A comparison of neutron and ultrasonic determinations of residual stress

Stress is a principal cause of material failure. This has been a well-recognized problem for decades yet neutron diffraction remains the only unambiguous way to measure sub-surface residual stresses without either destroying the component or having access to a reference state. An array of stress-measurement standards that are characterized by neutron diffraction is being developed to evaluate quantitatively the potential of other methods. In the present work an aluminium ring-plug reference specimen was fabricated to provide a means for testing new techniques to be used for the determination of residual stress. The residual-stress distribution in the ring plug was determined by neutron diffraction and strain gauges. The distribution was in excellent agreement with that expected From elasticity theory. The ring plug was also studied using an electromagnetic-acoustic transducer (EMAT) as an 'ultrasonic strain gauge'. Results over the region of the specimen examined were in excellent agreement with the other techniques and represent an excellent first step towards validating a field-portable residual-strain gauge.