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Full-Text Articles in Physics

Analytic Calculations And Numerical Simulations Of Box-Car Thermal Wave Images Of Planar Subsurface Scatterers, D. J. Crowther, L. D. Favro, P. K. Kuo, R. L. Thomas Jan 1992

Analytic Calculations And Numerical Simulations Of Box-Car Thermal Wave Images Of Planar Subsurface Scatterers, D. J. Crowther, L. D. Favro, P. K. Kuo, R. L. Thomas

Review of Progress in Quantitative Nondestructive Evaluation

The purpose of this study is to improve the quality of thermal wave infrared (IR) images in terms of the real shape of the defect. Due to heat diffusion into the sample, thermal wave images are usually blurred, especially for deep defects or long times. Because of this feature the use of traditional image post-processing (gradient image, threshold…) to assess the size and the shape of the defect quite often leads to false results. In order to increase the accuracy in the shape recovery, we need to “unblur” the thermal wave image, i.e. to reverse or invert the blurring ...


Time-Resolved Infrared Radiometry (Trir) For Characterization Of Impact Damage In Composite Materials, J. W. Maclachlan Spicer, W. D. Kerns, L. C. Aamodt, J. C. Murphy Jan 1992

Time-Resolved Infrared Radiometry (Trir) For Characterization Of Impact Damage In Composite Materials, J. W. Maclachlan Spicer, W. D. Kerns, L. C. Aamodt, J. C. Murphy

Review of Progress in Quantitative Nondestructive Evaluation

A quantitative thermographie NDE technique for the characterization of impact damage in composite materials is under development along with supporting theoretical analysis. We have previously shown that the technique of time-resolved infrared radiometry (TRIR) is an effective method for quantitatively detecting coating thickness variations and for characterizing the degree of coating disbonding in terms of equivalent air gaps [1,2]. Here we extend the TRIR technique to the study of composite systems by applying the results of a multilayer analytical model [3]. Experimental results in both simple and hybrid composite systems are discussed. The depth and lateral extent of interlaminar ...


Computed Speckle Decorrelation (Csd) And Its Application For Fatigue Damage Monitoring, J. Scott Steckenrider, James W. Wagner Jan 1992

Computed Speckle Decorrelation (Csd) And Its Application For Fatigue Damage Monitoring, J. Scott Steckenrider, James W. Wagner

Review of Progress in Quantitative Nondestructive Evaluation

A video-based laser speckle technique has been developed for non-contact surface deformation analysis and mapping at speeds approaching video frame rates. This technique, Computed Speckle Decorrelation (CSD), makes use of the speckle decorrelation associated with surface deformation. In its current application, CSD is a method of full field inspection which has been used both to locate fatigue damage sites and to measure damage severity during fatigue deformation in reverse bending fatigue of a cylindrically notched aluminum specimen. With the development of the CSD method it will now be possible to examine in greater detail the progression of fatigue damage in ...


Dynamic Thermal Tomography: New Nde Technique To Reconstruct Inner Solids Structure Using Multiple Ir Image Processing, V. Vavilov, X. Maldague, J. Picard, R. L. Thomas, L. D. Favro Jan 1992

Dynamic Thermal Tomography: New Nde Technique To Reconstruct Inner Solids Structure Using Multiple Ir Image Processing, V. Vavilov, X. Maldague, J. Picard, R. L. Thomas, L. D. Favro

Review of Progress in Quantitative Nondestructive Evaluation

Nondestructive evaluation (NDE) technique appeared as the natural consequence of materials analysis by using a variety of physical fields and particles which being propagated through the specimen are able to produce the image of its inner structure. Disadvantage of traditional “shadow” or “backscattered” images is that the “weak” details are scarcely seen on the background of “stronger” ones. This is why the introduction of the tomographic principles, allowing to “slice” the solid into individual layers, was viewed as a revolution in vision techniques (especially in X-ray imaging). Ultrasonic, ultra-high frequency and nuclear magnetic resonance tomography are under quick development now.


