The rate-dependent mechanical behavior of CNT-reinforced aluminum matrix composites under tensile loading

Aluminum composites reinforced with carbon-based nano-particles or fibers have been widely studied. Yet, the rate dependence of their properties has been barely reported. In the present study, CNTs-reinforced Al composites with CNTs of two aspect ratios were produced by different powder metallurgy methods, followed by spark plasma sintering and hot extrusion. The mechanical properties and the underlying mechanisms of CNTs-reinforced Al composites at various loading rates were studied, with the aim of exploring the role of CNTs on strengthening, esp. on rate-dependent properties. The mechanical experiments revealed that the addition of CNTs not only increased the strength but also the strain rate sensitivity in comparison with pure Al. It was found that, under dynamic loading, the materials showed an increased strength and elongation-to-failure simultaneously, due to improved strain hardening rates. A careful analysis suggested that the long-range back stress produced at the CNTs-Al interfaces and the geometrically necessary dislocations accumulated due to strain gradient along the interface, mainly contributed to the strain hardening of CNTs/Al composites. A novel microstructure-based model using microscopically non-uniform dispersion of CNTs was proposed to account for the mechanical properties with better prediction than the traditional models. The results might shed some light on understanding metal matrix composites reinforced with nano-particles or fibers.