Patrick Terriault

Design of Shape Memory Alloy Actuators for Morphing Laminar Wing With Flexible Extrados

An active structure of a morphing wing designed for subsonic cruise flight conditions is composed of three principal subsystems: (1) fexible extrados, (2) rigid intrados, and (3) an actuator group located inside the wing box. The four-ply laminated composite flexible extrados is powered by two individually controlled shape memory alloy (SMA) actuators. Fulfilling the requirements imposed by the morphing wing application to the force-displacement characteristics of the actuators, a novel design methodology to determine the geometry of the SMA active elements and their adequate assembly conditions is presented. This methodology uses the results of the constrained recovery testing of the selected SMA. Using a prototype of the morphing laminar wing powered by SMA actuators, the design approach proposed in this study is experimentally validated.

Morphing laminar wing with flexible extrados powered by shape memory alloy actuators

An active structure of a morphing wing designed for subsonic cruise flight conditions combines three principal subsystems: (1) flexible extrados, (2) rigid intrados and (3) an actuator group located inside the wing box. A structural model of the flexible extrados built with ANSYS finite element software is coupled with X’Foil fluid dynamics software to evaluate mechanical and aerodynamic performances of the morphing wing in different flight conditions. Using the multicriteria optimization technique, an active structure consisting of the 4-ply laminated composite flexible extrados powered by two individually controlled actuators is selected. Shape memory alloy (SMA) actuators are designed as power elements for the morphing wing. To meet the functional requirements of the application, the geometry of the SMA elements is calculated using the results of the constrained recovery testing of the selected material.Copyright

Damping in civil engineering using SMA. The fatigue behavior and stability of CuAlBe and NiTi alloys

Two types of application in damping of structures by SMA in Civil Engineering are considered. The first one is related to the reduction of the damage produced by earthquakes. The second one is concerned with the increase of the lifetime of the stayed cables in bridges. The analyses of the experimental conditions required for each application are different: Several years or decades without any activity (excepted the summer-winter room temperature parasitic effects) followed by one or two minutes of oscillations under the earthquake affects, or near 100000 oscillations per day with pauses of several hours or days in the damping of stayed cables in bridges. This article analyzes the fatigue behavior of the CuAlBe alloy (appropriate for earthquakes) and of the NiTi alloy. Measurements of the damping of stayed cables indicate that the oscillation amplitude could be reduced up to one-third by using a NiTi wire as a damper device.

Finite element analysis of a shape memory alloy three-dimensional beam based on a finite strain description

In the present work a modified phenomenological model of the shape memory alloy (SMA) constitutive law is proposed that is capable of reproducing some aspects of SMA thermomechanical behavior like superelasticity and the one-way shape memory effect. The modified law uses strain and temperature as control variables, which eliminates the need for transformation correctors in finite element analysis. It is implemented in a structural model developed to analyze three-dimensional (3D) structures made out of thick beam elements with features such as taper and curvature, given that SMA products typically fall in this category of shapes. Moreover, a finite strain and large displacement description is adopted to account for the large deformations exhibited during phase transformation. Results, produced by the proposed model, of simulated tensile, three-point and four-point bending tests are presented and compared with experimental data taken from the literature.

Testing of Superelastic Recentering Pre-Strained Braces for Seismic Resistant Design

Over the past decade, the use of shape memory alloys (SMAs) in passive control devices has been explored. Nevertheless, some aspects in regards to the cyclic behavior of SMAs and the effect of pre-straining need to be clarified. In this study, small-scale shake table tests have been performed to explore the effectiveness of SMA bracing systems as compared to steel bracing systems. The reduced-scale experimental results imply that SMAs used in braces are more effective in controlling the response of a steel frame compared with a traditional bracing system. A finite element model (FEM) of the frame is developed in order to compare the analytical results with the shake table tests. Further, the effect of pre-straining the SMA braces is evaluated through both experimental and analytical studies. The results show that pre-straining improves the performance of the frame compared to the nonpre-strained case. However, as the level of pre-straining increases above approximately 1.0% to 1.5%, the benefits of pre-straining decrease compared with low-to-moderate pre-strain levels.

Characterization and design of antagonistic shape memory alloy actuators

Antagonistic shape memory actuators use opposing shape memory alloy (SMA) elements to create devices capable of producing differential motion paths and two-way mechanical work in a very efficient manner. There is no requirement for additional bias elements to ?re-arm? the actuators and allow repetitive actuation. The work generation potential of antagonistic shape memory actuators is determined by specific SMA element characteristics and their assembly conditions. In this study, the selected SMA wires are assembled in antagonistic configuration and characterized using a dedicated test bench to evaluate their stress?strain characteristics as a function of the number of cycles. Using these functional characteristics, a so-called ?working envelope? is built to assist in the design of such an actuator. Finally, the test bench is used to simulate a real application of an antagonistic actuator (case study).

