Air-coupled, focused ultrasonic dispersion spectrum reconstruction in plates

This paper presents and demonstrates a noncontact method for measuring the Lamb wave dispersion spectrum of a plate. Noncontact air-coupled source and receive transducers are used with line-focus mirrors and 50–700 kHz broadband apparatus for simultaneous measurement over a broad spectrum of refractive angles and multiple guided modes. Broadband, wide-angle wave forms are measured as a function of position. The Fourier transform of these wave forms from the t – x domain to the v – k domain gives an approximate spectrum of the dispersion relation. We measure the dispersion spectra of Lucite™, aluminum, balsa wood, and a carbon fiber epoxy laminate, and show that the measured spectra agree well with the dispersion relation calculated from Lamb wave theory

A Noncontacting Method for Measuring Paper Sheet Grammage and Thickness Using Acoustic Tone Bursts

The grammage, ie., mass per unit area, is one of the most important quality factors in paper industry. The grammage of the paper web is constantly monitored during the paper manufacturing, and the ever rising pulling speeds and wider reels demand more accurate and faster methods to monitor the grammage changes in both the cross direction and in the machine direction. Nowadays, the standard method is to use radioactive beta rays, which method was invented in 1950s. The beta radiation is attenuated as a function of sample grammage, but the temperature of surrounding air, and the atomic number of the sample also affect the measured intensity of the beta rays. These effects can be conquered by calibration and by monitoring the temperature. But one technical difficulty remains, though. Only one measuring head is traversing across the paper web, which is quite a slow method to achieve the cross profile of the paper web [1–2].</p

NUMERICAL ANALYSIS OF THERMAL WAVES IN STRATIFIED MEDIA FOR NON-DESTRUCTIVE TESTING PURPOSES

Nous présentons une analyse numérique des ondes thermiques dans le cas d'objets dont les caractéristiques thermiques peuvent être fonctions des coordonnées. Les résultats sont appliqués à l'acier traité en surface.We present a numerical analysis of thermal waves in case of samples in which thermal properties may be functions of coordinates. The results are applied to surface hardened steel

Study Site Standard Operating Procedure SOP: P8 - Recruitment of subjects

Recently, improvements in instrumentation have provided the option of gas- or air-coupled ultrasonic testing as a realistic alternative to immersion or contact testing. In this paper we present theoretical and experimental results on resonant sound transmission methods mediated by ultrasonic coupling directly through ambient air. Although these methods are not new [1], they have only recently been considered for MHz applications. Advances in transducer technology [2–5] have further improved signal to noise ratios

Fast Photothermal Inspection of Plasma-Sprayed Coatings of Primary Circulation Seal Rings of a Nuclear Reactor

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.</p

Fast Photothermal Inspection of Plasma-Sprayed Coatings of Primary Circulation Seal Rings of a Nuclear Reactor. Part Two: After the Trial Run

In the 1991 QNDE conference [1] we described a photothermal inspection of the plasma-sprayed coatings of two seal rings used in the main pump of the primary circulation in the PWR-type nuclear reactor. The measurements concentrated on detecting the most critical flaw type, adhesion defects at the interface between the coating and the substrate. The samples were tested immediately after they were coated and lapped, and already then two thermal anomalies could be found.</p