Fatigue in aluminum–steel and steel–steel composite foams

The compression–compression fatigue behavior of two classes of composite metal foams (CMF) manufactured using different processing techniques, was investigated experimentally. Aluminum–steel composite foam processed using gravity casting technique comprises of steel hollow spheres and a solid aluminum alloy matrix. Steel–steel composite foam, processed using powder metallurgy (PM) technique consists of steel hollow spheres packed in a steel matrix. Under compression fatigue loading, the composite foam samples showed a high cyclic stability at maximum stress levels as high as 90 MPa. The deformation of the composite foam samples was divided into three stages – linear increase in strain with fatigue cycles (stage I), minimal strain accumulation in large number of cycles (stage II) and rapid strain accumulation within few cycles culminating in complete failure (stage III). Composite foams under cyclic loading undergo a uniform distribution of deformation, unlike the regular metal foams, which deform by forming collapse bands at weaker sections. As a result, the features controlling the fatigue life of the composite metal foams have been considered as sphere wall thickness and diameter, sphere and matrix materials, processing techniques and the bonding strength between the spheres and matrix.