Damage detection in membrane structures using non-contact laser excitation and wavelet transformation

Abstract

Abstract:In this paper, a vibration testing and health monitoring system based on an impulse response excited by laser is proposed to detect damage in membrane structures. A high power Nd: YAG pulse laser is used to supply an ideal impulse to a membrane structure by generating shock waves via laser-induced breakdown in air. A health monitoring apparatus is developed with this vibration testing system and a damage detecting algorithm which only requires the vibration mode shape of the damaged membrane. Artificial damage is induced in membrane structure by cutting and tearing the membrane. The vibration mode shapes of the membrane structure extracted from vibration testing by using the laser-induced breakdown and laser Doppler vibrometer are then analyzed by 2-D continuous wavelet transformation. The location of damage is determined by the dominant peak of the wavelet coefficient which can be seen clearly by applying a boundary treatment and the concept of an iso-surface to the 2-D wavelet coefficient. The applicability of the present approach is verified by finite element analysis and experimental results, demonstrating the ability of the method to detect and identify the positions of damage induced on the membrane structure.

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

“…2 shows the Lamb wave generation system using a LIP shock wave [49,[54][55][56][57][58][59][60][61][62][63] . A laser beam from a Nd:YAG pulse laser (Continuum, Continuum surelite III-10: wavelength, 1064 nm; beam diameter, 9.5 mm; pulse width, 5 ns; maximum output power, 1 J; beam divergence angle, 0.5 mrad) installed on the optical surface plate becomes condensed by a plano-convex lens and exceeds the threshold of the laser fluence by LIP formation in air.…”

“…This paper proposes a non-contact and non-destructive method to generate Lamb waves against a target structure using the impulse excitation force generated by laser-induced plasma (LIP) [54][55][56][57][58][59][60][61][62][63] . Generation of non-contact and non-destructive Lamb waves should contribute tremendously to the development of damage detection technologies for large structures.…”

“…We use these shock waves as the non-contact and non-destructive excitation force against a target structure. We show that the shock waves can be used to measure the frequency response functions [61] , to detect damages or to suppress vibrations in a membrane structure [58,62] and to evaluate the firmness of apples [63] .…”

“…This study demonstrates that, within a standoff distance range of 5-40 mm, Lamb waves suitable for damage detection can be produced. Previous research [54][55][56][57][58][59][60][61][62][63] has not employed LIP shock waves as the impulse excitation force to generate Lamb waves. Furthermore, the dynamic characteristics of the lamb waves generated by LIP shock waves have yet to be controlled by changing the standoff distances in the previous research [54][55][56][57][58][59][60][61][62][63] , even though it is expected that an amplitude, a frequency band and an excitation area of the impulse excitation force generated by LIP shock waves can be adjusted by changing the standoff distance.…”

High spatial and temporal resolution measurement of mechanical properties in hydrogels by non-contact laser excitation

“…LA has various applications, including plasma growth, 23 LA shockwave in air, 24 LA in water, 25 cavitation bubble, 26 laser propulsion, 27,28 laser micromachining, 29 laser deposition, 30 laser peening, 31 and vibration tests and acoustic tests using LA or laser-induced breakdown (LIB). [32][33][34][35][36][37][38][39][40][41] Although multiple stress waves in silica glass generated by femtosecond LA 20 have been visualized using the shadowgraph technique, using LA as an excitation force for gels has yet to be investigated.…”