Finite Element-Based Numerical Investigations of a Beamlike Actuator Combining Shape Memory and Superelastic Effects

It has been amply demonstrated that the development of SMA actuators has a great potential of application in several branches of industry. Obviously, the efficiency of the actuators depends both on the inherent features of the materials they are made of and the geometric characteristics of the devices. This work considers a particular type of actuator first conceived by [1], consisting in the association of two cantilever beams, the first presenting the shape memory effect and the second presenting the superelastic effect, coupled mechanically so as to guarantee two equilibrium positions and thus a stand-alone cyclic actuator, in which the superelastic beam provides the bias action. Numerical simulations of the behavior of the actuator are performed using the commercial finite element software COMSOL, which implements the Boyd-Lagoudas thermomechanical model. The goal of the simulations is to characterize the actuation range of the actuator, in terms of maximum displacement obtained at the tip. The effect of the dimensions of the beams on the tip displacement under some load scenarios is investigated. The results provide guidelines for the design of the actuator to fulfill specific requirements, also suggesting the use of numerical optimization for the optimal design of the actuator accounting for constraints.

Recent Progress and Future Perspectives in Magnetic and Metamagnetic Shape-Memory Heusler Alloys

Magnetic shape-memory properties refer to the ability of certain materials to show strong response in strain to an applied magnetic field. This strain is caused by either inducing the martensitic transition or rearranging martensitic variants. In the first, case a superelastic effect is possible, while in the second, the system is able to show the shape-memory effect. The complex behaviour displayed by these materials is mainly a consequence of a strong interplay between magnetism and structure which is driven by a martensitic transition. This interplay is the source of many other observed effects such as giant magneto-resistance, exchange bias and magnetocaloric effects. In this paper, we will overview the present state of the art, discuss present challenges and outline some future perspectives in the field.

A New Constitutive Model of Superelastic SMA

The shape memory alloys (SMAs) have received increasing interest attributed to their unique superelastic effect and the shape memory effect. The existing models of superelastic SMAs are generally complex for practical use. In this paper, cyclic loading tests of superelastic SMA wires are first performed. Based on the experiments, a simple constitutive model is set up. Simulations testify that the model can approximately describe the hysteretic characteristics of the superelastic SMA and the simulated mechanical parameters agree well with the experimental values.

Martensitic Transformations Using a Two-Body Isotropic Potential: Strain-Stress Simulations and Superelasticity in Monocrystals

We use an isotropic interaction potential for a set of classical identical particles to model martensitic transformations and the processes that are usually associated with them. We performed 2D numerical simulations of a strain-stress experiment and show that superelastic effect is present in our model.

Superelastic Shape Memory Elements Using Intrinsic Sensor Effects

The superelastic effect of shape memory alloys (SMA) allows reversible material deformations of up to 8% of an element’s length. Although such SMA elements are commonly used for medical applications, only a few utilizations are used in the field of industrial automation. An often disregarded advantage of superelastic elements is the option to replace a conventional elastic element with a smart element including elastic characteristics as well as a deformation sensor. The resistance change of pseudoplastic and superelastic alloys in dependency of varying ambient temperatures, their characteristics during deformation and concepts for different elastic elements with intrinsic sensor functions are the topics of the paper at hand. Additionally, this paper offers an overview over possible combinations of both alloy types utilized as sensing elements. A demonstrator device, capable of elastic-deformation and sensor-feedback signals is presented at the end of this publication.

The Effects of Laser Forming on NiTi Superelastic Shape Memory Alloys

This work focuses on application of the laser forming process to NiTi shape memory alloys. While all NiTi shape memory alloys exhibit both superelasticity and the shape memory effect, this study is restricted to a temperature range over which only the superelastic effect will be active. Specifically, this work addresses laser forming induced macroscopic bending deformations, postprocess residual stress distributions, and changes in microstructure. Like traditional ferrous alloys, the laser forming process may be used as a means for imparting desired permanent deformations in superelastic NiTi alloys. However, this process, when applied to a shape memory alloy also has great potential as a means for shape setting “memorized” geometric configurations while preserving optimal shape memory behavior. Laser forming may be used as a monolithic process, which imparts desired deformation while maintaining desired material behavior. Characterization of the residual stress field, plastic deformation, and phase transformation is carried out numerically and is then subsequently validated via experimental results.