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Wednesday, December 5, 2007 - 2:40 PM

Cyclic Behavior and Energy Approach of the Fatigue of Shape Memory Alloys

Z. Moumni, UME-MS, Ecole Nationale Superieure de Techniques Avancees, Paris, France; W. Zaki, Henri Tudor public research center, Kirchberg-Luxembourg, Luxembourg; H. Maitournam, LMS,École Polytechnique, Palaiseau, France

This paper provides a thermomechanical model and an energybased

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. Following these observations, a macro-scale approach

is used to develop a three dimensional model, within the framework

of generalized standard materials with internal constraints (Moumni

1995), which accounts for the cyclic behavior of SMAs. Numerical

simulations are provided and validated in the case of cyclic superelasticity.

Using this model and 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.


Summary: This paper provides a thermomechanical model and an energybased 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. Following these observations, a macro-scale approach is used to develop a three dimensional model, within the framework of generalized standard materials with internal constraints (Moumni 1995), which accounts for the cyclic behavior of SMAs. Numerical simulations are provided and validated in the case of cyclic superelasticity. Using this model and 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.