Multiple element continuity gage measures plane stress crack growth plus surface crack growth under plane strain conditions. The gage measures flat and curved surfaces and operates at cryogenic temperatures

Orange, T. W.

Sullivan, T. L.

English

NASA Technical Reports Server

October 1967	 .	 .	 Brief 67-10384 
NASA TECH BRIEF C' 
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. 
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Crack Growth Measured on Flat and Curved Surfaces at
Cryogenic Temperatures 
—Test Cell	 - 4	 Control Room 
The problem: 
Determination of the fracture toughness of a ma-
terial requires knowledge of the crack length at the 
onset of rapid fracture or unstable crack growth. 
Cinematography, electrical potential measurement, 
and displacement (compliance) gaging have been used 
but become difficult or impractical when the test 
specimen is immersed in a cryogenic liquid or when a 
curved surface is involved, such as that of a cylindrical 
pressure vessel.
The solution: 
A multiple element continuity gage for measuring 
plane stress crack growth plus surface crack growth 
under plane strain conditions. 
How it's done: 
The multiple element foil gage resembles a conven-
tional foil gage but consists of 20 elements of high 
resistivity alloy foil physically and electrically in 
parallel. The gage is mounted on the test specimen at 
(continued overleaf) 
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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.
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the crack tip with the elements perpendicular to the 
expected direction of crack propagation, with the 
leading edge of the shortest filament at the tip of the 
crack. If the crack growth is expected to exceed the 
gage width, additional gages may be placed in tandem 
with the first. 
The continuity gage is designed to be used with a 
1.5-ohm shunt resistor. As the crack grows, the 
elements are broken, from the shortest to the longest 
in turn, and the resistance of the assembly increases in 
a finite and relatively linear stepwise manner. A 
resistance of 119 ohms is added in series to make the 
assembly compatible with existing 120-ohm bridge cir-
cuitry used for recording strain gage data. Bridge 
output is fed to a direct recording oscillograph along 
with an applied load signal.
Notes: 
1. This gage has performed satisfactorily at —320° 
and —423°F with 301 stainless steel, 5 aluminum-
2.5tin—titanium, and 2014-T6 aluminum sheet 
specimens and pressure vessels. 
2. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B67-10384 
Patent status: 
No patent action is contemplated by NASA. 
Source: Timothy L. Sullivan and Thomas W. Orange 
(LEW-389) 
Brief 67-10384
	 Category 01


Crack growth measured on flat and curved surfaces at cryogenic temperatures

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