Anisotropic spall behavior of CNT/2024Al composites under plate impact

Plate impact experiments are conducted on the carbon nanotube (CNT) reinforced 2024Al composite fabricated by flake powder metallurgy and hot extrusion, to investigate the effects of microstructural anisotropy on its dynamic deformation and damage, as well as the role of CNTs. Three loading directions are explored with the loading axis being parallel to the extrusion, transverse or normal direction. Free-surface velocity histories are measured to evaluate the mechanical properties and damage processes, including the Hugoniot elastic limit (HEL; similar to 0.8 GPa) and dynamic spall strengths (1.4 - 1.9 GPa). Postmortem samples are characterized with synchrotron X-ray computed tomography and scanning electron microscopy. The microstructural anisotropy of the composite (in terms of the orientation of lamellar microstructures) has a negligible effect on HEL but induces an anisotropy in spall strengths; spall strength is the highest for loading along the extrusion direction, the long axis of the lamellar microstructures. CNTs appear to increase the spall strengths of the 2024Al matrix, in contrast to other reinforcing fibers/particles. The crack propagation direction and damage features can be correlated with collinear propagation of microcracks following the lamellar microstructures. (C) 2020 Elsevier Ltd. All rights reserved.