Designation: E 739 – 91 (Reapproved 2004)
Standard Practice for
Statistical Analysis of Linear or Linearized Stress-Life (
S-N
)
and Strain-Life (e-
N
) Fatigue Data
1
This standard is issued under the fixed designation E 739; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers only S-N and e-N relationships that
may be reasonably approximated by a straight line (on appro-
priate coordinates) for a specific interval of stress or strain. It
presents elementary procedures that presently reflect good
practice in modeling and analysis. However, because the actual
S-N or e-N relationship is approximated by a straight line only
within a specific interval of stress or strain, and because the
actual fatigue life distribution is unknown, it is not recom-
mended that (a) the S-N or e-N curve be extrapolated outside
the interval of testing, or (b) the fatigue life at a specific stress
or strain amplitude be estimated below approximately the fifth
percentile (P . 0.05). As alternative fatigue models and
statistical analyses are continually being developed, later
revisions of this practice may subsequently present analyses
that permit more complete interpretation of S-N and e-N data.
2. Referenced Documents
2.1 ASTM Standards:
2
E 206 Definitions of Terms Relating to Fatigue Testing and
the Statistical Analysis of Fatigue Data
3
E 467 Practice for Verification of Constant Amplitude Dy-
namic Forces in an Axial Fatigue Testing System
E 468 Practice for Presentation of Constant Amplitude Fa-
tigue Test Results for Metallic Materials
E 513 Definitions of Terms Relating to Constant-
Amplitude, Low-Cycle Fatigue Testing
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E 606 Practice for Strain-Controlled Fatigue Testing
3. Terminology
3.1 The terms used in this practice shall be used as defined
in Definitions E 206 and E 513. In addition, the following
terminology is used:
3.1.1 dependent variable—the fatigue life N (or the loga-
rithm of the fatigue life).
3.1.1.1 Discussion—Log (N) is denoted Y in this practice.
3.1.2 independent variable—the selected and controlled
variable (namely, stress or strain). It is denoted X in this
practice when plotted on appropriate coordinates.
3.1.3 log-normal distribution—the distribution of N when
log (N) is normally distributed. (Accordingly, it is convenient
to analyze log (N) using methods based on the normal
distribution.)
3.1.4 replicate (repeat) tests—nominally identical tests on
different randomly selected test specimens conducted at the
same nominal value of the independent variable X. Such
replicate or repeat tests should be conducted independently; for
example, each replicate test should involve a separate set of the
test machine and its settings.
3.1.5 run out—no failure at a specified number of load
cycles (Practice E 468).
3.1.5.1 Discussion—The analyses illustrated in this practice
do not apply when the data include either run-outs (or
suspended tests). Moreover, the straight-line approximation of
the S-N or e-N relationship may not be appropriate at long lives
when run-outs are likely.
3.1.5.2 Discussion—For purposes of statistical analysis, a
run-out may be viewed as a test specimen that has either been
removed from the test or is still running at the time of the data
analysis.
4. Significance and Use
4.1 Materials scientists and engineers are making increased
use of statistical analyses in interpreting S-N and e-N fatigue
data. Statistical analysis applies when the given data can be
reasonably assumed to be a random sample of (or representa-
tion of) some specific defined population or universe of
material of interest (under specific test conditions), and it is
desired either to characterize the material or to predict the
performance of future random samples of the material (under
similar test conditions), or both.
1
This practice is under the jurisdiction of ASTM Committee E08 on Fatigue and
Fracture and is the direct responsibility of Subcommittee E08.04 on Structural
Applications.
Current edition approved May 1, 2004. Published June 2004. Originally
approved in 1980. Last previous edition approved in 1998 as E 739 – 91 (1998).
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
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Withdrawn.
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