Crack growth relationship

(1) Under the action of cyclic stress range Act the crack front will move into the material according to the crack propagation law. In the direction of'a' the rate of propagation is given by:

where A is the fatigue crack growth rate (FCGR) material constant m is the crack growth rate exponent y is the crack geometry factor depending on the crack shape, orientation and surface boundary dimensions.

NOTE: The most common units for stress intensity factors AK are MPam0,5 (Nmm 2 m0,5) and for crack growth rate da/dN is m/cycle. Data given in B.3. are only valid for these units.

(2) This can be rewritten in the form da/dN = A AKm where AK is the stress intensity range and equals Aa a0'5 y.

(3) After the application of N cycles of stress range Aa the crack will grow from dimension a\ to dimension a2 according to the following integration:

(4) For the general case A, AK and m are dependent on 'a1.

(5) For further information on fracture mechanics techniques, particularly for welded structures, see References B.8.1 and B.8.2.

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