抄録
Residual stress affects the failure of machines and structures by contributing to buckling and brittle fracture when those failures occur at low applied stress levels. In addition, residual stress may contribute to fatigue and corrosion cracking. For in-process and in-service failure prediction of the machine and structure, nondestructive methods for residual stress measurement are required. The research on nondestructive evaluation of residual stress using ultrasonci technique has attracted special interest recently. A few works have been reported on the ultrasonic measurement of residual weld stress. However, reports on nondestructive evaluation of stress relieving have apparently not been published to date.
In the present study, ultrasonic stress measurement techniques are applied to mild steel plate welded by shielded metal arc welding and aluminum alloy plate heated by TIG arc. In addition, the effect of mechanical stress relief treatment is examined by the ultrasonic method. Most ultrasonic stress measurement techniques measure some combination of stresses, such as the sum or difference of principal stresses. In order to evaluate the effect of residual stresses on the failure of structures, stresses must be determined absolutely. In the present paper, the ultrasonic technique for measurement of absolute residual stresses is examined. The residual stress distributions are compared with those measured by stress-relaxation techniques which use electric strain gauges or contact balls. It is clarified that residual stresses measured by ultrasonic technique are very close to those by conventional stress-relaxation methods. Consequently, the residual stress can be measured nondestructively and absolutely by means of the ultrasonic method.
