Non-destructive testing of plates based on the visualisation of Lamb waves by double-pulsed TV holography

Abstract

We describe a new technique, currently under development, intended to detect the presence of flaws such as cracks and holes in thin-walled mechanical components. This technique combines ultrasonics with optics, both at a low power density, that allows to perform the tests in the non-destructive range. Lamb waves, a kind of surface acoustic waves that propagate in thin plates, are generated to explore metallic samples while double-pulsed TV holography, a whole-field interferometric technique, is used to detect them. This scheme provides maps of the instantaneous surface displacements produced by the waves, where the effects of the flaws can be visualised by contrast against the smooth propagation of the wavefront in defect free plates. Images with reasonable resolution can be achieved almost in real-time. Several examples of detection of typical flaws in plates using the proposed method complete this work. r

Video Ultrasonics by Pulsed TV Holography: A New Capability for Non-Destructive Testing of Shell Structures

“…Several authors have employed pulsed HI to visualize and even to extract quantitative data of instantaneous displacement fields of transient vibrations of mechanical components and of SAW (Gagosz 1974, 78-83;Vest 1979, 224-5 and 242-4;Pohl et al 1992;Fällströ m et al 1989;Henning and Mewes 1995). However, to the best of our knowledge, only our group has reported the detection of SAW by pulsed TVH (Cernadas et al 2002;Trillo et al 2003a;Cernadas et al 2006). Moreover, we developed a specific phase evaluation technique that renders quantitative data of transient SAW, namely the instantaneous out-of-plane acoustic displacement field and the out-of-plane acoustic displacement amplitude and phase fields, with a minimum measurable displacement of the order of one nanometer (Trillo et al 2003b).…”

“…As stated in the introduction, it has been developed by our research group over the last decade, with successive improvements in the optical and electronic hardware and, especially, in the information processing scheme. Some parts of the current system have been incorporated from former prototypes already described elsewhere (Trillo et al 2003b;Cernadas et al 2002), for which the details will not be repeated here.…”

“…Taking into account that the acoustic displacements to measure are of the order of a few nanometers, different sources of noise need to be controlled, which imposes severe requirements to the whole system, especially to the laser and image acquisition hardware. An estimation of the main contributions to the system noise was made in (Cernadas et al 2002). Also, information processing procedures like the employment of differential phase evaluation algorithms (Trillo et al 2003b) and the numerical cancellation of the phase mismatch between the laser cavities, made by a technique similar to that reported in , contribute to the quality of the measurements.…”

Non-contact and non-destructive Lamb wave generation using laser-induced plasma shock wave

“…Numerous studies on Lamb wave applications to detect damage in large structures such as airplanes, factories, and ships are underway. Lamb wave generation techniques can be divided into two main categories: those using a contact-type device (e.g., piezoelectric zirconate titanate) [8][9][10][11][12][13][14][15][16][17][18][19][20][21] and those using a non-contact type device [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] . Damage detection using a contact-type device seems inefficient, but inserting the device into a target structure can improve the efficiency.…”

Simulation of Rayleigh waves in cracked plates

“…Non-destructive evaluation (NDE) in engineering has great importance in this process. One of the most common techniques is the use of ultrasonic tests based on guided waves, like Lamb or Rayleigh waves, which are usually used to prove structures with simple geometry as with beams and plates (see References [1][2][3] for example).…”