A comprehensive study on the damage tolerance of ultrafine-grained copper

► The fracture behavior of UFG-copper produced by high pressure torsion was characterized. ► The critical J-Integral, JIC, and the initiation toughness, CODi, were evaluated. ► Grain refinement leads to a decrease in the fracture initiation toughness. ► The critical J-Integral remains remarkably high with simultaneous good strength.