Practical considerations of the use of cross-weld and compact tension specimens’ creep data

Abstract

The present article gives an overview of the use of cross-weld and compact tension specimen modelling and analyses data to characterise creep behaviour of high temperature components. Cross-weld and CT specimens are used to describe creep crack growth in heterogeneous material structures, such as welds, and a number of factors that affect the creep behaviour of the structure, associated with this heterogeneity, have been identified. Creep data obtained from cross-weld specimen modelling is substantially affected by the material model used (e.g. Norton Power law, Liu/Murakami model, etc.), stress singularities that arise at the material interfaces and in between the columnar and equiaxed zones of the weld material, residual stresses which arise though the thickness of a multi-pass weld and the extraction orientation of the specimen relative to the welding direction. Creep crack growth data obtained from CT specimen testing and analyses is strongly dependent on the material models used (isotropic hardening models, Norton Creep law, Liu/Murakami model, etc.), the path-dependence of the C*-contour integral fracture parameter for certain heterogeneous material configurations and the accurate computation of material constants for damage mechanics models, and the agreement between loading state to the actual stress state of the component to which the CT specimen creep data is applied to. The present study examines typical results and observations from cross-weld specimen and CT specimen creep analyses, identifying the advantages, disadvantages and limitations of each specimen procedure.