RU2052808C1 - Ultrasonic method for detection of cracks in article hole walls - Google Patents

Abstract

FIELD: ultrasonic inspection of materials. SUBSTANCE: ultrasonic method for detection of cracks in article hole walls includes excitation of ultrasonic vibrations in article under inspection at two different angles, reception in one cycle of radiation-reception of two echo signals (from walls of hole and crack) and determination on their base of presence of defects of article. Angles of introduction-reception of ultrasonic beams and their feed directional patterns are selected from condition of obtaining maximum echo signals from cracks under detection by computing expressions so that overlapping of feed directional patterns is effected in the region of optimal angle of crack sounding, and time drift of echo signals received from crack and hole wall does not exceed the calculated value. EFFECT: higher confidence and efficiency of inspection with simultaneous simplicity of method realization. 2 cl, 2 dwg

Description

 The invention relates to ultrasonic flaw detection, and more particularly to ultrasonic testing of materials and products in the construction of which holes are provided, and can be applied to detect cracks in the walls of bolt holes in the zone of joints of railway rails.

Fatigue crack emanating from the bolt hole in the neck of the rail under an angle of about ⁴⁵ ° to the axis of the rail (53.1 defect of "Classification of defects and damages rails RTM 32 / CP-1-66". Vehicles M., 1957, p. 38), is one of the reasons for removing the rail from the track. Currently, of all defective rails removed from the track, 41% is removed due to the detection of cracks in them, developing from bolt holes. As a result of the development of such a crack, a piece of rail head with a length approximately equal to the height of the rail is punctured from the end, which can lead to the rolling stock coming off (Tyrin V.P. et al. Crack resistance of the rail in the area of bolt holes // Vestnik VNIIZhTa, 1991, N 6, s . 36-40). Therefore, the development of methods for the timely detection of these fatigue cracks is the most important task.

A known method of ultrasonic (ultrasound) control of cracks in the walls of the holes of the product with plane-parallel surfaces, in particular rails, which consists in the fact that perpendicular to the surface of the product (input angle of ultrasonic vibrations of 0 ^about ) introduce ultrasonic vibrations, take reflected from the opposite surface of the product (bottom surface ) echo signals (bottom impulse), observe the appearance of echo signals in the time interval between the probe and bottom impulses, and the presence of a crack is judged by the disappearance (or decrease) of the bottom signal and the appearance iju echo in said gap at the location of the electroacoustic transducer is not over the hole in the article.

 The known method has low reliability and is only suitable for monitoring products with equidistant surfaces and to identify highly developed cracks.

A known ultrasonic method for detecting cracks in the walls of the holes of the products, which consists in the fact that the product is voiced by two electro-acoustic transducers that emit at an angle of 0 ^about and receive pulses reflected from the bottom surface (bottom pulses) at two points at a distance from each other slightly larger than the diameter holes in the product. The presence of a crack developing from the walls of the hole is judged by the simultaneous disappearance (or decrease below a predetermined threshold) of bottom pulses in both transducers.

 The known method has low reliability and insufficient sensitivity of the control, as it allows to identify only cracks with significant dimensions, the projection of which extends beyond the projection of the hole. In addition, with a slight difference in the parameters of the product’s holes from the nominal values or a violation of the roundness of the hole (for example, due to wear, the cylindrical hole takes an ellipsoidal shape), the flaw detector indicators may be falsely triggered and the product re-cast.

 A known method of ultrasonic quality control of assembly of parts connected on a cylindrical surface with an interference fit, namely, that emitting and receiving inclined transducers with parallel acoustic axes are installed on the surface of the product, they emit ultrasonic (ultrasonic vibrations at an angle to the cylindrical surface and take transverse ultrasonic vibrations, transformed from inhomogeneous surface vibrations running around the hole, sequentially install the specified pair of transducers on loskoparallelnye surface so that ensounding carried out in opposite directions. The quality of the assembly is determined by the arithmetic mean of the amplitudes obtained for sounding with each of the surfaces.

