Experimental Investigation and Numerical Simulation of the Mechanical and Thermal Behavior of a Superelastic Shape Memory Alloy Beam During Bending

Abstract

Superelastic Shape Memory Alloys (SMA) are typically used in applications where the martensitic phase transformation is exploited for its reversible, large deformation such as medical applications (e.g. stents). In this work, we focus on the mechanical and thermal behavior of a Nickel-Titanium SMA strip in bending mode. One possible application of this mode is to provide a restoring force when used in joints of SMA wire actuator systems making the need for an antagonistic SMA actuator redundant. In these applications mentioned above, typically only the mechanical properties are of interest while the temperature is considered constant, even though the martensitic phase transformation in SMA is a thermo-mechanically coupled process. As a part of the DFG (German Research Association) Priority Programme SPP1599 “Ferroic Cooling” which aims at advancing the development of solid state cooling devices, we have an equally large interest for the thermal evolution of Nickel-Titanium SMA during deformation and its induced phase transformation. In this paper we investigate the thermal and the mechanical response of a SMA beam during bending experiments in which the deformation is induced by holding one end of a SMA strip fixed while the other end is subject to a prescribed deflection. Sensors and high speed thermal cameras are used to capture reaction forces, deformations and temperature changes. We compare these experimental results with numerical simulation results obtained from Finite Element simulations where a thermo-mechanically coupled SMA model is implemented into a finite deformation framework.

Scientific test setup for investigation of shape memory alloy based elastocaloric cooling processes

“…However, the study of the parameter variation, which was the main aim of this work, is not affected. Future work will address optimization of the process parameters, testing of different SMA material compositions for different temperature ranges of operation and also correlation of the experimental data with novel coupled multifield simulation models (Ullrich et al, 2014).…”

NiTi‐Based Elastocaloric Cooling on the Macroscale: From Basic Concepts to Realization

“…[9,[50][51][52] Theg eometry and loadingt ype of the SMA are not only limited to macroscopic wires under tensilel oading since each application requires ad ifferent geometry and loading type. [53,54] In addition to the various types of elastocaloric devices mentioned in Section 2.5, also bendingo fr ibbons is ap otential load case as presented by Ullrich et al [55] Investigation of the fatigue life of NiTi, as well as NiTiCu wires,s hows am aterial lifetime of up to 10 6 cycles for small strains below 2%. [56] NiTiCu thin films for small-scale applications have been shown to have very high cyclic stability and am aterial lifetimeo fu pt o1 0 7 cycles.…”

“…[18,60,[97][98][99] Thermomechanically coupledf inite element simulations based on an extended version of the 1D Müller-Achenbach-Seelecke( MAS)m odel [91,92] have been conducted on actuator wires, [100] superelastic wires, [101] and beams. [55,102] Other1 D simulations of actor wires [18,103] have been based on the approach proposed by Shaw and co-workers. [104,105] Multidimensional simulationsh ave been performed as well.…”

“…Startinga tt he clamps,t he phase fronts travel towards the center of the sample.T he number of phase fronts dependso nt he applied strain rate and changes from two at 0.001 s À1 ,t os even at 0.01 s À1 ,t oanear Figure 19. Comparison of experimental data (solid lines) and simulation (dotted lines) for displacement, spatiotemporal temperature evolution,specific mechanical work and thermalenergy using sputter-deposited thin-film of Ti 55 [91,92] in COMSOL, the simulation is extended by 3D effects such as lateral contraction with different Poisson ratios for elastic and transformation strain.I nternal stresses at the phase front preferring full transformation due to lattice mismatch of martensite and austenite are captured by a phase fractiond ependent transformation stress.Agradient term, added in the kinetic equation of the phase fractions, ensures am inimal transition zone length between neighboring phases.A fter ap arameter identification on the mechanical and thermal data, comprising all three strain rates,t he model is able to recreatethe material behavior quantitatively with one set of parameters.…”

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

“…Furthermore, the timing of the temperature peak formation and the resulting stress decrease shows good agreement. The applied model approach is not only limited to the simulation of the material behavior at tensile load, also a bending load can be simulated 25 . The physically motivated model allows for detailed analysis of the underlying mechanisms and supports process and material optimization by reducing experimental and material development effort.…”