BS ISO 12108:2002 Metallic materials. Fatigue testing. Fatigue crack growth method

[ir_71]

BS ISO 12108:2002 Metallic materials. Fatigue testing. Fatigue crack growth method

Introduction
This International Standard is intended to provide specifications for generation of fatigue crack growth rate data. Test
results are expressed in terms of the fatigue crack growth rate as a function of crack-tip stress intensity factor range,
, as defined by the theory of linear elastic fracture mechanics [1]-[6]. Expressed in these terms the results
characterize a material's resistance to subcritical crack extension under cyclic force test conditions. This resistance
is independent of specimen planar geometry and thickness, within the limitations specified in clause 6. All values are
given in SI units [7].
This International Standard describes a method of subjecting a precracked notched specimen to a cyclic force. The
crack length, , is measured as a function of the number of elapsed force cycles, . From the collected crack length
and corresponding force cycles relationship the fatigue crack growth rate, , is determined and is expressed as
a function of stress intensity factor range, .
Materials that can be tested by this method are limited by size, thickness and strength only to the extent that the
material must remain predominantly in an elastic condition during testing and that buckling is precluded.
Specimen size may vary over a wide range. Proportional planar dimensions for six standard configurations are
presented. The choice of a particular specimen configuration may be dictated by the actual component geometry,
compression test conditions or suitability for a particular test environment.
Specimen size is a variable that is subjective to the test material's proof strength and the maximum stress
intensity factor applied during test. Specimen thickness may vary independent of the planar size, within defined
limits, so long as large-scale yielding is precluded and out-of-plane distortion or buckling is not encountered. Any
alternate specimen configuration other than those included in this International Standard may be used, provided
there exists an established stress intensity factor calibration expression, i.e. stress intensity factor function,
[9]-[11].
Residual stresses [12], [13], crack closure [14], [15], specimen thickness, cyclic waveform, frequency and environment,
including temperature, may markedly affect the fatigue crack growth data but are in no way reflected in the
computation of , and so should be recognized in the interpretation of the test results and be included as part of
the test report. All other demarcations from this method should be noted as exceptions to this practice in the final
report.
For crack growth rates above the typical scatter in test results generated in a single laboratory for a
given can be in the order of a factor of two [16]. For crack growth rates below , the scatter in the
calculation may increase to a factor of 5 or more. To assure the correct description of the material's
versus behaviour, a replicate test conducted with the same test parameters is highly recommended.
Service conditions may exist where varying under conditions of constant or control [17] may be
more representative than data generated under conditions of constant force ratio; however, these alternate test
procedures are beyond the scope of this International Standard.

Scope
This International Standard describes tests for determining the fatigue crack growth rate from the threshold stressintensity
factor range, , to the onset of unstable crack extension as the maximum stress intensity factor
approaches controlled instability, as determined in accordance with ISO 12737 [8].
This International Standard is primarily intended for use in evaluating isotropic metallic materials under
predominantly linear-elastic stress conditions and with force applied only perpendicular to the crack plane (mode I
stress condition), and with a constant stress ratio, .

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BS ISO 12108:2002 Metallic materials. Fatigue testing. Fatigue crack growth method

Author: ISO/TC 164 | Size: 0.95 MB | Format: PDF | Quality: Original preprint | Publisher: ISO | Year: 2002 | pages: 45 | ISBN: 0580429628

Please see above.

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