The current candidate material for the structural parts of this new reactor is 316L(N) austenitic stainless steel, an extremely ductile material due to its high Ni content. In order to build MYRRHA, the materials should be characterized and the mechanical properties should be measured. One of the more important properties of a structural material is its fracture toughness, or its resistance to a crack growing. This is often done by tests where a tensile load is applied on fatigue pre-cracked CT specimen. For brittle materials with limited plasticity a KIC test is performed. JIC tests are performed when there should be accounted for more plasticity in the material.
Analysis of the flow curve and CTOD data can be done with different techniques such as unloading compliance (UC), normalisation data reduction (NDR), energy normalization (EN), etc… For materials with limited plasticity, all of these techniques should result in same J-values and J-curves, within a reasonable statistical error. However, it has been observed that for highly ductile materials such as the 316L(N) under investigation for MYRRHA, the techniques give results differing in some cases by an order of magnitude.
During this internship, tests can be conducted on materials ranging from brittle to materials with small plasticity to extremely ductile. The goal is to investigate the practical limit of each of the different techniques and evaluate in what situations some technique is preferred over another. Additional information about the local plasticity of the material will be gained from the newly obtained DIC-system in the SMA group. This state-of-the-art technique allows us, by digital image correlation, to see the strain field on a flat surface, for example one side of a sample which is being tested.