摘要:

This paper presents a study of crack detection methods for holes in structures with limited accessibility containing fasteners with variable interface conditions. For far crack detection, a method was first designed using models, and refined using a signal processing parameter optimization scheme and an iterative neural network training process. For near crack detection, a method incorporating the spatial variation of the principal components was developed. Using these methods, improvements in crack detection performance were achieved. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570134

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper presents a study of ultrasonic NDE models for a cylindrical hole containing an elastic layer and a fluid‐filled hole. For the elastic layer case, both dispersion relations and analytical solutions were solved to assess the sensitivity of leaky Rayleigh waves to annulus properties. A BEM model was formulated for the scattering of shear waves by a fluid‐filled hole with a notch. Through simulated studies, a viable inspection technique was derived and validated experimentally. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570135

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The nondestructive detection of fatigue cracks at fastener holes in aircraft structures employing guided waves is studied. Experimentally the first antisymmetric Lamb wave mode A0is excited using piezoelectric transducers and the scattered field is measured by means of a heterodyne laser interferometer. The detectability of small defects is investigated and quantified by a parameter study at a model system and using finite difference calculations. The main influence is found to be the ratio of wavelength and defect size. Measurements employing shorter wavelength Rayleigh waves show the predicted good detectability of a small quarter‐elliptical fatigue crack. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570136

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A study of the interaction of Lamb waves with a circular defect is presented. The Lamb wave mode chosen was the S0mode in the low frequency‐thickness regime excited by a circular source. A three dimensional Finite Element model was used to simulate the reflection behaviour. Experimental results were also obtained using an array transducer. Circular holes of 50&percent; depth and various diameters were studied. The specular reflection of an incident S0wave was predicted and compared with the experiments. The significance of the path lengths, wavelengths and defect sizes on the reflection characteristics were assessed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570137

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The principles of the synthetic aperture focusing technique (SAFT) are generalized for application to high frequency plate wave signals. It is shown that a flaw signal received in long‐range plate wave propagation can be analyzed as if the signals were measured by an infinite array of transducers in an unbounded medium. It is shown that SAFT‐based flaw sizing can be performed with as few as three or less actual measurement positions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570138

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Dispersion curves are essential for analyzing and understanding the physical behaviors of guided waves propagating in structures. For circumferential waves in annular structures, the calculation of dispersion curves can be very time consuming. Furthermore, due to the nature of the mathematical functions involved in the curved structure geometry, the solutions can become unstable at high frequencies. In this paper three asymptotic approximation methods are introduced, which resolve the instability problem and speed up the calculations. Comparison of dispersion relations evaluated from the exact and asymptotic approximation methods are presented, showing errors to be typically less than 0.1&percent;, except for the very low frequency region. Results obtained using a two dimensional finite element technique are also presented for comparison. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570139

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

When a waveguide surrounded by vacuum enters an embedding material, guided waves are scattered at this entry point due to the change in the surface impedance. This paper is concerned with the numerical modelling of the entry reflection of the fundamental longitudinal mode, L(0,1), in cylindrical waveguides. An approach based on modal analysis is used to characterize this reflection. It is validated against Finite Element modeling, very good agreement being obtained. As an example application, the cure monitoring of epoxy resins is discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570140

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Since scale in water supplying pipes is one of the major sources of water contamination and user’s complaint, detection of scale is very important for the proper maintenance of water piping. In the present study, the potential of guided waves was explored for the detection of scale in water supplying pipes. Using variable angle wedges, several modes of guided waves were generated and identified. In the experiments, it were observed that the amplitude of F(M,2) (M=1,2,3,4) modes decreased significantly as the increase of the amount of scale. The result of the present study recommended that the F(M,2) modes are optimal to detect scale in water supplying pipes. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570141

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Low frequency guided acoustic waves will propagate many tens of metres along a rail. The guided wave modes that can exist in a rail are found using a 2‐dimensional finite element (FE) technique and their interaction with a variety of features and defects is investigated with 3‐dimensional time‐marching FE models. Results obtained from a prototype testing system are presented and excellent agreement is obtained with FE predictions. Good sensitivity to transverse defects and defects at alumino‐thermic welds is demonstrated. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570142

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Non‐axisymmetric guided waves have been applied to pipe inspection recently. Due to the non‐axisymmetric characteristics of the waves, the circumferential displacement distribution is non‐axisymmetric. It shows a natural focusing phenomenon. With the aid of a circumferential transducer array, we developed an algorithm to focus wave energy at arbitrary locations. The algorithm is based on applying different amplitude and time delay to each of the excitation elements. A series of experiments were carried out to show the focusing effect. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570143

出版商:AIP    

年代:1903

数据来源: AIP