MECHANICAL TESTING

Fatigue Crack Growth (da/dN) - ASTM E 647

"Standard Test Method for Measurement of Fatigue Crack Growth Rates"

ASTM E647 covers the determination of steady-state fatigue crack growth rates from near-threshold to Kmax controlled instability using either compact type, C (T), or center-cracked-tension, M (T), specimens. Results are expressed in terms of the crack-tip stress-intensity factor range (DK), defined by the theory of linear elasticity.

This test method involves cyclic loading of notched specimens which have been acceptably pre-cracked in fatigue. Crack length is measured, either visually or by an equivalent method, as a function of elapsed fatigue cycles and these data are subjected to numerical analysis to establish the rate of crack growth. Crack growth rates are expressed as a function of the stress-intensity factor range, DK, which is calculated from expressions based on linear elastic stress analysis.

Fatigue crack growth rate expressed as a function of crack-tip distress-intensity factor range, da/dN versus DK, characterizes a material's resistance to stable crack extension under cyclic loading.

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