Nondestructive evaluation of conformal sonar hull array manufacture and installation

The Conformal Array VElocity Sonar (CAVES) consists of an array of neutrally buoyant accelerometers mounted on a compliant layer that is adhered to the hull with an approximately one inch thick layer of Versathane. The performance of this sonar is dependent upon having uniform material properties and on having a bond to the hull free of voids and delaminations. Due to the high propagation loss in the compliant layer, conventional ultrasonic techniques cannot be utilized. There is also the need to directly measure the physical properties of the compliant layer since it has been demonstrated that QA samples do not have the same properties. Two non‐destructive evaluation techniques are presented. In the first, a point drive is used to excite elastic waves in the compliant layer. The resulting motions are measured with a Laser‐Doppler Vibrometer and an optimization technique is used to determine the complex (real and imaginary components) material properties. This method also lends itself to finding macrovoids within the compliant layer. In the second technique the vibration source excites the bond layer from a free edge. The array sensors are then used to determine the presence of bond failures. Both theory and experimental results are presented.