MECHANISM MAP OF TORSIONAL FATIGUE FRACTURE

Studies have been made of the torsional fatigue fracture life of notched specimens,themacroscopic fractography and microscopic fracture mechanism of steel 40Cr after varioustempering treatments under different stresses,With the increase of stress,the fracture modelchanges from normal stress fracture to longitudinal shear one,and then transversal shear one.Under same stress,with the increase of strength,the fracture mode transfers from shear tonormal stress fracture.The mechanism of normal stress fracture may be:transgranular frac-ture→striation+intergranular fracture→dimple+intergranular fracture,and of shear fracturemay be:transgranular fracture→shear trace→dimple.Based on the experimental results,afracture mechanism map of torsional fatigue has been drawn up.