Surface mechanical properties of shot-peened CNT/Al–Mg–Si alloy composites

Abstract

A carbon nanotube (CNT)-reinforced Al matrix composite was fabricated and treated by shot peening. After shot peening, isotropic compressive residual stress fields were induced in surface shot-peened layers. As the mechanical properties of the peened layers were improved and therefore varied from the base metal, a specific in-situ X-ray stress analyzer combined with the tensile test technique was used to measure the stress–strain relationship of the strengthened surface layer. On the basis of the measurement and the Von Mises stress criterion, the surface yield strength was calculated and improved by 25% relative to that of the matrix. Moreover, a relaxation behavior of compressive residual stress was observed under cyclic loading. The results showed that the rapid relaxation of surface residual stress chiefly occurred in the first few cycles and then stabilized gradually in subsequent cycles. The retained residual stress under all given applied cyclic loadings possibly occurred in the compressive state consistently.