摘要:

Piping in nuclear power plants is exposed to severe environmental conditions so that it is very susceptible to failure caused by the growth of defects. Thus, it is necessary to have thorough inspection of piping in order to detect defects before failure. Unfortunately, however, inspection of piping in nuclear power plants is not easy in practice because of its long length as well as the radioactive environment. To take care of this difficulty, a research endeavor to develop techniques to monitor piping in nuclear power plants continuously and actively using ultrasonic guided wave is currently undertaken. This paper reports initial results of our endeavor including design of an ultrasonic array system for active monitoring of piping. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711622

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Circumferential guided waves are used for the inspection of stress corrosion cracking (SCC). A simplified two dimensional model for crack sizing in pipes is presented. 2‐dimensional hybrid boundary element modeling analysis was used to study defect sizing and discrimination in a pipe‐like structure. The theoretical results agree with the experiments in utilizing a magnetostrictive sensor (MsS) technology for generating circumferential shear horizontal guided wave in pipe. An approximate 2‐dimensional theory based on an axial scan has been developed that improves the defect depth estimate considerably. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711623

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Non‐axisymmetric guided waves including flexural longitudinal and flexural torsional modes have shown natural focusing characteristics in pipe inspection. A flexural torsional mode theory was developed in this paper based on flexural longitudinal mode theory. Flexural mode experiments were then carried out to show the natural focusing phenomena. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711624

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Transient leaky Rayleigh waves in a solid‐fluid half space system are studied using integral transform techniques. The obtained analytical solutions provide necessary theoretical background for optimization of air‐coupled ultrasonic detection in experiments. The leaky Rayleigh wave velocity can be obtained from the established characteristic equation. The leaky Rayleigh wave response under a normal point loading, which varies in time as a step function, is first derived. Closed‐form displacement and stress component expressions are then presented. The impulse responses owing to point loading can be obtained by taking differentiation of step responses; therefore, solutions to both arbitrary time‐varying and space‐varying transient impact loadings can be obtained by taking convolution in time and space domains. Numerical simulation (Finite integration technique) is used to verify the solution. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711625

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The guided wave field excited in a plate‐like structure from any weakly coupled transducer can be calculated from the superposition of the guided wave fields due to a number of suitable point or line excitation sources. In this paper, the fields from various point and line excitation sources are reviewed and relationships between them are demonstrated. The performance of pancake coil EMATs is modeled using the superposition of the fields from point sources and the results compared with experiment. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711626

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Guided waves are potentially very useful for the rapid NDE of plate structures. In the aerospace industry in particular, they have been proposed for the structural health monitoring of carbon fibre skin panels, in either an active or a passive configuration. In an active configuration a guided wave is deliberately generated and then later received after it has travelled through the structure; in a passive configuration an acoustic emission sensor is used to listen to sound created by the structure itself. The successful development of these ideas depends on a good knowledge of the properties of the guided waves, yet it has been found that the properties of guided waves in such materials are very much more complicated than those in a simple metal skin. The complications include steering of the direction of the group velocity by the anisotropy of the plate, and attenuation because of damping of the matrix material and scattering by the fibres. The authors have studied these phenomena both analytically and experimentally. This paper presents an overview of the findings and identifies the key implications for practical developments of structural health monitoring techniques. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711627

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The possibility of using long range ultrasonic guided wave non‐destructive testing for the inspection of metallic structures coated with attenuative layers is extremely attractive. However, the material damping may cause severe attenuation of the acoustic signal, resulting in reduction of the test range. This paper addresses the dispersion of shear horizontal waves propagating in metallic plates coated with viscoelastic layers and the implications for long range testing. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711628

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A Finite Element code is used in a stationary mode to compute, at single a frequency, the stress and displacement fields in a plate made of anisotropic viscoelastic materials. An appropriated spatial load at one boundary of the plate is applied to generate a guided Lamb wave mode. The number of frequency iterations (≈ usually less than 30) is limited by the frequency content of the excitation. Then, the temporal response at any node of the plate can be reconstructed with inverse FFT. The velocity, attenuation and nature of one or several propagating modes can be identified in the classical frequency/wave number representation. This paper shows the effect of the attenuation on the propagation of Lamb waves in a cross‐ply, carbon‐epoxy material plate. Focus is made on some limitations that the attenuation causes on the detection of a delamination between plies. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711629

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Transient ultrasonic guided waves in anisotropic bi‐layered plates with finite‐width are investigated in this paper. Composite bi‐layered plates consisting of GaAs substrate coated with Nb sheath is considered as an example because of its application to electronics and calorimetry. The purpose is to investigate the acoustic mode coupling (“pinching”) phenomena for phonon transport. A semi‐analytical finite element (SAFE) method is adopted to study the guided wave dispersion behavior in finite‐width elastic plates. Nine‐noded quadrilateral elements are used to model the cross section of the finite‐width plate. Propagation in the axial direction is modeled by analytical wave functions. Elastodynamic Green’s functions are derived using modal summation in the frequency‐wavenumber and time‐space domains. Results for dispersion and transient analysis of guided waves in finite‐width plates are presented and compared for different aspect ratios. Group velocities are calculated and wave arrival times are computed for different plate cross sections as well as different excitation frequency. Numerical results show significant influence of the plate aspect ratio on the dispersion and transient wave response. Complex nature of quasi‐mode dispersion and propagation due to pinching phenomena in anisotropic plates require such quantitative analysis to afford easy interpretation. These results would be important for nondestructive material evaluation and for characterization of phonon transport in anisotropic bi‐layered plates. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711630

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This study investigates the utilization of guided waves for inspecting structures that consist of multiple layers. Advances have been made in recent years using guided waves to inspect single layer structures, such as pipes, tubes, and aircraft structures. Multi‐layered structures present many new aspects to guided wave propagation. A theoretical understanding of what modes exist, how do the modes behave, and what factors influence them needs to be acquired for many applications. Experiments must be carried out to evaluate potential for practical applications. Examples of practical applications include coated pipes, composites, diffusion bonded aircraft structures, and microelectronic structures. This work is a fundamental study of ultrasonic guided waves in multi‐layered plates. Experiments were conducted on multi‐layered plates to demonstrate defect detection in layer of interest of a multi‐layered structure by preferentially exciting modes with sufficient energy in that layer. Analysis of the dispersion curves show that some modes are more attractive candidates than others based on their displacements and energy distribution across the structure. Experimental results show that sweeping frequency and phase velocity can be performed to find suitable modes for inspecting a layer of interest for a given multi‐layered structure. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711631

出版商:AIP    

年代:1904

数据来源: AIP