Compressive Stress Effects on the Ultrasonic Detection of Cracks in Welds

Crack closure due to external bending forces or residual stresses is an important concern in any nondestructive examination. It is particularly important in ultrasonic examination since this technique depends on the change in acoustic impedance at the crack interface to produce the reflected wave. If the two surfaces come into intimate contact somewhere along the crack due to closure effects, partial transmission can occur [1]. This partial transmission reduces the reflected signal and so underestimates the flaw depth when sizing is based on the reflected signal amplitude