Analog circuit measures hysteresis loop areas as a function of time during fatigue testing of specimens subjected to sinusoidal tension-compression stresses at a frequency of Hz. When the sinusoidal stress signal is multiplied by the strain signal, the dc signal is proportional to hysteresis loop area

Hoffman, C.

Spilo, D.

English

NASA Technical Reports Server

December 1967	 Brief 67-10519 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Circuit Measures Hysteresis Loop Areas at 30 Hz 
Cycle 
Counter 
ZERO & CALIBRATE CIRCUITS 
Voltage Divider
Amplifier 
Conditioner	 Amplifier	 Fhase	 T4 
Voltage Divider
	
- J 
Extensometer Signal 1	 I 
(Strain) Conditioner Amplifier -	 Amplifier 
L -----
Strain Filter	 - 
Field
r 1 
Recorder Con
and Wattmeter 
Amplifier
Moving 
Coil 
"Loop Area"
Tape Recorder 
--The problem:	 90 degrees) is multiplied bythestrain signal, the dc 
To devise instrumentation that will measure hys- 	 signal component in the product is proportional to 
teresis loop areas as a function of time during fatigue 	 the hysteresis loop area. 
testing of specimens subjected to sinusoidal tension- 	 How it's done: 
compression stresses at a frequency of 30 Hz. An x-y	 A wattmeter is used to multiply the stress and strain 
plotter, which is generally used to measure hysteresis	 signals. An amplifier in series with another amplifier 
loop areas, does not have the frequency response 	 is used between the bridge signal conditioner and the 
necessary to follow loops at 30 Hz.	 wattmeter to increase the stress signal to a level 
acceptable to the wattmeter. Two amplifiers are used 
The solution:	 .	 in a similar manner to amplify the strajn signal. 
An analog circuit based on the analytically derived 	 The signal representing hysteresis loop area is fed 
fact that when.the sinusoidal stress signal (shifted by	 into a 2-channel tape recorder through a recorder 
-	
-	 (continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19670000518 2020-03-11T20:55:56+00:00Z
control and amplifier unit. The recording is a continu-
ous plot of hysteresis loop area versus time. A plot of 
strain amplitude versus time is also recorded. 
The wattmeter reads zero when its input consists 
of two sinusoids that differ in phase by 90 degrees. 
It is therefore necessary, after scaling by means of the 
voltage dividers (in the zero and calibrate circuits), to 
use the "phase adjust" resistor to shift one of two 
reference sinusoids from an oscillator until the watt-
meter reads zero. Two sinusoidal signals which differ 
in phase by a known amount, and of measured ampli-
tude, are fed into the wattmeter to provide a cali-
bration signal. This signal is also recorded on the tape. 
Notes: 
I. The wattmeter can be replaced by Hall Effect 
multipliers at a considerable reduction in cost.
Details concerning this innovation are given in 
Report No. 67-101, "Final Report of Experi-
mental Studies of Cumulative Damage," March 
1967, prepared by Midwest Applied Science 
Corporation. This report may be obtained from: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10519 
Patent status: 
No patent action is contemplated by NASA. 
Source: C. Hoffman and D. Spilo 
of Midwest Applied Science Corporation 
under contract to 
Marshall Space Flight Center 
(M FS- 13069) 
Brief 67-10519	 Category 01


Circuit measures hysteresis loop areas at 30 Hz

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