7878787878 QR of RTRI, Vol. 46, No. 2, June. 2005

PAPERPAPERPAPERPAPERPAPER

Hollow Axle Ultrasonic Crack Detection for Conventional Railway VHollow Axle Ultrasonic Crack Detection for Conventional Railway VHollow Axle Ultrasonic Crack Detection for Conventional Railway VHollow Axle Ultrasonic Crack Detection for Conventional Railway VHollow Axle Ultrasonic Crack Detection for Conventional Railway Vehiclesehiclesehiclesehiclesehicles

1. Introduction1. Introduction1. Introduction1. Introduction1. Introduction

On railway vehicles, every component is inspected incompliance with a fixed standard in order to preventbreakdown or damage. Since a failure may lead to a seri-ous accident, axles need to be inspected at the regularintervals specified. For Shinkansen vehicles, hollow ax-les with a bore diameter of 60 mm have been used to re-duce the unsprung mass since the debut of the Series 300Shinkansen cars in 1992. These axles are inspected au-tomatically through the bore with ultrasonic angle beams(see Fig. 1). On the other hand, solid axles are used mostlyfor conventional railway vehicles, though there are somecases where hollow axles with a bore diameter of 60 mmare used, for example on JR Hokkaido Series 183 and JRShikoku Series 2000 diesel railcars.

Recently, there have been calls for further automa-tion and labor saving in the inspection of conventionalrailway vehicles. If fine cracks in an axle can be detectedwith the wheelset assembled, part of the magnetic par-ticle test that is carried out by dislocating or dismount-ing wheels and other fittings can be omitted, thereby

improving axle inspection efficiency. The technique 1) thatuses grazing SH waves to detect fine cracks is difficult toapply because a high viscosity couplant is needed in or-der to transmit ultrasound.

Therefore, based on over 10 years experience withhollow axles used on Shinkansen vehicles, we developeda hollow axle and ultrasonic testing equipment that areapplicable to conventional railway vehicles. This paperprovides the results of tests on hollow axles, manufac-tured on a trial basis, carried out using this equipment.

2. Sol id axle ultrasonic test ing technique for2. Sol id axle ultrasonic test ing technique for2. Sol id axle ultrasonic test ing technique for2. Sol id axle ultrasonic test ing technique for2. Sol id axle ultrasonic test ing technique forconventional railway vehiclesconventional railway vehiclesconventional railway vehiclesconventional railway vehiclesconventional railway vehicles

The solid axle ultrasonic test for conventional railwayvehicles is now carried out with a combination of normalbeam, longitudinal wave angle-beam, and angle-beam tech-niques. An outline of the method is described in Fig. 2.

The normal beam technique positions a normal probeon an axle end face and tests the axle with ultrasound par-allel to the axial direction. However, it cannot test thepositions where the ultrasound does not reach, such as theouter end of the wheelseat. In addition, cracks at a depthof more than 10 mm at the non-fitted central part might

Kazunari MAKINOKazunari MAKINOKazunari MAKINOKazunari MAKINOKazunari MAKINOResearcher,

Jiro YOHSOJiro YOHSOJiro YOHSOJiro YOHSOJiro YOHSOSenior Researcher,

Hiroshi SAKAMOTOHiroshi SAKAMOTOHiroshi SAKAMOTOHiroshi SAKAMOTOHiroshi SAKAMOTOAssistant Senior Researcher,

Hiromichi ISHIDUKAHiromichi ISHIDUKAHiromichi ISHIDUKAHiromichi ISHIDUKAHiromichi ISHIDUKASenior Researcher, Laboratory Head,

An ultrasonic testing technique was studied for a hollow axle with a 30 mm bore di-ameter manufactured on a trial basis for conventional railway vehicles. To compensatefor the decrease in crack detection sensitivity due to the small bore diameter, apiezocomposite focal probe was designed. It has been demonstrated that the ultrasonictesting equipment thus developed could detect artificial flaws with a depth of 0.15 mm atthe non-fitted central part and those with a depth of 0.3 mm at the inner end of the wheelseat(fitted part). The accuracy of axle inspection for conventional railway vehicles equippedwith such hollow axles will match that of Shinkansen vehicles.

