Development of Non-Destructive Ultrasonic Residual Stress Measurement Method for On-Site Industrial Measurements
Project Code: 32898
Start date and planned duration: February 2019, 36 months
- 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 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.
Stress measurements using ultrasound rely on acoustoelasticity theory, which relates the stress-state to a macroscopic elastic wave velocity. The speed of ultrasonic waves travelling through a material is a function of the direction and magnitude of stresses present. By measuring the time of flight or birefringence of waves through both an unstressed and stressed region of the same material, the magnitude of the residual stresses present can be determined.
TWI has demonstrated effects of stress on ultrasonic waves using two approaches: the use of electromagnetic transducers (EMATs) with two linearly polarised shear waves to calculate stress from birefringence; and the use of a piezoelectric transducer (PZT) with a longitudinal wave to calculate the stress from time-of-flight measurements.
The following tasks will be carried out in the project: (1) Measurement and tabulation of acoustoelastic constants for a range of materials; (2) Stress measurement in uniform and non-uniform stress fields using each ultrasonic technique; (3) Residual stress measurement in welded joints using ultrasonic techniques, and comparison of results with those from more widely used techniques. If these steps are successful then a fourth phase of work might be carried out, investigating the use of ultrasonic techniques to monitor changes in residual stress during cyclic loading.
Benefits to Industry
A successful outcome will help industry to: (1) Reduce cost and lead-times for residual stress measurements and enable measurements on site; (2) Ensure safety, reduce failures and quickly assess residual stress in critical areas to provide justification for life extension; (3) Assess the effects of repairs, heat treatments, and relaxation from testing or service on residual stress; (4) Reduce residual stresses due to fabrication by assessing the influence of different parameters on residual stress; and (5) Monitor residual and/or applied stress in a component.