A study on the prediction of fatigue life in an axi-symmetric extrusion die

The present paper gives some results of the fatigue behavior of a typical axi-symmetric forward extrusion die. The extrusion process is analyzed by the rigid-plastic FEM and deformation analysis of the extrusion die is conducted by the elasto-plastic FEM. To approach the crack problem, LEFM (linear elastic fracture mechanics) is introduced. Using a special element in order to consider the singularity of stress-strain in the vicinity of the crack tip, the stress intensity factor and the effective stress intensity factor are calculated. Applying a proper fatigue crack propagation criterion such as the Paris-Erdogan fatigue law and maximum principal criterion to these data, the angle and the direction of fatigue crack propagation is then simulated. From the results, it is established that the simulated fatigue crack propagates in the zig-zag path along the radial direction and the fatigue life of the extrusion die is evaluated using the computed crack growth rate. (C) 1997 Elsevier Science S.A.