, was studied. In-situ observation of the deformation and failure behavior was conducted with a digital microscope. Stress-strain curves were measured, in which a non-contact extensometer was employed to detect the strain of the samples accurately. Electric resistance was measured to monitor the damage evolution. Finite element stress analysis was conducted to calculate the morphological change of cells with applied strain and the stress distribution in cells. It was revealed that the deformation and failure progressed through the following four stages; stage I characterized by the elastic deformation, stage II by plastic deformation, stage III by the co-occurrence of plastic deformation and cumulative failure of struts and stage IV by the chain reaction of strut failure nearly in a limited cross-section, respectively. Also it was found that the distribution of failure strain of struts in stage III, measured from the serrations in the stress-strain curve, could be described by the Weibull distribution, with which the transition from stage II to III was identified. Also, the result of the statistical analysis suggested that the average failure strain of the struts in the foam is much higher than the strain at ultimate stress of the foam.