Background technology
In recent years, raising speed by a large scale along with China railways, the travelling speed of train and dead weight capacity have all obtained large increase, caused steel rail defect new form to occur thus, a large amount of rail tread shear cracks has appearred on some circuits, investigation statistics shows that its shear crack average headway is 41mm, the bigger 160mm that reaches, the general oblique development down of direction that becomes 15 °~30 ° with rail tread of crackle, when crack growth to apart from tread 6~8mm the time, the almost extending transversely and quick fracture of crackle is so preferably can identify it during to the 5mm left and right sides at crack growth, so neither excess waste can be caused, also rail fracture can be prevented.
As seen the rail tread shear crack generally section of one-tenth distributes, visual, and therefore present principal contradiction is not the problem that crackle can detect, but to the problem how shear crack that exists is estimated, promptly how the degree of depth of shear crack is made quantitative accurately.Have only exactly the degree of depth of rail tread shear crack is carried out quantitatively, could accurately grasp the operation state of rail, understand its usability, in time targetedly the shear crack rail is taked corresponding anti-breaking measure, guarantee railway operation safety, save simultaneously rail maintenance costs, prolong rail serviceable life, reduce the cost that switches tracks.
Present railway interests both domestic and external all adopts ultrasonic technology to detect the various tired defective that rail in use produces.From defect-detecting equipment, mainly be divided into large-scale steel rail ultrasonic flaw detecting car and hand propelled flaw detection dolly (comprising defectoscope and dolly), two kinds of basic identical (see figure 1)s of the method for detection that equipment adopted mainly dispose 70 °, 45 ° (or between 37 °~45 ° other angles), 0 ° of three kinds of probe.70 ° of probes are mainly used to detect rail head nuclear hinders, and 37 ° of probes are mainly used to detect the shear crack of bolt hole crackle and rail inside, and 0 ° of probe is mainly used to survey the horizontal crackle of rail inside, is used for the couple state (as shown in Figure 1) of monitoring probe simultaneously.
As seen from the above analysis, existing inspection technique mainly is various defectives of surveying rail inside, the technical skill that detects and estimate at rail tread crack can only not rely on existing configuration, and the echo amplitude of the secondaries by measuring 70 ° of probes comes crackle is carried out quantitatively.And echo amplitude is not only relevant with the size of crackle, and is also relevant with other multiple factors, as crackle orientation, surfaceness, couple state etc.Rail tread shear crack echo amplitude standard measure mainly contains following some deficiency: (1) shear crack has a strong impact on the incident of sound wave, and then influences echo height and quantitative accuracy; (2) scope of crack depth can only be provided during the echo amplitude standard measure according to echo height roughly, the concrete degree of depth of crackle can not be provided; (3) ARTIFICIAL CRACK and the actual crack in the reference block that utilizes during the echo amplitude standard measure differs greatly, and influences quantitative accuracy; (4) because echo amplitude is subjected to multiple factor affecting, the measurement result poor repeatability.
And traditional defect-detecting equipment that utilizes the TOFD principle is mainly used in the detection of weld seam, scans along bead direction during use, and the crackle of detection mainly is the crackle along bead direction, obtains the accurate degree of depth everywhere of single crackle.And the crackle that the present invention will detect mainly is the shear crack on rail surface, and this crackle exists in a large number, and is less demanding to the levels of precision of its judgement, and but requirement can be made judgement simply rapidly.And this crackle often is substantially perpendicular to the rail bearing of trend or with angled (for example perpendicular to the direction of rail, 15 °, 30 ° or other angle), and traditional defect-detecting equipment that utilizes TOFD wants must the direction of scanning be set separately at each crackle to its measurement, probe positions angle etc. is set, to sum up, no matter consider from efficient still that it all is not suitable for the quick judgement that whether the rail shear crack degree of depth is surpassed threshold value from cost consideration.
Therefore present quantivative approach can't solve the quantitative problem of rail shear crack well, can't make exactly the rail shear crack and estimating.So, need a kind of detection method and pick-up unit with low cost, can carry out qualitative assessment fast and accurately to the rail tread shear crack.
Summary of the invention
At above-mentioned deficiency of the prior art, the invention provides a kind of detection method and pick-up unit with low cost, can carry out qualitative assessment fast and accurately to the rail tread shear crack.
On the one hand, the invention provides a kind of pick-up unit that is used for the rail tread shear crack, comprise detection probe and signal processing apparatus, wherein said detection probe comprises probing shell and is arranged on the first interior probe of described probing shell, second probe and the sound insulating layer, wherein said first probe and second probe are oppositely arranged on the both sides of described sound insulating layer, and described signal processing apparatus is used to receive the signal that described second probe receives and judges that described crack depth is whether greater than the crack depth standard of setting.
Above-mentioned pick-up unit, wherein, described crack depth standard setting is 5mm.
Above-mentioned pick-up unit, wherein, described detection probe incidence point spacing is 20mm, the refraction angle of probe is 60 degree
Above-mentioned pick-up unit, wherein, the frequency of sound wave that described detection probe adopts is 5MHz, 1.5~2 wavelength of pulse width.