KeywordsKeywordsKeywordsKeywordsKeywords: conventional railway vehicles, hollow axle, ultrasonic test, piezocomposite focalprobe

Vehicle & Bogie Parts Strength Laboratory, Vehicle Structure Technology Division

Fig. 1 Hollow axle ultrasonic testing technique forFig. 1 Hollow axle ultrasonic testing technique forFig. 1 Hollow axle ultrasonic testing technique forFig. 1 Hollow axle ultrasonic testing technique forFig. 1 Hollow axle ultrasonic testing technique forShinkansen vehiclesShinkansen vehiclesShinkansen vehiclesShinkansen vehiclesShinkansen vehicles

: Probe

: Ultrasound

Transducer

Axle

Wheel

Brake disk (or gear)

Bore

Angle-beamtechnique

Probe head(Scanning in axial directionwith rotation)6

0 m

m d

iam

.

Fig. 2 Sol id axle ultrasonic test ing technique forFig. 2 Sol id axle ultrasonic test ing technique forFig. 2 Sol id axle ultrasonic test ing technique forFig. 2 Sol id axle ultrasonic test ing technique forFig. 2 Sol id axle ultrasonic test ing technique forconventional railway vehiclesconventional railway vehiclesconventional railway vehiclesconventional railway vehiclesconventional railway vehicles

(or brake disk seat)

Axle

Wheel

Normal beam technique

Longitudinal wave angle-beam technique

Angle-beamtechnique

Brake disk (or gear)Difficult part to inspect using normal beam technique

Wedge

WheelseatFlaw

Flaw depth

Non-fitted central part

Gear seat

Outer end

Inner end

7979797979QR of RTRI, Vol. 46, No. 2, June. 2005

not be detected because of the beam spread or attenuationof the ultrasound.

The longitudinal wave angle-beam technique positionsa wedge at an appropriate angle between a normal probeand an axle end face according to each part to be inspectedsuch as the journal, the inner and outer ends of thewheelseat, the gear seat and the non-fitted central part.Then, each position is tested with an ultrasonic longitudi-nal wave, the refraction angle of which is normally 4 to 28degrees. Figure 2 also shows the test set-up for the innerend of the wheelseat. The longitudinal wave angle-beamtechnique can detect shallower cracks than the normalbeam technique, but the inspection accuracy is limitedbecause the path length (the propagation distance to theultrasound reflection source) is longer than that of theangle-beam technique explained below. The automaticultrasonic equipment for testing solid axles using the lon-gitudinal wave angle-beam technique has been introducedat some workshops for conventional railway vehicles.

The angle-beam technique transmits an ultrasonicshear wave whose angle of refraction is larger than that ofthe longitudinal wave angle-beam technique (normally 37to 55 degrees) from an axle surface to test the oppositeside of the axle surface. The path length is shorter thanthose of the normal beam and longitudinal wave angle-beam techniques, and the shear wave with a shorter wave-length is used, therefore the inspection accuracy is good.Since the probe cannot scan the positions where parts suchas a wheel, brake disk and gear are fitted, however, probesat various angles of refraction are needed to make the ul-trasound transmit from the surface where there are no fit-tings or differences in level.

As mentioned above, there are both merits and demer-its in each solid axle testing technique for conventionalrailway vehicles. To improve the efficiency and accuracyof the axle inspection drastically, it is necessary to discussthe introduction of hollow axles on both conventional rail-way and Shinkansen vehicles.

3. Bore diameter of axles for conventional railway3. Bore diameter of axles for conventional railway3. Bore diameter of axles for conventional railway3. Bore diameter of axles for conventional railway3. Bore diameter of axles for conventional railwayvehiclesvehiclesvehiclesvehiclesvehicles

Axle journal diameters on conventional railway ve-hicles are mostly either 110 mm or 120 mm. If an axlejournal with a 110 mm diameter is bored to a diameter of60 mm, as has been experienced in Shinkansen axles, thenthe bending stress at the journal is about 1.10 times thatof a solid axle. This does not pose a serious problem.However, the deflection and its angle at the journal willincrease because of the decreased stiffness of the axle asa whole. Then, fretting damage at the part where theaxle is fitted with the journal bearing inner ring or theback cover may increase as the axle rotates. It is desir-able to make the bore diameter small, in order to mini-mize fretting damage. In addition, in the case of a jour-nal bearing structured to install the front cover to theaxle end face with bolts, it is not possible to machine theaxle to a bore diameter of 60 mm because there are boltholes at the axle end face. For these reasons, we adopteda 30 mm bore diameter for hollow axles on conventionalrailway vehicles (see Fig. 3).

