Fatigue limit assessment of a 6061 aluminum alloy based on infrared thermography and steady ratcheting effect
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Fatigue limit assessment of a 6061 aluminum alloy based on infrared thermography and steady ratcheting effect Ru-yi Feng 1), Wen-xian Wang 1,2,3), Zhi-feng Yan 1,2,3), Deng-hui Wang 1), Shi-peng Wan 1), and Ning Shi 1) 1) College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China 2) Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China 3) Shanxi Key Laboratory of Advanced Magnesium-based Materials, Taiyuan University of Technology, Taiyuan 030024, China (Received: 4 October 2019; revised: 3 November 2019; accepted: 1 December 2019)
Abstract: To quickly predict the fatigue limit of 6061 aluminum alloy, two assessment methods based on the temperature evolution and the steady ratcheting strain difference under cyclic loading, respectively, were proposed. The temperature evolutions during static and cyclic loadings were both measured by infrared thermography. Fatigue tests show that the temperature evolution was closely related to the cyclic loading, and the cyclic loading range can be divided into three sections according to the regular of temperature evolution in different section. The mechanism of temperature evolution under different cyclic loadings was also analyzed due to the thermoelastic, viscous, and thermoplastic effects. Additionally, ratcheting strain under cyclic loading was also measured, and the results show that the evolution of the ratcheting strain under cyclic loading above the fatigue limit undergone three stages: the first increasing stage, the second steady state, and the final abrupt increase stage. The fatigue limit of the 6061 aluminum alloy was quickly estimated based on transition point of linear fitting of temperature increase and the steady value of ratcheting strain difference. Besides, it is feasible and quick of the two methods by the proof of the traditional S–N curve. Keywords: 6061 Aluminum; temperature evolution; fatigue limit; ratcheting strain
1. Introduction The wide use of aluminum alloys as various structures and mechanical components in the military and aerospace fields is promising due to their low density, high specific strength, and good plasticity [1–2]. In these applications, most of the components are inevitably serviced under cyclic loading and are more inclined to suddenly rupture, which causes great loss or disaster [3]. Fatigue failure under cyclic loading is a process of damage accumulation in which most of the plastic work is consumed in the form of heat, causing an increase in the surface temperature [4]. Therefore, it is of great significance to study the relationship between the change in surface temperature and fatigue cyclic loading. Infrared thermography (IRT), detecting heat waves generated by materials during dynamic loading with the infrared camera, has been efficiently used to record the surface temperature evolution and investigate the thermomechanical behavior of materials in a wide
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