Method and apparatus for testing wear, size and residual stress conditions

• US 3,978,712 A
• Filed: 05/24/1974
• Issued: 09/07/1976
• Est. Priority Date: 11/17/1971
• Status: Expired due to Term

• Current Assignee: Scanning Systems Incorporated
• Original Assignee: Scanning Systems Incorporated
• Inventors: Cowan, John Vincent, Cowan, Gerald De G., Cowan, John Gerald
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Beauchamp, John P.
• Application Number:
  US05/473,308
• Time in Patent Office: 837 Days
• Field of Search: 73/67.5 R, 73/67.6
• US Class Current: 73/598
• CPC Class Codes: G01B 17/06 for measuring contours or curvatures
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/0425 Parallel to the surface, e.g. creep waves
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 2291/2626 Wires, bars, rods
• CPC Class Codes: G01N 2291/2636 cylindrical from inside
• CPC Class Codes: G01N 2291/2696 Wheels, Gears, Bearings
• CPC Class Codes: G01N 29/041 on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
• CPC Class Codes: G01N 29/043 in the interior, e.g. by shear waves
• CPC Class Codes: G01N 29/27 by moving the material relative to a stationary sensor

Abstract

Wheel testing apparatus according to the invention comprises at least one search unit positioned "in-track" replacing a portion of a rail so that the gauged wheels of a passing railroad train roll thereover. Each search unit has a thin vertical rail aligned with the gauge edge of the track for supporting each passing wheel adjacent to its flange, and thereby exposing the running surface of the wheel for testing in a zone which does not interfere with the wheel'"'"'s path.

Each search unit has two ultrasonic transducers enclosed in a flexible fluid-filled boot and are positioned adjacent to the thin vertical rail in the test zone under the running surfaces of passing wheels, the fluid-filled boot providing good ultrasonic coupling therewith.

The transducers are angled and opposed to send ultrasonic pulses around the wheel in opposite directions. Echoes indicate defects and through transmission times indicate wheel size and wear. Failure of the wheel to accept any significant amount of energy indicates high residual stress.

Claims

1. The method of testing the physical condition of a wheel comprising the steps of:

A. coupling a tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer inclined with respect to the tangent zone at an angle wherein low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel, penetrates to a substantial depth therein, and is refracted substantially tangent to the curved surface; and

whereby the energy which penetrates the wheel to a substantial depth travels along a path near to and converging toward the curved surface and having a progressively increasing radius of curvature, and thereby migrates toward the curved surface thereof, as it travels along said path;

C. coupling a second tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel, said second tangent zone being at a known angular distance from the first tangent zone;

D. positioning a second ultrasonic transducer in the coupling medium at the second tangent zone with the sonic axis of the second transducer inclined with respect to the tangent zone at an angle corresponding and opposite to the angle of the sonic axis of the first transducer relative to its tangent zone wherein ultrasonic energy delivered to the wheel by the first transducer and entering the tangent zone from within the wheel is refracted out of the wheel to the coupling medium to impinge upon the second transducer;

E. pulsing the first ultrasonic transducer with a low frequency pulse to produce an ultrasonic energy pulse traveling along the sonic axis into the wheel, refracted substantially tangent to the surface thereof, and thereafter traveling about the periphery of the wheel adjacent to the surface;

E. thereafter monitoring the second transducer for receipt of the ultrasonic energy pulse thereat; and

G. measuring the time interval between pulsing the first transducer and receiving the ultrasonic energy pulse at the second transducer wherein the time interval is determined by the length of the circumference of the wheel within the known angular distance and therefore indicates the diameter of the wheel.

2. The method of testing a wheel as defined in claim 1 and further comprising the steps of:

H. comparing the measured diameter of the wheel with the original diameter of the wheel; and

I. signalling if an unacceptable deviation between the measured diameter and the original diameter exists.

3. A method for testing a wheel for both wear and residual stress conditions therein comprising the method steps defined in claim 1, and further comprising the step of:

H. triggering a residual stress signal if a through-transmission pulse is not received at the second transducer within a predetermined time period after the pulsing of the first transducer.

4. The method of testing the physical condition of a wheel having a first wearing surface and a second concentric surface comprising the steps of:

A. coupling a tangent zone of the wheel with an ultrasonic energy-transmission medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to the tangent zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface;

C. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the tangent zone at an angle corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the tangent zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer;

D. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof with a portion adjacent to the first surface and a portion adjacent to the second concentric surface;

E. monitoring for through-transmission pulses received by the second transducer, the first through-transmission pulse received thereby having traveled about the smaller inner one of said two concentric surfaces, and the second through-transmission pulse having traveled about the outer one of said two concentric surfaces; and

F. measuring the time interval between receiving the first through-transmission pulse and the second through-transmission pulse, the time interval corresponding to the difference in diameter between the first wear surface and the second concentric surface and thereby indicating the relative wear thereof.

