Arrangement for use in the study of the propagation of cracks

• US 3,918,299 A
• Filed: 03/21/1974
• Issued: 11/11/1975
• Est. Priority Date: 03/23/1973
• Status: Expired due to Term

• Current Assignee: Henri Donnadieu
• Original Assignee: Henri Donnadieu
• Inventors: Donnadieu, Henri
• Primary Examiner(s): Myracle, Jerry W.
• Application Number:
  US05/453,355
• Time in Patent Office: 600 Days
• Field of Search: 73/91,88R,104,95
• US Class Current: 73/772
• CPC Class Codes: G01N 2203/0019 Compressive
• CPC Class Codes: G01N 2203/0066 Propagation of crack
• CPC Class Codes: G01N 2203/027 Specimens with holes or notches
• CPC Class Codes: G01N 27/9006 Details, e.g. in the structure or functioning of sensors
• CPC Class Codes: G01N 3/066 with electrical indicating or recording means

Abstract

A crack-detecting unit is operative for examining a limited portion of an object to determine whether such portion is cracked. When the crack-detecting unit determines that the portion of the object being examined is cracked, a control unit automatically causes the crack-detecting unit to examine the next portion of the object, thus proceeding from one limited portion of the object to the next, along the direction of propagation of the crack. A recording unit automatically makes a record of the examination by the crack-detecting unit of the successive portions of the object, to thereby make a record of the propagation of the crack.

Claims

1. An arrangement for use in the study of the propagation of cracks, comprising, in combination, crack-detecting means operative for examining a limited portion of an object to determine whether such portion is cracked;

control means automatically operative in response to determination by said detecting means that the portion being examined is cracked for causing the crack-detecting means to examine the next portion of the object in the direction of propagation of the crack; and

recording means for automatically making a record of the examination by the detecting means of the successive portions of the object to thereby make a record of the propagation of the crack.

2. An arrangement as defined in claim 1, wherein said crack-detecting means comprises means operative for generating a first signal having a value indicative of the extent to which the portion of the object being examined is cracked, and wherein said control means includes reference means operative for generating a second signal, comparator means having first and second inputs connected to respectively receive said first and second signals and operative for generating a control signal when the difference between said first and second signals exceeds a predetermined value, and wherein said control means further comprises means operative in response to generation of said control signal for causing said crack-detecting means to examine the next portion of the object in the direction of propagation of the crack.

3. An arrangement as defined in claim 1, wherein said crack-detecting means comprises means operative for dissipating energy in a limited portion of the object to a degree dependent upon whether such limited portion is cracked, and means for generating a signal having a value dependent upon such energy dissipation.

4. An arrangement as defined in claim 1, said crack-detecting means being operative for detecting cracks in an object comprised of electrically conductive material, and wherein said crack-detecting means comprises means for establishing a high-frequency magnetic field passing through a limited portion of the object to establish the flow of eddy currents in such portion and thereby dissipate electrical energy in such portion to an extent dependent upon whether such portion is cracked, and means for generating a signal having a value dependent upon the degree of such dissipation of electrical energy.

5. An arrangement as defined in claim 1, wherein said crack-detecting means comprises an inductive transducer and a source of high-frequency energizing current for said inductive transducer.

6. An arrangement as defined in claim 1, wherein said crack-detecting means comprises means for generating a signal having a value indicative of the extent to which the portion of the object being examined by the crack-detecting means is cracked, and wherein said control means comprises deactivating switch means operable for deactivating said control means to prevent said crack-detecting means from examining the next portion of the object.

7. An arrangement for use in the study of the propagation of cracks, comprising, in combination, crack-detecting means operative for detecting the existence of a crack in an object;

control means operative for automatically effecting relative movement between the crack-detecting means and the object in the direction of propagation of a crack detected by the crack-detecting means; and

recording means operative for automatically making a record of the relative movement and thereby a record of the propagation of the crack.

8. An arrangement as defined in claim 7, wherein said control means comprises means operative for automatically moving said crack-detecting means in the direction of propagation of a crack detected by said crack-detecting means.

9. An arrangement as defined in claim 8, wherein said recording means comprises a position-detecting transducer operative for generating a signal indicative of the position of said crack-detecting means, said position-detecting transducer comprising a linear potentiometer having a wiper mechanically coupled to said crack-detecting means.

10. An arrangement as defined in claim 8, wherein said control means comprises an elongated supporting structure supporting said crack-detecting means, means mounting and guiding said elongated supporting structure for longitudinal movement, and wherein said control means comprises non-rotatable first screw-threaded means connected to said longitudinally movable supporting structure, second screw-threaded means operative for driving said first screw-threaded means, and drive means for rotating said second screw-threaded means to cause longitudinal movement of said first screw-threaded means along the direction of propagation of a crack detected by said craCk-detecting means.

11. An arrangement as defined in claim 7, and further including stressing means operative for holding a test object and causing the formation and propagation of a crack in the test object by stressing the test object, and wherein said control means comprises means operative for automatically effecting relative movement between said crack-detecting means and said stressing means in the direction of propagation of a crack detected by said crack-detecting means.

12. An arrangement as defined in claim 11, wherein said control means comprises means operative for automatically moving said crack-detecting means in the direction of propagation of a crack detected by said crack-detecting means.

