A fracture locus for a 1 wt% aluminum-graphene metal matrix composite at 300 °C

A fracture locus for a 1 wt% aluminum-graphene metal matrix composite is obtained from experiments at 300 °C. The fracture locus determines a functional dependence of ultimate metal ductility on the stress state characteristics. Tensile tests of smooth cylindrical specimens, notched cylindrical specimens, bell-shaped specimens and tests on conventional and “supported” pressing of the bottoms of thick-walled cups are performed. The tests are simulated by the finite-element method to evaluate the stress-strain state in the fracture region. The fracture locus makes it possible to evaluate the ultimate ductility of the composite as a function of the stress triaxiality factor k and the Lode-Nadai coefficient μσ. The fracture locus can be used in the range of k from −0.08 to 1.39 and in the full range of μσ. The composite under study manifests a significant ductility. The plastic strain to fracture of the composite under axisymmetric deformation, when μσ = −1, is at least 2.6 times higher than that of commercially pure aluminum, while under the plane stress state the excess ratio is at least 2.2. The plastic strain to fracture of the composite under axisymmetric deformation for μσ = +1 and k = +1 is approximately the same as that of commercially pure aluminum. As the stress state becomes less severe, the ductility of the composite becomes higher than that of commercially pure aluminum. The obtained fracture locus is applicable to the evaluation of damage accumulated in the composite in a metal forming process.