Above-mentioned pick-up unit, wherein, during detection, the line direction of the probe of first in the detection probe and second probe be arranged in parallel with the rail bearing of trend substantially, and scans along the rail bearing of trend.
On the other hand, the invention provides a kind of detection method that adopts the described pick-up unit of claim 1 to detect the rail tread shear crack, comprising:
A. utilize first probe towards described rail emission sound wave,
B. utilize second probe to accept the lateral sweep diffracted wave of described sound wave
C. judge in the time gate of setting and whether have diffracted wave
D. if in the time gate of setting, have diffracted wave, judge whether described diffraction wave intensity surpasses the certain strength threshold value.
Above-mentioned detection method, wherein, described time gate is corresponding to the rail tread shear crack more than the 5mm.
Above-mentioned detection method, wherein, the distance between described first probe and second probe is 20mm, the described first probe emitting sound wave frequency is 5MHz, 1.5~2 wavelength of pulse width.
Above-mentioned detection method, wherein, during detection, the line direction and the rail bearing of trend of described first probe and second probe be arranged in parallel substantially, and scan along the rail bearing of trend.
Embodiment
At first the TOFD principle is simply introduced below.
Fig. 2 is the interaction synoptic diagram of sound wave and defective.
As shown in Figure 2, when incident wave 1 incided on the crack-like defect, sound wave also can produce diffracted wave 4,5 at the tip of defective except producing reflection wave 2 and transmitted wave 3.The most advanced and sophisticated diffracted wave 4,5 that produces of defective, although its energy is well below the energy of reflection wave 2, in the echo amplitude sizing technique, generally seldom utilize, but because it is to propagating all around, do not have tangible directive property, sound wave is easier to receive, and is comprising abundant spatial positional information in its travel-time, therefore the last lower prong of travel-time that can be by measuring lower prong diffracted wave 4,5 on the defective to defective positions, and then the size of defective is carried out quantitatively.
Rail shear crack sniffer provided by the invention and method can scan along the rail bearing of trend, identify the rail surface shear crack that is higher than the safety standard that sets fast.
According to one embodiment of the invention pick-up unit of the present invention is described in detail below.
Pick-up unit in the present embodiment comprises detection probe and signal processing apparatus.As shown in Figure 3, the detection probe in the present embodiment comprises first probe and second probe, sound insulating layer and the probing shell.Wherein first probe comprises first wafer 1, first plug connector 2 and the first probe wedge 3; Second probe comprises second wafer 1 ', second plug connector 2 ' and the second probe wedge 3 '.Described first wafer 1 and second wafer 1 ' are separately positioned on the inclined-plane of the first probe wedge 3 and the second probe wedge 3 '.Described first probe and described second probe be the both sides that are arranged on described sound insulating layer 4 of symmetry substantially.And for ease of carrying and use, above-mentioned two probes and place sound insulating layer 4 therebetween to be packaged together by probing shell 6.Signal processing apparatus in the present embodiment adopts accepts the also common signal processing apparatus of shows signal.
Pick-up unit in the present embodiment is designed for and detects the degree of depth is the above rail tread shear crack of 5mm.So, reach analysis by experiment, the probe parameter of this example is preferably: Probe index spacing 20mm, frequency of sound wave 5MHz, about 1.5~2 wavelength of pulse width, refraction angle 60 degree (being meant when acoustic signals is propagated in measured workpiece and the angle between the surface of the work normal) of probe.
The pick-up unit that utilizes in the foregoing description is described below carries out the process that the rail tread shear crack detects.
For convenience of explanation, Fig. 4 (a) two probes among Fig. 3 that only schematically drawn.Shown in Fig. 4 (a), first probe, 1 and second probe 2 is staggered relatively, first probe, 1 emission sound wave, and second probe 2 receives sound wave.The wafer vibration of first probe, 1 (transmitting probe) produces sound wave, enters workpiece through sound wave behind the probe wedge, and sound wave is at first propagated and received by second probe, 2 (acceptance probes) along surface of the work, is called lateral wave.If there is crackle in workpiece, sound wave will produce diffracted wave with the crack tip effect, and diffracted wave is to propagating all around, and part energy is received by second probe 2.Because the diffraction wave trajectory is longer than lateral wave travel path,, diffracted wave received by second probe so being later than lateral wave.When the fixed distance between receiving transducer and the transmitting probe, the received time of lateral wave is fixed, and promptly lateral wave is gone up the stationkeeping that occurs at signal processing apparatus (on its signal display curtain).In like manner, because the travel-time of diffracted wave is only relevant with the degree of depth of crackle,, just can judge the degree of depth of crackle so, perhaps compare the mistiming between lateral wave and the diffracted wave by measuring the received time of diffracted wave.
Pass between the sound time difference Δ t between depth of defect d and probe half interval S, lateral wave and the diffracted wave is:
Make c
LΔ t=n λ, then following formula can be rewritten as:
C in the formula
LBe longitudinal wave velocity, λ is a wave length of sound, and n is the pulse echo periodicity, and f is a frequency probe.