13. An arrangement as defined in claim 7, wherein said crack-detecting means comprises means operative for generating a first signal having a value indicative of the extent of said crack, and wherein said control means includes reference means operative for generating a second signal, comparator means having first and second inputs connected to respectively receive said first and second signals and operative for generating a control signal when the difference between said first and second signals exceeds a predetermined value, and wherein said control means further comprises means operative in response to generation of said control signal for effecting relative movement between the crack-detecting means and the object in the direction of propagation of the crack detected by the crack-detecting means.

14. An arrangement as defined in claim 7, wherein said crack-detecting means comprises means operative for dissipating energy in a limited portion of the object to a degree dependent upon whether such limited portion is cracked, and means for generating a signal having a value dependent upon such energy dissipation.

15. An arrangement as defined in claim 7, said crack-detecting means being operative for detecting cracks in an object comprised of electrically conductive material, and wherein said crack-detecting means comprising means for establishing a high-frequency magnetic field passing through a limited portion of the object to establish the flow of eddy currents in such portion and thereby dissipate electrical energy in such portion to an extent dependent upon whether such portion is cracked, and means for generating a signal having a value dependent upon the degree of such dissipation of electrical energy.

16. An arrangement as defined in claim 7, wherein said crack-detecting means comprises an inductive transducer and a source of high-frequency energizing current for said inductive transducer.

17. An arrangement as defined in claim 7, wherein said crack-detecting means comprises a bridge circuit including a source of high-frequency current, an inductive transducer responsive to cracks in electrically conductive material and comprised of first and second substantially identical windings connected across said source.

18. An arrangement as defined in claim 17, wherein said bridge circuit further includes a potentiometer connected across said source, the output signal of said bridge circuit being the A.C. voltage drop between the junction of said first and second windings and the wiper of said potentiometer.

19. An arrangement as defined in claim 18, and further including an additional potentiometer connected across said source, the wiper of said additional potentiometer being electrically connected to the junction between said first and second windings, whereby to facilitate balancing of said bridge circuit.

20. An arrangement as defined in claim 17, wherein said first and second windings are constituted by respective first and second adjacent coils having parallel axes mounted for displacement in direction parallel to said axes, and biasing means for urging said coils into contact with an object to be examined by said crack-detecting means.

21. An arrangement as defined in claim 20, wherein said crack-dEtecting means further includes a casing at least partially surrounding said coils.

22. An arrangement as defined in claim 20, wherein said crack-detecting means further includes a shield of high-magnetic permeability at least partly surrounding said coils to shield said coils from the influence of stray magnetic flux.

23. An arrangement as defined in claim 7, wherein said crack-detecting means comprises means operative for generating an A.C. voltage having an amplitude indicative of the extent of said crack, and wherein said control means comprises an amplifier having an input connected to said crack-detecting means for receiving and amplifying said A.C. voltage, a rectifier connected to the output of said amplifier, and a low-pass filter connected to the output of said rectifier for converting said A.C. voltage into a D.C. voltage having a magnitude indicative of the extent of said crack.

24. An arrangement as defined in claim 23, wherein said control means further includes a source of variable voltage comprised of a reference potentiometer having a wiper, a comparator comprised of an operational amplifier having a first input connected to the output of said low-pass filter for receipt of said D.C. voltage and having a second input connected to said wiper of said reference potentiometer and operative for generating an output control signal when the difference between the voltages at the inputs thereof exceeds a predetermined value.

25. An arrangement as defined in claim 24, wherein said control means further includes an electromagnetic relay comprised of a relay winding, a transistor having an output current path connected in circuit with said relay winding for furnishing current to said relay winding and having an input circuit connected in circuit with the output of said comparator for receipt of said control signal.

26. An arrangement as defined in claim 7, wherein said control means comprises moving means for effecting said relative movment, and wherein said moving means comprises a movably mounted supporting structure, a drive motor for moving said supporting structure in the direction of propagation of the crack, and electromagnetic clutch means automatically operative for coupling said drive motor to said movably mounted supporting structure in force-transmitting manner in response to detection of a crack by said crack-detecting means.

27. An arrangement as defined in claim 7, wherein said control means comprises moving means for effecting said relative movement, and wherein said moving means comprises a movably mounted supporting structure, a drive motor for moving said supporting structure in the direction of propagation of the crack, said drive motor being an electrical stepper motor having an input and being operative for moving said movably mounted supporting structure a predetermined distance in response to receipt of a control pulse at said input of said motor, and pulse-generating means operative for applying a control pulse to said input of said motor when said crack-detecting means detects a crack.

28. An arrangement as defined in claim 27, wherein said pulse-generating means comprises means for generating a train of such control pulses for as long as said crack-detecting means continues to detect the existence of a crack.

29. An arrangement as defined in claim 7, wherein said crack-detecting means comprises means for generating a signal having a value indicative of the extent to which the portion of the object being examined by the crack-detecting means is cracked, and wherein said control means comprises deactivating switch means operable for deactivating said control means to prevent said control means from automatically effecting said relative movement.

30. An arrangement for use in the study of the propagation of cracks, comprising, in combination, detecting means for detecting the existence of a crack in an object;

monitoring means for automatically monitoring the propagation of a crack detected by said detecting means; and

recording means for automatically making a record of the operation of said monitoring means to thereby make a record of the propagation of the crack.