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Articles 1 - 16 of 16

Full-Text Articles in Mechanical Engineering

Numerical Calculation Of Diffraction Coefficients In Anisotropic Media, J. Temple, L. White Jan 1993

Numerical Calculation Of Diffraction Coefficients In Anisotropic Media, J. Temple, L. White

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic inspection is used to detect and size crack-like defects in pressure vessels and pipework used in the nuclear industry. Reliable inspection can only be achieved if the inspection technique is understood, is optimised and subsequently applied correctly. Austenitic steels are used because of their corrosion resistance and toughness. Welds and centrifugally cast materials tend to crystallise with grains larger than the ultrasonic wavelength required to achieve the desired resolution in the inspection and thus appear anisotropic. Since the grains in a weld grow along the, varying, directions of maximum heat flux during cooling, the welds are inhomogeneous as well ...


2-D Elastodynamic Scattering From A Finite Closed Crack, Gert Persson Jan 1993

2-D Elastodynamic Scattering From A Finite Closed Crack, Gert Persson

Review of Progress in Quantitative Nondestructive Evaluation

In the present paper the problem of 2-D elastodynamic scattering of horizontally polarized transverse waves from a finite planar or nonplanar closed crack is studied. The boundary conditions on the flaw are of a type which incorporate restoring forces (as well as energy dissipation), and this enables the modelling of a crack which is partly closed under a static background pressure. Given an incident plane wave and the crack geometry we calculate the backscattered far field in the time-harmonic case. In this study there are also a numerical comparison between two well known theoretical methods for 2-D scattering of ultrasonic ...


The T Matrix For Elastic Scattering By A Partly Closed Circular Crack, Arne Eriksson Jan 1993

The T Matrix For Elastic Scattering By A Partly Closed Circular Crack, Arne Eriksson

Review of Progress in Quantitative Nondestructive Evaluation

The object of this work is to calculate the T (transition) matrix for a circular crack in a homogeneous, isotropic, linear elastic medium. The T matrix method is a building block technique for multiple scattering, where the T matrix is calculated for each scatterer separately without prior knowledge of the other scatterers (cracks, inclusions, surfaces, etc.).This means that we solve the scattering problem for arbitrary incoming time harmonic elastic waves. A solution for the scattering by an open circular crack can be found in [1], and for multiple scattering see [2]. On the crack surface the so called spring ...


A Theoretical Approach For The Discrimination Of Crack Tip And Small Defect Echoes, Alain Lhemery, Raphaele Raillon, Mourad Ouamer Jan 1993

A Theoretical Approach For The Discrimination Of Crack Tip And Small Defect Echoes, Alain Lhemery, Raphaele Raillon, Mourad Ouamer

Review of Progress in Quantitative Nondestructive Evaluation

Due to diffraction of US by crack tips, a misinterpretation of C-Scans can be made by mistaking detection of a large misoriented crack for a small flaw. As the latter is often tolerable, the former jeopardizes the life of the piece. Fig. 1. shows C-Scans at various amplification levels. The two spots due to diffraction by the near and far tips of a crack can be interpreted as arising from two small defects, even at high amplification level (+18 dB) for which S/N ratio becomes unacceptable.


Ultrasonic Scattering From A Crack Which Emanates From A Rivet Hole, David Budreck Jan 1993

Ultrasonic Scattering From A Crack Which Emanates From A Rivet Hole, David Budreck

Review of Progress in Quantitative Nondestructive Evaluation

In this article we present the exact solution, to first order of the interacting field, of the following canonical problem. We consider the scattering system consisting of an isotropic elastic medium containing an infinite cylindrical void (= hole), from which emanates a half-penny-shaped crack. The crack lies in a plane containing the axis of the cylindrical void, also the crack intersects the void at its own axis of symmetry. In the paragraph below we define what is meant by obtaining the solution ‘to first order’.


Scattering By An Infinite Array Of Randomly Spaced Coplanar Cracks, Yozo Mikata Jan 1993

Scattering By An Infinite Array Of Randomly Spaced Coplanar Cracks, Yozo Mikata

Review of Progress in Quantitative Nondestructive Evaluation

In this paper, the investigation is carried out for the scattering of an anti-plane shear (SH) wave by an infinite array of randomly spaced coplanar cracks. This study was motivated by the desire to better understand the detection and characterization of a flaw plane, i.e., a plane of microcracks, in a more realistic situation. The first thing we can do to model a flaw plane is to model it as a periodic array of cracks [1–5]. In reality, however, an array of cracks is never periodic but rather random. Thus in a previous paper [6], we have treated ...


