摘要:

Presented in this paper is a guided wave focusing feasibility study in the thickness direction to precisely tune modes for monitoring layered materials. The in‐plane energy distributions through the thickness of multi‐layered waveguide models are numerically calculated. The experiments were also done with a pulse echo test using an angle beam transducer. The experimental results clearly show that the defect detection in a particular layer of multi‐layered specimens can indeed be established by appropriate manipulation of the phase velocity and frequency values based on the information from the wave structure profiles. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711632

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Recent interest in applications like the measurement of compressive surface residual stresses due to shot peening using Rayleigh type surface acoustic waves have brought into the spot light the adverse effects surface roughness might have on such measurements. Surface roughness produces significant dispersion of the Rayleigh wave used in the measurements. Therefore an accurate understanding of the effect of surface roughness on the dispersion of Rayleigh waves is of crucial importance for this application and others in which surface roughness is a natural by‐product of the manufacturing processes used to produce the part. In this paper, the dispersion of Rayleigh surface wave on a 2D‐randomly‐rough surface is studied numerically using Wave2000Pro, finite difference wave propagation simulation software. First the dispersion of the wave due to the discretization of the model is investigated to establish the accuracy of the model. Wave 2000Pro is then used to analyze the dispersion of Rayleigh wave propagating on the rough surface. The results of the numerical analysis are then compared to the calculations of Kosachev and Shchegrov. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711633

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Optical amplification of the detection laser light seems an elegant method to improve the sensitivity of a system for the optical detection of ultrasound. However, the amplified spontaneous emission associated to the optical amplification process is a source of both phase and intensity noises. Two configurations are possible, one with the amplifier located ahead of the inspected surface (pre‐amplification) and one after (post‐amplification). We discuss the advantages and drawbacks of these two schemes when a photorefractive two‐wave mixing demodulator is used. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711634

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A Scanning Laser Line Source (SLLS) technique is demonstrated using a true thermoelastic line source which leads to generation of monopolar Rayleigh waves. As the SLLS is scanned over a surface‐breaking flaw, the monopolar signal is shown to become bi‐polar, dramatically indicating the presence of the flaw. The SLLS technique is demonstrated both experimentally and numerically through hybrid mass‐spring lattice simulations. Experiments for the SLLS technique are performed using a line focused Nd:YAG laser and an interferometric detector. Both numerically‐ and experimentally‐generated Rayleigh waves show characteristic monopolar shape in the absence of flaws and become bi‐polar as the SLLS approaches the flaw. Numerical simulations performed to gauge the effect of crack depth on the SLLS signatures demonstrate that the technique can also be used to size cracks. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711635

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A non‐contact laser‐ultrasonic technique is applied to the nondestructive measurement of the stiffness properties of cylindrical rods. Acoustic waves generated in a cylinder by a laser line source under thermoelastic regime are identified by the comparison between experiment and theory. Two stiffness coefficientsc11andc12are determined by measuring the arrival time of the reflected longitudinal wave (LL) and that of the head wave (HW). The effects of laser beamwidth and time duration on the measurement are found by numerical simulations. For such an application, a radius of 0.3 mm appears as a minimum limit for the sample size using a laser source of 0.1 mm beamwidth and 20 ns time duration. Stiffness coefficients of three aluminum rods are experimentally measured with good accuracy. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711636

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Functionally graded materials (FGMs) have spatial variations in composition and structure resulting in corresponding changes in material properties. In this work, a model for the laser generation of ultrasound in FGMs is used to explore the dependence of the generated acoustic waves on the compositional profile, and to evaluate the feasibility of using laser generated surface acoustic waves (SAWs) to determine the depth dependent properties of graded coating materials. The materials studied are coatings which exhibit elastic property gradations from the coating surface to the interface with the substrate. The graded coatings are modeled as multilayer systems and the number of layers required to achieve a desired level of convergence of the model over a given frequency range is determined. For an assumed compositional profile, the elastic properties of the respective layers are calculated using a modified rule of mixtures formulation. Numerical results showing the sensitivity of SAW dispersion behavior to various compositional profiles are presented. In addition, an inversion algorithm is developed to extract position dependent elastic properties from measured SAW dispersion behavior and preliminary results are obtained using simulated experimental data. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711637

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Laser‐ultrasonics has been used with success for the microstructure evaluation of metals by measuring ultrasonic attenuation and velocity. Extension of this technique to fiber reinforced polymer composites could provide useful information such as fiber contents and porosity. Ultrasonic generation in composite materials is usually performed by using a pulsed TEA‐CO2laser operated on several transverse modes. The intensity profile of this laser could change from shot‐to‐shot, thus affecting the ultrasonic generation pattern and the accuracy of attenuation measurement. Two solutions are possible to overcome this problem. The first reported approach consists in numerically correcting for the diffraction effect by using a Monte Carlo integration after simultaneous acquisition of the ultrasonic signal and the laser mode pattern. The second reported approach consists in modifying the laser resonator to get a single transverse mode while maintaining high energy per pulse, and to make the diffraction correction much simpler. Both approaches have been tested on a bare carbon epoxy plate with laser generation in the thermoelastic regime. The results obtained from using either approaches show a significant improvement and are compared to those obtained by conventional ultrasonics. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711638

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

An infrared version of the Multiplexed Two‐Wave Mixing (MTWM) Interferometer system using a long pulse laser system as the source has been developed at Northwestern University. This infrared version has higher optical power which makes it possible to build large array laser ultrasonic detectors. A 16‐element laser ultrasonic array detector and its imaging applications using surface acoustic waves and bulk waves are reported. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711639

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In nuclear plants, the inspection of heat exchanger tubes is usually carried out by using eddy current nondestructive testing. A numerical model, based on a volume integral approach using the Green’s dyadic formalism, has been developed, with support from the French Institute for Radiological Protection and Nuclear Safety, to predict the response of an eddy current bobbin coil to 3D flaws located in the tube’s wall. With an aim of integrating this model into the NDE multi techniques platform CIVA, it has been validated with experimental data for 2D and 3D flaws. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711640

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Calculations have been performed to determine the transient response of an eddy current probe due to an open subsurface crack in conducting half‐space. In previous work, the transient probe response due to an idea crack was calculated using boundary elements. The ideal crack has zero opening yet acts as a perfect barrier to eddy currents. The theoretical formulation of the problem has now been modified to take account of the fact that the crack may have a significant finite opening. The effects of the opening on the probe response have been investigated. Comparisons with experiment show reasonable agreement. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711641

出版商:AIP    

年代:1904

数据来源: AIP