Engineering assessment of minimum fatigue life for given probability of its non-exceedance

• Main Authors: Kirill B. Proskuryakov, Oleg B. Shagniev, Anna R. Shkadova
• Format: Article
• Language: English
• Published: Krylov State Research Centre 2021-03-01
• Series: Труды Крыловского государственного научного центра
• Subjects: cyclic durability; weibull distribution; fatigue curve; structural materials; gamma percentage resource
• Online Access: https://transactions-ksrc.ru/eng/archive/Engineering-assessment-of-minimum-fatigue-life-for-given-probability-of-its-non-exceedance/
• ISSN: 2542-2324; 2618-8244

Object and purpose of research. This paper discusses structural materials under cyclic load. The purpose is to determine the minimum fatigue life corresponding to a certain non-exceedance probability of this value. Materials and methods. The study was performed on three structural materials: steel 15ХМ, steel 08Kh18N10Т and titanium alloy PТ-7М. Initial estimate of fatigue life distribution parameters relied on the data about guaranteed maximum and minimum values of temporary resistance and relative cross-section tapering. The assessment was performed as per a common curve “conditionally elastic stress amplitude versus number of cycles to failure” taking into account the mechanical properties of given material. The values of minimum fatigue life were obtained as per two different methods: statistical simulation of the random values following the Weibull distribution law and the analytical expression for probability density of the lows for given distribution function of random value and fixed scope of sampling. Main results. The lows yielded by statistical simulation are more conservative than those yielded by the analytical formula. The margin in terms of the number of cycles to failure stipulated as 10 in several regulatory documents seems to be somewhat unsubstantiated. This margin is too great in the low-cycle domain and too small in the high-cycle one. Conclusion. This paper postulates the existence of guaranteed maximum and minimum values for mechanical properties of structural materials, namely temporary resistance and relative cross-section tapering. These values were applied to well-known analytical curves of fatigue, which finally yielded possible variation ranges for fatigue life at various amplitudes of conditionally elastic reduced stresses, assuming the existence of a certain shift in the sensitivity limit of fatigue life distribution. These data were further used to establish standard deviations and mathematical expectations for the number of cycles to failure.