5. The method of testing a wheel as defined in claim 4 and further comprising the step of:

G. marking the wheel if the relative wear is excessive.

6. The method of testing the physical conditions in a wheel comprising the steps of:

A. coupling a tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer inclined with respect to the tangent zone at an angle wherein low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel, penetrates to a substantial depth therein, and is refracted substantially tangent to the curved surface; and

whereby the energy which penetrates the wheel to a substantial depth travels along a path near to and converging toward the curved surface and having a progressively increasing radius of curvature, and thereby migrates toward the curved surface thereof, as it travels along said path;

C. coupling a second tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel, said second tangent zone being at a known angular distance from the first tangent zone;

D. positioning a second ultrasonic transducer in the coupling medium at the second tangent zone with the sonic axis of the second transducer inclined with respect to the tangent zone at an angle corresponding and opposite to the angle of sonic axis of the first transducer relative to its tangent zone wherein ultrasonic energy delivered to the wheel by the first transducer and entering the tangent zone from within the wheel is refracted out of the wheel to the coupling medium to impinge upon the second transducer;

E. pulsing the first ultrasonic transducer with a low frequency pulse to produce an ultrasonic energy pulse traveling along the sonic axis into the wheel, refracted substantially tangent to the surface thereof, and thereafter traveling about the periphery of the wheel adjacent to the surface;

F. thereafter monitoring the second transducer for receipt of the ultrasonic energy pulse thereat; and

G. triggering a residual stress signal if the ultrasonic energy pulse is not received by the second transducer within a predetermined time period.

7. The method of testing for residual stress conditions in a wheel defined in claim 6, and further comprising the step of:

H. marking the wheel upon the triggering of said residual stress signal.

8. The method of testing for residual stress conditions in a wheel comprising the steps of:

A. coupling a tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer inclined with respect to the tangent zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel, is refracted substantially tangent to the wheel surface and thereafter travels about the periphery of the wheel;

C. coupling a second tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel, said second tangent zone being at a known angular distance from the first tangent zone;

D. positioning a second ultrasonic transducer in the coupling medium at the second tangent zone with the sonic axis of the second transducer inclined with respect to the tangent zone at an angle corresponding and opposite to the angle of sonic axis of the first transducer relative to its tangent zone wherein ultrasonic energy delivered to the wheel by the first transducer and entering the tangent zone from within the wheel is refracted out of the wheel to the coupling medium to impinge upon the second transducer;

E. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse traveling along the sonic axis into the wheel, refracted substantially tangent to the surface thereof, and thereafter traveling about the periphery of the wheel adjacent to the surface;

F. thereafter monitoring the second transducer for receipt of the ultrasonic energy pulse thereat;

G. reducing the gain of the amplified output of the first transducer as a function of the amplitude of through transmission pulses received by the second transducer; and

H. triggering a residual stress signal when the amplitude of through transmission pulses received by the second transducer fails to exceed a predetermined threshold amplitude required to initiate said gain reduction.

9. Apparatus for testing railroad wheels comprising:

A. means presenting an ultrasonic energy-transmitting medium positioned in a test zone for ultrasonic coupled with the running surface of a railroad wheel, the ultrasonic energy-transmitting medium having an index of refraction substantially lower than the index of refraction of ultrasonic energy in the railroad wheel;

B. a first transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle wherein low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel, penetrates to a substantial depth therein, and is refracted substantially tangent to the curved surface; and

whereby the energy which penetrates the wheel to a substantial depth travels along a path near to and converging toward the curved surface and having a progressively increasing radius of curvature, and thereby migrates toward the curved surface thereof, as it travels along said path;

C. a low ultrasonic frequency pulse generator connected to the first transducer for pulsing the first transducer to produce a low frequency ultrasonic energy pulse along its sonic axis;

D. a second transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle substantially equal and opposed to the angle of inclination of the sonic axis of the first transducer;

E. a through-transmission signal detector connected to the second transducer for detecting through-transmission pulses comprising a portion of the ultrasonic energy pulse produced by the first transducer, traveling about the periphery of the wheel in a first direction returning to the coupling medium, and refracted out of the wheel to impinge upon the second transducer.

