Deformation and Fracture in Small Punch Creep Tests, and Influence Factors on Creep Rupture Life (Testing Environment and Radius of Lower Die)

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Small Punch, hereinafter termed SP, creep test has been proposed as a semi destructive testing methodology to examine the residual creep life of high temperature components. A series of SP creep tests were conducted on low alloy steel at 600°C both in air and in high vacuum to investigate influences of testing environment and the radius of the lower die on the SP creep rupture life. The thickness of the oxide scale on the SP creep specimen in air increased with the test duration, e.g., about 30μm in thickness after 400 hours exposure. The SP creep rupture life in air reduced to a half of the life in vacuum due to an increase of both the actual stress in the specimen and the coefficient of friction. In addition, the magnitude of the radius at the lower die shoulder also affected the SP creep rupture life. The influence of this radius on the SP creep rupture life was studied experimentally and numerically. The SP creep rupture life with a smaller die radius had twice longer than that with a larger one. This fact was also demonstrated by the FE analysis.