HOLOGRAPHIC-INTERFEROMETRY MEASUREMENTS OF TRANSIENT BENDING WAVES INTUBES AND RINGS

Propagating bending waves are studied in a tube of steel and in a ring of aluminum. The waves are generated by the impact of a ballistic pen dulum. Holographic interferometry, with a double-pulsed ruby laser as light source, is used to record the waves. A conical mirror is placed axially inside the tube. Axial illumination and axial observation dire ctions, make it possible to view all sides of the tube simultaneously with a high sensitivity to radial deformation. The interferograms, whi ch have an unusual perspective, are captured with a CCD-camera and the n spatially transformed into an unwrapped strip of the tube wall. This makes the interpretation of the measurements simpler. The geometry of the tube causes the wave pattern to propagate with different speed an d amplitude along and across the tube, even when the material itself i s isotropic. A finite-element simulation of the impact is compared to the corresponding experiment. An impact on a ring with a defect is per formed in order to study the effect on the wave pattern. The proposed method could be used in nondestructive testing of pipes.