Enhanced assessment of technological factors for Ti-6Al-4V and Al-Cu-Mg strength properties

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 Enhanced assessment of technological factors for Ti-6Al-4V and Al-Cu-Mg strength properties Kirill Zakharchenko 1, 2, a, * , Vladimir Kapustin 2, 1, b , Alexey Larichkin 1, 3, c 1 Lavrentyev Institute of Hydrodynamics SB RAS, 15 Ac. Lavrentieva ave., Novosibirsk, 630090, Russian Federation 2 Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russian Federation 3 Novosibirsk State University, 1 Pirogova Str., Novosibirsk, 630090, Russian Federation a https://orcid.org/0000-0003-2626-6184 , zaharchenkok@mail.ru , b https://orcid.org/0000-0001-6124-2503 , macler06@mail.ru , c https://orcid.org/0000-0002-7306-9522 , larichking@gmail.com Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2021 vol. 23 no. 4 pp. 125–139 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2021-23.4-125-139 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO Article history : Received: 04 August 2021 Revised: 16 September 2021 Accepted: 23 September 2021 Available online: 15 December 2021 Keywords : Enhanced assessment Cyclic loading Elastoplastic strain Strain characteristics Dissipative characteristics Finite element method Funding The reported study was funded by RFBR and Novosibirsk region according to the research project № 19-48-543028. ABSTRACT Introduction. The strength of construction materials when used under cyclic loads is of great importance in design engineering. A signi fi cant number of factors that affect the fatigue resistance have predetermined the creation of numerous methods that consider such in fl uence. Nondestructive methods that are based on the connection of the physical degradation of material with strain properties enable evaluating experimentally the fatigue properties of materials. Purpose of study : the analysis of the processes of energy dissipation and strain accumulation during the inelastic cyclic strain of samples, using the VT6 ( Ti-6Al-4V ) titanium alloy and the D16 ( Al-Cu-Mg ) aluminum alloy before and after the technological impact. The work experimentally investigates the physical processes of degradation of the VT6 and D16 alloy samples that accompany the process of fatigue failure in materials with homogeneous and inhomogeneous stress-strain states in the concentrator (in the form of a hole and a weld). Typical modes are used to reach the fatigue testing that determine the critical stress in a material sample – the stress at which physical properties (temperature, strain) change without reaching the fatigue failure of samples. Critical stress amplitudes in the cycle, based on the data obtained during the experiment and the results of mathematical simulation, are compared. The effect of stress concentrators on critical loads that a detail can withstand after a unit operation is estimated by the fi nite-element method ( FEM ). As a result , the effect of the operational and technological factors on critical stress determined by strain and temperature is estimated. Comparative tests of the VT6 and D16 alloy samples with and without stress concentrators showed that the amplitudes of critical stress decrease by more than 30% in comparison with the ones that are without stress concentrators. The low-cycle fatigue tests of the D16 alloy samples are carried out. Mathematical simulation of the cyclic strain of the samples is carried out using MSC.Marc package. The results of the cyclic loading tests, which show that the characteristics of the technological process reduce the amplitudes of the critical stress of the VT6 and D16 alloys and affect the fatigue properties of the D16 aluminum alloy, are discussed . Mathematical simulation corresponded positively to the experimental data. Such correspondence indicates the possibility of conducting qualitative numerical assessments of the beginning of the inelastic strain accumulation process in structures with stress concentrators under the cyclic stress and the increasing stress amplitude, using the typical sample made of hardening elastoplastic material. For citation: Zakharchenko K.V., Kapustin V.I., Larichkin A.Yu. Enhanced assessment of technological factors for Ti-6Al-4V and Al-Cu-Mg strength properties. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2021, vol. 23, no. 4, pp. 125–139. DOI: 10.17212/1994-6309-2021-23.4-125-139. (In Russian). ______ * Corresponding author Zakharchenko Kirill V. , Ph.D. (Engineering), Associate Professor Novosibirsk State Technical University, 20 Prospekt K. Marksa, 630073, Novosibirsk, Russian Federation Tel.: 8 (383) 346-17-64, e-mail: zaharchenkok@mail.ru Introduction A large number of works [1] are devoted to methods for determining the characteristics of resistance, including the methods described in GOST 25.502-79. In enhanced methods of computational and experimental evaluation of the endurance limit of a material, several main groups can be conventionally distinguished.