4. Ultrasonic testing probe improvements4. Ultrasonic testing probe improvements4. Ultrasonic testing probe improvements4. Ultrasonic testing probe improvements4. Ultrasonic testing probe improvements

4.1 Improvement of ultrasound directivity4.1 Improvement of ultrasound directivity4.1 Improvement of ultrasound directivity4.1 Improvement of ultrasound directivity4.1 Improvement of ultrasound directivity

The probe that is most commonly used for the ultra-sonic testing of hollow axles on Shinkansen vehicles has aflat transducer with a 50-degree angle of refraction. Fig-ure 4 shows a schematic view of the ultrasound propaga-tion oscillated with a flat transducer. When the bore di-ameter is 30 mm, the ultrasound is focused on and radi-ates from a point behind the part to be inspected (axle sur-face). In order to assure inspection accuracy, it is neces-sary to shape the transducer into a three-dimensionalcurved surface and focus the ultrasound on the part to beinspected.

We therefore designed the shape of the transducer tofocus the ultrasound on the part to be inspected 2). Thedesign concept of the focal transducer in Fig. 5 is outlinedbelow.(1) A lattice at the bore surface of an axle is assumed.(2) A straight line that connects each lattice and the focal

point at the part being inspected, which is the ultra-sound propagation path, is defined. The lattice andthe straight line guide the angle of refraction.

(3) The angle of incidence of the ultrasound is calculatedfrom the ratio of the ultrasound velocity in an axle tothat in a wedge and the angle of refraction defined in(2).

(4) A straight line is defined from each lattice toward thetransducer with the angle of incidence calculated in(3).

(5) When the ultrasound propagates from a focal point to-

Fig. 3 Schematic view of hollow axle for conventionalFig. 3 Schematic view of hollow axle for conventionalFig. 3 Schematic view of hollow axle for conventionalFig. 3 Schematic view of hollow axle for conventionalFig. 3 Schematic view of hollow axle for conventionalrailway vehiclesrailway vehiclesrailway vehiclesrailway vehiclesrailway vehicles

Bolt holeStamp

Axle end face

Journal bearingFretting damaged part

Inner ringOuter ring

Front cover

End cover

Bore

AxleBolt

110 mm diam.30 mm diam.

Fig. 4 Schematic view of ultrasound propagation oscillatedFig. 4 Schematic view of ultrasound propagation oscillatedFig. 4 Schematic view of ultrasound propagation oscillatedFig. 4 Schematic view of ultrasound propagation oscillatedFig. 4 Schematic view of ultrasound propagation oscillatedwith flat transducerwith flat transducerwith flat transducerwith flat transducerwith flat transducer

30 mm diam. bore

Axle center

Ultrasound focal point

Flat transducer

Part to be inspected (axle surface)

Ultrasound radiation

60 mm diam. bore

Axle center

Ultrasound focal point

Flat transducer

Part to be inspected(axle surface)

(a) Bore diameter: 30 mm (b) Bore diameter: 60 mm

8080808080 QR of RTRI, Vol. 46, No. 2, June. 2005

ward the transducer via each lattice, a set of the posi-tions where each ultrasound arrives at a certain timeis determined as the temporary shape of the trans-ducer.

(6) The phase shift by refraction or reflection is calculatedwhen the ultrasound is oscillated from each positionof the transducer shape determined in (5). The tem-porary shape of the transducer is corrected to agree inthe phase of the received wave at all positions of thetransducer, and the final shape of the transducer isdetermined.

