1. Scope

1.1 This test method2 covers the determination of fatigue crack growth rates from near-threshold (see region I in Fig. 1) to K_max controlled instability (see region III in Fig. 1.) Results are expressed in terms of the crack-tip stress-intensity factor range (∆K), defined by the theory of linear elasticity.

1.2 Several different test procedures are provided, the optimum test procedure being primarily dependent on the magnitude of the fatigue crack growth rate to be measured.

1.3 Materials that can be tested by this test method are not limited by thickness or by strength so long as specimens are of sufficient thickness to preclude buckling and of sufficient planar size to remain predominantly elastic during testing.

1.4 A range of specimen sizes with proportional planar dimensions is provided, but size is variable to be adjusted for yield strength and applied force. Specimen thickness may be varied independent of planar size.

1.5 The details of the various specimens and test configurations are shown in Annex A1 – Annex A3. Specimen configurations other than those contained in this method may be used provided that well-established stress-intensity factor calibrations are available and that specimens are of sufficient planar size to remain predominantly elastic during testing.

1.6 Residual stress as well as a variety of shielding effects such as crack closure may significantly influence the interpretation of fatigue crack growth rate data, particularly at low stress-intensity factors and low force ratios (1, 2).3 None of these variables are incorporated into the classical computation of applied ∆K.

1.7 Values stated in SI units are to be regarded as the standard. Values given in parentheses are for information only.

1.8 This test method is divided into two main parts. The first part gives general information concerning the recommendations and requirements for fatigue crack growth rate testing. The second part is composed of annexes that describe the special requirements for various specimen configurations, special requirements for testing in aqueous environments, and procedures for non-visual crack size determination. In addition, there are appendices that cover techniques for calculating da/dN, determining fatigue crack opening force, and guidelines for measuring the growth of small fatigue cracks. General information and requirements common to all specimen types are listed as follows:

	Section
Referenced Documents	2
Terminology	3
Summary of Use	4
Significance and Use	5
Apparatus	6
Specimen Configuration, Size, and Preparation	7
Procedure	8
Calculations and Interpretation of Results	9
Report	10
Precision and Bias	11
Special Requirements for Testing in Aqueous Environments	Annex A4
Guidelines for Use of Compliance to Determine Crack Size	Annex A5
Guidelines for Electric Potential Difference Determination of Crack Size	Annex A6
Recommended Data Reduction Techniques	Appendix X1
Recommended Practice for Determination of Fatigue Crack Opening Force from Compliance	Appendix X2
Guidelines for Measuring the Growth Rates of Small Fatigue Cracks	Appendix X3
Recommended Practice for Determination of ACR-Based Stress-Intensity Factor Range	Appendix X4

1.9 Special requirements for the various specimen configurations appear in the following order:

The Compact Specimen	Annex A1
The Middle Tension Specimen	Annex A2
The Eccentrically-Loaded Single Edge Crack Tension Specimen	Annex A3

1.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.11 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

FIG. 1 — Defined Regions of a Typical Fatigue Crack Growth Rate Curve

ASTM E647 - 24

Standard Test Method for Measurement of Fatigue Crack Growth Rates

Current

Published:

1 May 2024