PhD Viva - Applying the contour method of residual stress measurement to irregular components

Description

Reliable evaluation of residual stress (RS) is essential in structural integrity assessment for high value metallic components. The contour method (CM) is a destructive technique to analyse RS that is released by a planar cut, usually realised with wire electrode discharging machining (WEDM). By converting the out-of-plane deformation caused by a stress relaxing cut into nodal displacements of a finite element (FE) model, the original stresses can be reconstructed according to elastic superposition theory. The CM was first developed and validated for components which adhere to a set of geometric and experimental cutting conditions for components with rectangular cross-sections, but for non-rectangular components with complicated geometry and inhomogeneous stress distribution, approaches are somewhat untested. A WEDM cut can potentially introduce cutting artefacts (CAs) when cutting through these types of irregular components. These CAs can be misinterpreted as artificial stresses as they are superimposed with displacement stemming from stress relaxation. This is most apparent when the instantaneous cross-section of the workpiece changes with respect to the cutting orientation. Typically, sacrificial material is employed to regularize the cutting cross-section to mitigate artefacts, but the limitation of this approach is not well identified and there is a paucity of applications that have been documented. The current data processing routines also has limitations in deriving short wavelength stresses from contour measurements that contain local defects, which are common in the assessment of irregular components. The present work is aligned with developing a reliable routine of applying the CM to irregular components, and developing a more robust surface fitting models to process datasets which may have limitations imposed by localised errors with three discrete aims.

Period	28 Feb 2024
Examinee	Zhe Cai
Examination held at	The University of Manchester
Degree of Recognition	International