 The known method, although close to the claimed invention, but has several disadvantages and, in addition, is not suitable for detecting cracks in the walls of the holes of the product. The method requires two-way access to the product. As experimental studies show, the amplitude of the received signals generated from the wave propagating around the cylindrical surface of the hole has a very small value in comparison with the echo signal from the surface of the hole wall and significantly depends on both the diameter of the hole and the state of the hole surface. In real situations, the wall of the hole of the product may have microcracks and a rusted surface, which completely excludes the reception of the wave of propagation and the implementation of the known method.

The closest to the claimed technical solution and adopted for the prototype method is a method for detecting cracks in the walls of the holes of the product, used to detect cracks from the walls of bolt holes in the area of the butt pads of rail rails by defectoscopy cars of foreign companies and domestic development. The known method consists in the fact that in the controlled product at an angle to the surface of the product emit pulsed. h. vibrations, take ultrasonic vibrations reflected from the surface of the hole and a possible crack, and judging by their temporary position relative to the probe pulse, as well as by changing this position as the transducer moves, a crack develops from the hole wall. The known method allows you to identify these cracks at a fairly early stage of development, however, is difficult to implement, since it requires analysis of the temporary position of the echo signals from the walls of the hole and from possible cracks in several radiation-receiving cycles of ultrasonic vibrations. To create the possibility of this analysis, type B scanning is used (in the coordinates of the propagation time t _{p of the} ultrasonic vibrations in the product and the travel time t _{x of the} receiving-emitting system over the surface of the controlled product) with the brightness modulation of the CRT beam when echo signals appear and this ultrasound is recorded on a specific storage medium (on film or paper tape). Memorization and analysis of the temporal positions of the received echo signals in several radiation-reception cycles of ultrasonic vibrations are also possible with the help of modern electronic computing means (for example, computers). Sounding of the walls of the hole with potential cracks only at one fixed angle results in a low reliability of control, since the maximum echo signal from the crack is formed when sounding with ultrasonic beam, the acoustic axis of which is oriented normally to the surface of the crack.

 The known method has insufficient performance and low noise immunity, since the requirement to analyze the echo signals in several cycles of radiation-reception (in tens or more) for their subsequent analysis limits the speed of control (especially with high-speed monitoring of rails with the help of flaw detectors) and can lead to when receiving interference pulses in several cycles instead of echoes from cracks to product rejection.

 The purpose of the invention is to increase the reliability and performance of the control and simplify the implementation of the method for detecting cracks in the walls of the holes of the products.

This goal is achieved by the fact that in the controlled product at an angle to the scanned surface of the product, pulsed ultrasonic vibrations are excited, during the movement of the receiving-emitting transducer, the holes and cracks reflected from the walls are received, echo signals are measured, their parameters are measured and the defectiveness of the product is determined from them. Carry out additional radiation and receiving ultrasonic vibrations at a different angle that differs from the first by a certain amount. The presence of cracks is judged by the reception in one cycle of radiation-reception of two echo signals, the time shift between which does not exceed the calculated value. Ensure the coincidence of the points of emission and reception of ultrasonic vibrations at both angles. The input angles α ₁ and α ₂ and the opening angles 2Φ ₁ and 2Φ _{2 of} ultrasonic rays are selected from the condition for obtaining maximum echo signals from the desired cracks according to the relations:
α ₁ 1/2 (θ + A), 2Φ ₁ ≥ A θ (1)
α ₂ 1/2 (θ + B), 2Φ ₂ ≥ θ B. (2) The time shift between the received echo signals (from the walls of the hole and from the crack) does not exceed
Δt≅ 2R / C, (3) where C is the speed of propagation of ultrasonic vibrations in the product;
θ angle of the preferred orientation of the cracks relative to the longitudinal axis of the product;
R is the radius of the hole in the product;
Δt time interval between received echoes;
A arctan (tanθ + D) (4)
In arctan (tanθ D) (5) where D R / h _c cosθ
h _{c the} depth of the center of the hole in the product.

 In FIG. 1 shows the sounding scheme of the product and the parameters of the emitted ultrasound beams; in FIG. 2 temporary position of the echo signals when voicing a hole with a radial crack.

 The method of ultrasonic detection of cracks in the walls of the holes of the products is implemented as follows.

