Test fixture has the capability of producing biaxial stress fields in test specimens to the point of failure. It determines biaxial stress by dividing the applied load by the net cross section. With modification it can evaluate materials, design concepts, and production hardware at cryogenic temperatures

Helf, J. C.

Kelly, R. E.

Kerr, D. A.

Waldron, C. R.

English

NASA Technical Reports Server

April 1968	 Brief 68-10070
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. 
Development of Biaxial Test Fixture Includes Cryogenic Application 
p.
	
-.Idiom 
A test fixture has been developed v. ith the capa-
bility of producing biaxial stress fields in test speci-
mens to the point of failure. This fixture offers the 
advantage of determining a biaxial stress by dividing 
the applied load by the net cross section. With rela-
tively minor modification, the test fixture can be used 
to evaluate materials, design concepts, and production 
hardware in a biaxial stress field at cryogenic tempera-
tures. 
With recent development of large pressurized 
tanks, a need has existed for an inexpensive method of 
testing critical tank areas to failure. In all pressurized 
tanks there are small areas of discontinuity that
require structural certification. Since no Facilit y
 existed 
with the capability of testing these small areas, a 
complete tank had to be built. Testing a complete 
tank is unsatisfactor y
 because the exact location 
of rupture is often difficult to pinpoint and the 
design reserve of undamaged critical areas cannot be 
established. Numerous attempts to produce the stress 
fields experienced in a pressurized tank have met with 
limited success but were confined to very small test 
specimens. 
A new biaxial test facility is capable of producing 
pressure vessel stress fields in panels 2 ft by 2 ft. The 
test panel is machined on both sides to form a frame 
conunucd ocrkaI 
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.
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around the test area. Clamp-type grips are used to 
transfer load into the corners of the test panel through 
bolts loaded at the centroid of area. Load is applied 
by 50-kip hydraulic actuators attached to the grips and 
to load plates on the ends of the fixture. Load trans-
mitted to the test panel is controlled by calibrated 
load rods between the hydraulic actuators and the 
fixture frame. Since the load can be controlled to 
apply a uniform stress to the test panel, failure load 
can be determined simply by dividing the total applied 
load at failure by the net cross section of the panel. 
For cr yogenic application, a metal tub is fabricated 
beneath the test panel and filled with a liquid cryogen. 
Cryogenic liquid is also sprayed on the test panel and 
loading grips from perforated tubing. A plastic 
thermal barrier is secured above the metal tub to con-
trol splash and air currents.
Note: 
Inquiries concerning this innovation ma hc di 
rected to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10070 
Patent status: 
No patent action is contemplated by NASA. 
Source: J. C. HeIf, R. E. Kelly, 
D. A. Kerr, and C. R. Waldron 
of North American Aviation. Inc. 
under contract to 
Marshall Space Flight Center 
(MFS-14185. 14189) 
Brie I 6- ()07()
Category 01


Development of biaxial test fixture includes cryogenic application

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