SAFT imaging of flaws in the rail base blade with consideration of multiple reflections of an ultrasonic pulse from the boundaries of a test object

The possibility of obtaining images of type-69 flaws in blades of the railroad rail base is considered. For this purpose, a modification of the SAFT algorithm is proposed, in which, during the calculation of echo-signal delays, multiple reflections of an ultrasonic pulse from the rail boundaries are taken into account. The Fermat principle is used to calculate the delay times. Typical acoustic schemes, each of which can be used to obtain partial flaw images, are determined. Combining the partial images in a final image allows the detection of type-69 flaws. It is shown that the proposed algorithm can be applied for obtaining type-69 images in P65 railroad rails.     

Obtaining flaw images that take the effect of multiple ultrasonic pulse reflections from the boundaries of a test object into account

The problem of obtaining flaw images from echo signals multiply reflected from the boundaries of a test object and modifications of the FT-SAFT and SAFT algorithms for obtaining flaw images in a test object with plane-parallel boundaries are considered. The reason that a transducer operating on transverse waves in the transceiver mode cannot yield information on flaw location depth is stated. It is shown that the detecting signals in the double-scanning mode, obtaining a set of partial images by the SAFT method, and combining them into a final image allow one to solve this problem. To obtain a combined image, the moduli of partial images were summed and their median was calculated. Because of difficulties in determining the velocity of sound and the thickness of a particular object, the coherent summation, which is potentially the most efficient combining technique among the considered ones, does not allow one to obtain a high-quality image. The results of a numerical simulation of the procedure of obtaining images of point defects are presented. The results of model experiments aimed at obtaining an image of a 1-mm-deep groove in a 20-mm-thick metal slab are presented as well. It is shown that measuring echo signals in the double-scanning mode and obtaining images by the DS-M-SAFT method make it possible to determine the flaw location depth.     

Determining the flaw type from images obtained by the C-SAFT method with account for transformations of wave types upon reflections of ultrasonic pulses from the irregular boundaries of a test object

The application of antenna arrays (AAs) for obtaining flaw images during automated non-destructive testing is considered. The conventional technique of using an AA as a phased AA has a number of drawbacks. An alternative approach is proposed in which echo signals are registered using an AA operating in the double scanning mode, and a modified algorithm of the combined SAFT, which takes into account multiray ultrasound propagation with consideration of transformations of wave types upon reflections from irregular boundaries of a test object, is used to obtain flaw images. The results of testing a specimen with a model of a volumetric flaw in the form of a 2-mm-diameter side hole drilled at a depth of 12 mm and a specimen with a crack model with a tip at a 12-mm depth are presented. Both specimens have rough bottoms. The obtained images allow determination of not only the dimensions and locations of flaws, but also their type.     

Simultaneous measurement of the velocity of an ultrasonic shear wave and the thickness of a test object with plane-parallel boundaries using two antenna arrays

Methods for the determination of the unknown velocity of the propagation of shear US waves and the unknown thickness of a test object were considered. Two antenna arrays working in the double-scanning mode, where echo signals are recorded, which were emitted and received by all pairs of antenna-array elements, were suggested. Antenna arrays on prisms were mounted on the test-object surface towards each other. An algorithm for the treatment of measured echo signals was designed using a method that is similar to the least-squares method. The use of the algorithm enables one to simultaneously determine the sound velocity and thickness of a test object with plane-parallel boundaries with an exactness greater than 0.5%. In this article, the factors were studied that affect the exactness of measurements and methods of their elimination or minimization. The results of numerical experiments and the use of the method on three samples relative to measurements using an IN-5101A instrument are given.     

Thermoelastic problem of friction of plane-parallel layers with allowance for nonstationarity of thermal processes

An unbound quasistatic thermoelasticity problem of the friction of plane-parallel layers with allowance made for their wear is considered. The exact solution of the problem for the transient thermal contact of layers is obtained. The criteria of the thermal-force stability of a tribosystem for various thermal models are studied.     

