Anisotropic compression response of functionally gradient syntactic foam comprising of fly ash cenosphere and polyurethane

Abstract

A novel functionally gradient (FG) syntactic foam with hierarchical cell structure was prepared by incorporating fly ash cenosphere of different size distribution into rigid polyurethane foam (PUR). The mechanical anisotropic behavior was experimentally studied by axial and traverse compression, and the influence of density gradient on failure mechanism was discussed through digital image correlation (DIC) technique. Results shown that the density graded (GD) syntactic foam produced stepwise stress strain response under axial compression, but failed by global shear pattern under traverse compression. The plateau stress of layered density (LD) syntactic foam gradually increased under both compression modes. The mechanical anisotropic property of FG syntactic foam was much smaller than that of functionally gradient aluminum foam. Failure mechanism of FG syntactic foam under axial compression was mainly controlled by the compression strain band generated in low density layers, and the deformation band successively extended to high density region. Under traverse compression, the material interfaces in LD foam significantly affected the propagation of shear deformation bands generated in high density layers, producing more short-range interpenetrating shear bands. The layered density gradation shown great potential in decreasing the anisotropic characteristics of syntactic foams. These findings can provide a valuable guide for designing and optimizing the impact resistance of functionally gradient foams.