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Mechanical Engineering Commons

Open Access. Powered by Scholars. Published by Universities.®

1983

Ames Laboratory

Acoustics, Dynamics, and Controls

Articles 1 - 9 of 9

Full-Text Articles in Mechanical Engineering

Progress On Ultrasonic Flaw Sizing In Turbine Engine Rotor Components: Bore And Web Geometries, James H. Rose, T. A. Gray, R. Bruce Thompson, J. L. Opsal Jan 1983

Progress On Ultrasonic Flaw Sizing In Turbine Engine Rotor Components: Bore And Web Geometries, James H. Rose, T. A. Gray, R. Bruce Thompson, J. L. Opsal

Review of Progress in Quantitative Nondestructive Evaluation

The application of generic flaw sizing techniques to specific components generally involves difficulties associated with geometrical complexity and simplifications arising from a knowledge of the expected flaw distribution. This paper is concerned with the case of ultrasonic flaw sizing in turbine engine rotor components. The sizing of flat penny shaped cracks in the web geometry will be discussed and new crack sizing algorithms based on the Born and Kirchhoff approximations will be introduced. Additionally we propose a simple method for finding the size of a flat, penny shaped crack given only the magnitude of the scattering amplitude. The bore geometry ...


On The Effects Of A Finite Aperture On The Inverse Born Approximation, Vladimir G. Kogan, James H. Rose Jan 1983

On The Effects Of A Finite Aperture On The Inverse Born Approximation, Vladimir G. Kogan, James H. Rose

Review of Progress in Quantitative Nondestructive Evaluation

One of the most important effects of complex part geometry is that the available entrance and exit angles for ultrasound are limited. We will present a study of the Inverse Born Approximation in which we have data for incident (and exit) directions confined to a conical aperture. Modeling the direct problem by the Born Approximation, we obtained analytical results for (1) a weak spherical inclusion, and (2) a penny shaped crack (modeled by an oblate spheroid). General results are: (a) the value of the characteristic function γ is constant in the interior of the flaw, but reduced in value; (b ...


Absolute Determination Of Stress In Textured Materials, R. Bruce Thompson, John F. Smith, S. S. Lee Jan 1983

Absolute Determination Of Stress In Textured Materials, R. Bruce Thompson, John F. Smith, S. S. Lee

Review of Progress in Quantitative Nondestructive Evaluation

The continuum theory of elastic wave propagation in deformed, anisotropic solids is reviewed with emphasis on those features which might be used to distinguish between stress induced changes in ultrasonic velocity and changes due to material anisotropy, such as would be produced by preferred grain orientation in a polycrystalline metal As noted by previous authors, one such feature is the difference in velocity of two shear waves, whose directions of propagation and polarization have been interchanged. In particular, when these directions fall along the symmetry axes of a rolled plate (assuming orthorhombic symmetry) and these are also the directions of ...


Elastic Wave Scattering From Multiple Voids (Porosity), Donald O. Thompson, Samuel J. Wormley, James H. Rose, R. Bruce Thompson Jan 1983

Elastic Wave Scattering From Multiple Voids (Porosity), Donald O. Thompson, Samuel J. Wormley, James H. Rose, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

The purpose of the work described in this paper is the development of an ultrasonic measurement technique which provides a convenient way to detect dilute porosity conditions in materials and to extract certain properties of the flaw distribution which are important in failure prediction. Use has been made entirely of ultrasonic backscatter measurements; thus, the technique differs considerably from other investigations which lead to porosity determinations in that no reliance is placed upon either attenuation measurements or precise ultrasonic velocity measurements [1,2]. The technique thus possesses a distinct advantage for practical implementation, i.e., it is a “one-sided” measurement ...