4.2 Control of ultrasound wave shape4.2 Control of ultrasound wave shape4.2 Control of ultrasound wave shape4.2 Control of ultrasound wave shape4.2 Control of ultrasound wave shape

Piezoelectric ceramics such as lead zirconate titan-ate (PZT) are conventionally used as the material fortransducers. In this case, the damping effect of the trans-ducer is small and the flaw echo becomes a waveform ac-companied by several waves. On the other hand, fittedparts such as a wheelseat generate the press-fit echo con-sisting of multipeak waves, because there are very smallcavities caused by the surface roughness of the axle andfittings that make the ultrasound reflect. When a flaw issmall, it is difficult to distinguish the flaw echo from thepress-fit echo. If the waveform is controlled and the ul-trasound accompanying a small number of waves can betransmitted, the shape of flaw echoes becomes sharp,making it more easily separated from press-fit echoes.

It is possible to control the waveform by such meth-ods as placing damping material at the back of the trans-ducer or making adjustments to electrical circuit damp-ing, but the sensitivity of the transducer decreases at thesame time. We therefore tried to increase the sensitivityto flaw echoes in comparison with press-fit echoes by us-ing a piezocomposite transducer that combines thepiezoceramics and a polymer (damping material) and bymaking the number of accompanying waves nearly one,as shown in Fig. 6.

The piezocomposite transducer is composed ofpiezoceramics. Its edges, which are several dozen mi-crometers in length, are wrapped and formed by a poly-mer in a latticed shape. It can reduce the number of ac-companying waves with minimizing the decrease in sen-sitivity. This transducer is flexible, can be easily formedinto any shape, and is suitable for the focal transducermentioned above. In addition, its acoustic characteris-tics are close to those of a wedge for an angle probe thatis generally made of acrylic resin, and increases the sen-sitivity of an angle probe in particular.

4.3 Piezocomposite focal probe4.3 Piezocomposite focal probe4.3 Piezocomposite focal probe4.3 Piezocomposite focal probe4.3 Piezocomposite focal probe

Figure 7 shows the piezocomposite focal probe manu-factured on a trial basis, and Table 1 gives its specifica-tions. A test piece on which several kinds of artificialflaws were machined was prepared and tested with a ce-ramics probe, a piezocomposite probe and apiezocomposite focal probe, each having a 40-degree angleof refraction. A comparison of the heights of flaw echoeshas proved that the flaw sensitivity increased about 6 dBwhen a piezocomposite probe was used instead of a ce-ramics one, and about 6 dB more when a focal one wasused.

Fig. 5 Design concept of focal transducerFig. 5 Design concept of focal transducerFig. 5 Design concept of focal transducerFig. 5 Design concept of focal transducerFig. 5 Design concept of focal transducer

eAxle

Axle surface(part to be inspected)

Optimized shape of transducer(focal transducer)

Bore surface

Probe

Wedge

Angle of incidence

Angle of refraction

Lattice

Focal point

Fig. 6 TFig. 6 TFig. 6 TFig. 6 TFig. 6 Transducer types and flaw and press-fit echoransducer types and flaw and press-fit echoransducer types and flaw and press-fit echoransducer types and flaw and press-fit echoransducer types and flaw and press-fit echowaveformswaveformswaveformswaveformswaveforms

Fig. 7 Piezocomposite focal probe and its transducerFig. 7 Piezocomposite focal probe and its transducerFig. 7 Piezocomposite focal probe and its transducerFig. 7 Piezocomposite focal probe and its transducerFig. 7 Piezocomposite focal probe and its transducer

TTTTTable 1 able 1 able 1 able 1 able 1 Specifications of piezocomposite focal probeSpecifications of piezocomposite focal probeSpecifications of piezocomposite focal probeSpecifications of piezocomposite focal probeSpecifications of piezocomposite focal probe

50 m

Piezoceramics

Polymer

Item SpecificationTransducer material PiezocompositeTransducer size 15 mm x 12 mmNominal frequency 5 MHzNominal angle of refraction 40 degreesShape of contact surface Cylinder of 15 mm radius

5. Ultrasonic test on hollow axle with small bore5. Ultrasonic test on hollow axle with small bore5. Ultrasonic test on hollow axle with small bore5. Ultrasonic test on hollow axle with small bore5. Ultrasonic test on hollow axle with small borediameterdiameterdiameterdiameterdiameter

