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Title: Optical method and apparatus for detection of surface and near-subsurface defects in dense ceramics

A laser is used in a non-destructive manner to detect surface and near-subsurface defects in dense ceramics and particularly in ceramic bodies with complex shapes such as ceramic bearings, turbine blades, races, and the like. The laser's wavelength is selected based upon the composition of the ceramic sample and the laser can be directed on the sample while the sample is static or in dynamic rotate or translate motion. Light is scattered off surface and subsurface defects using a preselected polarization. The change in polarization angle is used to select the depth and characteristics of surface/subsurface defects. The scattered light is detected by an optical train consisting of a charge coupled device (CCD), or vidicon, television camera which, in turn, is coupled to a video monitor and a computer for digitizing the image. An analyzing polarizer in the optical train allows scattered light at a given polarization angle to be observed for enhancing sensitivity to either surface or near-subsurface defects. Application of digital image processing allows subtraction of digitized images in near real-time providing enhanced sensitivity to subsurface defects. Storing known "feature masks" of identified defects in the computer and comparing the detected scatter pattern (Fourier images) with the storedmore » feature masks allows for automatic classification of detected defects.« less
Inventors:
 [1];  [2]
  1. (Naperville, IL)
  2. (Goleta, CA)
Issue Date:
OSTI Identifier:
869941
Assignee:
University of Chicago (Chicago, IL) ANL
Patent Number(s):
US 5426506
Contract Number:
W-31109-ENG-38
Research Org:
Argonne National Laboratory (ANL), Argonne, IL
Country of Publication:
United States
Language:
English
Subject:
optical; method; apparatus; detection; surface; near-subsurface; defects; dense; ceramics; laser; non-destructive; manner; detect; particularly; ceramic; bodies; complex; shapes; bearings; turbine; blades; races; wavelength; selected; based; composition; sample; directed; static; dynamic; rotate; translate; motion; light; scattered; subsurface; preselected; polarization; change; angle; select; depth; characteristics; detected; train; consisting; charge; coupled; device; ccd; vidicon; television; camera; video; monitor; computer; digitizing; image; analyzing; polarizer; allows; observed; enhancing; sensitivity; application; digital; processing; subtraction; digitized; images; near; real-time; providing; enhanced; storing; feature; masks; identified; comparing; scatter; pattern; fourier; stored; automatic; classification; surface defects; enhanced sensitivity; optical method; television camera; charge coupled; coupled device; turbine blade; scattered light; turbine blades; dense ceramic; ceramic bodies; digital image; providing enhanced; near real-time; subsurface defects; time providing; near-subsurface defects; optical train; selected based; image processing; complex shapes; selected base; digitized image; complex shape; dense ceramics; /356/250/