Lamb wave generation using nanosecond laser ablation to detect damage

Abstract

This paper proposes a non-contact damage detection method based on Lamb waves generated by laser ablation (LA). Previously, Lamb waves generated by contact-type sensors such as acoustic emission or piezoelectric zirconate titanate devices have been studied to detect damage. Lamb wave generation systems with embedded contact-type excitation devices to objective structures to be inspected may quickly realize large-area damage detection on a huge object such as an aircraft. However, replacing contact-type devices with non-contact devices in Lamb wave generation systems, the systems will have sufficient potential to excite under the specific conditions such as submerged target structures in liquid and high-temperature substances. The LA-generated Lamb waves that have amplitudes several hundred times larger than those generated by conventional laser-thermoelastically generated Lamb waves are of advantage from the viewpoint of the signal-to-noise ratio in the measurements. When the laser fluence reaches 10 12-10 14 W/m 2 , which is greater than that for laser-thermoelastic regime, a LA regime is induced. The amplitudes of the LA-generated Lamb waves might be higher than those of the laser-thermoelastically generated Lamb waves; this is within the scope of the assumption. Since the LA process entails a number of nonlinear processes such as melting, vaporization, and sublimation, it is important to confirm that LA could generate a Lamb wave and its mode. In this paper, Lamb waves that contain broadband frequency elements of more than several hundred kHz are generated by non-contact impulse excitation using LA, which is common in vibration tests in the high-frequency range, laser peening, propulsion of micro-aircraft, bolt loosening diagnosis, etc. The present method is evaluated by comparing the measured and calculated propagation phase and group velocities of the Lamb waves. Furthermore, the feasibility of our approach is demonstrated by non-contact damage detection against an aluminum alloy 2024 plate with a crack.

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

“…By observing the propagation of these Lamb waves, we have also demonstrated that damage detection is possible [46] . If we could generate non-contact and nondestructive Lamb waves against a target structure, which have about the same level of amplitude as that of the conventional methods, the field of damage detection using Lamb waves may advance even further.…”

“…We compared and evaluated the A 0 mode phase and the group velocities obtained from this method to the results of the Rayleigh-Lamb frequency equations. This paper obtains the A 0 mode phase and group velocities using the following steps [46] .…”

“…When the laser fluence reaches 10 12 − 10 14 W/m 2 , laser ablation (LA) forms [39][40][41][42][43][44][45][46][47][48][49] . LA is the formation of a high-temperature high- Fig.…”

“…When a plasma plume of mass Δm is released by velocity v, the gained momentum (impulse) is Δmv and this becomes the excitation force against a target structure. LA has been researched for vibration tests [40][41][42][43][44][45][46][47]49] , laser vapor deposition [50] , thrust [51] , laser micromachining [52] , laser peening [53] , detection of bolt loosening [42] , and acoustic tests [48] . It is a newly established as non-contact excitation technology [40][41][42][43][44][45][46][47][48][49] , but it is destructive as sub-millimeter damage is generated on the target structure.…”

Dynamic characterizations of underwater structures using noncontact vibration tests based on nanosecond laser ablation in water: evaluation of passive vibration suppression with damping materials

“…Input-detection-free FRF measurements with reliability factors for underwater structures 2.1. Underwater LA excitation force LA has various applications, such as in microfabrication (McCann et al, 2016), propulsion of flying objects (Yabe et al, 2002), peening (Hatamleh, 2008), laserinduced bubbles in inside liquids (Lazic et al, 2012), vibration testing (Kajiwara and Hosoya, 2011;Hosoya et al, 2012Hosoya et al, , 2016a, acoustic analysis (Hosoya et al, 2014), and damage detection (Huda et al, 2013;Hosoya et al, 2016cHosoya et al, , 2016dHosoya et al, , 2017a. Figure 1 shows the principle of underwater LA excitation force generation (Hosoya et al, 2016a).…”