Elastic-plastic failure assessment of cold worked stainless steel pipes

The change in fracture strength due to cold working was investigated for cracked stainless steel pipes. The cold working was introduced into Type 316 stainless steel plates. Then, material properties were identified in order to make elastic–plastic fracture assessments for a pipe with a circumferential crack under bending load. The two-parameter method was employed for deriving fracture strength considering the change in the flow stress (yield and ultimate strengths), fracture toughness and stress–strain curve caused by the cold working. It was found that the fracture strength was not reduced even if 40% cold working was introduced, while the failure mode was altered from the plastic collapse mode to the elastic–plastic failure mode. Although cold working decreased the fracture toughness, the change in the stress–strain curve reduced the driving force for fracture (J-integral) and increased the fracture strength. It was shown that the failure assessment curve of cold worked material can be derived using the yield and ultimate strengths of the material that is free of cold working.