From the surface of the controlled product 1 (Fig. 1) with an opening 2 and radial cracks 3 and 4, ultrasonic vibrations in the form of beams 7 and 8 are excited using emitters-receivers 5 and 6. During the movement of the system, consisting of interconnected transducers 5 and 6, along the surface of the product 1, the ultrasonic beams 7 and 8 successively sound a crack 3, the wall of the hole 2 and a crack 8. The parameters of the receiving-emitting system (input angles α ₁ and α _{2 of the} ultrasonic beams 7 and 8 and the angles 2Φ ₁ and 2Φ _{2 of} opening these beams) are selected in such a way as to ensure the reception of two echo signals 9 10 (Fig 2). In one cycle-receiving radiation from the walls of the holes 2 and 3 from cracking or 4. When input angles α ₁ and α ₂ account for a preferred orientation of the radial cracks 3 and 4, the angle θ relative to the longitudinal axis of the article (FIG. 1) and parameters h _{c the} depth of the center and R is the radius of the hole in the product. 0 the presence of a crack developing from the wall of the hole is judged by the appearance of two echo signals with amplitudes above the threshold level 11 in a given time interval 12 relative to the probe pulse 13 having a time shift between themselves of no more than the calculated value Δt (Fig. 2).

 When moving the system of electro-acoustic transducers 5 and 6 over the surface of the product 1 above a defect-free hole 2, the wall of the hole will also be sequentially voiced by ultrasound beams 7 and 8. However, for any position of the transducers 5 and 6 relative to the hole in each radiation cycle, only one echo pulse will be received, which indicates the absence of cracks near the hole and the defect-freeness of the controlled product.

If necessary, identify cracks oriented at an angle θ + π / 2 with respect to that adopted in FIG. 1 of the longitudinal (horizontal) axis, it is possible to deploy a system of transducers 5 and 6 by 180 ^° , or to excite and receive ultrasonic vibrations using an additional pair of transducers 5 'and 6' (Fig. 1). During continuous testing of products with holes, the orientation of the cracks from which is not known in advance, it is advisable to control using two pairs of transducers 5-6 and 5'-6 ', emitting ultrasonic vibrations in mutually opposite directions.

Due to the fact that the opening angles of excited ultrasound beams have a certain sector, crack detection by the claimed method will be carried out not only at angles θ and θ + π / 2, but also at other angles practically throughout the entire generatrix of the hole, excluding the lower quarter. When the crack base is located near the reflection point of ultrasonic vibrations from the surface of the hole wall, it is possible to obtain double echo signals (in one radiation-reception cycle) even when voiced by one of the transducers. For example, for vertically oriented cracks propagating from the upper wall of the hole, two echo signals are received in one radiation-reception cycle by sounding by one of the transducers, for example, with an input angle α ₁ Naturally, the time interval between received echo signals ( from the wall of the hole and crack) is less than the time value determined by expression (3). The inclusion of an additional transducer (taking into account the introduction of ultrasound rays α ₂ ) significantly expands the area of the hole wall, in which echo signals from possible radial cracks are recorded, while receiving reflections from the hole wall. The presence in the radiation patterns of transducers with input angles α ₁ and α _{2 of a} common section (sector), including the angle α _opt optimal sounding of cracks of the preferred orientation θ, allows one to obtain the maximum echo signal from the desired defects, comparable or greater than the echo pulse from the hole wall. This allows you to set the threshold 11 (U _then ) amplitude selection of echo signals at a sufficiently high level (Fig. 2), which increases the noise immunity and reliability of the control.

