Cryogenic Fracture Toughness Evaluation of Structural Alloys and Weldments for Superconducting Magnets in Fusion Energy Systems by Small-punch Testing

Abstract

This paper investigates the use of the small-punch (SP) test to estimate the elastic-plastic fracture toughness (J_IC) of structural alloys and weldments for superconducting magnets in fusion energy systems. SP testing was performed with thin-plate specimens of 10×10×0.5mm at liquid helium temperature (4K). Correlations between SP energy, equivalent fracture strain, and J_IC were assessed. All J_IC data were obtained using 25-mm-thick compact specimens that followed the standard test method for J_IC. Finite element analysis was also performed to convert the experimentally measured load-displacement data into useful engineering information. The criterion for fracture used is the strain-energy density (strain energy absorbed per unit volume) required to produce crack initiation in a solid, uncracked specimen. The fracture strain-energy density was calculated and correlated with J_IC.