Fractographic principles used for analyzing failure in metals are applied to the analysis of the microstructure and fracture of polytetrafluoroethylene. This material is used as seals in cryogenic systems

Nerren, B. H.

English

NASA Technical Reports Server

March 1969	 Brief 69-10066 
NASA TECH BRIEF 
NASA Teèh 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. 
Fractography Can Be Used to Analyze Failure Modes
in Polytetrafluoroethylene 
.
Techniques for analyzing failures in metals are well 
established, and an abundance of data on failure 
modes in these materials is available. Fractography 
has been a common analytical technique for studying 
the fracture face of a failed metal by means of both 
macro- and micro-photography. The minute topo-
graphical features revealed in the fractographs are 
then compared with standards which were fractured 
under controlled conditions. Similarities between the 
fractographs representing service failures and the 
standards indicate the failure mode. 
A study was undertaken to determine the feasibil-
ity of applying fractographic principles used for metals 
to the analysis of the microstructure and fracture char-
acteristics of polytetrafluoroethlene (PTFE), a mate-
rial used as seals in cryogenic systems. Notched and 
unnotched samples of 1/4-inch-thick PTFE were pre-
pared and tested in tensile and fatigue testing ma-
chines at room temperature and at the temperature of 
liquid nitrogen. The test conditions approximate the 
stress and temperature environments to which the 
PTFE would be exposed in space systems hardware. 
Replicas of the fractured surfaces were prepared by 
the commonly used two-stage acetate replica tech-
nique. All fractures were studied in two magnification
ranges: the macro-range, from I to lOx; and the mi-
cro-range, from 3500 to 15,000x (with the electron 
microscope). The various topographical features noted 
on the fracture faces were defined in terms of observ-
able patterns (chevrons, dimples, tears, ridges, and 
striations) and tabulated for all samples. 
The results of the study demonstrate that fractogra-
phy can be used to analyze fractured surfaces of PTFE 
to determine modes of failure in this material. 
Note: 
Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69-10066 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C., 20546.
Source: B. H. Nerren 
(M FS-20294) 
Category 03 
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=19690000066 2020-03-16T17:53:55+00:00Z


Fractography can be used to analyze failure modes in polytetrafluoroethylene

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server