Direct stress measurement by ultrasound

A device has been developed permitting the direct display of the axial forces applied to bolts or other components on the basis of ultrasonic measurements. The device measures the time taken for an ultrasonic wave incident on the bolt head to propagate through the bolt, which time is increased according to the level of stress experienced by the bolt. The measured axial force can be displayed digitally, along with the velocity of sound and the specimen thickness, by a microprocessor built into the device. Experiments have shown that the stress meter is capable of accurate measurements nearly up to the yield point, as well as measurements of elastic coefficients.