Matlab® Algorithm to Simulate the Dynamic Behavior of an NiTi Alloy through Ansys® APDLTM Models

In recent years, technological advances related with the so-called intelligent materials have been exploited for problem solving in many engineering fields. In this regard, shape memory alloys (SMA) seem suitable for medical and engineering applications and many others. These alloys have the ability to return to the original form after an apparently plastic deformation by applying heat and the also ability to perform phase changes with voltage variations under a specific temperature. These properties allow the development of a hysteretic loop with energy dissipation, which can be used as  a damping element in a vibratory system. In this paper, a MATLAB algorithm was developed to create an interface with the Ansys® APDLTM software that simulate the dynamic behavior of a SMA. The software is capable to obtain the cyclical behavior of a vibratory mechanical system based on the energy dissipation properties of the SMA. The results show that the free vibration of a mass-damper (alloy) system presents the energy dissipation related in magnitude with the area of the hysteresis loop until the deformation caused by the motion which does not correspond to a voltage required to initiate the (direct) phase transformation of the material, thus reducing the displacement to a constant level. Keywords: SMA, ANSYS APDLTM, Matla

Vibration control with shape-memory alloys in civil engineering structures

Dissertação apresentada à Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Doutor em Engenharia CivilThe superelastic behavior exhibited by shape-memory alloys shows a vast potential for technological applications in the field of seismic hazard mitigation, for civil engineering structures. Due to this property, the material is able to totally recover from large cyclic deformations, while developing a hysteretic loop. This is translated into a high inherent damping, combined with repeatable re-centering capabilities, two fundamental features of vibration control devices. An extensive experimental program provides a valuable insight into the identification of the main variables influencing superelastic damping in Nitinol while exploring the feasibility and optimal behavior of SMAs when used in seismic vibration control. The knowledge yielded from the experimental program, together with an extensive bibliographic research, allows for the development of an efficient numerical framework for the mathematical modeling of the complex thermo-mechanical behavior of SMAs. These models couple the mechanical and kinetic transformation constitutive laws with a heat balance equation describing the convective heat problem. The seismic behavior of a superelastic restraining bridge system is successfully simulated, being one of the most promising applications regarding the use of SMAs in civil engineering structures. A small-scale physical prototype of a novel superelastic restraining device is built. The device is able to dissipate a considerable amount of energy, while minimizing a set of adverse effects, related with cyclic loading and aging effects, that hinder the dynamic performances of vibration control devices based on passive superelastic wires.Fundação Calouste Gulbenkian (bolsa de curta duração) and of Fundação para a Ciência e Tecnologia (FCT/MCTES grant SFRH/BD/37653/2007

Effect of Geometry And Material on the Response of A Shape Memory Alloy (sma) Earthquake Damper

Shape memory alloys (SMAs), such as Nitinol (i.e., NiTi), are of numerous importance in engineering applications due to their exceptional superelasticity and shape memory properties. Applications of a Shape Memory Alloy (SMA) in alleviating the seismic vibration response of civil infrastructure is attaining momentum. “Shape Memory” indicates that the material recollects its original formed shape. SMA has two simple properties, Super-Elasticity and Shape Memory Effect (SME). The “Super-Elastic” behavior revealed by SMA materials, allows a full recovery of strains up to 8% from big cyclic deformations, whereas developing a hysteretic loop. SME permits the material to recover the primary shape which is considered as re-centering mechanism. The mechanism of shape recovery comprises two crystallographic phases, Martensite and Austenite, and the transformations amongst them. The Austenite phase offers more stiffness than the Martensite phase. Phase transformation happens among Martensite and Austenite subject upon temperature and stress. These exceptional properties result in high damping and repeatable re-centering abilities which is an advantage in several civil infrastructure applications, exclusively in seismic vibration control devices. In recent years, additive manufacturing (AM) processes have been used to produce complex NiTi components, which provide the ability to tailor microstructure and thus the critical properties of the alloys. SMAs have also been explored progressively by the earthquake engineering community, because of their extraordinary self-centering (SC) and energy-dissipating competences. This work analytically presents numerical investigations iv executed to comprehend the numerical behavior of an SMA damper. Part of the numerical model is assessed against an experimental result by Zhai et al. (2020) and exhibited reasonable accuracy. The SMA damper with SC function under monotonic, fatigue cyclic and quasi-static cyclic loading is presented. The numerical results demonstrate that outstanding and stable flag-shaped hysteresis loops are exhibited in multiple loading cycles, indicating good energy dissipation, large deformation and ductility abilities. The stress-strain states with dissimilar phase transformation are also discussed in this work