The derivation of expressions (1-5), allowing to determine almost all the parameters of the receiving-emitting system, is based on the following premises:
for maximum echo signal from the crack must orient the ultrasonic beams at the optimum angle α _ort providing beam fall on the reflective crack plane at an angle close to ⁹⁰ °. In this case, the angle of beam entry should be close to the angle θ of the crack (the angle θ is counted from the longitudinal axis of the product, and the angle α, as is customary in ultrasonic inspection, from the normal to the surface being repaired), i.e. α _ort ≈ θ;
in order to receive echo signals from the crack and from the wall of the hole in one radiation-receiving cycle, the transducers 5 and 6 must ensure the simultaneous passage of at least one beam within the radiation pattern of one of the transducers through the center of the hole, of the second transducer, the beam incident on the crack surface at an angle of 90 ^about ;
to identify cracks at an early stage of development, i.e. when its dimensions do not exceed several millimeters, the condition for simultaneous scoring is mandatory: an angular reflector transformed by the crack root and the hole wall by one of the transducers, and the other transducer, the second point on the hole wall located on a conditional line passing through the ultrasound ray entry point and the center of the hole ( this case is shown in Fig. 1);
when the crack is oriented at any angle θ relative to the longitudinal axis of the product and the crack is voiced at an angle of 90 °, ^the distance between the two reflection points on the surface of the hole and the crack does not exceed the radius R of the hole.

(θ+A), 2Φ≥A-θ (6)
α₂=

(θ+B) 2Φ₂≥θ-B (7) где: A arctg (tgθ + Д) (8)
В arctg (tgθ Д) (9) а Д коэффициент, зависящий от параметров отверстия (радиуса R и глубины залегания центра h_ц) и трещины (угла θ ориентации ее относительно продольной оси изделия), причем
Д R/h_ц ·cos θ (10)
По физическому смыслу коэффициенты А и В представляют собой минимально необходимые крайние лучи в пределах диаграмм направленности преобразователей 5 и 6 (на уровне, определяющем уровень амплитудного порога 11). Как следует из изложенных предпосылок, в секторе углов УЗ пучков 7 и 8 должны содержаться углы α_iθ Поэтому можно принять, что для УЗ пучка 8 как минимум одним из крайних (верхний на фиг. 1) лучей должен быть угол α_В2 θ а нижний угол сектора пучка 8 определяется углом α_Н2 В. Выражение (9) для В получается из решения треугольника аов при известных R, h_ц и заданном угле α_В2 θ (фиг. 1).Based on the listed prerequisites based on geometric acoustics (Fig. 1) and the physical foundations of ultrasonic flaw detection, the following expressions (6-10) are obtained for calculating the desired parameters. The angles α ₁ and α ₂ input ultrasound rays and, respectively, the angles of their disclosure 2Φ ₁ and 2Φ ₂ :
α ₁ =

(θ + A), 2Φ≥A-θ (6)
α ₂ =

(θ + B) 2Φ ₂ ≥θ-B (7) where: A arctan (tgθ + D) (8)
In arctan (tanθ D) (9) a D is a coefficient depending on the parameters of the hole (radius R and the depth of the center h _c ) and the crack (angle θ of its orientation relative to the longitudinal axis of the product), and
D R / h _q cos θ (10)
In the physical sense, the coefficients A and B are the minimum necessary extreme rays within the radiation patterns of transducers 5 and 6 (at a level that determines the level of the amplitude threshold 11). As follows from the above assumptions, the angles α _i θ should be contained in the sector of the angles of ultrasound beams 7 and 8. Therefore, we can assume that for ultrasound of beam 8 at least one of the outermost (upper in Fig. 1) rays must be angle α _B2 θ and lower the angle of the beam sector 8 is determined by the angle α _H2 B. Expression (9) for B is obtained from the solution of triangle aov for known R, h _c and a given angle α _B2 θ (Fig. 1).

Similarly, the extreme rays A and B of the ultrasound beam 7 and 8 and assuming that their radiation patterns are axisymmetric in accordance with expressions (6) and (7) as a half-sum of the values of the extreme angles of the beam, we obtain the values of the input angles of the ultrasonic beam α ₁ and α ₂ , and as the difference between the extreme values of the sectors, the angles 2Φ ₁ and 2Φ _{2 of the} disclosure of beam patterns.

The condition determining the maximum possible time shift Δt between the echo signals is obvious from the analysis of the premises. The lower limit follows from the possibility of unambiguity of separation of the two echo signals and is determined mainly by the duration τ _{3 of the} probe (and hence the echo pulse. For modern flaw detectors, Δt _min ≈τ ₃ is 1-3 μs.

