Showing papers in "Materials evaluation in 1986"

NDE of fiber-reinforced composite materials: a review

Abstract: Article de synthese de 51 references sur les essais non destructifs (NDE) au stade production, assemblage, en service, de plastiques renforces de fibres utilises en aviation

The remote-field through-wall electromagnetic inspection technique for pressure tubes

Abstract: Controle electromagnetique par champ lointain, avec propagation a travers la paroi pour des tubes sous pression

Reliability of void detection in structural ceramics by use of scanning laser acoustic microscopy

Abstract: The reliability of scanning laser acoustic microscopy (SLAM) for detecting surface voids in structural ceramic test specimens was statistically evaluated. Specimens of sintered silicon nitride and sintered silicon carbide, seeded with surface voids, were examined by SLAM at an ultrasonic frequency of 100 MHz in the as fired condition and after surface polishing. It was observed that polishing substantially increased void detectability. Voids as small as 100 micrometers in diameter were detected in polished specimens with 0.90 probability at a 0.95 confidence level. In addition, inspection times were reduced up to a factor of 10 after polishing. The applicability of the SLAM technique for detection of naturally occurring flaws of similar dimensions to the seeded voids is discussed. A FORTRAN program listing is given for calculating and plotting flaw detection statistics.

NDE of advanced ceramics

Abstract: Radiographic, ultrasonic, and scanning laser acoustic microscopy (SLAM) techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus X-ray techniques were found capable of detecting minute high-density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was capable also of detecting voids, inclusions, and cracks in finished test bars. Consideration is given to the potential for applying thermoacoustic microscopy techniques to green and densified ceramics. Some limitations and the detection probability statistics of the aforementioned nondestructive evaluation (NDE) processes are also discussed.

A comparison of laser and EMAT techniques for noncontact ultrasonics

Abstract: Ultrasons generes par laser et detectes par interferometrie et transducteurs acoustiques interferometriques

A method for quantitative characterization of flaws in sheets by use of thermal-response data

Abstract: Caracterisation quantitative de defauts dans des materiaux en feuilles par etude de la reponse thermique

An nondestructive measurement of residual bulk stresses in welded steel specimens by use of magnetically induced velocity changes for ultrasonic waves

Abstract: Mesure non destructive des onctraintes residuelles moyennes dans des elements soudes en acier par modification magnetique de la vitesse d'une onde ultrasonore

Some laser-based techniques for the characterization of sintered ceramics

Abstract: Some laser-based techniques for the characterization of ceramic materials fired at different temperatures are described and discussed. The first method is based on ultrasonic velocity measurements by laser generation and detection of a convergent surface wave. In the second approach, the thermal parameters of the ceramic material are measured by laser-pulsed heating and infrared temperature detection. The third technique monitors the optical scattering properties of the translucent ceramic material. In all cases, a good correlation is obtained between the measured parameter and the density of the ceramic samples. 25 references.

Scaling attenuation data characterizes changes in material microstructure

Abstract: Ultrasonic attenuation was measured for polycrystalline samples of nickel and copper with various grain-size distributions produced by heat treatment. Attenuation as a function of frequency was determined for a sample having a known mean grain diameter D. It was found that, once this function is determined, it can be scaled to determine the mean grain size of other samples of the same material with different mean grain diameters. These results were obtained using broadband pulse-echo ultrasound in the 25 to 100 MHz frequency range. The results suggest an ultrasonic, nondestructive approach for verifying heat treatment of metals.

Ultrasonic characterization of model defects in ceramics (Part. 1): voids in glass. Theory and Practice

Abstract: Adaptation de la theorie de l'onde plane a l'etude de la diffusion d'ultrasons de defauts microscopiques. Des cavites de diametres inferieurs a 100 μm ont ete introduites dans une matrice vitreuse utilisee comme modele des matrices ceramiques. Les verres permettent une caracterisation optique directe de ces defauts et donc de comparer directement les calculs aux resultats experimentaux

Ultrasonic signal processing for thickness measurements and detection of near-surface defects

Abstract: Traitement du signal ultrasonore pour la mesure d'epaisseurs ou la detection de defauts voisins de la surface

Stress waves in isotropic elastic plate excited by circular transducer

Abstract: Steady state harmonic stress waves in an isotropic elastic plate excited on one face by a circular transducer are analyzed theoretically. The transmitting transducer transforms an electrical voltage into a uniform normal stress at the top of the plate. To solve the boundary value problem, the radiation into a half-space is considered. The receiving transducer produces an electrical voltage proportional to the average spatially integrated normal stress over its face due to an incident wave. A numerical procedure is given to evaluate the frequency response at a receiving point due to a multiply reflected wave in the near field. Its stability and convergence are discussed. Parameterization plots which determine the particular wave whose frequency response has maximum magnitude compared with other multiple reflected waves are given for a range of values of dimensionless parameters. The effects of changes in the values of the parameters are discussed.

Determination of grain-size distribution function using two-dimensional Fourier transforms of tone-pulse-encoded images

Abstract: Microstructural images may be tone pulse encoded and subsequently Fourier transformed to determine the two-dimensional density of frequency components. A theory is developed relating the density of frequency components to the density of length components. The density of length components corresponds directly to the actual grain size distribution function from which the mean grain shape, size, and orientation can be obtained.

Quantitative flaw characterization with scanning laser acoustic microscopy

Abstract: Surface roughness and diffraction are two factors that have been observed to affect the accuracy of flaw characterization with scanning laser acoustic microscopy. Inaccuracies can arise when the surface of the test sample is acoustically rough. It is shown that, in this case, Snell's law is no longer valid for determining the direction of sound propagation within the sample. The relationship between the direction of sound propagation within the sample, the apparent flaw depth, and the sample's surface roughness is investigated. Diffraction effects can mask the acoustic images of minute flaws and make it difficult to establish their size, depth, and other characteristics. It is shown that for Fraunhofer diffraction conditions the acoustic image of a subsurface defect corresponds to a two-dimensional Fourier transform. Transforms based on simulated flaws are used to infer the size and shape of the actual flaw.

Time-domain deconvolution: a new technique to improve resolution for ultrasonic flaw characterization in stainless steel welds

Abstract: Deconvolution dans le domaine temporel. Utilisation d'une nouvelle technique pour ameliorer la resolution dans le cas de la caracterisation des fissures par ultrasons pour le soudage des aciers inoxydables

Inspection proposals ― A regulatory view

Abstract: The United Kingdom safety legislation places absolute liability on the licensee as regards the safe design and operation of nuclear installations. In this paper, the approach taken by HM Nuclear Installations Inspectorate (NII) in assessing the structural integrity safety case for the Sizewell B PWR reactor pressure vessel and the other incredible failure components is described. Attention is focused on the ultrasonic inspection proposals which must satisfy the NII Safety Principles in terms of the Special Case Procedure, appropriate inspection standards, the setting of realistic inspection goals, the extent of the validation, redundancy and diversity to be built into the inspection programme and the avoidance of common mode effects. It is argued that these safety concepts should be incorporated into the appropriate codes and standards and whilst these measures may appear excessive when compared with past practice, the increase in safety and the case of in-service inspection in later years, for outweigh the initial costs.

Radiation safety and visual enhancement in the fluorescent dye penetrant processes

Abstract: Securite face aux radiations et amelioration de la vision lors du controle par penetrants fluorescents

High defect-resolution capability from a computer-controlled fluorescent penetrant processing and viewing system

Abstract: Systeme commande par ordinateur de controle et de visualisation de haute resolution pour les essais par penetrants fluorescents