Application and modelling of shape-memory alloys for structural vibration control : state-of-the-art review

One of the most essential components of structural design for civil engineers is to build a system that is resistant to environmental conditions such as harsh chemical environments, and catastrophic disasters like earthquakes and hurricanes. Under these circumstances and disturbances, conventional building materials such as steel and concrete may demonstrate inadequate performance in the form of corrosion, deterioration, oxidizing, etc. Shape Memory Alloys (SMAs) are novel metals with distinct features and desirable potential to overcome the inadequacies of existing construction materials and enable the structure to tolerate disturbances more efficiently. Shape Memory Effect (SME) and Pseudoelasticity (PE) have been the most attractive characteristics that scientists have focused on among the various features that SMAs exhibit. The SME enables the material to retain its original shape after severe deformation, whereas the PE behaviour of SMAs provides a wide range of deformation while mitigating a substantial amount of susceptible stresses. These behaviours are the consequence of the phase transformation between austenite and martensite. Many investigations on the modelling and application of SMAs in structural systems to endure applied dynamic loadings in the form of active, passive, and hybrid vibration control systems have been undertaken. The focus of this paper is to present an overview of the SMA-based applications and most frequently employed constitutive modelling, as well as their limits in structural vibration control and seismic isolation devices

Modeling and Simulation of Shape Memory Alloys using Microplane Model

In this chapter, a three-dimensional phenomenological constitutive model for the simulation of shape memory alloys is introduced. The proposed macromechanical model is based on microplane theory. Microplane approach is chosen to have limited material parameters in that all of those are measurable by simple tests. User material subroutine is developed to implement the proposed model in a commercial finite element package. NiTi hollow tube specimens are under various loading conditions in order to experimentally study the superelastic response of shape memory alloys. Comparing experimental data with numerical results in simple tension and pure torsion as well as proportional and nonproportional tension-torsion loadings demonstrates the capability of proposed model in constitutive modeling of shape memory alloys

