Fundamental considerations in fracture in nuclear materials

Abstract

The motivation of this work is to derive a means of monitoring the structural integrity of components used in nuclear power plants since there are a diverse range of materials, under variable loading, with a range of prior loading histories under complex environmental conditions. An experimental technique has been developed to characterize brittle materials which, using linear elastic fracture mechanics, has given accurate measurements of the global quantity fracture toughness. Here we extend this geometry to X-ray measurements in order to track the crack front as a function of loading parameters as well as to determine the crack surface area as loads increase. We have applied these advances to fracture in beryllium, to determine the onset of damage within the target as strain increases. Further, visualization of crack front advance and the correlated strain fields that are generated during the experiments, have allowed determination of the fracture surface generated as a function of load. This accurate tracking of the micromechanics controlling the energy balance in dynamic failure will provide a vital step in validating multiscale predictive modelling. By these means we aim to produce a micro-and mesoscale justification for macroscale concepts such as K IC.

4D synchrotron X-ray microtomography of fracture in nuclear graphite after neutron irradiation and radiolytic oxidation

“…The applied stress in the graphite sample was calculated using eq. ( 1), the standard method for this test [34][35][36][37]:…”

“…The instability of crack growth in quasi-brittle systems like graphite under conventional fracture techniques presents a major challenge for X-ray tomographic microscopy studies as a finite time is required to obtain the images [31][32][33]. Therefore, a double cleavage drilled compression (DCDC) test geometry, based on the seminal work of Sammis and Ashby [34], in which a stable crack is formed and propagates under compressive applied loading with decreasing crack tip KIC at increasing crack length, has been adopted for this study [35][36][37].…”