Simulations on Jacket Material Failure of NET-Superconductors by Surface Crack Growth in 316LN Type Materials at 12K

Abstract

Two-dimensional fatigue crack growth rate (FCGR) properties of 316LN type stainless steels were investigated at 12K. The investigations were done with plate material in as received condition and with cold worked jacket material. Using a new tensile specimen configuration, sinusoidal and triangular cyclic load tests with constant and alternating amplitude, respectively, were performed. The FCGR of the plate material was found to be lower by a factor of about 3 compared with that of the cold drawn U-section jacket material. To simulate the loading under magnet operational condition, specimens were tested under constant stresses making use of a calculated peak load vs. crack length function. These tests were carried out between 0.5 and 2.5 mm surface crack length. From this investigation a prediction for the material’s cyclic life number could be derived. Further, surface FCGR tests under pure 4-point cyclic bending load were performed and a comparison between different crack growth shapes obtained under bending and tensile loads were given. Plate materials “short crack” behaviour were determined from constant K-max, AK-decreasing test.

This work is performed within the Euratom Fusion Technology Program under the NET-contract No. 92287