Ioonsete elektroaktiivsete täiturite elektromehaaniline modelleerimine ja juhtimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneIoonsed elektroaktiivsed polümeerid e. tehislihased on polümeermaterjalid, mille oluline iseärasus on võime muuta elektrienergiat mehhaaniliseks energiaks. Elektroaktiivsetest polümeeridest valmistatud pehmetel täituritel on mitmed huvipakkuvad omadused, näiteks suur deformatsioon madala rakendatud pinge korral, märkimisväärne tekitatud jõu ja massi suhe ning võime töötada nii vesikeskkonnas kui õhus. Niisuguste täiturite kasutamine on paljutõotav eriti just miniatuursetes elusloodusest inspireeritud robootikarakendustes. Näiteks võib tuua aktiivsed mikro-manipulatsioonisüsteemid või isepainduvad pehmed kateetrid, mis on iseäranis nõutud meditsiini-tehnoloogias. Käesoleva väitekirja uurimissfääriks on sellistest materjalidest valmistatud täiturmehhanismide modelleerimine, valmistamine ja juhtimine, päädides sisuliselt ühes tükis valmistatud mitme vabadusastmega paralleelmanipulaatorite väljatöötamisega. Kasutades kompleksset füüsikalistel, elektrokeemilistel ning mehaanilistel alusteadmistel põhinevat mudelit kirjeldatakse ja ennustatakse sellist tüüpi täiturmehhanismide elektrilise sisendi ja mehhaanilise väljundi vahelisi seoseid. Mudel kirjeldab ioonide transpordi dünaamikat elektriväljas, kombineerides Nernst-Plancki ja Poissoni võrrandeid. Mitmekihilise polümeermaterjali mehhaaniline käitumine on seotud laengu- ja massitasakaalu poolt põhjustatud eri kihtide erineva ruumilise paisumisega ja kahanemisega. Kõike seda kokku võttes ning rakendades numbrilist modelleerimist lõplike elementide meetodil saadakse kvantitatiivsed tulemused, mis suudavad prognoosida täiturmehhanismi käitumist ja võimaldavad projekteerida, simuleerida ja optimeerida ka neil täituritel põhinevaid keerulisemaid mehhanisme. Koostatud mudeli valideerimiseks modelleeriti ja valmistati kaks tööpõhimõtteliselt sarnast, kuid erinevatel elektroaktiivsetel polümeermaterjalidel põhinevat ning eri metoodikatel valmistatud mitmest täiturist koosnevat mitme vabadusastmega mikromanipulaatorit. Väitekirjas demonstreeritakse, et koostatud mudel on suure täpsusega võimeline ennustama nii iga individuaalse täituri kui ka mõlema manipulaatori käitumist. Demonstreerimaks piisksadestusprintimismeetodil valmistatud manipulaatori efektiivsust, kirjeldatakse kahte erinevat kontrollrakendust. Esmalt näidatakse tagasisidestamata kontrollitavat seadet, kus pööratakse nelja täituri abil peeglit, suunates laserikiirt X-Y tasapinnas ettemääratud punktidele. Teiseks näidisrakenduseks on tagasisidestatud kontrollmetoodikaga juhitav mikroskoobi preparaadiliigutaja, mille abil saab preparaati nii tõsta-langetada kui ka pöörata. Manipulaatorite valmistamise käigus leiti, et piisksadestusprintimise meetodi täpsus, jõudlus ja skaleeritavus võimaldavad suure tootlikkusega valmistada identseid keerulisi mitmeosalisi manipulaatoreid. See tulemus näitab ilmekalt uue tehnoloogia eeliseid traditsiooniliste valmistamisviiside ees.Ionic electroactive polymers (IEAPs) actuators are kind of smart composite materials that have the ability to convert electrical energy into mechanical energy. The actuators fabricated using IEAP materials will benefit from attractive features such as high compliance, lightweight, large strain, low voltage, biocompatibility, high force to weight ratio, and ability to operate in an aqueous environment as well as in open air. The future of soft robotic actuation system with IEAP actuators is very promising especially in the microdomain for cutting edge applications such as micromanipulation systems, medical devices with higher dexterity, soft catheters with built-in actuation, bio-inspired robotics with better-mimicking properties and active compliant micromechanisms. This dissertation has introduced an effective modelling framework representing the complex electro-chemo-mechanical dynamics that can predict the electromechanical transduction in this kind of actuators. The model describes the ion transport dynamics under electric field by combining the Nernst-Planck and Poisson’s equation and the mechanical response is associated with the volumetric swelling caused by resulting charge and mass balance. The framework of this modelling method to predict the behavior of the actuator enabled to design, simulate and optimize compliant mechanism using IEAP actuators. As a result, a novel parallel manipulator with three degrees of freedom was modelled and fabricated with two different types of electrode materials and is characterized and compared with the simulation model. It is shown that the developed model was able to predict the behavior of the manipulator with a good agreement ensuring the high fidelity of the modelling framework. In the process of the fabrication, it is found that the manipulator fabricated through additive manufacturing method allows to fabricate multipart and intricate patterns with high throughput production capability and also opens the opportunity to print a matrix array of identical actuators over a wide size scale along with improved performance. Finally, to showcase the competence of the printed manipulator two different control application was demonstrated. At first, an open loop four-way optical switch showing the capability of optically triggering four switches in the X-Y plane in an automated sequence is shown followed by closed-loop micromanipulation of an active microscope stage using model predictive control system architecture is shown. The application of the manipulator can be extended to other potential applications such as a zoom lens, a microscope stage, laser steering, autofocusing systems, and micromirror. Overall this dissertation results in modelling, fabrication, and control of ionic electroactive polymer actuators leading to the development of a low cost, monolithic, flat, multi DOF parallel manipulator for micromanipulation application.https://www.ester.ee/record=b524351

