Mechanical Response of CNT/2024Al Composite to Compression and Tension at Different Strain Rates

Abstract

Compressive and tensile properties of a carbon nanotube (CNT) reinforced 2024Al composite are investigated under quasi-static and dynamic compression as well as quasi-static tension, along three different directions (extrusion, normal and transverse directions). Upon compression, yield and fracture strengths of the composite show negligible strain rate effect and mechanical anisotropy as manifested in the compressive stress–strain curves. Fractography and profilometry show that fracture surfaces are rough shear fracture planes for quasi-static compression; however, smooth conical fracture surfaces are observed for dynamic compression as a result of more homogeneous damage nucleation and growth, leading to high ductility under high strain rate loading. Pronounced mechanical anisotropy is observed for the composite under quasi-static tensile loading. Ductility or fracture strain is the highest along the normal direction, because debonding along the particle and lamellar interfaces is suppressed along this direction. In situ optical imaging along with digital image correlation is utilized to obtain the deformation dynamics of the composite along the three different directions. Stripe-shaped strain localizations appear in the strain fields along the extruded and tangential directions, while the strain fields are approximately uniformly distributed along the normal direction, consistent with the stress–strain curves.