ASTM E647 PDF

Results are expressed in terms of the crack-tip stress-intensity factor range DK , defined by the theory of linear elasticity. 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. Materials that can be tested by ASTM E 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. By means of our fatigue testing expertise and modular product design, we will help find the testing solution that is right for you.

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More E Background information on the ration-ale for employing linear elastic fracture mechanics to analyze fatigue crack growth rate data is given in Refs 1 5 and 2. Attention needs to be given to the proper selection and control of these variables in research studies and in the generation of design data.

Specification of any two of these variables is sufficient to define the loading condition. However, data on the influence of thickness on fatigue crack growth rate are mixed. Thickness effects can also interact with other variables such as environment and heat treatment. The potential influence of specimen thickness should be considered when generating data for research or design. The effect can be significant when test specimens are removed from materials that embody residual stress fields; for example weldments or complex shape forged, extruded, cast or machined thick sections, where full stress relief is not possible, or worked parts having complex shape forged, extruded, cast or machined thick sections where full stress relief is not possible or worked parts having intentionally-induced residual stresses.

Specimens taken from such products that contain residual stresses will likewise themselves contain residual stress. While extraction of the specimen and introduction of the crack starting slot in itself partially relieves and redistributes the pattern of residual stress, the remaining magnitude can still cause significant error in the ensuing test result.

Residual stress is superimposed on the applied cyclic stress and results in actual crack-tip maximum and minimum stress-intensities that are different from those based solely on externally applied cyclic forces or displacements. For example, crack-clamping resulting from far-field 3D residual stresses may lead to partly compressive stress cycles, and exacerbate the crack closure effect, even when the specimen nominal applied stress range is wholly tensile.

Use of long crack data to analyze small crack growth often results in non-conservative life estimates. The small crack effect may be accentuated by environmental factors.

Steady-state near-threshold data, when applied to service loading histories, may result in non-conservative lifetime estimates, particularly for small cracks This implies that the conditions in the wake of the crack and prior loading history can have a bearing on the current propagation rates. The understanding of the role of the closure process is essential to such phenomena as the behavior of small cracks and the transient crack growth rate behavior during variable amplitude loading.

This complicating factor needs to be considered in using constant-amplitude growth rate data to analyze variable amplitude fatigue problems Scope 1. Specimen thickness may be varied independent of planar size.

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.

Values given in parentheses are for information only. 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.

General information and requirements common to all specimen types are listed as follows:.

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ASTM E647 – Measurement of Fatigue Crack Growth Rates da/dN

More E Background information on the ration-ale for employing linear elastic fracture mechanics to analyze fatigue crack growth rate data is given in Refs 1 5 and 2. Attention needs to be given to the proper selection and control of these variables in research studies and in the generation of design data. Specification of any two of these variables is sufficient to define the loading condition. However, data on the influence of thickness on fatigue crack growth rate are mixed. Thickness effects can also interact with other variables such as environment and heat treatment. The potential influence of specimen thickness should be considered when generating data for research or design.

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ASTM E647 Fatigue Crack Growth Test Equipment

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