A local method for loading a tested object during acoustic-emission diagnostics

A new acoustic-emission diagnostics method in which there is no need to load an entire structure has been studied. This method of monitoring (as a conventional acoustic-emission method) is based on making a deformation of the tested surface; however in this case, the load is applied to a preliminarily chosen site of the tested object in the most dangerous area.     

Restoring the image of reflectors using the C-SAFT method during multiple reflection of echo signals from the boundaries of a cylindrical inspection object

A modified method of combined SAFT (C-SAFT) for restoring the images of reflectors is considered; it allows the multiple reflection of a pulse from the boundaries of the wall of a cylindrical inspection object. To verify the efficiency of the proposed algorithm, images of a crack were restored from echo signals that were calculated using the CIVA software package, which is intended for modeling the propagation and scattering of ultrasonic pulses. It was shown in a model experiment that the consideration of changes in the pulse phase during reflection from the inspection-object boundaries at various incident angles of an S-wave in the image-restoration algorithm increases the frontal resolution by more than two times. The consideration of five reflections from the inspection-object boundaries made it possible to obtain images of reflectors by the M-C-SAFT method using many acoustic schemes. The images allow one to determine the type of defects, as well as their dimensions and location in the depth of the wall of a pipeline that is 720 mm in diameter.     

Detection of flaws in the railhead by the mirror method under the condition of multiple reflection of ultrasonic oscillations

Issues of detection of flaws in the railhead by the echo and mirror methods are considered. The influence of the degree of rail wear on the path of propagating ultrasonic beams has been studied. It has been shown that, owing to multiple reflection of ultrasonic beams inside the railhead, transverse cracks can be reliably detected on both the working and nonworking faces of the railhead. Computer-simulation-based calculations are confirmed by data on detection of actual flaws in the railhead. The results are used in the development of sounding systems for AVIKON-type multichannel demountable ultrasonic flaw detectors for total inspection of rails.     

Experimental study of the features of the method for illuminating the surface of a tested object for measuring displacements with laser interferometers

This paper presents the results of experimental studies of the features of a new method for measuring displacements of a tested object’s surface with a laser interferometer: a method of illuminating the object’s surface, the theoretical and computational substantiation of which is presented in detail in [1]. Recommendations for using this method during diagnosis of the engineering state of load-bearing structural elements are proposed.     

Selection of the separation between source and tested object for a gamma-absorption densimeter in the divergent-beam configuration

Formulas estimating the effect of gamma-beam divergence on the systematic and statistical components of errors in density measurements have been obtained. An engineering method for selection of the separation between the source and tested object for a gamma-absorption densimeter operating in the configuration of divergent beam with amplitude compensation for scattered radiation has been developed. We have estimated the efficiency of the densimeter using an isotopic gammasource with the error in density measurements prescribed on the stage of design.     

超声车铣圆环斜槽传振杆设计

针对超声波车铣加工,设计了一种谐振频率30 kHz的圆环斜槽传振杆,阐述了30 kHz圆环斜槽传振杆纵扭共振的基本原理。利用有限元分析方法,计算了圆环斜槽传振杆的尺寸和斜槽的位置以及力学特性,并比较了有限元分析结果和理论结果。有限元分析结果比理论值结果小,是由于将圆环斜槽传振杆作为理想的模型。用阻抗分析仪对圆环斜槽传振杆进行了测试,并比较了测试结果和有限元分析值,偏差较小,相对偏差符合要求。实验测试结果表明,测试参数和设计结果一致。     

Reconstruction of images of reflectors using the correlation method at an arbitrary number of reflections of an ultrasonic pulse from the boundary of a test object that consists of regions with different acoustic properties

