Deformation and fracture behavior of beams composed of alumium foam core and ceramic Al2O3 under monolithic bending

Deformation and fracture mechanisms of sandwich and multilayer beams composed of aluminum foam core and ceramic face sheets under four-point bending condition were investigated in situ by surface displacement analysis (SDA) software. The toughening mechanism of the beams was discussed and a model was given for the computation of the fracture energy of the beams. Beams containing foam core with 5-, 10-, and 20-mm thickness and Al2O3 face sheets of 0.5-and 1-mm thickness were prepared. The results show that collapse of the beams is by two basic modes, indentation (ID) and face plate failure (PF). The SDA results illustrated that indentation is localized compression on the portion of the beam adjacent to the loading rollers, where displacement and strain are at the maximum. In PF, the beam entirely bends. It is also found that before collapse of the beams with pure PF mode, the foam core undergoes uniform compressive deformation, which contributes most to the fracture energy of the beams. As for the beams with ID characteristic, the localized compressive deformation plays a key role rather than the uniform compressive deformation in the fracture energy of the beam. The total fracture energy W of a beam under bending condition is proposed as W=WUC+WLC+WCB+WPF where WUCis the energy of uniform compressive deformation of the foam core, WLCis the energy of localized compression of the foam core and WCBand WPFare the bending fracture energy of the monolithic foam core and ceramic face sheet, respectively. For the beams with pure PF mode, WLCis zero. The estimated values of the fracture energy are in good agreement with the measured fracture energy of the beams.