A METHOD FOR AUTOMATICALLY QUANTIFYING STRESS, STRAIN, AND DISPLACEMENT FROM HOLOGRAPHIC IMAGES
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-21
Phillip A. Green: AUTHOR [+2]
Holographic interferometry is a usefi~l optical technique used for visual analysis ofthe microdefor- mations of test objects resulting from the applica- tion of internal or external forces. Applications of holographic analysis include: * Failure mode analysis associated with vibra- tional excitation, mechanical loading, and ther- mal or pressure stressing. * Delamination and crack detection. * FEM verification and boundary condition determination.
MOTOROLA INC. Technical Developments Volume 20 October 1993
A Ml3HOD FOR AUTOMATICALLY QUANTIFYING STRESS, STRAIN; AND DISPLACEMENT FROM HOLOGRAPHIC IMAGES
by Phillip A. Green and Michael P. Fleming
PROBLEM TO BE SOLVED
Holographic interferometry is a usefi~l optical technique used for visual analysis ofthe microdefor- mations of test objects resulting from the applica- tion of internal or external forces. Applications of holographic analysis include:
* Failure mode analysis associated with vibra- tional excitation, mechanical loading, and ther- mal or pressure stressing.
* Delamination and crack detection.
* FEM verification and boundary condition determination.
* Creep and relaxation analysis.
Holographic analysis is generally performed qualitatively through visual inspection of the fringe patterns produced on a test object. When attempting to quantify the analysis, many have experienced dif- ficulties in obtaining accurate measurements of the holographic fringe locations. Previous attempts have been to measure directly off a hard copy of the image, referencing a scaled grid that was painted onto the object, and estimating the measurements. These methods were not only time consuming, due to the absence ofan automated measurement method, but were also somewhat inaccurate. The inaccuracies associated with the measurement ofthe fringe loca- tions can lead to serious calculation errors for the quantities of stress and strain, since these measure- ments are typically dependent on mathematical approximations to differential equations. Since these earlier methods were very time consuming and inac- curate, most holographic analysis was performed strictly qualitatively, therefore creating the need for an accurate, automated quantitative holographic fringe analysis method.
for producing quantitative measurements from holographic images. The system drastically reduces cycle time by automating the location and measure- ment of binges patterns. Subsequent calculations pro- duce displacement, strain and stress measurements for out-of-plane deformations of a test object. Also, measurement accuracy is greatly improved due to processing methods integrated into the computer vision software.
The holographic system can be used for quanti- tative analysis of both real-time and.double expo- sure holograms. The system is composed of two major components:
1) The vision system. The vision system is based on Image Analyst, a Macintosh vision analy- sis and image processing software package, which has been modified to include quantita- tive holographic measures.
2) The Newport HC-1034 holographic worksta- tion. The workstation consists of a light tight enclosure, which houses a real-time holo- graphic camera, laser, and associated optics,
and a separate system controller.
The complete system is shown in Figure 1. The software modifications to Image Analyst utilize a novel analysis process which allows the user to quickly perform qua...