Method and apparatus for fatigue crack detection and propagation analysis
OwnerAllen C. Eberhardtinventor
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Abstract
A fatigue testing system subjects a test specimen to a rotary stress applied about an axis at one or both ends which is perpendicular to the axis of the test specimen. The stress applied may be selected from sinusoidal, random, impulse or a signal generated by the stresses applied to an actual in service specimen. A servo applies the stress to the test specimen through a coupler and the changes in the electrical resistance of a portion of the test specimen is sensed to detect the initiation and propagation of a stress failure.
Claims40
A fatigue monitoring system in which a test specimen is subjected to repeated stresses comprising:
- means to support the test specimen to be monitored at one end region of said test specimen with the test specimen extending outward from the support means;
- means to apply a repeated stress to a region of said test specimen remote from said support means;
- said repeated stress being a rotational stress applied about an axis transverse to the axis of said specimen extending outward from said support means through said test specimen;
- and
- means to detect variations in the characteristics of said test specimen resulting from said stress.
The fatigue monitoring system of claim I wherein the type of said repeated stress may be selected from the group consisting of oscillatory, random, impulse and one derived from actual service.
A method of fatigue analysis of a test specimen to determine crack formation and crack propagation in the test specimen comprising:
- supporting one end of the test specimen in a support to extend outward therefrom along a first axis;
- applying a rotational torque to the free end of said test specimen about a second axis which is transverse to said first axis;
- and
- monitoring an electric characteristic of said free end of said test specimen to detect changes in the electrical characteristic as an indication of the fatigue characteristics of said test specimen.
A fatigue monitoring system in which a specimen is subjected to repeated stresses comprising a holder to support a test specimen to be monitored at one end region of said specimen with the test specimen extending outward from said holder;
- means to apply a repeated stress to a region of said specimen remote from said holder;
- said repeated stress being a rotational stress applied about an axis transverse to the axis extending outward from said holder through said test specimen;
- a motor coupled to apply said stress to said test specimen;
- a servo amplifier driving said motor in response to one or more input signals;
- a bridge circuit to detect variations in the electrical characteristics of said test specimen resulting from said stress;
- and
- data acquisition and analysis circuitry to determine the initiation of cracks in said test specimen and to monitor the propagation of said cracks based on said variations in the electrical characteristics of said test specimen.
A method of fatigue analysis of a test specimen to determine crack formation and crack propagation in the test specimen comprising:
- supporting the test specimen to extend along its axis;
- applying a rotational torque to one or more separated regions of said test specimen about axes transverse to the axis of said test specimen;
- and
- monitoring an electric characteristic of said free end of said test specimen to detect changes in the electrical characteristic as an indication of the fatigue characteristics of said test specimen
A fatigue monitoring system in which a specimen is subjected to repeated stresses comprising at least 2 couplers to support a specimen to be monitored with the specimen extending between said couplers;
- at least 2 servo motors connected through said couplers to apply repeated stress to said specimen;
- said repeated stress being rotational stresses applied about separated axes transverse to the axis of said specimen extending between said couplers;
- at least one servo amplifier driving said servo motors in response to at least one input signal;
- means to detect variations in the electrical characteristics of said specimen resulting from said repeated stress;
- and
- data circuitry to indicate the formation of cracks in said specimen and to monitor the propagation of said cracks based on said variations in the electrical characteristics of said specimen.
Dependencies are inferred from the claim text.