5.1 T5.1 T5.1 T5.1 T5.1 Testing equipment and test methodesting equipment and test methodesting equipment and test methodesting equipment and test methodesting equipment and test method

Figure 8 shows the ultrasonic testing equipment forhollow axles with a small bore diameter in which apiezocomposite focal probe with a 40-degree angle of re-fraction is installed. Figure 9 shows the system struc-ture. The probe head is inserted into the bore and movedin the axial and circumferential directions, and the ul-trasound transmitted from the bore surface propagatesforward (the direction to the axle center) and backward

Piezocompositetransducer

Normal transducer

Flaw echo + Press-fit echo

Press-fit echoFlaw echo

8181818181QR of RTRI, Vol. 46, No. 2, June. 2005

(the direction to the axle end).With this equipment, an ultrasonic test was carried

out on a model hollow axle with a small bore diameterthat was manufactured on a trial basis. The model axlehas artificial flaws machined in positions where cracksmay arise and is used to confirm the inspection accuracyof the testing equipment. Figure 10 shows an outline of amodel hollow axle and Table 2 shows the positions andshapes of 25 artificial flaws. The flaws on fitted partssuch as the position I-I were machined at a position 3mm inside the fit edge. After artificial flaws had beenmachined, a model gear and inner rings of gear bearingwere fitted on the gear side of the axle and a model wheeland journal bearing were fitted on the counter gear side.

Table 3 shows the conditions under which automatictesting was carried out on the model hollow axle. Themovable range of the probe head in the axial directionwas about 1,350 mm, and each half part of the axle lengthwas tested from both ends of the axle. The position of theprobe head and the testing sensitivity were adjusted us-ing the 1S flaw (a square flaw of 1 mm depth) in the posi-tion D-D on the non-fitted central part. The flaw detec-

Fig. 8 Ultrasonic testing equipment for hollow axles withFig. 8 Ultrasonic testing equipment for hollow axles withFig. 8 Ultrasonic testing equipment for hollow axles withFig. 8 Ultrasonic testing equipment for hollow axles withFig. 8 Ultrasonic testing equipment for hollow axles withsmall bore diametersmall bore diametersmall bore diametersmall bore diametersmall bore diameter

Fig. 9 Ultrasonic testing equipment systemFig. 9 Ultrasonic testing equipment systemFig. 9 Ultrasonic testing equipment systemFig. 9 Ultrasonic testing equipment systemFig. 9 Ultrasonic testing equipment system

Model axle

Elevator

Motor

Probe head

Motor controller

PC

Flaw detector

Oil pump

Head position output

PC

Flaw detector

Display

Motor controller

X-axis motor

To axle

Oil pump

I/O

sig

nals

fro

m m

otor

, en

cod

er a

nd

sen

sor

Couplant (oil)

Waveform

RS-232C

Probe head

Flaw detectiongate output

Probe

-axis motor

Control signal

A/D converter board

Motor controller board

Digital I/O board

Symbol Part

Distancefromgear-sideaxle end[mm]

Distancefromcountergear-sideaxle end[mm]

EDM-machinedartificial flaw(s)

A-A Inner end of gear-sidewheelseat 436 1464 0.3S, 0.6S, 1S; 1E

B-B Inner end of gear seat 625 1275 1SC-C Non-fitted central part 950 950 0.5AD-D Non-fitted central part 1000 900 1SE-E Non-fitted central part 1050 850 0.6SF-F Non-fitted central part 1100 800 0.5NG-G Non-fitted central part 1150 750 0.3SH-H Non-fitted central part 1200 700 0.15S

I-I Inner end of counter gear-side wheelseat 1464 4360.5N, 1N; 0.3S, 0.6S, 1S;0.3E, 0.6E, 1E, 3E

J-J Outer end of counter gear-side wheelseat 1607 293 1S

K-K Fit edge of counter gear-side journal bearing 1736.5 163.5 0.5N; 0.3S, 0.6S, 1S

1) The types of artificial flaws are described as A (all-round flaw), N (notched flaw), S (square flaw) and E (semi-elliptic flaw).2) The number in front of flaw types (A, N, S, E) indicates the flaw depth [unit: mm].