17. Apparatus for testing railroad wheels as defined in claim 9 and further comprising;

f. a test certification indicator responsive to the output of the through-transmission signal detector to produce a test certification signal upon receipt of through transmissions about the periphery of the wheel by the through-transmission signal detector.

10. Apparatus for testing railroad wheels comprising:

A. means presenting an ultrasonic energy-transmitting medium positioned in a test zone for ultrasonic coupling with the running surface of a railroad wheel, the ultrasonic energy-transmitting medium having an index of refraction substantially lower than the index of refraction of ultrasonic energy in the railroad wheel;

B. a first transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle wherein low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted therein substantially tangent to the wheel surface, thereafter passing about the periphery of the wheel;

C. a pulse generator connected to the first transducer for pulsing the first transducer to produce a low frequency ultrasonic energy pulse along its sonic axis;

D. a second transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle substantially equal and opposed to the angle of inclination of the sonic axis of the first transducer;

E. a through-transmission signal detector connected to the second transducer for detecting through-transmission pulses comprising a portion of the ultrasonic energy pulse produced by the first transducer, traveling about the periphery of the wheel in a first direction returning to the coupling medium, and refracted out of the wheel to impinge upon the second transducer;

wherein the pulse generator is a synchronizing pulse generator set at a pulse interval greater than the time necessary for an ultrasonic energy pulse to travel about the periphery of the largest wheel to be tested, and wherein the output of the through-transmission signal detector controls the output of the synchronizing pulse generator to inhibit further pulsing upon receipt of the first through-transmission pulse, thereby permitting only one ultrasonic energy pulse to be delivered to the wheel.

11. Apparatus for testing railroad wheels comprising:

A. means presenting an ultrasonic energy-transmitting medium positioned in a test zone for ultrasonic coupling with the running surface of a railroad wheel, the ultrasonic energy-transmitting medium having an index of refraction substantially lower than the index of refraction of ultrasonic energy in the railroad wheel;

B. a first transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle wherein low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted therein substantially tangent to the wheel surface, thereafter passing about the periphery of the wheel;

C. a pulse generator connected to the first transducer for pulsing the first transducer to produce a low frequency ultrasonic energy pulse along its sonic axis;

D. a second transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle substantially equal and opposed to the angle of inclination of the sonic axis of the first transducer;

E. a through-transmission signal detector connected to the second transducer for detecting through-transmission pulses comprising a portion of the ultrasonic energy pulse produced by the first transducer, traveling about the periphery of the wheel in a first direction returning to the coupling medium, and refracted out of the wheel to impinge upon the second transducer;

F. a time delay connected to the output of the through-transmission signal detector and initiated by the first through-transmission signal to provide a time interval following the first through-transmission pulse selected to permit substantial attenuation of the first ultrasonic energy pulse in the wheel to occur, and connected to provide an output signal following the time interval at a time delay output terminal;

G. a plurality of switches responsive to the output signal of the time delay and connected to;

12. switch the output of the synchronizing pulse generator from the first transducer to the second transducer, andswitch the output of the first transducer to the through-transmission signal detector,

whereby the functions of the first and second transducers are reversed and the wheel is tested by passing an ultrasonic energy pulse about its periphery in a second, opposite direction;

and

H. a timer initiated by the arrival of an ultrasonic energy pulse at the test zone and stopped by the next through-transmission pulse thereafter, thereby timing the interval during which an ultrasonic energy pulse passes around the periphery of the wheel being tested; and

I. a wheel size indicator responsive to the time interval for indicating the size of the wheel being tested.

15. Apparatus for testing railroad wheels as defined in claim 12 and further comprising:

J. a second timer initiated by an ultrasonic energy pulse in the wheel at the test zone and stopped by the next through-transmission pulse thereafter, thereby timing the interval during which an ultrasonic energy pulse passes around the periphery being tested;

K. a wheel size indicator responsive to the time interval for indicating the size of the wheel being tested; and

L. a test certification indicator responsive to the output of the excessive wear indicator and the wheel size indicator to produce a test certification signal in both a wheel size indication and a wear measurement.

16. Apparatus for testing railroad wheels as defined in claim 12 and further comprising:

J. a pressurized paint spray having an output nozzle directed toward the wheel being tested and a valve controlling the release of paint therefrom; and

K. means for operating the valve responsive to an excessive wear alarm signal, whereby an excessively worn wheel is marked with paint.

20. Apparatus for testing railroad wheels as defined in claim 16 wherein the thin support rail is aligned with the inside gauge edge of the rail segments for supporting the running surface of a railroad wheel rolling thereover adjacent to its flange.

