Ultrasonic Attenuation Measurement Using Backscattering Technique

Ultrasonic backscattering measurements by means of spatial averaging technique were carried out in steel to determine the ultrasonic attenuation coefficient. The attenuation coefficients were evaluated from the exponential decay of the backscattering signal. The results were compared with those obtained by evaluating the amplitude decay of the main pulse. Good agreement is observed provided the condition α s · λ \u3c\u3c 1 is valid, i.e. Rayleigh scattering with d/λ ≤ 0.2 and/or weak elastic anisotropy of the single crystal. Otherwise multiple scattering becomes dominant and the amplitude decay of the backscattering curve is no longer related to the attenuation coefficient

Characterization of Defects and Heterogeneities in Silicon Nitride and Silicon Carbide by Different NDE Methods

The brittleness of ceramic materials like silicon nitride and silicon carbide makes it necessary to fabricate homogeneous structures and to detect small defects in the region of 10 to 100 microns diameter. In the German program on NDE for the gas turbine therefore a study was made to compare different NDE methods and to develop new techniques. Tests were made with ultrasonics, microradiography, vibration analysis, acoustic emission and optical-holographical interferometry on test samples and real components of the gas turbine (rotor, stator, combustor). The results show that especially microradiography with projection technique and X-ray focus of ≈ 10 µm diameter, ultrasonics with different kind of transducers, equipment and wave modes in the frequency range until about 150 MHz are well suited to detect the small defects and to characterize structure heterogeneities. Vibration analysis seems to be a good method to compare many samples of the same kind and to detect matter of the fabrication process data. The comparison between UT, vibration analysis, acoustic emission and destructive tests (fracture strength) indicates that there are more or less correlations between NDE and the destructive analysis

Fast Signal-Averaging Unit for Ultrasonic Testing: Characterization of Materials Properties and SNR-Improvement for Coarse Grained Materials

The scattering of ultrasonic waves depends on the relation scatterer diameter to wavelength. Coarse grained materials and high frequency ultrasonic waves therefore ere exciting high scattering amplitudes. During pulse-echo testing a backscattering signal is the result of superimposing all the single scattering processes in the sound beam for a given time of flight. Rectifying, digitizing and adding up several A-scans from several different probe positions, angles of incidence or frequencies equalizes interference maxima and minima. The resulting backscattering curve can be evaluated qualitatively and quantitatively for the materials structure characterization. Additionally, an improvement of the signal-to-noise ratio (SNR) is achieved for a defect surrounded by a coarse grained structure. The application in practice depends among other things on the time in which a sufficient number of digitized A-scans is averaged and on the dimensions and operating conditions of the equipment. With these limits a prototype instrument was developed. Up to 1024 digitized A-scans (each 400 ps long, digitizing rate 20 MHz) are averaged in 0.4 sec. The result is recorded on a CRT-display and the whole unit is microcomputer-controlled. The equipment consists of an ultrasonic instrument (USIP 11) and the averager unit (averager, ADC,display, μP). Examples are given of applications to the characterization of materials structure (detection of heterogeneities in steel, grain size determination) and to the ultrasonic testing of coarse grained materials( austenitic welds, castings, fibre reinforced plastics)

Inspection of Refinery Vessels for Hydrogen Attack Using Ultrasonic Techniques

Hydrogen attack is a damage mechanism occurring in steels exposed to high pressure hydrogen at elevated temperatures. Under such conditions, hydrogen atoms diffuse into steels and react with carbides. The reaction leads to formation of methane and, subsequently, intergranular fissuring and losses of material strength and toughness

Septin/anillin filaments scaffold central nervous system myelin to accelerate nerve conduction

Myelination of axons facilitates rapid impulse propagation in the nervous system. The axon/myelin-unit becomes impaired in myelin-related disorders and upon normal aging. However, the molecular cause of many pathological features, including the frequently observed myelin outfoldings, remained unknown. Using label-free quantitative proteomics, we find that the presence of myelin outfoldings correlates with a loss of cytoskeletal septins in myelin. Regulated by phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P2)-levels, myelin septins (SEPT2/SEPT4/SEPT7/SEPT8) and the PI(4,5)P2-adaptor anillin form previously unrecognized filaments that extend longitudinally along myelinated axons. By confocal microscopy and immunogold-electron microscopy, these filaments are localized to the non-compacted adaxonal myelin compartment. Genetic disruption of these filaments in Sept8-mutant mice causes myelin outfoldings as a very specific neuropathology. Septin filaments thus serve an important function in scaffolding the axon/myelin-unit, evidently a late stage of myelin maturation. We propose that pathological or aging-associated diminishment of the septin/anillin-scaffold causes myelin outfoldings that impair the normal nerve conduction velocity

Microstructure Characterization with a Pulsed Laser Ultrasonic Source

Localized heating produced by absorption from a pulsed laser provides an efficient noncontacting source of ultrasonic waves in materials. This paper describes the results of experiments conducted to illustrate the feasibility of this type of source fot microstructure characterization in metal and ceramic materials. Piezoelectric and capacitive wide bandwidth detection transducers have been used to record attenuation and scattering in these materials for comparison with the conventional pulse echo technique. The laser source was found to be art efficient, versatile, and wide bandwidth noncontacting source

Elastic Wave Scattering from Multiple Voids (Porosity)

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 which does not require ultrasonic echo returns from an opposite face of the sample in order to be useful. At present, the work is limited to dilute porosity concentrations. Reasons for this limitation will become clear in the paper. With additional effort it is expected that this limitation can be removed and the work extended to larger concentrations