Study was initiated to determine methods or test specimens for evaluating stress corrosion cracking characteristics of common structural materials. It was found that the methods of externally loading and corrosion testing were reliable in yielding reproducible results for stress corrosion evaluation

Humphries, T. S.

English

NASA Technical Reports Server

November 1967
	 .-	 Brief 67-10451 
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. 
Study Made of Procedures for Externally Loading 
and Corrosion Testing Stress Corrosion Specimens 
.
A study was initiated because there are no specific 
methods or special test specimens for evaluating the 
stress corrosion cracking characteristics of the com-
mon structural materials such as those used for deter-
minining mechanical properties. In general, the in-
vestigator is at liberty to choose the types of specimens 
and corrosive environments for conducting stress cor-
rosion tests. This usually leads to conflicting published 
results which are confusing to the designer in apprais-
ing the susceptibility of various materials to stress 
corrosion cracking. 
Other uses of stress corrosion test data, in addition 
to the selection of structural material by the designer, 
are in developing alloys, maintaining uniformity of 
products, and determining new applications for speci-
fic structural materials. It is doubtful if any single 
stress corrosion test procedure would be suitable for 
evaluating all common structural materials or all 
service environments. However, standard stress cor-
rosion test procedures are necessary to obtain com-
parable results among investigators. 
There is little doubt that the most reliable method 
of stress corrosion testing is to expose the material 
in the specific atmosphere of service environment. 
This method, however, is far too time consuming, and 
it is necessary to use an accelerated test environment 
to obtain results within a reasonable period of time. 
It is of paramount importance that the accelerated 
test environment be realistic of general service con-
ditions and yield reproducible results. 
The type and geometry of the material and the grain 
direction to be tested are some of the major factors 
to be considered in choosing the specimen designs for 
stress corrosion tests. In most cases, specimen de-
sign must be based on the geometry of the material
to be evaluated. For instance, flat tensile specimens 
normally are used for testing sheet material; for thick 
plate and forging, round specimens can be used; weld-
ments generally require relatively thick specimens 
with the as-welded surfaces intact. 
During the course of the study, it was found that 
the types of specimens described and the methods 
of externally loading and corrosion testing were 
reliable in yielding reproducible results for stress 
corrosion evaluation of most aluminum alloys, and 
have shown promise for ferrous and nickel alloys. 
More consistent results have been obtained with the 
threaded-end tensile specimens, stressed by constant 
deformation, than have been obtained with specimens 
(flat tensile, beam specimens, and C-rings) stressed 
by constant deflection. 
Note: 
Additional details are contained in: Procedures for 
Externally Loading and Corrosion Testing StressCor-
rosion Specimens, TM-X-53483, by T. S. Humphries, 
Marshall Space Flight Center, June 29, 1966. Copies 
are available from: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10451 
Patent status: 
Inquiries about obtaining rights for the commer-
cial use of this invention may be made to NASA, 
Code GP, Washington, D. C. 20546. 
Source: T. S. Humphries 
(M FS- 12064) 
Category 03 
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.
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Study made of procedures for externally loading and corrosion testing stress corrosion specimens

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