A Computational Tool For The Design Of Ultrasonic Systems, Sam J. Wormley, Donald O. Thompson, Kenneth M. Lakin Jan 1983

A Computational Tool For The Design Of Ultrasonic Systems, Sam J. Wormley, Donald O. Thompson, Kenneth M. Lakin

Review of Progress in Quantitative Nondestructive Evaluation

Advances in elastic wave scattering and inversion techniques have shown that advances in transducer technology are needed in order to fully exploit them. This is particularly true in the case of flaw sizing algorithms in which it has been demonstrated that a need exists for transducers with specified bandwidth characteristics. As a part of an effort to develop a composite, multiviewing ultrasonic transducer for flaw characterization, a computational tool has been developed which provides a convenient way to select driver pulse shapes and transducer characteristics which optimize this property. The purpose of this paper is to discuss this computational tool.


Effects Of Crack Closure On Ultrasonic Transmission, R. Bruce Thompson, B. J. Skillings, L. W. Zachary, L. W. Schmerr, Otto Buck Jan 1983

Effects Of Crack Closure On Ultrasonic Transmission, R. Bruce Thompson, B. J. Skillings, L. W. Zachary, L. W. Schmerr, Otto Buck

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic waves are attenuated as they propagate past the tip of a crack due to the reflection of the energy at the crack face and diffraction at the crack tip. Crack closure modifies the situation since partial transmission can occur at points along the crack face where asperities come in contact. This phenomenon is important in defining the ability to nondestructively detect closed cracks and in developing a more detailed understanding of the closure phenomenon itself. Modified compact tension specimens were used to investigate the effects of partial crack closure on focussed, through-transmission ultrasonic signals. Data obtained from fatigue cracks ...


Simulation Of Closure: Effects On Crack Detection Probability And Stress Distributions, Otto Buck, B. J. Skillings `, L. K. Reed Jan 1983

Simulation Of Closure: Effects On Crack Detection Probability And Stress Distributions, Otto Buck, B. J. Skillings `, L. K. Reed

Review of Progress in Quantitative Nondestructive Evaluation

It is well known that partial contact of two rough crack surfaces will lead to transmission of an acoustic signal across the crack, thus giving rise to a reduced probability of detection (POD). To explore the effects and consequences of such partial contact, impression experiments—using small spheres—have been performed to determine the effects of contact area on the amplitude transmitted. The results have been compared with a theory described elsewhere in these Proceedings. Based on the experimental results it will be speculated that the residual stress field responsible for the crack closure may be calculated based on a ...


Detection Of Closed Internal Fatigue Cracks, B. R. Tittmann, L. Ahlberg, Otto Buck, F. Cohen-Tenoudji, G. Quentin Jan 1983

Detection Of Closed Internal Fatigue Cracks, B. R. Tittmann, L. Ahlberg, Otto Buck, F. Cohen-Tenoudji, G. Quentin

Review of Progress in Quantitative Nondestructive Evaluation

This paper reviews some recent work on the detection and sizing of closed internal fatigue cracks by ultrasonic techniques. Major emphasis is put on the diffraction of shear waves at the crack tip. Both fully open as well as partially closed cracks were considered. The effect of crack closure stress on back- scattered (pulse-echo) shear waves was studied with the aid of an A1 compact tension specimen. Noticeable changes with crack closure stress were documented for the structure of both the time- domain and frequency-domain representations. The techniques acquired with this specimen were applied to the study of a 50 ...


Analytic Diffraction Corrections To Ultrasonic Scattering Measurements, R. Bruce Thompson, T. A. Gray Jan 1983

Analytic Diffraction Corrections To Ultrasonic Scattering Measurements, R. Bruce Thompson, T. A. Gray

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic theories generally predict a scattering amplitude which relates a spherically spreading, far-field scattered wave to an incident plane wave. In ultrasonic immersion measurements, the frequency and angular dependences of the scattering amplitude are convolved with those of the transmitting and receiving transducers and the propagation through the liquid-solid and solid-liquid interfaces. This paper presents a set of approximate corrections for these effects for the cases of angle beam inspection through planar, spherically curved or cylindrically curved surfaces. The primary parameters in the correction are the function D, which corrects for the diffraction effects occurring during a transducer calibration experiment ...