A Direct Methodology for Small Punch Creep Test

Small punch creep test (SPCT) has strong advantages in practice compared with traditional uniaxial creep test because a small sheet specimen (10x10x0.5 mm) can be obtained from in-service facilities or mechanical components without damage. In this paper, a novel investigation is proposed to directly interpret SPCT results in consideration of Chakrabarty's membrane stretching theory, which features strain analysis on thin sheet material forced by large punch ball, and it is applied to derive equivalent strain and strain rate from SPCT results. Also, the Monkman-Grant model for evaluation of creep life is investigated by using equivalent strain and strain rate data obtained from the Chakrabarty's membrane stretching theory. To validate this methodology, both uniaxial creep test and SPCT have been performed for STS 316L stainless steel at 650 degrees C. Displacement and time data in SPCT were converted into equivalent strain and strain rate. The Monkman-Grant models derived from two different creep tests show a great potential such that SPCT with the proposed methodology can be substituted for uniaxial creep test.