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Vol 52, No 1 (2016)
- Year: 2016
- Articles: 6
- URL: https://journal-vniispk.ru/1061-8309/issue/view/11279
Acoustic Methods
Ultrasonic testing on a singly reflected beam using sparse antenna arrays and 3D echo-signal processing
Abstract
Testing of welded joints in the main shutoff valves (MSVs) of the first circuit of a ВВЭР-440 reactor plant is impeded due to the high structural-noise level and the necessity of using pulses that are singly reflected from the tilted bottom of a branch pipe. Testing on a longitudinal wave leads to the appearance of false reflections, which are formed by pulses at a transverse wave, in the reconstructed image. Since the amplitude of false reflections can be commensurable with the amplitude of reflections that were obtained at longitudinal waves, the analysis of such images may be hampered. To increase the quality of an image, it is proposed to record echo signals using sparse antenna arrays and use 3D processing of echo signals. Numerical and model experiments showed that this approach increases the frontal resolution in the additional plane by several times and reduces the amplitude of false reflections, thus making it possible to increase the sensitivity and reliability of expert ultrasonic testing of the principal shutoff valve.
1-13
A correction factor for the amplitude adjustment for the pulse echo ultrasonic inspection of components with curved surfaces
Abstract
On the basis of analyzed factors that lead to the amplitude variation of an echo signal from identical reflectors in a quality-control sample and a test sample with curved surfaces, the correction factor for the amplitude adjustment is represented as the product of several factors. Calculation methods are proposed for the components of the correction factor for the case of a curved entry surface of an arbitrary shape and a position relative to the transducer.
14-22
Strength tests of samples made from carbon plastics with various monolayer packings
Abstract
The results of static strength tests of samples made from T700 carbon plastic with various thicknesses and packings of monolayers are given. The coordinates of the destruction range were determined and the loading values were chosen at which the destruction of samples is initiated. During the loading of samples, their state was monitored using the AE method and strain measurement.
23-31
Eddy-Current Methods
Flaw detection of alloys using the eddy-current method
Abstract
A subminiature transformer eddy-current transducer (ECT) that is intended for the study of different nonuniform materials, alloys, miniature parts, printed-circuit boards, and microscopic defects has been designed. A block diagram of the transducer is given and its basic technical characteristics ensuring localization of the magnetic field on areas of approximately 50 × 50 μm are stated. A scheme that uses a computer as a generator and receiver of signals from windings is proposed. It is capable of automatically changing the filtering cutoff frequency and operating frequency of the device. The designed measuring system eliminates the main drawback of eddy-current transducers (the small area of the electromagnetic field), simultaneously significantly reducing the noise level due to the use of high-quality amplifiers and filters, and searches for defects in printed circuit boards, metal–dielectric–metal-junctions, and alloys of different metals. A measurement procedure that allows one to perform high-accuracy monitoring of flaws in different alloys is described. The eddy-current transducer was successfully tested on several objects, e.g., a 5.5-μm thick Al–Mg alloy and welded seams of 5-mm thick titanium plates, as well as other objects. The dependences of the ECT signal on the flaws in these structures are given.
32-37
General Problems of Nondestructive Testing
The classification of flaws of metal materials synthesized by the selective laser melting method and the capabilities of nondestructive testing methods for their detection
Abstract
Flaws in metal parts that are typical for the selective laser melting technique are considered. The flaws are divided into four groups by the degree of their danger. The quantitative and qualitative indices of the flaws are given and the causes of their formation are described.
38-43
Contribution to the issue of evaluating the compressive strength of concrete exposed to high temperatures using the Schmidt rebound hammer
Abstract
Concrete properties change as a result of ambient conditions. The internal microstructure changes under high temperatures. As a consequence, this change affects both physical and mechanical properties of concrete and therefore the parameters determined from nondestructive testing. It was determined that for concrete exposed to temperatures in the range of 200 to 400°C the rebound number measured by the rebound hammer is approximately 9% higher after heat load than for wet concrete placed in a standard environment. Temperatures from 600 to 800°C cause a drop in the rebound number, which correlates with a decrease in the concrete’s compressive strength. A strength dependency was established for the N-type Schmidt rebound hammer expressing the relationship between the rebound number and the compressive strength of concrete exposed to heat load, which is characterized by a high correlation between variables (correlation coefficient is 0.98). To estimate the compressive strength of concrete in a structure which has been exposed by fire, can be used both the calculated strength relationship, both the calibration curves for N-type Schmidt rebound hammer calculated by manufacturer, eventually the basic curve from CSN EN 13791. If the calibration equation for N-type Schmidt rebound hammer or basic curve of CSN EN 13791 is taken, the calculated strength for the rebound numbers should be lowered using the corrective coefficient, the value of which is 0.54, respectively 0.65.
44-52