Fast Photothermal Inspection Of Plasma-Sprayed Coatings Of Primary Circulation Seal Rings Of A Nuclear Reactor, R. Lehtiniemi, J. Hartikainen, J. Rantala, J. Varis, M. Luukkala Jan 1992

Fast Photothermal Inspection Of Plasma-Sprayed Coatings Of Primary Circulation Seal Rings Of A Nuclear Reactor, R. Lehtiniemi, J. Hartikainen, J. Rantala, J. Varis, M. Luukkala

Review of Progress in Quantitative Nondestructive Evaluation

A need for NDE of plasma-sprayed coatings has been a serious problem in the industry for a long time. Traditional methods like ultrasonics or x-ray absorption usually cannot be used because of the high attenuation and the heterogeneity of the coating. On the other hand, sub-surface flaws cannot be detected with liquid penetration technique and electromagnetic methods are not suitable for dielectric coating. However, photothermal techniques have been successfully applied [1,2], but first the introduction of fast infrared scanning systems has lead to reasonable speed of inspection from the practical point of view.


Ir Thermal Wave Tomographic Studies Of Structural Composites, L. D. Favro, H. J. Jin, Y. X. Wang, T. Ahmed, X. Wang, P. K. Kuo, R. L. Thomas Jan 1992

Ir Thermal Wave Tomographic Studies Of Structural Composites, L. D. Favro, H. J. Jin, Y. X. Wang, T. Ahmed, X. Wang, P. K. Kuo, R. L. Thomas

Review of Progress in Quantitative Nondestructive Evaluation

Vavilov et al [1] have recently described a technique for making tomographic thermal wave images. Their method involves recording a succession of thermal wave images after a flash-heating pulse, followed by a numerical pixel-by-pixel search of the images for the time at which the reflected thermal waves from subsurface features have their peak amplitudes. Since the peak time is related to the depth of the scatterer, this information enables one to separate the image into time (or depth) slices. The result is a thermal wave tomogram. Since their process involves post-processing and a search through a large number of stored ...


Flying Laser Spot Thermal Wave Ir Imaging, Y. Q. Wang, P. Chen, P. K. Kuo, L. D. Favro, R. L. Thomas Jan 1992

Flying Laser Spot Thermal Wave Ir Imaging, Y. Q. Wang, P. Chen, P. K. Kuo, L. D. Favro, R. L. Thomas

Review of Progress in Quantitative Nondestructive Evaluation

In a previous report, some of the authors have described the basic experimental technique for flying laser spot thermal wave IR imaging, and demonstrated its potential usefulness for the detection of closed vertical cracks [11. The objective of the present work is to provide a theoretical description of the temperature distribution from a Gaussian-shaped surface heat spot, scanned at constant speed, and to compare the predictions of that theoretical description with temperature distributions measured experimentally with our thermal wave flying spot imaging system.


Numerical Solutions For Heat Flow In Adhesive Lap Joints, P. A. Howell, William P. Winfree Jan 1992

Numerical Solutions For Heat Flow In Adhesive Lap Joints, P. A. Howell, William P. Winfree

Review of Progress in Quantitative Nondestructive Evaluation

The detection of disbonds in riveted lap joints is of increasing interest to the aerospace community. Adhesively bonded and riveted lap joints are used to bond the thin overlapped sheets of aluminum which comprise the outer skin of an aircraft. Through time, the integrity of the bond can become compromised by disbanding, leading to corrosion and stress concentrations at the rivets and subsequent cracking leading to joint failure. A thermal technique for determining bond integrity in these structures has been investigated by Winfree, et al [1]. This technique involves active heating of the aircraft fuselage with a measurement of the ...


Comparison Of Heating Protocols For Detection Of Disbonds In Lap Joints, William P. Winfree, B. Scott Crews, P. A. Howell Jan 1992

Comparison Of Heating Protocols For Detection Of Disbonds In Lap Joints, William P. Winfree, B. Scott Crews, P. A. Howell

Review of Progress in Quantitative Nondestructive Evaluation

With the increased concern for the safety and reliability of aging aircraft, new nondestructive techniques are being sought for detecting and characterizing defects in these structures. These techniques must be both reliable and economical to impact the current safety of the fleet. To meet both of these requirements, more focus is being placed on large area inspection techniques. These offer the possibility for greatly reduced inspection times as compared to current point measurement techniques.