Recentering Shape Memory Alloy Passive Damper for Structural Vibration Control

This paper presents a preliminary study on the evaluation of an innovative energy dissipation system with shape memory alloys (SMAs) for structural seismic protection. A recentering shape memory alloy damper (RSMAD), in which superelastic nitinol wires are utilized as energy dissipation components, is proposed. Improved constitutive equations based on Graesser and Cozzarelli model are proposed for superelastic nitinol wires used in the damper. Cyclic tensile-compressive tests on the damper with various prestrain under different loading frequencies and displacement amplitudes were conducted. The results show that the hysteretic behaviors of the damper can be modified to best fit the needs for passive structural control applications by adjusting the pretension of the nitinol wires, and the damper performance is not sensitive to frequencies greater than 0.5 Hz. To assess the effectiveness of the dampers for structural seismic protection, nonlinear time history analysis on a ten-story steel frame with and without the dampers subjected to representative earthquake ground motions was performed. The simulation results indicate that superelastic SMA dampers are effective in mitigating the structural response of building structures subjected to strong earthquakes

FEM analysis of NiTi rotary endodontic instruments to fatigue stress conditions: influence of geometrical parameters and design optimization

The aim of this paper was to analyse the mechanical behaviour of NiTi endodontic rotary instruments when subjected to fatigue stresses. Four different commercial endodontic files, characterized by different cross-section shapes, were tested. Two finite element models were built to identify the cross-section shape with the best performance. In the first FEM model, rotary instruments were fixed near the tip, while a transverse displacement was applied to the bottom. Von Mises equivalent stresses were evaluated to compare the bending response of the different instruments. In the second FEM model the low-cycle fatigue life of these instruments was examined, when constrained to displace in a curved root canal and contemporary rotate. The comparison of the results, in terms of cyclic fatigue, allowed to identify the commercial instrument whose particular geometric conformation ensures better mechanical strength under test conditions. Subsequently, an analysis of geometry parameters influences on the fatigue life was performed and a design optimization was carried out. In the design optimization process, the output parameter is the total deformation. The results obtained showed that it is possible to achieve an increase in fatigue life of up to 50%. Finally, the fatigue life of the optimized geometry has furthermore tested in a double curvature root canal

STR-807: ANSYS MODELING OF POST-TENSIONED STEEL BEAM-COLUMN CONNECTIONS UNDER CYCLIC LOADING

Permanent deformations in a steel moment resisting frame can be eliminated by using post-tensioned (PT) elements. This paper presents the development of three-dimensional finite element models of PT steel beam-column connection subassemblies. Knowing that there is limited experimental data in the literature on PT steel connections with top-and-seat angles, reliable finite element models can be used to investigate the load carrying behaviour of PT steel connections as well as producing more data for these new connections. In this paper, finite element modelling, meshing, and analysis are performed in the commercial software, ANSYS. The analysis includes geometric and material nonlinearities, pre-loaded bolts and strands, gap opening and closing behaviour, in addition to contact and sliding phenomena. The results of finite element simulations are verified against previous test results on five interior PT steel beam-column connections with top-and-seat angles. In addition, parametric studies are conducted to investigate the effects of three factors on the cyclic response of PT steel connections. These factors include the yield strength and strain hardening of steel angles, the amount of initial post-tension force in PT strands, and the use of beam flange reinforcing plates