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629.7.015.4:539.43 and V. G. PetrusenkoWe present the results of experimental investigations of the mechanical characteristics, fatigue characteristics, cyclic crack growth resistance and residual strength of aluminum alloy materials for a wing and fuselage skin of airplanes having a service life from 8 to 38 years.Separate problems of degradation in the properties of aluminum alloys in the process of the long-term aircraft operation were studied by a number of scientists [1][2][3][4][5].In this work, the problems of degradation are studied thoroughly by experimental determination of the static strength, fatigue and crack growth resistance of materials of various types of domestic and foreign aircraft.The experimental investigation of the degradation in the material characteristics was performed using specimens cut from wing (W) and fuselage (F) structures of aircraft that have been in service for long periods of time (old materials) and from sheets taken from warehouses (new materials).The mechanical characteristics were determined by tensile tests of specimens in accordance with standards available. The investigation on the low-cycle fatigue N was performed using specimens in the form of bands 36 mm in width, 170 mm in length with a central hole 6 mm in diameter and stress intensity factor in the net cross section α σ = 2 6 . . The low-cycle fatigue of specimens was studied under a repeating cycle of loading (R = 0) with the maximum stresses in the gross cross section, σ max gross =133 MPa and a frequency of 3 Hz.The investigation of the cyclic and static crack growth resistance of the materials was performed using unfixed specimens with a central crack. All specimens were tested in the initial state (the cladding and anodizing were retained) without applying anti-buckling plates.Two types of specimens, namely, wide and narrow specimens, were tested. The wide specimens taken from the wing had the width W = 495 to 750 mm, those from the fuselage had a width W =1200 mm. The specimen length was equal to the triple width. To simulate cracks, a notch was made at the center of each specimen. The wide specimens were tested for crack growth rate at the stress ratio R = 0 023 . and stress range Δσ σ σ = − = max min 130 MPa at a frequency of f = 0 17 . Hz. After testing for crack growth time (rate), the specimens with laboratory-grown cracks were tested for residual strength.The narrow specimens had the width W ranging from 160 to 200 mm. Tests of the narrow specimens for crack growth time were performed at an oscillating cycle of loading with Δσ σ σ = − = max min 130 MPa and at a frequency of 1 Hz. A part of the narrow specimens under study was preliminarily subjected to annealing at a temperature of 400°C.Tests were performed using electrohydraulic testing machines of the following types: PSA-10 Schenck, MTS-100, MTS-250, and MTS-1000.The experimental data on the crack growth resistance of the materials were processed by the nonlinear fracture mechanics methods [1]. The percentage of impurities of iron (Fe) and sil...

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The results of experimental studies of the static strength, fatigue and crack resistance of modern improved aluminum alloys 1163ATV, 1163RDTV, 1441RT1, 1163T, 1163T7, 1161T, V95ochT2, B96-3pchT12., 1973T2 developed at the All-Russian Scientific Research Institute for Aviation Materials (VIAM, Russia); and 2524-T3, 6013-T6 HDT, 2324-T39, C433-T351, 7055-T7751 developed at ALCOA (USA) are presented. Those materials are used in the construction of modern operated and designed aircraft. The experimental data were obtained in testing standard specimens on electro-hydraulic machines MTS (USA), Instron (Great Britain) and Schenk (FRG). The tested specimens were cut from semi-products manufactured according to serial technologies. The mechanical properties of materials under tension (σb, σ0.2, δ), fatigue characteristics, fatigue crack growth rate, stress crack propagation curves under static loading (R-curves), conditionally critical stress intensity factors are determined according to domestic standards. To ensure high weight efficiency combined with a high resource and high performance characteristics of the aircraft structures, aluminum alloys must have the following set of necessary characteristics: high resistance to variable loads, low rate of fatigue cracks growth, required residual strength, and good corrosion resistance. The obtained results of experimental studies clearly demonstrate the advantages and disadvantages of the strength properties of the materials under study. The results of experimental studies provide the possibility to compare the strength properties of the materials under study to optimize their use for the specific zone of the structure and thus increase the life and safety of the aircraft design.

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