Bonds Nde Using Stimulated Infrared Thermography, P. M. Delpech, D. M. Boscher, F. Lepoutre, A. A. Deom, D. L. Balageas Jan 1992

Bonds Nde Using Stimulated Infrared Thermography, P. M. Delpech, D. M. Boscher, F. Lepoutre, A. A. Deom, D. L. Balageas

Review of Progress in Quantitative Nondestructive Evaluation

Among all the photothermal techniques that have appeared since some years, the photothermal radiometry is very attractive because of its noncontact and rapid-scanning ability [1,2]. In our laboratory, we developed pulsed stimulated infrared (IR) thermography [3]. Due to the relatively low refreshment frequency of the currently used IR cameras, the application of the method was restricted to low thermal conductors. In particular, we applied it to carbon/epoxy composites [4,5]. Some new developments of the data reduction procedure were presented last year [6] to use this technique with good heat conductors. Satisfactory results were obtained in the case ...


Nondestructive Evaluation Using Shearing Interferometry, Thomas C. Chatters, Sridhar Krishnaswamy Jan 1992

Nondestructive Evaluation Using Shearing Interferometry, Thomas C. Chatters, Sridhar Krishnaswamy

Review of Progress in Quantitative Nondestructive Evaluation

Coherent shearing interferometry involves the interference of a coherent optical wavefront with a spatially shifted version of itself. The resulting interference pattern carries information which for small shears (spatial shifts) can be related to the gradients of the phase of the wavefront. The primary advantage of this optical technique is that it is relatively insensitive to rigid body motion. A coherent wavefront that is transmitted through a body or is reflected from the surface of a body will carry information about the resulting stress state or deformation of the body. This information can be used for nondestructive evaluation applications using ...


Nanosecond Scale Optical Pulse Separations For Holographic Investigation Of High-Speed Transient Events, Michael J. Ehrlich, James W. Wagner Jan 1992

Nanosecond Scale Optical Pulse Separations For Holographic Investigation Of High-Speed Transient Events, Michael J. Ehrlich, James W. Wagner

Review of Progress in Quantitative Nondestructive Evaluation

The dynamics of detonation for dispersed solid particulate explosives are not well understood. These explosives, used for mine neutralization, are comprised of a fine, solid particulate dust which is dispersed as a cloud over a given area. When detonation is initiated in some portion of the cloud, the ensuing detonation wave propagates throughout the entire cloud and results in an explosion, generating a tremendous pressure which serves to destroy any land mines present. However, the mechanism with which individual explosive particles interact to sustain detonation in these solid dispersed particle explosives is not clear. In liquids, for example, it is ...


Error Arising From Original Approximation In Photothermal Measurement Of Weak Absorption Of Optical Thin Film, Baixuan Shin, Wenbin Chen, G. G. Siu, D. S. Chiu Jan 1992

Error Arising From Original Approximation In Photothermal Measurement Of Weak Absorption Of Optical Thin Film, Baixuan Shin, Wenbin Chen, G. G. Siu, D. S. Chiu

Review of Progress in Quantitative Nondestructive Evaluation

The technique of photothermal deflection spectroscopy (PTDS) for absorption measurement of optical thin film is simple in installation and fast in detection. However, while measurable absorbance reaches the order of magnitude of 10-7, e.g. in studies of optical thin film and investigation of laser damage mechanisms [1,2], we are still doubtful of its precision because of the lack of independent evaluation with available instruments whose precision could reach this lower limit. This work aims at giving a theoretical investigation on the source of error in order to obtain a realistic estimate of measurement error and hence to find ...


Effect Of Magnetic And Density Fluctuations On The Propagation Of Lower Hybrid Waves In Tokamaks, George Vahala, Linda L. Vahala, Paul T. Bonoli Jan 1992

Effect Of Magnetic And Density Fluctuations On The Propagation Of Lower Hybrid Waves In Tokamaks, George Vahala, Linda L. Vahala, Paul T. Bonoli

Electrical & Computer Engineering Faculty Publications

Lower hybrid waves have been used extensively for plasma heating, current drive, and ramp-up as well as sawteeth stabilization, The wave kinetic equation for lower hybrid wave propagation is extended to include the effects of both magnetic and density fluctuations. This integral equation is then solved by Monte Carlo procedures for a toroidal plasma. It is shown that even for magnetic/density fluctuation levels on the order of 10-4, there are significant magnetic fluctuation effects on the wave power deposition into the plasma. This effect is quite pronounced if the magnetic fluctuation spectrum is peaked within the plasma. For ...


Sliding-Mode Observers Based On Equivalent Control Method, Sergey V. Drakunov Dec 1991

Sliding-Mode Observers Based On Equivalent Control Method, Sergey V. Drakunov

Sergey V. Drakunov

No abstract provided.