ISO 12108 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.
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.
ISO 12018 describes tests for determining the fatigue crack growth rate from the threshold stress-intensity factor range to the onset of unstable crack extension as the maximum stress intensity factor approaches controlled instability. It 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.