Structural integrity research
Developments in experimental and numerical techniques including surface strain mapping, weld modelling, residual stress characterisation and fracture modelling are enabling conservatisms in current assessment methods to be more fully understood.
A New Way of Measuring Plastic Strain using Electron Back Scatter Diffraction
Lai Mei Li, PhD Student
To know the plastic strain stored in material due to forming, welding or any other processes is highly relevant to a number of issues in materials science and engineering such as the initiation of pitting, stress corrosion and brittle fracture cracking in metals. Information about the level of plastic strain in a microstructure is difficult to obtain, although observations of dislocation density or measurement of micro-hardness provide some detail. Further details on A New Way of Measuring Plastic Strain using Electron Back Scatter Diffraction
Crack Nucleation and Short Crack Behaviour by Non-destructive in-situ Observations
Andy King and Greg Johnson
Since crack growth rates generally increase with crack length, the majority of the lifetime of a crack in structural components is spent when the crack is short. Uncertainties in short crack propagation behaviour therefore have a strong influence on lifetime prediction. Unfortunately, this is also the regime within which the study and modelling of crack behaviour is most difficult.
Important technological advances mean that for the first time the growth of a crack and its relationship to its local environment can be studied non-destructively in detail in 3D.
The key technical advances are:
- 3D imaging by ultrahigh resolution X-ray microtomography, and
- 3D grain mapping using the 3D X-ray microscope
Grain Boundary Engineering for Intergranular Stress Corrosion Resistance in Austenitic Stainless Steel
Dirk Engelberg, PDRA
Austenitic stainless steels are frequently used for engineering applications in aggressive environments. However their corrosion resistance at grain boundaries is compromised in some environments and under certain metallurgical conditions leading to intergranular degradation. The purpose of this project was to investigate the effect of microstructure on intergranular stress corrosion cracking (IGSCC). Further details on Grain Boundary Engineering for Intergranular Stress Corrosion Resistance in Austenitic Stainless Steel.
Residual Stress and Constraint
Granson Lee, PDRA
Defects which develop in welds can potentially propagate in a brittle manner under the influence of primary and secondary (residual stresses). Current assessment methods provide assessments which may be unduly conservative. This project addresses the influence of combined primary and secondary (residual) stresses on the behaviour of defects in brittle materials under conditions of high and low constraint.
Residual stress calculation
John Francis, PDRA
Residual stresses generated during welding are known to have a deleterious effect upon the fatigue life of welded components. In high integrity structures, particularly those in safety critical applications, failure in service cannot be tolerated. Accurate characterisation of the residual stresses present in these components is therefore necessary if reasonable estimates of the serive life are to be obtained. Detailed characterisation of the nature and origins of residual stresses also offers the opportunity to identifying and applying techniques to mitigate the risks associated with residual stresses in such components.
Residual Stress Measurement
Joe Kelleher, PDRA
The presence of residual (secondary) stresses in critical NRSP components can lead to an increased propensity for degradation and premature failure, thereby compromising structural integrity and necessitating costly servicing overheads. Much of the assessment of residual stress is undertaken at the component macro-scale. However, degradation mechanisms actually occur at many different length scales, whether that is the grain boundary chemistry of stress corrosion, the heat affected zone associated with a weld, or the crack tip process zone associated with a fatigue crack.
The Measurement and Modelling of Residual Stress Effects on the Propagation of Cracks
Kerry Taylor, PhD Student
The primary theme of this project is to understand how combinations of primary and secondary residual stress influence crack growth in ductile materials. This will involve a combination of new test methods to fully characterise ductile growth within a range of residual stress fields, analytical work using optical and electron microscopy to characterise material and failure mechanisms and modelling to predict behaviour. Further details on The Measurement and Modelling of Residual Stress Effects on the Propagation of Cracks.
The Performance of Real Defects in Service
Anthony Horn, PhD Student
Defects in engineering structures are often blunt. Current assessment procedures assume these to be sharp, to enable the use of fracture mechanics and to ensure conservative predictions of structural integrity. Benefits may be obtained by developing new mechanics and modelling approaches that can take account of the real shape of defects.