 The main idea of the claimed method is the simultaneous reception of two echo signals of approximately the same amplitude in one radiation-reception cycle from a defective hole by forming an appropriate radiation pattern containing an ultrasound beam (sector), providing sounding of a possible crack at an optimal angle. In the claimed technical solution, this problem is solved using two electro-acoustic transducers that emit and receive ultrasonic vibrations at two different, mutually spaced angles. The radiation patterns of these transducers have a mutually overlapping section containing the optimum sound angle of the crack, and the width of the radiation patterns of each of the transducers has a linear aperture at the depth of the hole equal to or slightly larger than the radius of the hole. This ensures reliable reception of double echo signals (from the hole wall and the crack plane) with sufficiently large and approximately the same amplitudes for any direction of crack development (up or down from the hole wall).

This problem can also be solved with the help of a single transducer having a wide enough opening (from α _Н2 to α _В1 ) and containing an angle α _ort θ within the radiation pattern. However, this does not provide simultaneous reception of echo signals from a crack and from a hole wall with approximately equal amplitudes. The echo from the crack will be many times smaller than the echo from the wall of the hole. This will require a sharp decrease in the threshold level 11 (Fig. 2) of the amplitude selector of double pulses and will lead to a decrease in noise immunity and reliability of the control results. Obtaining sufficiently wide radiation patterns of ultrasonic transducers is usually achieved by reducing the linear dimensions of the radiating element (piezoelectric plate), which sharply reduces the intensity of the emitted and received oscillations. This further reduces the noise immunity and reliability of the control. As experimental studies show, when trying to expand the radiation pattern by known methods, the negative factor is also that the levels of the side lobes of the diagram increase, which leads to the reception of interfering signals (in particular, caused by surface waves), leading to the appearance of second pulses in the expected time zone selection when voicing defect-free holes. This factor virtually eliminates the implementation of the method for isolating cracks from the walls of the holes using a single transducer with a wide radiation pattern.

 Therefore, in the inventive method, two transducers are used with combined radiation-reception points and providing excitation of ultrasonic vibrations at two different angles. Overlapping their radiation patterns in the region of the optimal sounding angle of possible cracks helps to summarize the intensities of the emitted vibrations in this sector of the angles and to receive echo signals of sufficient amplitude from the cracks even under adverse conditions (for example, with a diffuse surface of the crack or when its orientation deviates from the expected). In this regard, in all real situations, the amplitudes of the echo signals from cracks and from the walls of the hole are approximately the same and, as the experiment shows, for bolted holes of rails with cracks, their difference is no more than 8 dB.

As an example, let us calculate the parameters of the sounding system for implementing the proposed method for monitoring railroad tracks (detecting cracks near the bolt holes of the joints) for the following initial parameters: radius of the bolt hole R 17.5 mm; the depth of the center of the hole h _c 83.5 mm; the angle of the predominant orientation of the cracks θ 45 ^about ; the propagation velocity of shear ultrasonic vibrations in steel C 3260 m / s.

The calculation using expressions (6-10) gives the following values: coefficient D in accordance with (10) has a value of 0.296; angles A and B in accordance with expressions (8) and (9) are: A 52.35 ^about ; B = 35.15 ^o ; the input angle α _{1 of the} first ultrasonic beam and its opening angle 2Φ ₁ in accordance with (6): α ₁ 48.7 ^o ; 2Φ ₁ ≥ 7.35 ^o ; input angle α ₂ and 2Φ ₂ in accordance with (7): α ₂ 40.1 ^about ; 2Φ ₂ ≥ 9.85 ^about .

Angles disclosure 2Φ main lobe of ultrasonic beams from the top usually limited frequency applied ultrasonic vibrations of piezoceramic plates and standard sizes for typical piezoelectric transducer at a frequency of 2.5 MHz and a prism made of organic glass does not exceed ^about 10-12 (Gurvich AK Kuzmin A I. Reference patterns of seekers of ultrasonic flaw detectors. Kiev: Technique, 1980).

 The time shift between the echo signals (from the walls of the hole and the crack) does not exceed Δt≅ 10.7 μs.

The values obtained are in good agreement with experimental data obtained from ultrasonic railroad rail inspection of type F 50 with the actual crack length of 3.8 mm and an angle of ^about θ≈43 bolt hole.

