Laser Ultrasonic Waves Research Articles

603 はく離損傷部でのレーザ超音波の伝播挙動に関する基礎的研究

603 はく離損傷部でのレーザ超音波の伝播挙動に関する基礎的研究

Characterizing Phantom Arteries with Multi-channel Laser Ultrasonics and Photo-acoustics

Multi-channel photo-acoustic and laser ultrasonic waves are used to sense the characteristics of proxies for healthy and diseased vessels. The acquisition system is non-contacting and non-invasive with a pulsed laser source and a laser vibrometer detector. As the wave signatures of our targets are typically low in amplitude, we exploit multi-channel acquisition and processing techniques. These are commonly used in seismology to improve the signal-to-noise ratio of data. We identify vessel proxies with a diameter on the order of 1 mm, at a depth of 18 mm. Variations in scattered and photo-acoustic signatures are related to differences in vessel wall properties and content. The methods described have the potential to improve imaging and better inform interventions for atherosclerotic vessels, such as the carotid artery.

Development of Thickness Measurement System for Hot Steel with Laser-Ultrasonic Wave Technology

Development of Thickness Measurement System for Hot Steel with Laser-Ultrasonic Wave Technology

Laser Ultrasonic Detection of Drilling-induced Delamination in Composite Laminates

The positioning and quantitative testing of drilling-induced delamination in aircraft composite structures is not only one of the main difficulties in the field of non-destructive testing(NDT), but also a security problem need to be solved in aviation industry. Laser ultrasonic testing technique is a possible way to solve the problem. An experiment study concerning the verification of the feasibility of detecting drilling-induced delamination with laser ultrasonic technique is carried out. A composite laminate with drilling holes is made as specimen, the broadband characteristics of ultrasonic waves in composites generated by pulse laser are studied, and the wave signals with good signal-to-noise ratio(SNR), high sensitivity and resolution are extracted. The effects of the interface of drilling-induced delamination on the propagation characteristics of laser ultrasonic waves are studied, and the characterization methods of drilling-induced delamination with laser ultrasonics are acquired. Based on the pulse echo and transmission method, the laser ultrasonic C scan testing of the composite laminate with drilling holes is accomplished, and the morphologies, dimensions and positions of drilling-induced delamination are obtained. The research results show that laser ultrasonic testing is an effective method to detect the drilling-induced delamination in aircraft composite structures.

Laser ultrasonic anomalous wave propagation imaging method with adjacent wave subtraction: Algorithm

The anomalous wave propagation imaging (AWPI) method is proposed for the laser ultrasonic propagation imaging system using a Q-switched laser and a laser mirror scanner to highlight the anomalies in complex structures. The AWPI algorithm was developed based on the observation that the waves from two adjacent scanning points are very similar, and that the propagation direction of the incident wave is different from that of the anomalous wave caused by structural anomalies including damage. The structural anomaly is highlighted by suppressing the incident waves and exaggerating the anomalous wave through adjacent waves subtraction after arrival time and amplitude matching. The variable time window amplitude mapping (VTWAM) method was also developed, based on the difference in arrival time between the residual incident wave and anomalous waves. The VTWAM method enhances anomaly visualization and sizing, notably for composite damages, by mapping the amplitudes of the confining wave within the damage. Our results showed that the AWPI increased the signal-to-noise ratio of a back-surface hole damage in a steel plate by 13.76dB, while in another inspection of a composite wing with two impact damages, the AWPI results enhanced by the VTWAM compared favorably with the results of the immersion ultrasonic C-scan. The AWPI and VTWAM adopt implicit spatial referencing wherein all necessary data can be obtained through a single-time scan, therefore circumvent the disadvantages of conventional temporal baseline referencing.

Laser ultrasonic anomalous wave propagation imaging method with adjacent wave subtraction: Application to actual damages in composite wing

Laser ultrasonic wave propagation imaging methods have great potential for integrated structural health management and non-destructive evaluation. However, application of these techniques to complex structures in the field is difficult because they give rise to complicated wave propagation patterns. We developed an anomalous wave propagation imaging method with adjacent wave subtraction using laser ultrasonic scanning to solve this problem. The proposed method is suitable for non-destructive evaluation of complex structures because it highlights the propagation of anomalous waves related to structural discontinuities, and suppresses complex incident waves without the need of pre-stored reference data. In this study, the method was applied to a real composite wing subjected to bending and impact tests. The method enhanced the visibility of the anomalous waves related to damages such as stringer tip debonding, skin-spar debonding, and invisible impact damage. Based on these anomalous waves, variable time window amplitude mapping was performed to show the damage location, size, and shape resemble to the actual damage. Comparisons showed that the methods performed better than the ultrasonic A-scan in terms of damage detection and sizing accuracy. The presence of structural elements such as spars, stringers, ribs, and surface-mounted PZT elements did not adversely affect the inspection. The proposed wing test setup with a built-in ultrasonic propagation imaging system for automatic NDE could be easily expanded throughout a hanger for maintenance inspection.

