Mechanisms of fatigue crack initiation and propagation in cast aluminum alloy AL5 of hydropumps NP-89D in aircraft Tu-154M

摘要

The paper demonstrates results of quantitative fractographic analyses of in-service fatigued cast AL5 Al-based alloy of hydropumps NP-89D. A model based on Vickers hardness of metal matrix and the area~(1/2) of defects (the "area~(1/2) model") has been introduced. It describes microcracks threshold originating from cast porosities. Crack growth period estimated by the result of meso-beach marks spacing measurements and stress equivalent calculated by the "area~(1/2) model" are used to discuss causes of the in-service cracking of the pump casing. It is shown that damping of self-oscillations with simultaneous decrease in an equivalent stress level of the hydrounit will allow increasing the operating time up to pump probable failure corresponding to more than 10~(10) cycles. It will lead to an increase in the period of operation of casings without their fatigue cracking by more than of two orders.