Generation Of Guided Waves In Hollow Cylinders By Wedge And Comb Type Transducers, John Ditri, Joseph L. Rose, Aleksander Pilarski Jan 1993

Generation Of Guided Waves In Hollow Cylinders By Wedge And Comb Type Transducers, John Ditri, Joseph L. Rose, Aleksander Pilarski

Review of Progress in Quantitative Nondestructive Evaluation

It was shown by Denos C. Gazis in 19591 that in linearly elastic hollow circular cylinders there exists an infinite number of “normal modes”, each of which has its own propagation characteristics such as phase and group velocity as well as their own displacement and stress distributions throughout the cross section of the cylinder. It was also shown that, even for a given mode, these characteristics changed with changing frequency. In general, when such a cylinder is loaded by external forces, all of the modes of the structure will be excited in varying strengths determined by the characteristics of the ...


Application Of A Self-Calibrating Ultrasonic Technique To The Detection Of Fatigue Cracks By The Use Of Lamb Waves, I. N. Komsky, Jan D. Achenbach Jan 1993

Application Of A Self-Calibrating Ultrasonic Technique To The Detection Of Fatigue Cracks By The Use Of Lamb Waves, I. N. Komsky, Jan D. Achenbach

Review of Progress in Quantitative Nondestructive Evaluation

The reliability of fatigue-crack detection plays an important role in the safety of aircraft structures. Improvements in this reliability can be achieved by making the inspection technique independent of the coupling of the sensor to the specimen. A self-calibrating technique previously developed by the authors [1] makes it possible to detect and quantitatively characterize defects in aircraft structures with greater reliability.


Acoustic Harmonic Generation And Dislocation Dynamics Of Fatigued Aluminum Alloys, John H. Cantrell, William T. Yost Jan 1993

Acoustic Harmonic Generation And Dislocation Dynamics Of Fatigued Aluminum Alloys, John H. Cantrell, William T. Yost

Review of Progress in Quantitative Nondestructive Evaluation

Concern over the aging of the global commercial aircraft fleet has stimulated renewed interest in the development of new methodologies and re-exploring old techniques for the nondestructive evaluation and characterization of metal fatigue. The purpose of the present work is to explore the potential of using bulk acoustic nonlinearity measurements in the determination of metal fatigue with particular emphasis on aluminum alloys (especially A12024-T4).


The Temperature Dependence Of Third-Order Elastic Constants In Metal-Matrix Composites, H. Mohrbacher, K. Salama Jan 1993

The Temperature Dependence Of Third-Order Elastic Constants In Metal-Matrix Composites, H. Mohrbacher, K. Salama

Review of Progress in Quantitative Nondestructive Evaluation

Elastic nonlinearity is responsible for the deviation of a material’s stress-strain response from the linear relationship represented by Hooke’s law. This law can be written in its most general form as σij=Cijklεkl where σij and ɛkl are the stress and strain tensors respectively, and Cijkl is the tensor of the second order elastic constants. The nonlinear elastic behavior can be determined from measurements of the stress dependence of ultrasonic velocities as well as the distortion of ultrasonic waves by the generation of higher harmonics. Consequently, these effects can be used to nondestructively characterize a material’s elastic ...


Ultrasonic Resonance Method With Emat For Stress Measurement In Thin Plates, H. Fukuoka, M. Hirao, T. Yamasaki, H. Ogi, G. L. Peterson, C. M. Fortunko Jan 1993

Ultrasonic Resonance Method With Emat For Stress Measurement In Thin Plates, H. Fukuoka, M. Hirao, T. Yamasaki, H. Ogi, G. L. Peterson, C. M. Fortunko

Review of Progress in Quantitative Nondestructive Evaluation

Metallic thin plate structures such as airplanes are often severely loaded due to high load/weight requirement. Measurement of stress in the loading test are normally done with wire strain gauges. Since such a stress measurement technique is rather inefficient, a new technique of stress measurement has been requested. Birefringence acoustoelasticity is one of the possible alternatives [1, 2, 3]. Stresses in the material make it acoustically anisotropic and the ultrasonic shear wave shows acoustic birefringence. The principal stress difference is proportional to the difference in the propagation velocities of two shear waves polarized in the principal stress directions [4 ...


