Local approach applied to fatigue crack initiation and growth in cold forging tools

摘要

Local approach of fracture with damage mechanics was applied to establish a more precise method of estimation of service life of cold forging dies.First,a modeling of Elastic-plastic-damage behavior of the tool steel was conducted in the framework of thermodynamics.Then the initiation and propagation of fatigue crack of cold forward extrusrion die was analyzed by the local approach.The inititation and propagation of faituge crack in the vicinity of the die radius was found as the extrusion number increased.Furthermore,the calculated rate of crack length to an extrusion number was found that the present approach could estimate the actual behavior of the fatigue crack growth in good accordance.The calculated crack propagation rate also tends to decrease due to the decrease of the major principal stress at the crack tip as the crack propagates.