Transmission of Ultrasonic Waves Via Optical Silica Glass Fiber Doped by 7.5% of TiO2 with the Use of Power Sandwich Transducer

Abstract The possibility of acoustic wave propagation in optical waveguides creates new prospects for simultaneous transmission of laser beams and ultrasonic waves. Combined laser-ultrasonic technology could be useful in e.g. surgical treatment. The article presents the results of experimental studies of transmission of ultrasonic wave in optical fibres, the core of which is doped by 7.5% of TiO2, using a sandwich-type transducer. It also presents amplitude characteristics of an ultrasonic signal propagated in the optical fibre. Authors studied the effect which the length of the fibre has on the achieved output signal amplitudes. They presented the relation of the output signal amplitude from a capacitive sensor to the power applied to the sandwich-type transducer. The obtained results were compared with the results produced when using an optical fibre with a core doped by 3% of GeO2, in order to select optical fibre suitable for simultaneous transmission of ultrasonic waves and laser rays.

Evaluation of Fracture Toughness of Interface Crack between Thin Film and Substrate Using Laser Ultrasonic Waves

In the present paper, fracture toughness of interface crack between thin film and substrate is evaluated by inverse analysis using laser ultrasonic waves. The laser beam is irradiated on the substrate which have a thin film on the lower side. The elastic-ultrasonic wave is excited by the laser beam, and it propagates in the transverse direction for the plate. The supersonic wave reflects on the back of monotony, becomes an expansion wave, and reaches the interface. Finally, the interface crack progresses caused by the expansion wave. In the present study, the interfacial stress is estimated by inverse analysis using Laplace-transformed boundary element method. The displacement history on the back-surface of the specimen can be related to interfacial stress by the transfer function. The transfer function can be obtained numerically by 3-dimensional analysis employing boundary element method. The specimens made from SiC substrate and Diamond thin layer are used in the present study. The fracture toughness of the interfacial crack can be extrapolated from the stress distribution in the vicinity of the crack tip. It is confirmed that the interfacial fracture toughness of SiC/Diamond is 0.16J/m2 from the present investigation.

The Possibility of a Simultaneous Transmission οf Ultrasound and Laser Radiation via Flexible Optical Silica Glass Fibre

Glass optical fibres are a promising medium for simultaneous laser-ultrasonic applications. The proposed application system is based on simultaneous transmission of laser radiation and ultrasounds in a flexible silica glass fibre. The optical fibre’s core was made of SiO2 (97%) and GeO2 (3%) and the cladding was 100% SiO2. The material the optical fibre is made of enables simultaneous transmission of laser radiation and ultrasonic wave. Experiments were performed using a Mach–Zehnder optical waveguide interferometer with single-mode optical fibre coupler. This paper presents measurement results for delivering ultrasonic waves to the optical fibre using longitudinal vibrations generated by a sandwich ultrasonic transducer with a velocity transformer. The study presents the relations concerning simultaneous operation of both types of waves and the possibilities of transmission of low frequency, high power ultrasonic wave in optical fibres using a sandwich type transducer.

201 レーザー超音波による薄膜の強度評価に関する境界要素解析(OS2-1 薄膜強度・熱粘弾性特性,オーガナイズドセッション:2 先進材料の強度に関する計算固体力学の応用)

201 レーザー超音波による薄膜の強度評価に関する境界要素解析(OS2-1 薄膜強度・熱粘弾性特性,オーガナイズドセッション:2 先進材料の強度に関する計算固体力学の応用)

101 レーザー超音波による薄膜の密着強度測定法について(構造部材や加工プロセスの信頼性を支える計測・評価技術)

101 レーザー超音波による薄膜の密着強度測定法について(構造部材や加工プロセスの信頼性を支える計測・評価技術)

Noncontact, nondestructive elasticity evaluation of sound and demineralized human dental enamel using a laser ultrasonic surface wave dispersion technique