25. Apparatus for testing railroad wheels as defined in claim 15 and further comprising:

G. a pressurized paint spray having an output nozzle directed toward the wheel being tested and a valve controlling the release of paint therefrom; and

H. means for operating the valve responsive to a test certification signal, whereby a wheel having been tested is marked with paint.

13. Apparatus for testing railroad wheels comprising:

A. means presenting an ultrasonic energy-transmitting medium positioned in a test zone for ultrasonic coupling with the running surface of a railroad wheel, the ultrasonic energy-transmitting medium having an index of refraction substantially lower than the index of refraction of ultrasonic energy in the railroad wheel;

B. a first transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle wherein low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted therein substantially tangent to the wheel surface, thereafter passing about the periphery of the wheel;

C. a pulse generator connected to the first transducer for pulsing the first transducer to produce a low frequency ultrasonic energy pulse along its sonic axis;

D. a second transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to a tangent to the running surface in the test zone at an angle substantially equal and opposed to the angle of inclination of the sonic axis of the first transducer;

E. a through-transmission signal detector connected to the second transducer for detecting through-transmission pulses comprising a portion of the ultrasonic energy pulse produced by the first transducer, traveling about the periphery of the wheel in a first direction returning to the coupling medium, and refracted out of the wheel to impinge upon the second transducer;

F. a time delay connected to the output of the through-transmission signal detector and initiated by the first through-transmission signal to provide a time interval following the first through-transmission pulse selected to permit substantial attenuation of the first ultrasonic energy pulse in the wheel to occur, and connected to provide an output signal following the time interval at a time delay output terminal;

G. a plurality of switches responsive to the output signal of the time delay and connected to;

14. switch the output of the synchronizing pulse generator from the first transducer to the second transducer, andswitch the output of the first transducer to the through-transmission signal detector,

H. a timer initiated by a first lobe of a through-transmission pulse comprising a portion of the through-transmission pulse which has traveled about the running surface of the wheel, and stopped by a second lobe of a through-transmission pulse comprising a portion of the through-trans-mission pulse which has traveled about the larger diameter flange of the wheel, wherein the timed interval is proportional to the difference in diameter between the running surface and the flange;

and

I. an excessive wear indicator responsive to the time interval to produce an excessive wear output signal when the time interval exceeds a preset time interval determined by acceptable wear.

18. Apparatus for testing railroad wheels comprising:

A. a first rail segment comprising a portion of one rail of a railroad track;

B. a second rail segment positioned a spaced apart distance from the first rail segment and aligned therewith to comprise a second portion of the same rail of a railroad track; and

C. a thin vertical support rail

1. having a width substantially less than the width of the rail segments

2. positioned to span the longitudinal distance between the adjacent ends of the first and second rail segments

3. having its top surface aligned with the top surfaces of the rail segments

whereby a railroad wheel rolling along the thin vertical support rail is exposed to a test zone adjacent to the support rail closely juxtaposed to but not intruding into the normal path of the railroad wheel; and

further comprising;

D. an ultrasonic energy-transmitting medium positioned in the test zone adjacent to the thin vertical support rail for ultrasonic coupling with the running surface of a railroad wheel as it passes thereover, the ultrasonic energy-transmitting medium having an index of refraction substantially lower than the index of refraction of ultrasonic energy in the railroad wheel;

E. a first transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to the top surface of the thin vertical support rail at an angle wherein low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted therein substantially tangent to the wheel surface, thereafter passing about the periphery of the wheel;

F. a pulse generator connected to the first transducer for pulsing the first transducer to produce a low frequency ultrasonic energy pulse along its sonic axis;

G. a defect signal detector connected to the first transducer for reception of the echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel, returning along the periphery of the wheel to the ultrasonic energy transmitting medium, and refracted out of the wheel to impinge on the first transducer the defect signal detector producing a defect alarm signal upon receipt of a defect echo pulse;

H. a second transducer positioned in the ultrasonic energy-transmitted medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to the top surface of the rail at an angle substantially equal and opposed to the angle of inclination of the sonic axis of the first transducer;

I. a through-transmission signal detector connected to the second transducer for detecting through-transmission pulses comprising a portion of the ultrasonic energy pulse produced by the first transducer, traveling about the periphery of the wheel in a first direction returning to the coupling medium, and refracted out of the wheel to impinge upon the second transducer;

J. a time delay connected to the output of the through-transmission signal detector and initiated by the first through-transmission signal to provide a time interval following the first through-transmission pulse selected to permit substantial attenuation of the first ultrasonic energy pulse in the wheel to occur, and connected to provide an output signal following the time interval at a time delay output terminal;