TTTTTable able able able able 22222 Artificial flaws of model hollow axle with small bore diameterArtificial flaws of model hollow axle with small bore diameterArtificial flaws of model hollow axle with small bore diameterArtificial flaws of model hollow axle with small bore diameterArtificial flaws of model hollow axle with small bore diameter

K

Gear side

Countergear side

5

(mm)

J F EGHI DC B A

K J F EGHI DC B A

Model gear

Model wheel

Axle length: 1,900

100

1,0001,000

Gear-side test zone

0

1

50

100

Journal bearing

1

92

15

0

1

10

3

0

1

95

Counter gear-side test zone

Bearing inner ring

Fig. 10 Model hollow axle with small bore diameterFig. 10 Model hollow axle with small bore diameterFig. 10 Model hollow axle with small bore diameterFig. 10 Model hollow axle with small bore diameterFig. 10 Model hollow axle with small bore diameter

Square flaw: S

Depth: a

10

Length: 2c

a/2c = 0.35

Depth: a

Semi-elliptic flaw: E

Notched flaw: N

Depth: a

8282828282 QR of RTRI, Vol. 46, No. 2, June. 2005

tor amplifier gain when the echo height of this flaw was80 percent was defined as the specified sensitivity, andthe working sensitivity was adjusted to the specified sen-sitivity +18 dB to compensate for the decrease of flawsensitivity caused by the rotation of the probe head. Thescan of the probe head was in the shape of a spiral, asshown in Fig. 11. The axial scan pitch per one rotationwas 2 mm, the data recording pitch in the circumferen-tial direction was 2 degrees, and the rotation speed was100 rpm.

5.2 Flaw detection gate settings5.2 Flaw detection gate settings5.2 Flaw detection gate settings5.2 Flaw detection gate settings5.2 Flaw detection gate settings

In ultrasonic axle testing, flaw detection gates arenormally set at every test position such as a wheelseat ora non-fitted central part, as shown in Fig. 12. Flaw de-tection gates are set around the calculated path length tothe axle surface where particular attention needs to bepaid, and only the waveform indicated within the gaterange provides useful information.

Figure 13 shows a waveform tested at the inner endof the counter gear-side wheelseat (position I-I) when anormal-type flaw detection gate is used. When this posi-tion is tested, spurious echoes from the corner of thewheelseat and its fillet are generated in addition to theflaw echoes, as shown in Fig. 14. Even if the flaw echoand the spurious echo are separated, the echoes will ap-pear simultaneously within the range of the flaw detec-

tion gate when the difference of their path lengths isshort. In addition, the height of the spurious echo isincorrectly detected as the echo height in the flaw de-tection gate if the spurious echo is more pronounced thanthe flaw echo.

Therefore, as shown in Fig. 15, a trigger gate was setin a range including the path length at any position onthe axle surface from the minimum diameter (journal) tothe maximum diameter (wheelseat). A flaw detection gateof 2 mm width was set at the first echo that was abovethe trigger gate threshold level. If we use this method,only the flaw echo whose path length is shorter than thatof the spurious echo can be detected separately when theflaw echo and the spurious echo appear simultaneouslyat the positions where spurious echoes are generated.

The path lengths of echoes detected in scanning werecompared among the several data recording points ad-joining in the circumferential direction. If there wererecording points whose path lengths varied over the range

Item Setting valueTest zone 100-1000 mm from both axle endsWorking sensitivity 18 dB above the sensitivity of 80 % echo

height of 1S flaw on the position D-D in thenon-fitted central part

Scan of probe head Spiral scanRotation speed of probehead

100 rpm (maximum: 300 rpm)

Axial scan pitch 2 mm per one rotationData recording pitch incircumferential direc-tion

2 degrees

Trigger gate range The range including the path length at anyposition on the axle surface from the minimumdiameter (journal) to the maximum diameter(wheelseat)

Flaw detection gaterange

2 mm width from the first echo that exceededthe threshold level of the trigger gate

Recording information 1) The position of probe in the axial and cir-cumferential directions2) Maximum echo height and path lengthwithin the range of flaw detection gate

