Preparation, compression behavior and 3D damage evolution of epoxy syntactic foam with nickel hollow spheres

The nickel thin-walled hollow spheres (NHS) epoxy syntactic foam was fabricated by the infiltration method. The crystal structure and grain size of the NHS were quantitatively analyzed by FIB-TEM. The bulk compressive response of the NHS syntactic foam was determined and compared with glass bubble syntactic foam. The X-ray computed microtomography (XCT) coupling with the interrupted compression tests were conducted on a single NHS and the NHS syntactic foam to demonstrate the 3D deformation history. The bulk behaviors of the NHS syntactic foam were correlated with the XCT examinations to analyze the mechanisms of the failure process. The electrodeposited NHS shows the nanocrystalline and polycrystalline microstructure. The low air void content was achieved in the NHS syntactic foam produced by the infiltration method. Although the NHS syntactic foam's elasticity and yield strength are lower, the compressive resistance and toughness as well as the energy absorption of the NHS syntactic foam are higher than those of glass syntactic foam. The failure process of the NHS syntactic foam is dominated by the NHSs deformation and the resultant strain hardening. The damage initiates from the weak NHSs, then more crushed bands arise with the increased compressive stress. The further deformation of the damaged bands can intermittently develop owing to the strain hardening. During the deformation history, no visible macro cracks can be found in the epoxy matrix from the XCT slices.