Mechanical ratcheting of stainless-clad pipe subjected to internal pressure and cyclic axial load or cyclic bending.

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Mechanical ratcheting behavior of a stainless-clad pipe(SUS304/STPG38)subjected to internal pressure and cyclic axial straining or cyclic bending was investigated. An elastic-plastic FEM analysis of the mechanical ratcheting was perfomed and the analytical results were compared with the corresponding experimental results.(1)In the ratcheting of internal pressure with cyclic straining, circumferencial strain accumulated with strain cycles, and the higher ratcheting strain rate was observed under the conditions of larger cyclic strain range and larger internal pressure. Shakedown of ratcheting was obserbed in SUS304 after about 10 strain cycles, whearas remarkable ratcheting strain accumulated in every strain cycle in STPG38 steel. In the clad pipe remarkable ratcheting strain accumulation appearing in STPG38 was prevented by SUS304. and the ratcheting strain rate of the clad pipe was between the rates of SUS304 and STPG38. Ratcheting tests were performed in two levels of clad ratio(thickness ratio), SUS304/STPG38 = 0.5 and 1.0, but no apparent difference in ratcheting behavior was found.(2)In the ratcheting of internal pressure with cyclic bending, larger strain accumulation was observed compared with the ratcheting of internal pressure with cyclic axial straining.(3)The FEM analysis overestimated the ratcheting strain accumulation. It seems to come from the problem of constitutive modeling for the steels, and the improvement of the modeling is required.