Damping in civil engineering using SMA Part 2 – particular properties of NiTi for damping of stayed cables in bridges

Abstract Shape memory alloys (SMAs) show particular properties associated to their martensitic transformation between metastable phases. Their use requires a deep knowledge of the SMA behaviour according to the requirements of the application. In this paper, the following are studied: the required fatigue life of the NiTi SMA that easily overcomes 1 million of oscillations for a complete storm; the suitable thermomechanical treatment to minimise or stabilise the SMA creep; and the temperature effects on the damper and the dynamic phenomena effects modifying the hysteretic energy via the self-heating associated to the release and the absorption of the latent heat were studied. The study includes the effects on SMA of the external summer–winter temperatures. La transformation martensitique entre phases métastables est à l’origine des propriétés particulières des Alliages à Mémoire de Forme (AMF). L’utilisation des AMF nécessite une connaissance approfondie de leur comportement associé aux exigences de l’application. Dans cet article, on étudie: (a) la durée de vie requise de l’AMF NiTi, qui peut facilement avoir à surmonter 1 million d’oscillations lors d’une tempête entière. (b) Le traitement thermomécanique approprié afin de minimiser ou stabiliser le fluage de l’AMF. (c) Les effets de température sur l’amortisseur ainsi que des phénomènes dynamiques modifiant l’hystérésis de l’énergie par l’auto-échauffement associé au dégagement et à l’absorption de la chaleur latente. On étudie également l’effet des températures extérieures de l’été et de l’hiver sur l’AMF.

Nonlinear modelling of hysteretic material laws by dual kriging and application

Abstract Shape Memory Alloys (SMA) exhibit remarkable mechanical properties, which permit to contemplate a large number of potential applications as actuators, connectors as well as passive or active damping devices. Although a large body of existing patents is available on SMA materials, only a limited number of industrial applications have been implemented up to now. This is probably due to a series of factors, including the absence of recognized mechanical standards, the relatively high cost of raw material, the high temperature dependence of SMA mechanical properties, the sensitivity to heat treatments and finally, the difficulty to model correctly hysteretic material laws. All this is about to change, thanks to recent research advances in modelling and to the appearance of new and less expensive alloy families. The purpose of this paper is to describe the computer aided design tools developed at Ecole Polytechnique de Montreal to model the mechanical behavior of shape memory materials and to calculate the mechanical response of shape memory devices. A new kind of material law for hysteretic materials can be generated by combining a new phenomenological model based on dual kriging with a micromechanical model. The interface between the material law and finite elements can be improved by using, instead of a Von Mises transformation criterion, a Prager type criterion that is well suited for shape memory alloys. Finally, two examples of industrial applications, a Belleville washer for electrical contacts and a medical stent for non-invasive surgery, demonstrate the usefulness of this approach in the design and optimization of shape memory devices.

Application of Dual Kriging to the Construction of a General Phenomenological Material Law for Shape Memory Alloys

A large number of applications could benefit from the remarkable properties of shape memory alloys; but up to now, a relatively limited number have been brought to the market. This can be attributed, in part, to the lack of numerical tools dedicated to the computer aided design of shape memory devices. The development of a general material law is the first important step before reliable design calculations can be carried out. This paper presents a new phenomenological constitutive law based on dual kriging, which is a powerful mathematical tool used here as an interpolation method. The model was initially developed for a particular and limited purpose, namely, to simulate the macroscopic behavior of simple shape memory devices. From a few isothermal experimental forcedeflection curves at different temperatures, two surfaces are constructed which describe the loading and unloading behavior of the device.The response of the material subjected to complex thermomechanical loadings is calculated by successive interpolations on these surfaces via dual kriging. For hysteretic subcycles, the response is calculated through the volume delimited by the two surfaces in such a way that any recursive thermomechanical subcycles can be simulated. This methodology yields a uniaxial material law for shape memory alloys that includes in a single formulation superelasticity, pseudo-plasticity and shape memory effect. Preliminary validations on a set of simple examples show the potential of this approach.

Modeling of Shape Memory Alloy Actuators Using Likhachev’s Formulation

This article presents a simplified version of Likhachev’s micromechanical model and its integration in ANSYS, a commercial finite element software package used to simulate the response of a structure equipped with shape memory alloy wire actuators controlled by direct Joule heating. The original Likhachev’s formulation is adapted to obtain a model that is easy to characterize, numerically efficient, and general in the sense that it can simulate all the shape memory-related features using the same formulation (superelasticity, shape memory effect, stress generation, etc.). The adapted Likhachev’s formulation is coupled to an electro-thermal model to simulate temporal response of actuators heated by an electrical current. An experimental result obtained with a deformable airfoil powered by shape memory actuators is used to validate the proposed electro-thermo-mechanical model.