Noncontacting-strain-measuring gauge and extensometer remotely measures the mechanical displacement along the entire length of a test specimen. Measurement is accomplished by continuous scanning of a reflected light from reflective bench markings or stripes previously affixed to the specimen

Silver, R. H.

English

NASA Technical Reports Server

t 
Time
August 1970	 Brief 70-10292 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Noncontacting-Optical-Strain Device 
_________	 Test Sample	 V 
Voltage	 Intension 
A noncontacting-strain-measuring gauge and ex-
tensometer for remotely measuring the mechanical 
displacement along the entire length of a test specimen 
was developed. Measurement is accomplished by 
continuous scanning of a reflected light from reflec-
tive bench markings or stripes previously affixed to 
the specimen. 
In this measurement the following steps are in-
cluded: (1) applying reflective calibration marks to 
the test specimen; (2) illuminating the specimen while 
it undergoes displacement; (3) scanning the entire 
length of the specimen with a constant angular velocity
mirror or prism; (4) allowing the reflected image to 
fall upon a photocell with a narrow slit or aperture; 
(5) amplifying the output signal from the photocell; 
and (6) graphically displaying the resulting signal so 
that the distance between peaks is linearly related to 
actual mechanical movement during testing. A typical 
apparatus employing this method is shown schemat-
ically in the figure. The basic components of this 
device include a reflectively marked, test sample, an 
illumination source directed toward the sample, a 
lens system, a constant angular-velocity mirror or 
nrisni, an aperture, a photocell with rapid response, 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000281 2020-03-17T00:17:46+00:00Z
an amplifier, and a readout system that may be either 
a cathode-ray tube or strip-chart recorder or both. 
In the operation of this device, two narrow reflec-
tive strips of aluminum foil are affixed at each end of 
the test specimen, which is dark in color. The illumi-
nation source with reflector is positioned so as to 
illuminate the entire test specimen. A lens system and 
rotating mirror are set in place and serve to direct 
reflected light from the specimen to the photocell 
which has a slit-like aperture. A constant-speed motor 
provides the rotating motion for the mirror. An elec-
trical amplifier and strip-chart recorder convert the 
electrical output signal from the photocell to a graphic 
profile having two sharp peaks caused by reflective 
bench marks. The chart distance between peaks is 
then measured as well as the physical distance separa-
ting the reflective marks on the specimen itself; these 
data provide a calibration factor. Thereafter, as the 
test specimen is elongated, the scanning and readout 
provides a new graphic profile with a greater distance 
between peaks. Thus, the distance between peaks is 
proportional to sample movement, and gives a con-
tinuous measure of sample movement. The mirror 
scanning system may be replaced by a prism system. 
A typical scanning system with mirror or prism may 
be arranged to oscillate over a 10-to 120-degree arc, 
or alternately to rotate over a 360-degree arc. With 
a front and back silvered rotating mirror it is possible 
to achieve continuous readout. This device is not
limited to operation with a visible light source, and 
has been found to be operative with an infrared or 
ultraviolet light source. 
Notes: 
1. This device can be used to remotely measure 
changes in dimension during tests under extreme 
environmental conditions. 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B 70-10292 
Patent status: 
This invention is owned by NASA, and a . patent
application has been filed. Royalty-free, nonexclusive
licenses for its commercial use will be granted by

NASA. Inquiries concerning license rights should be

made to NASA, Code GP, Washington, D.C. 20546. 
Source: R.H. Silver of

Caltech/J PL
under contract to

NASA Pasadena Office 
(N P0-10778) 
Brief 70-10292	 Category 03


Noncontacting-optical-strain device

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server