Abstract
Components and structures are designed based in their material’s mechanical properties such as Young's modulus or yield stress among others. Often those properties are obtained under monotonic mechanical tests but rarely under cyclic ones. It is assumed that those properties are maintained during the material fatigue life. However, under cyclic loadings, materials tend to change their mechanical properties, which can improve their strength (material hardening) or degrade their mechanical capabilities (material softening) or even a mix of both. This type of material behaviour is the so-called cyclic plasticity that is dependent of several factors such as the load type, load level, and microstructure. This subject is of most importance in design of structures and components against fatigue failures in particular in the case of magnesium alloys. Magnesium alloys due to their hexagonal compact microstructure have only 3 slip planes plus 1 twining plane which results in a peculiar mechanical behaviour under cyclic loading conditions especially under multiaxial loadings. Therefore, it is necessary to have a cyclic elastic-plastic model that allows estimating the material mechanical properties for a certain stress level and loading type. In this paper it is discussed several aspects of the magnesium alloys cyclic properties under uniaxial and multiaxial loading conditions at several stress levels taking into account experimental data. A series of fatigue tests under strain control were performed in hour glass specimens test made of a magnesium alloy, AZ31BF. The strain/stress relation for uniaxial loadings, axial and shear was experimentally obtained and compared with the estimations obtained from the theoretical elastic-plastic models found in the state-of-the-art. Results show that the AZ31BF magnesium alloy has a peculiar mechanical behaviour, which is quite different from the steel one. Moreover, the state of the art cyclic models do not capture in full this peculiar behaviour, especially the cyclic magnesium alloys anisotropy. Further, an analysis is performed to identify the shortcomings inherent to the actual cyclic models in the capture of the magnesium alloys cyclic behaviour. Several conclusions are drawn.
Highlights
K nowing the material stress state under any kind of loadings is of utmost importance since the interpretation of the mechanical behaviour is based in that stress state[1, 2]
From these hysteresis loops can be inspected the yield stresses in tension and compression; in steels the yield stresses in tension and compression are the same or similar, but for other types of materials those stresses it may be quite different, which is the case of magnesium alloys
A key question may be raised: What is the real stress state of the material under cyclic loading conditions? There is some way to know those stress states? The answer to these questions is of utmost importance because it is only possible to reach reliable conclusions about the material mechanical behaviour knowing the real relation between stress and strain in any loading condition
Summary
K nowing the material stress state under any kind of loadings is of utmost importance since the interpretation of the mechanical behaviour is based in that stress state[1, 2]. One way to interpret the variation of the cyclic mechanical properties is to analyse the hysteresis loop resulting from several loading paths at several stress levels From these hysteresis loops can be inspected the yield stresses in tension and compression; in steels the yield stresses in tension and compression are the same or similar, but for other types of materials those stresses it may be quite different, which is the case of magnesium alloys. The answer to these questions is of utmost importance because it is only possible to reach reliable conclusions about the material mechanical behaviour knowing the real relation between stress and strain in any loading condition This relation depends on the stress level and of the load type. Additional multiaxial stress-strain experiments are needed to adjust and validate the considered multiaxial hypothesis
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
