Comprehensive survey presents current methods of fracture toughness testing that are based on linear elastic fracture mechanics. General principles of the basic two dimensional crack stress field model are discussed in relation to real three dimensional specimens. Methods of test instrumentation and procedure are described

Brown, W. F., Jr.

Jones, M. H.

Srawley, J. E.

English

NASA Technical Reports Server

March 1968
	 .	 Brief 68-10046 
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. 
Survey of Fracture Toughness Test Methods 
For aircraft and space applications, materials are 
utilized at stress levels close to their maximum capa-
bility; consequently, these requirements have given 
impetus to numerous research. studies on high strength 
materials. One such study which has been developed 
rapidly over the last decade is fracture mechanics. 
In the simplest terms, the fracture toughness of a 
material determines how large a crack the material is 
able to tolerate without fracture when loaded to a 
level approaching that at which crack-free material 
would fail by excessive plastic deformation. For 
example, how large a crack can be tolerated in the 
wall of a pressure vessel manufactured from Brand X 
steel when the nominal hoop stress is raised to 90 
percent of the yield strength? 
Naturally, every reasonable effort would be made 
to avoid having any cracks or like defects in the struc-
ture. But experience indicates unmistakably that it 
would be quite unrealistic to depend upon the total 
absence of crack-like defects. If something fairly quan-
titative about the crack tolerance of materials were 
known, more realistic and more effective measures 
could be taken with regard to inspection, quality 
control, proof testing, and avoidance of development 
of cracks in service. 
The most direct way of evaluating the crack toler-
ance of a material apparently would be to test a series 
of specimens provided with cracks of graded sizes to 
determine an empirical relation between strength and 
crack size. But the problem is not simply a matter of 
crack size. In addition, crack shape, bulk of the mem-
ber (i.e., thickness of a plate), orientation of the crack 
in relation to the fibering of the material, temperature, 
and rate of loading all may affect the fracture strength 
of a structural member of a given material. To take
into account all these factors in a purely empirical test 
program would require very large numbers of speci-
mens for each material evaluated. The burden of 
testing can be considerably reduced, however, by 
applying knowledge of the mechanics of fracturing, 
best represented at the present time by linear elastic 
fracture mechanics. 
A comprehensive survey has been prepared which 
presents current methods of fracture toughness testing 
that are based on linear elastic fracture mechanics. 
General principles of the basic two-dimensional crack 
stress field model are discussed in relation to real 
three-dimensional specimens. The designs and neces-
sary dimensions of specimens for mixed mode and 
opening mode (plane strain) crack toughness measure-
ment are considered in detail. Methods of test instru-
mentation and procedure are described. Expressions 
for the calculation of crack toughness values are given 
for the common types of specimens. 
Notes: 
Details of this survey are contained in: NASA 
Technical Note D-2599, Fracture Toughness Test-
ing, by J. E. Srawley and W. F. Brown, Jr., Lewis 
Research Center, Cleveland, Ohio, January 1965. 
Copies of TN D-2599 are available from, and 
inquiries concerning this survey may be directed 
to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B68-10046
(continued overleaf) 
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=19680000046 2020-03-12T05:46:01+00:00Z
Supplementary information on this subject is 
contained in ASTM-NASA STP 410: Plain Strain 
Crack Toughness Testing of High Strength Metal-
lic Materials, by W. F. Brown, Jr., and J. E. 
Srawley, 1967. Copies are available from: 
American Society for Testing 
and Materials 
1916 Race Street 
Philadelphia, Pennsylvania 19103
Patent status: 
No patent action is contemplated by NASA. 
Source: J. E. Srawley, M. H. Jones, 
and-W. F. Brown, Jr. 
(LEW- 10379) 
Brief 68-10046	 Category 03


Survey of fracture toughness test methods

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