Relation between the crack detection degree of depth and detection probe frequency f, detection probe half interval S and the sound wave periodicity n is as shown in table 1~table 4.From table data as can be seen, frequency probe is high more, probe half spacing is short more, the sound wave periodicity is few more (or the sound wave pulsewidth is short more), but the depth measurement degree of crackle is shallow more, otherwise, but the depth measurement degree of crackle is dark more.Because detection probe incidence point spacing (spacing between first probe and second probe) generally is about more than the 20mm, so desirable 10mm of detection probe half interval S minimum value, and the pulse width of detection probe generally can reach 1.5 λ~2 λ, if the detection probe frequency is got 5MHz commonly used, from table 1 and table 3 as can be seen, for the crackle more than the 5mm, shear crack sniffer with present embodiment can be surveyed, and the following crackle of 5mm since its lateral wave and diffracted wave overlap and can't differentiate.Promptly can judge with the shear crack sniffer of present embodiment whether rail tread opening crack depth surpasses 5mm.
When practical application, the bearing of trend along rail moves detection probe by this way: promptly the probe of first in the detection probe is parallel with bearing of trend substantially with the line direction of second probe.Like this, because the direction of rail tread shear crack is vertical substantially with the rail bearing of trend or angled with the direction perpendicular to rail, so the direction of rail tread shear crack is generally perpendicular to the direction of scanning.When the crackle more than the inswept 5mm of detection probe, as shown in Fig. 4 (b), signal processing apparatus is Δ t=n λ after receiving the lateral wave signal, will receive the diffracted wave signal.So can be by the time gate (corresponding to the diffracted wave travel-time of the above tread shear crack of 5mm) at the above tread shear crack of 5mm is set in signal processing apparatus, as long as the signal of certain strength threshold value (according to settings such as interference, signal intensities) in time gate, occurs being higher than, promptly the above crackle of 5mm appears in proof, thereby sends warning.According to concrete needs, the upper limit of the shear crack degree of depth that is detected can also be set, for example 8mm.
The table 1 crack detection degree of depth and frequency of sound wave and the relation between the sound time difference (f=5MHz, n=1.5)
S(mm) |
10 |
11 |
12 |
13 |
14 |
15 |
d(mm) |
4.5 |
4.5 |
4.7 |
4.9? |
5.1? |
5.3 |
The table 2 crack detection degree of depth and frequency of sound wave and the relation between the sound time difference (f=7MHz, n=1.5)
S(mm) |
10 |
11 |
12 |
13 |
14 |
15 |
d(mm) |
3.6 |
3.8 |
4.0 |
4.1 |
4.3 |
4.1 |
The table 3 crack detection degree of depth and frequency of sound wave and the relation between the sound time difference (f=5MHz, n=2)
S(mm) |
10 |
11 |
12 |
13 |
14 |
15 |
d(mm) |
5.0 |
5.3 |
5.5 |
5.7 |
5.9 |
6.1 |
The table 4 crack detection degree of depth and frequency of sound wave and the relation between the sound time difference (f=7MHz, n=2)
S(mm) |
10 |
11 |
12 |
13 |
14 |
15 |
d(mm) |
4.2 |
4.4 |
4.6 |
4.8 |
4.9 |
5.1 |
Adopting detection method of the present invention and pick-up unit to detect has the following advantages:
1. quantitative accuracy height
All multifactor impacts such as the examined surface state of conventional echo amplitude standard measure precision, defective orientation, blemish surface state, defect size, quantitative accuracy is relatively poor, and the quantitative accuracy of this technology is only relevant with acoustic transit time, has guaranteed that from principle this technology has higher precision and reliability.
2. detection speed is fast
The characteristics of this technology are to judge fast whether crack depth surpasses a certain limit value, needn't judge the concrete degree of depth of each bar crackle, promptly less to the degree of depth, dangerous less crackle can not considered, need only judge above this limit value, dangerous big crackle the degree of depth, therefore reduced the testing amount, saved the flaw detection worker and reached the standard grade the road occupying time.
3. simple to operate, testing cost is low
The limit value of the crackle that this technology detects is as required used this technology-specific detection probe, can detect crackle rapidly and whether surpass the limit value of setting in advance.Simple to operate, need only observe and in special time period, whether occur flaw indication on the signal processing apparatus and get final product, every defectiveness signal occurs, and then crack depth promptly surpasses the limit value of setting.And this technology needn't use special-purpose TOFD checkout equipment and scanning equipment, can save a large amount of expenses.
Though among the above embodiment, the incidence point spacing of described detection probe is 20mm, the refraction angle of probe is 60 degree, and the frequency of sound wave that described detection probe adopts is 5MHz, 1.5~2 wavelength of pulse width.But according to concrete application need, described Probe index spacing, frequency of sound wave and refraction angle can appropriate changes, for example the Probe index spacing changes in the 16mm-25mm scope, and frequency of sound wave changes in the 4MHz-7MHz scope, and refraction angle changes in 50-70 degree scope.
It should be noted last that above embodiment is only unrestricted in order to technical scheme of the present invention to be described.Although the present invention is had been described in detail with reference to embodiment, those of ordinary skill in the art is to be understood that, technical scheme of the present invention is made amendment or is equal to replacement, do not break away from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of the claim scope of the present invention.