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

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 of defects (the “area 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 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 1010 cycles. It will lead to an increase in the period of operation of casings without their fatigue cracking by more than of two orders.