TWI Industrial Member Report Summary 600/1997
K Bell, K A Yehia* and T H Hyde*
This report describes the findings from a collaboration between the University of Nottingham and TWI, partially funded by TWI's Core Research Programme. The work developed a local time-dependent (creep) property measurement technique suitable for testing engineering materials, and a rationale for application of the information to real structures.
Life of components operating at elevated temperatures is frequently limited by the creep performance of their welded joints. Measurement and prediction of weldment creep behaviour, especially secondary or steady state rate properties, is not a simple problem because of the many different microstructural constituents that make up a multi-pass weld and heat affected zone (HAZ).
Conventional cross-weld creep rupture testing requires a significant amount of test material to be removed from the component (and then repaired), and typically only gives information on the endurance of the weakest zone of material in the joint. Information on creep deformation rates in the disparate bands of material in a weldment are needed to optimise welding conditions, and hence reduce the chances of premature failure.
It was considered that an existing empirical method could be adapted and validated to provide a technique for determining local creep strain and strain rate properties, whilst only requiring a small volume of test material.
- To use numerical methods and the reference stress approach to obtain a better understanding of local time-dependent deformation behaviour around a small rigid cylindrical indenter in contact with creeping material.
- To improve the impression creep testing technique such that it could be used on industrially relevant materials under conditions typical of high temperature operation.