Axial scan pitch: 2 mm

Data recording pitch in circumferential direction: 2 degrees

Data recording point

TTTTTable able able able able 33333 Automatic test conditionsAutomatic test conditionsAutomatic test conditionsAutomatic test conditionsAutomatic test conditions

Fig. 1Fig. 1Fig. 1Fig. 1Fig. 11 Spiral scan of probe head1 Spiral scan of probe head1 Spiral scan of probe head1 Spiral scan of probe head1 Spiral scan of probe head

Fig. 12 Normal flaw detection gate settingsFig. 12 Normal flaw detection gate settingsFig. 12 Normal flaw detection gate settingsFig. 12 Normal flaw detection gate settingsFig. 12 Normal flaw detection gate settings

Fig. 13 WFig. 13 WFig. 13 WFig. 13 WFig. 13 Waveform at position I-Iaveform at position I-Iaveform at position I-Iaveform at position I-Iaveform at position I-I

Fig. 14 Ultrasound reflection at inner end of counter gear-Fig. 14 Ultrasound reflection at inner end of counter gear-Fig. 14 Ultrasound reflection at inner end of counter gear-Fig. 14 Ultrasound reflection at inner end of counter gear-Fig. 14 Ultrasound reflection at inner end of counter gear-side wheelseatside wheelseatside wheelseatside wheelseatside wheelseat

W1 W2W3 W4

Center of ultrasound beam

Angle of refraction: 40 deg.

Wi : Calculated path length to axle surface of each part

: Flaw detection gate (set around axle surface)

Probe

90 120

20

80

40

60

100

0

Flaw echo

Spurious echo

Flaw detection gate at wheelseat

Path length of flaw echo detected.

Height of spurious echoincorrectly detected.

Path length [mm]

Ech

o h

eigh

t [

%]

Bore

Probe

40 deg.Ultrasound

Reflection at flaw

Reflection at corner or fillet

Center of ultrasound beam

Calcu

late

d pa

th le

ngth

8383838383QR of RTRI, Vol. 46, No. 2, June. 2005

Fig. 15 Echo detection technique using trigger gateFig. 15 Echo detection technique using trigger gateFig. 15 Echo detection technique using trigger gateFig. 15 Echo detection technique using trigger gateFig. 15 Echo detection technique using trigger gate

of 1 mm by less than 15 degrees, it was decided that theirdata contained those of flaw echoes that appeared aheadof the spurious echoes.

Ech

o h

eigh

t [

%]

0.15 mm depth

0.3 mm depth

0.6 mm depth

1 mm depth

Notched flaw of 0.5 mm depth

Square flaws

Displayed range Displayed range

1 mm depth

Notched flaw of 1 mm depth

1 mm depth

0.5 mm depth

Semi-elliptic flawof 3 mm depth

0.6 mm depth0.3 mm depth

Notched flaws

Square flaws

Ech

o h

eigh

t [

%]

Circum

ferential position [deg.] Distan

ce from a

xle end fa

ce [mm]

Circumferential position [deg.]

Dis

tanc

e fr

om a

xle

end

face

[m

m]

(a) Non-fitted central part (b) Inner end of counter gear-side wheelseat (fitted part)

Fig. 16 Ultrasonic test results of model hollow axle with small bore diameterFig. 16 Ultrasonic test results of model hollow axle with small bore diameterFig. 16 Ultrasonic test results of model hollow axle with small bore diameterFig. 16 Ultrasonic test results of model hollow axle with small bore diameterFig. 16 Ultrasonic test results of model hollow axle with small bore diameter

5.3 T5.3 T5.3 T5.3 T5.3 Test resultsest resultsest resultsest resultsest results

Figure 16 shows the results of testing the non-fittedcentral part (positions from D-D to H-H) and the innerend of the counter gear-side wheelseat (position I-I, fit-ted part) when the ultrasound was transmitted forwardwith the probe head inserted from the axle end of thecounter gear side. This Figure shows the maximum echoheight in the flaw detection gate at every probe positionin scanning. All artificial flaws at the non-fitted centralpart, and all artificial flaws except those of semi-ellipticshape whose depth was equal to or smaller than 1 mm atthe inner end of the wheelseat, can be detected in a statethat spurious echoes are eliminated and the signal/noiseratio is sufficiently great.

