The use of wide band ultrasonic signals to estimate the stress condition of materials

This paper reports the results from experimental studies of the effect of applied stress on the propagation of broadband ultrasonic pulses in selected samples of aluminium alloy. For one particular 5086 alloy of aluminium used, results have shown changes in the spectral characteristics of the detected ultrasonic signals with applied stress. In this case, measurements of the relative transit times for various bulk wave modes exhibit two distinct dependences on stress, for stresses below and above approximately 40-50 MPa. These regions must be related to changes in the microstructural parameters of the material and we propose a possible mechanism for this that is consistent with the earlier published literature. It is also shown that by taking into account the influence of changes in the spectral characteristics of the signals in the process of loading in the elastic region, one is able to increase the accuracy of stress measurement by the ultrasonic method.