Method and apparatus for non-destructive evaluation utilizing the internal friction damping (IFD) technique
OwnerAlagu P. Thiruvengadam, Ambrose A. Hochrein, Jr.inventors
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Abstract
A non-destructive evaluation technique particularly suited for in situ testing utilizes significant changes in internal friction damping (IFD) as an indicating factor. A baseline for the specific damping capacity of an object is determined and a tolerance range is established from the baseline. Measurements of the specific damping capacity are periodically made and checked to see if they are within the tolerance range. Unexpected changes in specific damping capacity indicate the presence of an incipient flaw in the object. The evaluation technique can also be used to locate flaws, monitor crack growth and predict useful life. Apparatus for measuring specific damping capacity is also disclosed.
Claims23
A method for detecting an incipient flaw in an object by measurement of the specific damping capacity of the object, comprising the steps of:
- inducing an excitation having a predetermined amount of energy in the object to produce a stress in the anelastic stress range;
- measuring a value indicative of changes in the specific damping capacity occurring in the object;
- recording the measured value;
- periodically repeating the steps of inducing, measuring and recording;
- determining from the recorded values a baseline for the specific damping capacity of the object;
- establishing a set of predetermined values which indicates the expected relationship of said measured values to said baseline;
- and
- thereafter checking at intervals for a difference which is greater than a predetermined amount between the recorded values and the predetermined values.
An in-situ method of non-destructive determination of the specific damping capacity of an object comprising the steps of:
- inducing an excitation in an in-situ object by applying a series of pulses to a point on the object at a predetermined frequency, the amplitude of said pulses being such that stresses in the anelastic stress range are produced;
- measuring the amplitude of the pulses at a point on the object;
- and
- determining the logarithmic decrement from the amplitude of the measured pulses in the in-situ object.
Apparatus for non-destructive evaluation of the specific damping capacity of an in-situ object comprising:
- means for inducing an excitation having a predetermined amount of energy in an in-situ object to produce a stress in the anelastic stress range;
- means for measuring the changes in the specific damping capacity occurring in the in-situ object;
- and
- means for recording said measured changes.
Dependencies are inferred from the claim text.