EFFECT OF LOADING RATE AND TEMPERATURE ON DUCTILE-BRITTLE TRANSITION OF A CARBON STEEL

摘要

The dynamic fracture toughness of a mild steel has been studied at different loading rates andtemperatures.The material exhibits a transition from tough to brittle fracture with the chang-ing loading rate alone.Analysis of the fracture process by the theory of thermal activationsuggests that the fracture activation energy approximates to the bond energy of the{100}of aunit cell.The toughness can be resolved into two parts,J-（fd）=Ja+Jl,where Ja is the athermalpart,being independent on temperature and loading rate,whileJl=（K/Ko）1/nexp（Qf/nkT）,which controls the fracture process is temperature and load-ing rate dependent.The transition of fracture mechanism caused by both temperature andloading rate is associated with the thermal movement of atoms.