Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

Stress Measurements
With ultrasonic techniques, the velocity of ultrasonic waves in materials can
be measured and related to stress (Ref 16). These techniques rely on the
small velocity changes caused by the presence of stress, which is known as
an acousto-elastic effect. The technique is difficult to apply because of the
very small changes in velocity with changes in stress and because of the
difficulty in distinguishing stress effects from material variations (such as
texture; see Ref 17). However, with the increased ability to time the arrival of
ultrasonic pulses accurately (±1 ns), the technique has become feasible for a
few practical applications, such as the measurement of axial loads in steel
bolts and the measurement of residual stress (Ref 5).
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