Low cycle fatigue damage and critical crack length affecting loss of fracture ductility

• The main damage which affects fatigue life is initiation and growth of cracks.
• The fatigue life was extended by removing small cracks.
• There is a critical length of fatigue crack which causes the loss of ductility.
• The loss of fracture ductility is related to the fracture types in tensile tests.

The role of small cracks on fatigue life and loss of ductility are discussed to understand the reality of fatigue damage in low cycle fatigue. The series of low cycle fatigue tests were carried out paying attention to the role of small cracks and their influence on ductility loss. These tests showed that the fatigue lives were pronouncedly extended by removing surface cracks. Also, it was quantified that the loss of fracture ductility was correlated with crack length but not with the number of fatigue cycles. From those results, it is concluded that the behavior of small cracks is crucial to explain the mechanism of low cycle fatigue damage rather than the crack initiation process and change in bulk material properties.