An algorithm for reconstructing images of reflectors from echo signals that propagate in a test object, which consists of several regions with different acoustic properties, is considered. The ray trajectories are calculated using the method of direct construction of the family of rays that escape from the point where a transmitter is located but not the Fermat variational principle. After the family of rays is constructed, their belonging to a certain acoustic scheme can be analyzed and the approximation of the calculated delays on the spatial mesh of the image reconstruction region (IRR) can be performed. This will allow the reconstruction of both the pulse travel time from the transmitter to any point in the IRR and back to the receiver and the attenuation of the pulse amplitude caused by the divergence, reflection, and refraction effects at the boundaries of the regions that constitute the test object. Numerical and model experiments show the working capacity of the proposed algorithm for reconstructing reflector images.     

Cooperative manipulation of a virtual object by multiple remote users

In this paper, we explore the issues of force display in the cooperative virtual environment shared by multiple users distributed over the network with heterogeneous hardware platforms. The proposed method is to cope with the problem of small time delay and the difference of sampling rate in the distributed configuration. In the proposed approach the interaction forces of the participants are just treated as the independent sources of acceleration. Thus the action of a participant simply changes the acceleration of the virtual object and consequently the states of the virtual object will be updated. When the updated states are reported to all the participants, the information on the time of state changes is delivered, too. Employing the discrete state information updated by the other users, each user modifies his own virtual environment and pseudo-realtime simulation can be realized. Excluding the software interface and the communication technique, it is proposed the simulation method for the operation of respective users and the way of calculating the driving input to the display device. For experimental verification we construct a cooperative virtual environment shared by two remote users and outline the results of experiments.     

Analysis of ultrasonic waves excited in a metal plate by nanosecond laser pulses

Laser excitation of ultrasonic waves in ferromagnetic plates has been experimentally studied. The obtained results can be recommended for use in the development of methods and equipment for testing thin-walled metal articles.     

Numerical simulation of beam unloading from elastic linkages in a plane-parallel medium flow

The process of profile unloading from elastic linkages in a plane-parallel flow of an incompressible medium is examined. The beam model of profile deformation is used. The parameters of the transient mode under different pause durations between linkage breaks are determined. The procedure permitting the solution of the connected problem of aeroelasticity by means of the vortex elements method used to determine the nonstationary aerodynamic loads is verified and the results of the verification are given.     

Optimization of holographic memory parameters with allowance for cross-talk

The geometric and information parameters of the page-oriented holographic memory are optimized with allowance for the cross-talk influence on the recording density and on the bit error rate.     

Generators of high-voltage pulses with a repetition rate of 50000 pulses per second

We study the schematic and mechanical features of frequency (∼50000 pulses/s) generators of high-voltage (up to 10 kV) pulses of the microsecond range. We analyze (with the purpose of decreasing energy consumed from the power network) the energy transfer process from a low-voltage discharge circuit (with insulated-gate bipolar transistors as commutators) by means of a step-up pulse transformer to the load. We implement the design of a generator with pulse front sharpening in the load (into a reactor with pulsed corona discharge) using a multigap air discharger. The maximum achieved pulse repetition rate with a sharpened front was ∼27 000 pulses/s and a voltage of ∼3 kV.     

The twisting of a transversely braced thin-walled beam with allowance for localized flange deformations

The torsional stiffness of a channel-section beam braced by evenly spaced transverse beams is studied. Previous work by Vlasov and the writer is extended theoretically to include localized deformations which take place in the flanges. A family of curves, resulting from a finite difference analysis of the flange deformations, is used in conjunction with a simple expression to predict a “reduced” second moment of area for the transverse beams from which a modified St. Venant torsional constant for the braced channel can be calculated. Experiments on a series of braced Perspex channels show good agreement with the theoretical predictions when the ratio of the length of the transverse beams to their depth is large but as the beams become “deep”, the engineer's theory of bending with the usual shear correction inadequately describes their behaviour. A correction factor, obtained from a graph based upon a finite element analysis, is used to obtain closer agreement for all length to depth ratios.