Crease and fold resistance of polymeric films and test equipment for determining mechanical properties is discussed. Components of equipment and method of operation are described. Illustration of test device is provided

Muraca, R. F.

Neff, J.

English

NASA Technical Reports Server

October 1972	 B72-10552 
NASA TECH BRIEF	
A 
NASA Pasadena Office 
NASA Tech Briefs announce now 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 National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Micro-Scale Crease-and-Fold Apparatus 
The problem: 
To evaluate the crease-and-fold resistance of poly-
meric films in the presence of small amounts of highly 
reactive fluids. In particular, the evaluation was to 
involve the severe three-corner creases experienced 
by propellant expulsion bladders in spacecraft; more-
over, it was desired that results should be comparable 
with those obtained from a large, table-size three-
corner crease tester.
Polymeric 
Film 
Crease 
Fixture 
The solution: 
A micro-scale crease-and-fold test apparatus based 
on the use of a fixture which produces a three-corner 
crease on a strip of polymeric film while it is immersed 
in a small volume of reactive fluid.
How it's done: 
The crease fixture shown in the diagram is mounted 
on the end of a rod supported by a nickel-plated cir-
cular plate which acts as a support for all mechanical 
components of the test apparatus and also serves as 
the lid for a small bell jar or heavy-wall "test tube" of 
large diameter; hermetic seal between glass and the 
metal lid is effected by an 0-ring of inert material, 
and the assembly is maintained integral by suitable 
clamps. The shaft of a variable-speed motor passes 
through a polytetrafluoroethylene 0-ring rotary seal 
in the nickel-plated lid and drives a crank mechanism 
that imparts reciprocating motion to a drive pulley. A 
narrow band of 0.127-mm nickel foil is fixed to the 
pulley at one point and the test sample strip is 
fastened by clamps to the ends of the nickel foil; thus, 
the reciprocating action of the pulley causes the test 
strip to slide back and forth over the crease fixture. A 
spring-plunger tension gage interposed between one 
end of the nickel foil band and the test sample insures 
smooth operation and prevents undue tension when 
motion of the test sample is abruptly reversed. 
The test sample strip is forced to comply with the 
shape of the crease fixture by the tension exerted by 
the spring-plunger tension gage; thus, a three-corner 
crease is formed. However, since the test sample strip 
is forcibly slid back and forth, the three-corner crease 
is made to travel along a line 5 to 7 cm long, and 
when the sample fails, a pinhole will be formed on 
the line. Pinholes are detected by a spark probe con-
sisting of a wire (insulated by quartz tubing) attached 
to a 10,000-volt, 30-mA neon-sign transformer. Since 
the fixture defines the position of the three-corner 
crease at all times, it is possible to place the probe at a 
(continued overleaf) 
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	 information contained in this document, or warrants that such use 
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S point where a pinhole can be detected almost at the time it is formed; the pinhole allows more current to 
flow through the probe to ground, as is readily indi-
cated by a mffliammeter. Appropriate insulating ter-
minals in the lid of the test apparatus provide the 
means for activating the probe while it is in place 
within the bell jar. Of course, when reactive fluids are 
in the test apparatus, the spark probe cannot be turned 
on; in these instances, the crease test is allowed to run 
for a few cycles while a reactive fluid is present, and 
then the fluid is removed prior to the spark test. For 
convenience in removing fluids, a port is included in 
the lid of the test apparatus; fluids are best removed 
by evaporation under vacuum. 
A 75-mm bell jar which can hold 200 ml of test 
fluid is ordinarily used for inert liquids like the Freons 
(often used for low-temperature tests). A smaller jar, 
holding about 10 ml of test fluid, is used to immerse 
the crease fixture whenever there is likelihood of 
violent interaction between sample and fluid; since 
the test apparatus can be run unattended for a given 
number of cycles and the fluid removed by evacuation, 
the reactivity of sample and fluid poses no hazards to 
the operator. 
Notes: 
1. The glass vessel enclosing the crease fixture can be 
immersed in hot or cold baths for tests at prescribed
temperatures. As constructed, the glass vessel can 
withstand 276 kN/m2
 (40 psia); however,a metal 
vessel and an appropriate method for maintaining 
closure of the lid can provide an operational en-
vironment at considerably higher pressures. 
2. The angles of the defining surfaces of the crease 
fixture have been selected so that the results of the 
micro-scale apparatus are in statistical compliance 
with the results obtained from a large table-model 
crease tester. Other angles may be used to provide 
creases which are more or less rigorous. 
3. Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP72-10552 
Patent status: 
NASA. has decided not to apply for a patent. 
Source: Raffaele F. Muracaand 
Joseph Neff of 
Stanford Research Institute 
under contract to 
NASA Pasadena Office 
(NPO-12029)
Li 
B72-10552	 Category 06


Micro-scale crease-and-fold apparatus

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