The implementation of the claimed method in the practice of ultrasonic testing of products does not cause any particular difficulties and can be carried out using standard piezoelectric inclined transducers. To implement the method in the considered example, a special converter was made, consisting of two organic glass prisms riveted together on the side end face with angles α ₁ 39 ^о and α ₂ 32 ^о calculated in accordance with Snell's formula. TsTS-19 piezoelectric plates with dimensions of 8 x 12 mm are glued to prisms at a frequency of ultrasonic vibrations of 2.5 MHz. In the process of gluing prisms, the exit points of ultrasonic vibrations of the prisms are combined.

 The possibility of excitation of ultrasonic vibrations by other known methods is not excluded, for example, by means of an electromagnetoacoustic (EMA) conversion or a laser.

The proposed ultrasonic method for detecting cracks in the walls of the holes of the product and the calculated expressions are verified experimentally on models and real cracks developing in the walls of the bolt holes of railway rails. It was found that the sensitivity of the method is very high and allows you to identify cracks at an early stage of development (from 1.5 mm or more), while known methods are detected when their length is exceeded 5-10 mm. Very reliably detected cracks developing in virtually all directions (normal to the rolling surface, along the longitudinal axis of the rail, and the like) other than the lower wall of the hole with a sector angle of about 15 ^o. At the same time, according to statistics, in particular in rails, cracks developing from the bottom of the hole are very rare (not more than 0.03% of all defects). Moreover, the possibility of their detection by the proposed method with the help of ultrasound rays that have undergone a single reflection from the sole (bottom) of the rail is not ruled out.

 The ability to recognize signals from defects by the appearance of paired echo pulses in one radiation-reception cycle allows increasing the control speed to 90 km / h. At the same time, the arrangement of the ultrasonic beams emitted in the manner indicated in the proposed method allows one to confidently receive paired echo signals of approximately the same amplitude in several radiation-receive cycles even with small cracks and thereby increase the noise immunity and reliability of the control. A fairly simple sign of product defectiveness is the appearance of two pulses in the same radiation-reception cycle with a known time offset relative to each other, which significantly simplifies the processing of received signals compared to the prototype, does not require the development of a B scan and multi-cycle analysis as in the prototype. This allows you to implement the proposed method using a typical ultrasonic flaw detector with some improvement of the automatic defect signaling unit (ASD) by incorporating a pair of pulse pulses into it.

Claims (2)

 1. ULTRASONIC METHOD FOR DETECTING CRACKS IN WALLS OF PRODUCT HOLES, which consists in the fact that in the controlled product using the receiving-emitting transducer at an angle to the surface of the product in the direction of the hole, pulse ultrasonic vibrations are excited, the receiving-emitting transducer is moved along the surface of the product, -signals from the walls of the holes and cracks, measure the parameters of the received echo signals and determine from them the defectiveness of the product, characterized in that they additionally excite The oscillations at the excitation points of the former, but at an angle different from the angle of their entry, indicate the presence of a crack by the appearance of echo signals from the walls of the hole and crack in one cycle of radiation-reception, the time shift between which does not exceed the calculated value. 2. The method according to claim 1, characterized in that the input angles and the opening angles of ultrasonic rays are selected from the conditions for obtaining maximum echo signals from cracks in the ratios
α ₁ = 1/2 (θ + A), 2Φ ₁ ≥A-θ,
α ₂ = 1/2 (θ + B), 2Φ ₂ ≥ θ-B,
and the time shift between the received echo signals in one cycle of radiation-reception of oscillations does not exceed
Δt≅ 2R / C,
where α ₁ and α ₂ are the angles of the input vibrations;
2Φ ₁ and 2Φ ₂ are the angles of disclosure of ultrasonic rays, respectively;
θ is the angle of preferred orientation of the cracks relative to the longitudinal axis of the product;
Dt is the time shift between the echo signals in one cycle of radiation-reception of oscillations;
R is the radius of the hole in the product;
C is the propagation velocity of ultrasonic vibrations in the product;
A and B are the angular coefficients defined by the expressions
A = arctan (tanθ + D),
B = arctan (tanθ-D),
where D = R / h _c • cosθ,
h _c - the depth of the center of the hole in the product.

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