Laser ultrasonic nondestructive evaluation (NDE) methods have been proposed to replace conventional in vivo dental clinical diagnosis tools that are either destructive or incapable of quantifying the elasticity of human dental enamel. In this work, a laser NDE system that can perform remote measurements on samples of small dimensions is presented. A focused laser line source is used to generate broadband surface acoustic wave impulses that are detected with a simplified optical fiber interferometer. The measured surface wave velocity dispersion spectrum is in turn used to characterize the elasticity of the specimen. The NDE system and the analysis technique are validated with measurements of different metal structures and then applied to evaluate human dental enamel. Artificial lesions are prepared on the samples to simulate different states of enamel elasticity. Measurement results for both sound and lesioned regions, as well as lesions of different severity, are clearly distinguishable from each other and fit well with physical expectations and theoretical value. This is the first time, to the best of our knowledge, that a laser-based surface wave velocity dispersion technique is successfully applied on human dental enamel, demonstrating the potential for noncontact, nondestructive in vivo detection of the development of carious lesions.

FE Simulation of Laser Ultrasonic Surface Waves in a Biomaterial Model

This paper describes a study of laser generated ultrasonic waves in an 2-layer elastic, isotropic biomaterial model, in order to establish a modelling technique to simulate the thermoelastic response of high-power short pulse laser beams in human skin. The theory proposed in this paper takes into consideration the fundamental understanding of the laser/material interface. A finite element model using the commercial finite element code ANSYS is used to study the effects of laser pulse duration and energy flux contribution to the surface waves. The simulation comprises a set of boundary conditions that approximate a heat flux point source located on top of the surface of the material. Because of the time scale of interest, the elastic effects do not feed back into the thermal problems, so that a sequential coupled-field analysis was performed where the thermal and elastodynamic fields are uncoupled and treated separately. The initial finite element analysis involves a transient thermal analysis using a heat flux with Gaussian spatial variation to simulate the laser pulse heating. The results from the thermal analysis were read and applied to the structural analysis where the out-of-plane displacements histories are analyzed in the skin model with varying thicknesses

Numerical simulation of laser-induced transient temperature field in film-substrate system by finite element method

The transient temperature fields generated by a pulsed laser in film-substrate system are obtained by using the finite element method. Time integrations of the semi-discrete finite element equations are achieved by using approximate one order derivative of temperature. The temperature dependences of material properties are taken into account, which has a great influence on the temperature fields indicated by the numerical results. The pulsed laser-induced transient temperature fields in aluminum/methyl-methacrylate system and aluminum/copper system are obtained, which will be useful in the research on thermoelastic excitation of laser ultrasonic waves in film-substrate system.

Investigation of the microstructure of cast iron by laser ultrasonic surface wave spectroscopy

We have used an all-laser surface wave ultrasonic method to investigate cast iron samples with a variety of morphologies of included graphite precipitation. The relation between ultrasonic attenuation and the microstructure of cast iron is discussed. The frequency dependence of ultrasonic attenuation was obtained in a broad frequency band including the three characteristic regions of scattering. The scatterer size of the samples could be evaluated from the measurement, and good agreement was found between the average scatterer size estimated from our ultrasonic data and micrographic data. The demonstrated sensitivity of the ultrasonic propagation parameters to the microstructural properties of cast iron illustrates the strong potential of this technique for non-destructive microstructural characterization of polycrystalline materials.

Laser ultrasonic surface wave inspection of alumina ceramics of varying density

In this paper, the surface acoustic wave velocity results acquired from the inspection of specially manufactured and characterised alumina ceramic materials are presented. Ultrasonic velocity data of alumina-based ceramics in the range 60–100% theoretical density was generated utilising non-contacting laser-ultrasonic measurements based on laser generation and detection of surface acoustic waves with the objective of creating a routine technique for industrial advanced alumina inspection. With linear fitting the surface acoustic wave velocity data serves as a calibration graph for using laser ultrasonics for routine monitoring of alumina. A second laser ultrasonic technique based on the laser generation and foil transducer detection of surface acoustic waves was used to validate the surface acoustic wave velocities measured by the laser generation/detection technique.

Quantitative theory for laser ultrasonic waves in a thin plate

Numerical inversion of the Hankel–Laplace transform has been performed for the case of ultrasonic displacements in an infinite, homogeneous, isotropic plate which is excited thermoelastically by a laser pulse. Values for the elastic moduli and the plate thickness may be extracted when the calculated displacements are compared directly to those obtained experimentally. Previous authors have demonstrated methods for determining the elastic modulus in thick plates; this letter shows that using a different method for the development of the theory allows similar modulus determinations to be made for thin as well as thick plates.