Personal research summary 2017

1. Summary of research interests : Structural
Integrity, fracture mechanics, residual stress,
high temperature materials
Professor David Knowles
Professor in Nuclear Engineering
Co- Director SW Nuclear Hub
Solid Mechanics Research Group

2. My key research areas
• Micromechanics of deformation and damage
• High Temperature Materials
• Mechanical Testing
High Temperature Centre
“Fundamental understanding of the
mechanical behaviour of metallic structural
materials operating at High Temperature”

3. Research Background
• As the Advanced Gas Reactors in the UK operate with temperatures in the carbon dioxide coolant gas well in excess of 500 deg C,
their structural components, pressurised containment systems and metallic thermal insulation are subject to the many degradation
processes including high temperature creep, fatigue and environmental attack. To substantiate long-term operation detailed
assessment procedures (‘R5’) have been developed over many decades to predict these damage mechanisms. These procedures
continue to evolve as many of the components are located in difficult to inspect regions of the reactor and many of those subject
to scrutiny have been operating well in excess of conventional plants and/or experimental data.
• In practical terms the majority of damage is observed at welds owing to the presence of stress concentrations, local changes in
microstructural, varying strength of material and small defects as a consequence of the joining process. The current approach to
predicting damage in weldments is highly empirical in nature, based on an adaption of the methods applied to the parent
(unwelded) material and somewhat limited in applicability to welds which are not full penetration (eg fillet welds). Considerable
work is in progress in which Bristol is involved to better understand the distribution of damage through the various regions of the
weldment and its associated heat affected zone in the parent. This involves modelling the change in material response across the
weldments (ie the associated high temperature constitutive behaviour) as well as the geometrical features of the weld, comparing
predictions of damage evolution with observed behaviour. The ultimate aim is to produce a substantial update for the method of
predicting damage at weld features in austenitic stainless steels and other metallic systems
3
3rd October 2016