tailieunhanh - Cyclic behavior and energy approach of the fatigue of shape memory alloys
This paper presents an energy-based low-cycle fatigue criterion that can be used in analyzing and designing structures made from shape memory alloys (SMAs) subjected to cyclic loading. Experimentally, a response similar to plastic shakedown is observed: during the first cycles the stress-strain curve shows a hysteresis loop which evolves during the first few cycles before stabilizing. | Vietnam Journal of Mechanics, VAST, Vol. 31, No. 3 &4 (2009), pp. 191 – 210 CYCLIC BEHAVIOR AND ENERGY APPROACH OF THE FATIGUE OF SHAPE MEMORY ALLOYS 1 Ziad Moumni, 2 Wael Zaki, 3 Habibou Maitournam 1 UME-MS, École Nationale Supérieure de Techniques Avancées 91761 Palaiseau Cedex, France 2 LMS, École Polytechnique, 91128 Palaiseau Cedex, France Abstract. This paper presents an energy-based low-cycle fatigue criterion that can be used in analyzing and designing structures made from shape memory alloys (SMAs) subjected to cyclic loading. Experimentally, a response similar to plastic shakedown is observed: during the first cycles the stress-strain curve shows a hysteresis loop which evolves during the first few cycles before stabilizing. By adopting an analogy with plastic fatigue, it is shown that the dissipated energy of the stabilized cycle is a relevant parameter for estimating the number of cycles to failure of such materials. Following these observations, we provide an application of the cyclic model, previously developed by the authors within the framework of generalized standard materials with internal constraints [16], in order to evaluate such parameter. Numerical simulations are presented along with a validation against experimental data in case of cyclic superelasticity. Keywords: cyclic loading, residual strain, internal stress, dissipation, fatigue. 1. INTRODUCTION The interesting behavior of SMAs is essentially due to their capability of undergoing a reversible diffusionless solid–solid phase transition known as “the martensitic transformation”[31, 24, 18]. This transition is characterized at the microscopic level by a modification of the crystallographic lattice structure, which can be induced by altering either the material temperature or the stress to which it’s subjected or both, hence a strong thermomechanical coupling. At high temperature, a shape memory alloy consists of a relatively ordered parent phase called austenite, which transforms .
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