Abstract
Based on electron backscatter diffraction (EBSD), hollow structures of Ni foam struts fabricated by electroplating on a chemically removable template were observed. Three-dimensional (3D) pore structures of Ni foams were also obtained using X-ray computed tomography (CT), and microstructural features such as porosity, pore size and strut thickness were statistically quantified. Evolution of microstructure and mechanical properties during ex situ compression of open-cell Ni-foams was investigated based on X-ray CT, and experimental results were compared with predictions by the finite element method (FEM). 3D microstructures obtained by X-ray CT revealed that the stress drop started with the buckling of struts at the center of the Ni-foams. The flow stress increased after the buckling of the struts spreads to most of the regions. For effective simulation of the compressive deformation and determination of the microstructural evolution, small domains of interest were selected from the entire set of observed 3D microstructures based on X-ray CT, and struts of Ni foams with a hollow structure were simplified with relevant thin-solid struts. Numerical 3D modeling comprehensively disclosed that compression caused the transverse buckling of the struts, with the bending and buckling of struts thus reducing the stress. Thickness variation of the struts causes a change in the porosity of Ni-foams without a change in pore shape or connectivity. The overall range of strut thickness was from 59 to 133 m, and the range of porosity values was from 80% to 93.7%. A stress drop was predicted with a decrease in the strut thickness or an increase in the porosity, as measured experimentally. It was also found that the stress drop contributed to an increase in the calculated energy absorption efficiency.
Highlights
Metal foams have an outstanding combination of mechanical properties, such as light weight, high strength-to-weight ratio, and good energy absorption capacity [1]
Rem et al [7] showed that the multi-layer aluminum foam sandwich structure has a much higher plateau stress than conventional bulky foam, and the stress oscillated during the plateau stage
Based on inverse pole figure (IPF) maps, it is found that struts usually possess a hollow structure in the center
Summary
Metal foams have an outstanding combination of mechanical properties, such as light weight, high strength-to-weight ratio, and good energy absorption capacity [1]. For this reason, they have been utilized in a variety of applications in many fields including the automobile, aerospace, and defense industries [2]. Various investigations on testing and design of energy absorbers using metal-based foams with good energy absorption capacity have been reported. Rem et al [7] showed that the multi-layer aluminum foam sandwich structure has a much higher plateau stress than conventional bulky foam, and the stress oscillated during the plateau stage. Reglero et al [8] concluded that the design and fabrication of an energy absorber prototype showed the potential of aluminum foam as an energy absorber material
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