Criterion of optimization of slow fatigue crack growth in metals and alloys

Based on macro structural analysis of a typical fatigue fracture of a cylindrical specimen of alloy D16T with an annular notch in bending is shown the technique of constructing the kinetic diagram of slow growth of fatigue cracks in the light of the third coordinate - the number of cycles. It is shown the quantification of growth up cracks in the projection plane: of quantity of cycles - the speed of the crack. A kinematic diagram of slow growth of a fatigue crack gives the possibility to assess the beginning of intensive increase to a stable crack growth of 10^-6 – 10^-4 mm/cycle. It is technically difficult to monitor fatigue crack growth at this level of growth rate. This is why the beginning stage of the transition from a slow-growing fatigue crack to a stably growing crack is an important technological safety parameter in the operation of parts with cracks. This work proposes a new criterion of assessing the optimality of slow fatigue crack growth on the example of the aluminum alloy D16T.