Size-effect method to determine mode-I fracture toughness of aluminium alloys

Abstract

Size-effect method is used to determine the fracture properties of three aluminium alloys. Mode-I tensile testing of thin rectangular sheets of aluminium alloys 5052−H32, 6061−T6 and 8011 is carried out. The test specimens are scaled geometrically in the ratio of 1:2:3:4 for a constant length (L) to width (D) ratio (L∕D=4). The notch depth (a) to width (D) ratio is 0.25. Size-dependency of strength is observed. The fracture toughness values and the crack growth resistance curves (R-curves) for these three alloys are determined using equivalent elastic crack model. The R-curves predict the peak loads accurately with only 0%–7% difference from the experimental values. The pre-peak load–deflection curves calculated from the R-curves closely match the experimental curves. Bažant’s size effect law could be used to fit the peak load data. Scaling laws for strains at peak loads are proposed. The transition length (D0) determined for these strain scaling laws differ from those obtained using the size effect law.