Quantitative Assessment Of Plastic Deformation Via Acoustic Microscopy, R. D. Weglein Jan 1993

Quantitative Assessment Of Plastic Deformation Via Acoustic Microscopy, R. D. Weglein

Review of Progress in Quantitative Nondestructive Evaluation

Acoustic microscopy has been used historically in the pursuit of two distinctly different diagnostic functions that are useful in material characterization as well as in the inspection of layered and composite structures. These functions, imaging and metrology, are completely nondestructive and the latter factor makes this generic technology a cost-effective tool not only in the development of new components and new process-control functions but also in on-line production testing of expensive parts. In this paper quantitative imaging of plastic deformation is described.


Fatigue Crack Characterization In Conducting Sheets By Non Contact Stimulation Of Resonant Modes, Buzz Wincheski, J. P. Fulton, R. Todhunter, Min Namkung Jan 1993

Fatigue Crack Characterization In Conducting Sheets By Non Contact Stimulation Of Resonant Modes, Buzz Wincheski, J. P. Fulton, R. Todhunter, Min Namkung

Review of Progress in Quantitative Nondestructive Evaluation

The natural frequencies and modes of vibration of a linearly elastic continuum are a function of the mass and stiffness of the body [1]. As many structural flaws, such as fatigue cracks, corrosion, and disbonds, will affect these attributes, vibrational analysis is a natural method by which to characterize such flaws. Finite element modeling techniques can be used to predict vibrational responses from various structure/defect combinations, so that test parameters can be selectively chosen for the requirements of the investigation. Critical areas can be isolated through the application of appropriate boundary conditions, and test frequencies chosen so as to ...


Determination Of Short Crack Depth With An Acoustic Microphone, D. Knauss, D. D. Bennink, T. Zhai, G. A. D. Briggs, J. W. Martin Jan 1993

Determination Of Short Crack Depth With An Acoustic Microphone, D. Knauss, D. D. Bennink, T. Zhai, G. A. D. Briggs, J. W. Martin

Review of Progress in Quantitative Nondestructive Evaluation

For the prediction of the lifetime of any component, subjected to alternating stresses, the knowledge of the growth behavior of defects is essential. Most methods of monitoring the propagation of short cracks are confined to measuring the length of the crack on the surface [1]. The depth of the crack must be determined indirectly, assuming the shape of the crack. Acoustic waves, on the other hand, offer the possibility of measuring the depth directly, since acoustic waves can penetrate into the material. This allows the measurement not only of the growth behavior of fatigue cracks on the surface, but also ...


The Spatial Resolution Of Rayleigh Wave, Acoustoelastic Measurement Fo Stress, J. C. Johnson, R. Bruce Thompson Jan 1993

The Spatial Resolution Of Rayleigh Wave, Acoustoelastic Measurement Fo Stress, J. C. Johnson, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

One of the challenges in the acoustoelastic measurement of stress is the achievement of high spatial resolution. Since stress induced velocity shifts are generally small (~0.01%), the required precision of time and distance measurements can be quite high for the short propagation distances required. This paper presents a set of design criteria which can guide the experimentalist in choosing the most suitable measurement configuration for Rayleigh wave techniques. Three approaches for measuring the acoustic velocity are considered: measurement of arrival time versus transducer separation for several discrete positions, measurement of arrival time for a pair of transducers at a ...


Crack Length Determination By Ultrasonic Methods, David Kent Rehbein, R. Bruce Thompson, Otto Buck Jan 1993

Crack Length Determination By Ultrasonic Methods, David Kent Rehbein, R. Bruce Thompson, Otto Buck

Review of Progress in Quantitative Nondestructive Evaluation

Accurate calculation of the stress intensity factor on a given component under load relies on an accurate size determination of the flaws present in the component. The challenge to the NDE community has been development of reliable techniques to provide that accurate size determination. Many research groups have investigated this problem using ultrasonic methods with summaries of their techniques and results provided by various authors [1–3]. In general, the techniques developed fall into three general categories; (1) determination of crack length from signal amplitude measurements, (2) determination of crack length from time-of-flight measurements, and (3) determination of crack length ...