Holovatyuk Y. Assessment of the physico-mechanical characteristics for degradation estimation of Д16 and В95 aluminium alloys during long-term exploitation.

Structure and properties of aluminum alloys Д16чT (Д16T) and В95пчT1 (В95T1) in the initial and degraded states. Based on the obtained destructive and non-destructive test methods of changing the structural-phase state, mechanical, electrochemical and physical characteristics of aluminum alloys such as Д16 and В95 after a long-term operation to establish characteristics that are susceptible to degradation, as well as correction coefficient to determine the fatigue durability of the elements of air craft constructions with account of structural materials degradation. Methodological basis of the work is optical and electronic microscopy, local thermo-electromotive force and eddy currents measuring, microfractography analysis, mechanical tests, under static loading for short-timed strength and under the cyclic loading for fatigue crack growth resistance and durability. It is shown that the most sensitive to in-service and model degradation of Д16чТ (Д16T) and В95пчТ1 (В95T1) aluminium alloys are elongation of smooth specimens under static loading, effective fatigue threshold of cracked specimens and fatigue durability of notched specimens. The decrease of mechanical characteristics and sensitivity to grain-boundary cracking in the corrosion environment of Д16 and В95 aluminium alloys after model and operating degradation due to the increase of the second phase precipitations (size of 0.01-0.05 mm) amount, microcracking of intermetallics of the initial microstructure, increase of dislocation density and accumulation of slip bands at the grain boundary of the matrix are determined. The elongation and fatigue durability decreasing for degraded Д16 and В95 alloys in 1.5 - 2.5 times is accompanied by 28-30% increase of electrical conductivity, that can be used for monitoring of aircraft materials degradation by a non-destructive method. The testing results and estimated values of correction coefficients are used for the evaluation of the residual life of "Antonov" airplanes after long-term operation.