Optics: measuring and testing – Material strain analysis – By light interference detector
Patent
1994-05-31
1996-04-16
Turner, Samuel A.
Optics: measuring and testing
Material strain analysis
By light interference detector
356347, 356348, G01B 902
Patent
active
055088015
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to methods for testing materials and structures, and more specifically, to a method and apparatus for nondestructive testing of objects for their mechanical behaviors.
2. Discussion of the Prior Art
Known in the art is a method to determine stresses and strains in a loaded object, wherein the object is illuminated by coherent laser radiation before and after loading in order to obtain pairs of superimposed speckle patterns. These speckle patterns are transformed into a diffraction pattern, which is then mathematically processed. Signal amplitudes obtained by this mathematical processing are used to obtain values of strains and stresses at various points of an elastically deformed object (e.g., PCT 87/07365).
The above mentioned method is deficient because it does not allow kinetics of plastic deformation process to be analyzed since it is not designed to obtain three dimensional waves of plastic deformation. The above mentioned method permits calculation of stress and distortion fields according to the detected deformation, but does not allow one to analyze the plastic flow caused by plastic deformation. Therefore, the above mentioned conventional method is suitable only for estimation of elastic deformation and is practically unsuitable for the region of plastic deformation.
Capability to analyze the dynamics of plastic deformation is extremely important for many application problems, especially for nondestructive testing of mechanical behaviors of objects under loading since a failure is always preceded by a localized plastic deformation. Inadequacy of conventional approaches to this problem has been outstanding for a long time.
Also known are methods aimed at determining contribution of various mechanisms of plastic deformation to the actual process of plastic flow of the material and its failure (Handbook on Experimental Mechanics, Ed. by A. S. Kobayashi, Prentice-Hall 1987). All these methods are based on microscopic investigations of a defective structure of deformed material in general after the load is removed. A wide range of investigation methods are used: optical and electronic microscopy, X-ray structural analysis, various types of microscopic mechanical testing, etc.
These methods are deficient since they are highly labor intensive; they require the use of sophisticated equipment as well as requiring an extremely accurate localization of the area under examination because they employ high-resolution techniques. The critical disadvantage of these methods is the fact that they are applicable only to the analysis of residual defects of the material and not applicable to the analysis of generation and movement of defects.
The most commonly used method for obtaining data on reliability of materials (See for example Collacott R. A. "Structural Integrity Monitoring", London, Chapman and Hall 1985) consists of mechanical tests of specimens under various types of loading conditions including tension, compression, bending, torsion, crack-sample test, etc. to obtain such characteristics as elastic limit, yield limit, ultimate strength, stress intensity factor; fracture toughness, ultimate fatigue, long-time strength, etc.
These tests are generally carried out utilizing specially prepared specimens of preset shape and dimensions. Numerical values of strength and plasticity characteristics thus obtained are used for strength calculations of machine parts and structural members as well as for calculations of their reliability characteristics.
This method is deficient in that a special set of mechanical characteristics and destruction criteria is used for each type of testing. These characteristics for various types of tests are not rigorously correlated to each other, and their physical interpretations are based on numerous contradictory models which often role each other out.
Another disadvantage of this method resides in problems associated with the use of data on mechanical properties of parts of mechanisms or machine
REFERENCES:
patent: 3911733 (1975-10-01), Bhuta et al.
patent: 3976380 (1976-08-01), Rottenrolber et al.
patent: 4702594 (1987-10-01), Grant
Danilov Vladimir I.
Gorbatenko Vadim V.
Makarov Pavel V.
Panin Victor Y.
Yegorushkin Valery E.
Hildebrand Christa
Kabushikigaisya Hutech
Rossiyskiy Materialoveduchesky Centr
Turner Samuel A.
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