摘要:

Accurate positioning and sizing of defects is a strong requirement for ultrasonic non destructive examination. In complex configurations, this positioning can be greatly improved by using results of simulation. In the case investigated here, the complexity arises from the austenitic cladding of the inspected part: Its surface presents irregularities which may disturb the ultrasonic beam and consequently make difficult the positioning of the defect. In addition, the anisotropy of the austenitic cladding has strong effects on detected echo‐structures. In this communication we present a simulation‐helped method developed in the aim of improving the accuracy of crack tips positioning in French nuclear reactor vessels. We describe this method, based on the CIVA modelling tools, and show results of experimental validation. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711612

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This paper presents a modeling approach to predict the angle beam ultrasonic pulse‐echo signals that can be captured from a surface breaking, vertical crack in a plate specimen in a computationally efficient manner. For this purpose, the 3‐D multi‐Gaussian beam models are adopted to describe the reflected beam fields from the surfaces of the crack and the specimen as well as the radiating beam field from the transducer, and the 2‐D ray methods to calculate the diffracted beam field from the crack tip. In addition, the characteristics of the ultrasonic testing system are considered in terms of the system efficiency factor. By combining these three ingredients, the surface breaking crack signals are predicted at different interrogating positions. The accuracy of the proposed models is verified by the initial experiments. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711613

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This paper concerns a boundary element method (BEM) for 2D SH‐wave scattering in an elastic layer sandwiched by two half spaces. The BEM is based on the integral equation having a Green’s function for a layer as its integral kernel. Since the Green’s function satisfies the interface conditions, numerical integration in the BEM is necessary only on the surface of scattering objects, thus the computational memory can be saved greatly. On the other hand, numerical evaluation of the Green’s function is critical and burdensome. In this paper, a hybrid ray‐mode representation of the Green’s function given by Kamel is employed. Numerical aspects of the representation are discussed in some detail, and the BEM code with the Green’s function is developed thereafter. As a numerical example, SH‐wave scattering by a cavity in a layer is considered. Some numerical results to investigate the interaction between the cavity and layer interfaces are presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711614

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Inspection techniques using guided waves require an accurate prediction of the propagation properties and the physical behaviour of the waves. Properties of these guided waves can be modelled using dispersion curves, which are calculated numerically. However, any curvature along the propagation direction can change the behaviour of the modes compared to those in the straight waveguide. There are currently few studies of the curvature effect along the propagation direction of any waveguide problem. We have used a 2D circumferential waveguide problem to study the curvature effect, from which the phase velocity and the mode shapes have been examined at various curvatures. The percentage difference in velocity of the low order plate modes, as a function of frequency and curvature, has been calculated numerically. Furthermore the changes in phase velocity have been correlated with the changes in mode shapes that are due to the curvature effect. This paper also presents an experimental study to validate the analytical predictions. The experiment involved a sensitive measurement of the change of velocity as the curvature of a waveguide was increased. Reasonably good agreement was obtained between the experimental measurements and the predictions. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711615

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A hybrid three‐dimensional boundary element normal mode expansion technique is developed to study the guided wave scattering from an arbitrary shape defect in a plate. Lamb wave incident into a circular through plate hole were studied as an example. The scattered wave displacement field and each normal mode component are given. Mode conversion from Lamb wave to SH wave and vice versa at the defect boundary were observed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711616

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The sensitivity of a permanently attached guided wave array for the detection of corrosion damage in plates is studied. The thickness reduction due to corrosion is modeled as a circular part‐through hole. The scattering and mode conversion of the A0Lamb wave mode is calculated numerically employing a three‐dimensional finite element model and verified in laboratory experiments. Good agreement is found and the sensitivity of the guided wave monitoring of large areas can be predicted. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711617

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The guided wave has been widely employed to characterize thin plates and layered media. The dispersion curves of phase and group velocities are essential for the quantitative application of guided waves. The technique using leaky Lamb wave (LLW) is one of the excellent methods to obtain dispersion curves. In the present work, a fully automated system for the measurement of backward radiation of LLW has been developed. The specimen moves in two dimensional planes as well as in angular rotation. The signals of backward radiation of LLW were measured from an elastic plate in which specific modes of Lamb wave were strongly generated. Phase velocity of the corresponding modes was determined from the incident angle. The generated Lamb waves propagated forward and backward with the leakage of energy into water. Backward radiated LLW was detected by the same transducer and its frequency components were analyzed to extract the related information to the dispersion curves. The dispersion curves of phase velocity were measured by varying the incident angle. Moving the specimen in the linear direction of LLW propagation, group velocity was determined by measuring the transit time shift in the rf waveform. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711618

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Ultrasonic attenuation is a combination of material losses and geometric effects. The current research quantifies the geometric effects in the far‐field, where the individual modes of a Lamb wave become separated. The overall ultrasonic signal, which is a superposition of these modes, depends on geometry, source type and individual mode characteristics. This research considers the amplitude decay of Lamb waves in an isotropic plate that are generated with an ablation source. A numerical simulation is developed using normal mode expansions, and is used to calculate amplitude decay. These numerical results are verified with an experimental program that uses laser generation and detection of multi‐mode, Lamb waves. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711619

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Guided wave calculation using a semi‐analytical finite element method is described in this study. Two dimensional discretization modeling and its optimization technique by the use of the symmetry of a pipe are developed for wave propagation in a pipe with a defect. The effect of guided wave focusing, having been developed by Penn State group, is investigated for torsional waves. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711620

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Ultrasonic guided waves have been used for a wide variety of ultrasonic inspection techniques. We describe here a new variation called helical ultrasound tomography (HUT). This new technique, among other things, has direct application to advanced pipe inspection. HUT uses guided ultrasonic waves along with an adaptation of the tomographic reconstruction algorithms developed by seismologists for what they call “cross borehole” tomography. In HUT, the Lamb‐like guided waves travel in various helical crisscross paths between two parallel circumferential transducer arrays instead of the planar crisscross seismic paths between two boreholes. Although the measurement itself is fairly complicated, the output of the tomographic reconstruction is a readily interpretable map of a quantity of interest such as pipe wall thickness. We demonstrate the feasibility of the HUT technique via laboratory scans on steel pipe segments into which controlled thinnings have been introduced. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711621

出版商:AIP    

年代:1904

数据来源: AIP