| Nondestructive evaluation using ultrasonic waves for crack identification is an important technique in failure prevention of materials and structures. Fatigue cracks usually experience crack surface contact because of the existence of residual stresses near the crack tips. These contacting crack surfaces will reduce the effective length of the crack and, therefore, affect the collected ultrasonic waves.;The current work provides an experimental study of the effect of crack surface contact on the collected ultrasonic signal. Cracked steel specimens were monotonically loaded in compliance testing to estimate their opening load. Ultrasonic shear wave was generated in the specimens and reflection from the crack was measured to estimate the effective crack length under different quasi-static bending moments. By controlling the opening load level, a relationship between the length of crack surface contact and reflected ultrasonic signal was established. Measurement accuracy of these contacting areas is further improved using the proposed graphical solution. |