6. Comparison of inspection accuracy6. Comparison of inspection accuracy6. Comparison of inspection accuracy6. Comparison of inspection accuracy6. Comparison of inspection accuracy

Table 4 shows the minimum flaws that can be detectedat every part of an axle when axles are tested by the tech-nique mentioned in this report, by the longitudinal waveangle-beam technique for conventional solid axle railwayvehicles using automatic testing equipment, and by theangle-beam hollow axle technique that also uses auto-matic testing equipment for Shinkansen vehicles 3).

With the ultrasonic test from a bore of 30 mm diam-eter machined in an axle for conventional railway vehicles,the inspection accuracy becomes higher than was the casein tests using the conventional technique with a longitu-dinal angle-beam from the end face of a solid axle. Wecould therefore obtain an inspection accuracy equal to thatof hollow axles for Shinkansen vehicles.

7. Conclusions7. Conclusions7. Conclusions7. Conclusions7. Conclusions

On the basis of experience gained with hollow axlesthat have been used on Shinkansen vehicles, a hollow axlewith a small bore diameter of 30 mm applicable to con-

Angle of refraction: 40 deg.

Probe

Center of ultrasound beam

: Trigger gate (constant in testing)

Trigger gate

Flaw detection gate(following first wave)

Flaw echoSpurious echo

Echo height and path length of flaw echo correctly detected.

Trigger gate

Spurious echo

Echo height and path length of spurious echo detected.

Detected path lengths compared and whether flaw echo exists or not decided.

Flaw detection gate

(a) Case of existing flaw echo and spurious echo

(b) Case of existing spurious echo only

8484848484 QR of RTRI, Vol. 46, No. 2, June. 2005

TTTTTable able able able able 44444 Comparison of inspection accuracyComparison of inspection accuracyComparison of inspection accuracyComparison of inspection accuracyComparison of inspection accuracyAngle-beam technique usedon 30 mm hollow axles forconventional railway ve-hicles (this report)

Longitudinal wave angle-beam technique used on solidaxles for conventional rail-way vehicles

Angle-beam techniqueused on 60 mm hollowaxles for Shinkansen ve-hicles

Fit edge of journal bearing 0.3S 1N 0.6SOuter end of wheelseat 1S 10N 1SInner end of wheelseat 0.3S3E 1N 1SInner end of gear seat 1S 3N 1SNon-fitted central part 0.15S 3N 0.15S

ventional railway vehicles was tested using ultrasonictesting equipment in which a piezocomposite focal probewith a 40-degree angle of refraction was installed. As aresult, a square-shaped artificial flaw 0.15 mm deep atthe non-fitted central part and another 0.3 mm deep atthe inner end of the wheelseat (fitted part) could be de-tected. By actively introducing hollow axles also into con-ventional railway vehicles, it would be possible to improvethe efficiency of inspections and increase the flaw detec-tion accuracy of automatic axle inspections.

AcknowledgementsAcknowledgementsAcknowledgementsAcknowledgementsAcknowledgements

We would like to thank Prof. H. Toda of WakayamaUniversity for guiding us in the design of focal probes.

ReferencesReferencesReferencesReferencesReferences

1) Yohso, J., Sakamoto, H., Makino, K. and Ishiduka,H., "Inspection of Rolling Stock Axles by Using theGrazing SH-wave Ultrasonic Method (in Japanese),"RTRI Report, Vol. 16, No. 5, pp. 35-40, 2002.

2) Hachiya, M., Toda, H., Murata, Y. and Yohso, J.,"Characteristics of Ultrasonic Transducer for BoredType Axle (in Japanese)," Proceedings of the 9th Sym-posium on Ultrasonic Testing, pp. 75-76, 2002.

3) Yohso, J., "Development of Automatic Ultrasonic Test-ing Equipment for General and Bogie Inspection ofShinkansen Hollow Axle," Proceedings of the 11thInternational Wheelset Congress, Vol. 2, pp. 47-50,1995.