K. a plurality of switches responsive to the output signal of the time delay and connected to;

23. The method defined in claim 18 wherein coupling of the wheel to the ultrasonic energy transmitting medium for both first and second transducers is confirmed by:

A. enclosing both transducers in a resiliently depressible boot filled with the medium and presented for interfering contact with the tangent zones of the wheel,

B. supporting both transducers in a carriage internally suspended within the depressible boot for free movement therewith,

C. and positioning a third depth-sounding transducer on the carriage with its sonic axis substantially normal to a floor of the boot which is itself substantially parallel to the average tangent zones of the wheel,

whereby wheel contact resiliently depressing the boot shortens the distance from the third transducer to the floor, producing a reduced-depth echo pulse signal received by the third transducer electrically confirming wheel contact.

19. switch the output of the synchronizing pulse generator from the first transducer to the second transducer,switch the output of the second transducer to the defect signal detector, andswitch the output of the first transducer to the through-transmission signal detector,

whereby the functions of the first and second transducers are reversed and the wheel is tested by passing an ultrasonic energy pulse about its periphery in a second, opposite direction;

and

L. a timer initiated by the arrival of an ultrasonic energy pulse at the test zone and stopped by the next through-transmission pulse thereafter, thereby timing the interval during which an ultrasonic energy pulse passes around the periphery of the wheel being tested; and

M. a wheel size indicator responsive to the time interval for indicating the size of the wheel being tested.

21. The method of testing for the physical conditions in a wheel comprising the steps of:

A. coupling a tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer inclined with respect to the tangent zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel, is refracted substantially tangent to the wheel surface and thereafter travels about the periphery of the wheel;

C. coupling a second tangent zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel, said second tangent zone being at a known angular distance from the first tangent zone;

D. positioning a second ultrasonic transducer in the coupling medium at the second tangent zone with the sonic axis of the second transducer inclined with respect to the tangent zone at an angle corresponding and opposite to the angle of sonic axis of the first transducer relative to its tangent zone wherein ultrasonic energy delivered to the wheel by the first transducer and entering the tangent zone from within the wheel is refracted out of the wheel to the coupling medium to impinge upon the second transducer;

E. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse traveling along the sonic axis into the wheel, refracted substantially tangent to the surface thereof, and thereafter traveling about the periphery of the wheel adjacent to the surface;

F. thereafter monitoring the second transducer for receipt of the circumperipheral through transmission ultrasonic energy pulse thereat; and

G. triggering a high-risk stress condition alarm whenever no through transmission pulse is received by the second transducer during a time period when at least one of two test-in-progress conditions is occurring;

22. backscattered acoustic noise is received by one of the transducers confirming coupling of first transducer'"'"'s output energy to the wheel;

or

2. a defect return echo signal is received by one of the transducers.

24. The method of testing for physical conditions in a wheel comprising the steps of:

A. coupling a tangent zone of the wheel with an ultrasonic energy transmitting medium having a index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer inclined with respect to the tangent zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel, is refracted substantially tangent to the wheel surface and thereafter travels about the periphery of the wheel;

C. coupling a second tanget zone of the wheel with an ultrasonic energy transmitting medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy in the wheel, said second tangent zone being at a known angular distance from the first tangent zone;

D. positioning a second ultrasonic transducer in the coupling medium at the second tangent zone with the sonic axis of the second transducer inclined with respect to the tangent zone at an angle corresponding and opposite to the angle of sonic axis of the first transducer relative to its tangent zone wherein ultrasonic energy delivered to the wheel by the first transducer and entering the tangent zone from within the wheel is refracted out of the wheel to the coupling medium to impinge upon the second transducer;

E. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse traveling along the sonic axis into the wheel, refracted substantially tangent to the surface thereof, and thereafter traveling about the periphery of the wheel adjacent to the surface;

F. thereafter monitoring the second transducer for receipt of the ultrasonic energy pulse thereat; and

G. positioning a third transducer in a resiliently depressible mounting with its sonic axis directed toward an underlying floor spaced a predetermined distance from the third transducer, with the mounting being depressible by a wheel coupled to the medium for the first and second transducers and thus reducing the predetermined distance and producing a reduced-depth echo pulse signal indicating wheel contact; and

H. delivering this wheel contact signal to initiate the operation of switching means alternately delivering energizing electrical pulses to the first and the second transducers until a circumperipheral through transmission ultrasonic energy pulse is received by one of the first and second transducers.