Project Code: 34236
Start date and planned duration: February 2021, 24 months
- Carry out a review of previous literature and capture any advancements reported in the residual stress measurement field. Ensure updated literature review is disseminated.
- Investigate the issue of texture effect and identify a method of negating the texture effect with respect to birefringence.
- Further develop and investigate the capability, accuracy and limitations of non-destructive ultrasonic techniques for quantification and monitoring of residual stresses in metallic materials.
- Develop a procedure for using the ultrasonic method to assess the residual stresses of materials and welds on site.
- Generate tables with acoustoelastic constants and calibration blocks for the most common materials to be used in combination with the above procedure.
- Use the residual stress measurement method to provide validation of weld repair regions, in addition to providing further data for validating the stress relaxation clauses provided in current Structural Integrity Standards.
This project will build on the output of Project 32898, which was placed on hold in 2020 due to disruption caused by the COVID-19 pandemic.
Residual stresses, often inherent to a fabrication process, have an important influence on the safe operation of engineering structures and are assessed using engineering critical assessments (ECAs). These stresses can also affect the fatigue behaviour and reaction to aggressive environments/corrosion resistance. Several residual stress measurement methods are currently used. These are classified as destructive (e.g. contour mapping, BRSL (block removal, splitting and layering), slitting and boring), semi-destructive (e.g. hole-drilling) and non-destructive (e.g. neutron, synchrotron and X-ray diffraction). These techniques are well validated with some providing high-resolution residual stress distributions. They are however, often costly and time-consuming to perform with most requiring a laboratory with dedicated facilities. For on-site measurements, hole-drilling can be used, however it provides only a surface measurement and the site often requires repair after the measurements are performed.
This project will attempt to develop a simple to apply non-destructive residual stress measurement solution based on ultrasonic or electromagnetic acoustic methods. Previous work has demonstrated the potential for either ultrasonic testing (UT) or electromagnetic acoustic transducer (EMAT) techniques to provide a portable, low-cost and safe solution, with adequate resolution and excellent depth penetration. The UT technique, using time of flight of critically refracted longitudinal waves (the LCR method) will be developed further. The EMAT method is based on using two linearly polarised shear waves to compute the stress from birefringence measurements. The project will also investigate this technique and develop it further.
Benefits to Industry
A successful outcome would be considered achieved if an accurate residual stress measurement were defined. This will enable a range of benefits, potentially including:
- A method of quickly validating critical areas in terms of residual stress to potentially provide justification for increasing a component’s service life.
- Enhanced safety with reduced failures.
- Reduction in cost and lead-times associated with laboratory residual stress measurements.
- The ability to measure residual stresses on site.
- Rapid and low-cost assessments of product quality from suppliers including weld repairs, post-weld heat-treatments and stress relaxation from loading or service environments.
- Economic product quality improvements by taking residual stress measurements at the optimisation or fabrication stage of a component.
- An economic method of assessing the influence of different parameters on residual stress.
- In-service monitoring of a component’s residual or applied stresses.
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