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La classe inversée gagne sans cesse en popularité depuis quelques années et des études montrent que les étudiants obtiennent généralement de meilleurs résultats académiques lorsqu’ils sont exposés à une classe inversée comparativement à une classe traditionnelle. Cependant, un aspect qui n’a pas vraiment été pris en compte jusqu’à présent concerne le temps que les étudiants consacrent à leurs apprentissages. En effet, certaines études soulèvent la possibilité que les meilleures performances académiques des étudiants exposés à une classe inversée soient la conséquence d’une charge de travail accrue, et non celle de la stratégie pédagogique proprement dite. Dans le but d’alimenter la littérature scientifique de données probantes sur cette question, une étude a été réalisée dans un cours obligatoire du programme de génie mécanique de l’École de technologie supérieure. Le cours a été simultanément offert à deux groupes distincts en conservant identique un maximum d’éléments comme les évaluations, le matériel pédagogique et le personnel enseignant. En fait, la seule différence entre les deux groupes est la stratégie pédagogique employée lors des séances de cours théoriques, soit une classe inversée pour un groupe et classe traditionnelle pour l’autre. Tout au long de la session, des données ont été collectées, notamment les évaluations faites par le professeur ainsi que le temps consacré aux études autodéclaré hebdomadairement par les étudiants. Une analyse préliminaire des résultats indique que les performances académiques des étudiants sont similaires entre les deux classes, mais qu’une différence émerge au niveau du temps consacré aux études. En effet, les étudiants ayant une moyenne cumulative élevée ont consacré moins de temps à leurs apprentissages dans la classe inversée, contrairement aux étudiants ayant une faible moyenne cumulative. En considérant les notes et le temps consacré aux études, les étudiants ayant une forte moyenne cumulative ont donc été plus efficaces dans la classe inversée, tandis que ceux ayant une faible moyenne cumulative l’ont été dans la classe traditionnelle.

There are still many questions to answer regarding the implementation and ongoing use of the CEAB graduate attributes (GAs) to guide engineering education content and student progression. How well doour students know and understand the twelve GAs? Which ones do they find most important? Do the knowledge and importance of the GAs vary over the course of students’ programs, or among institutions? Do students’ definitions of an engineer reflect the GAs? How do the definitions reflect students’ evolving understanding of engineering identity? Given the similarity of purpose, philosophy, and complementarity of questions and methods regarding the student perspective on engineering, the GAs, and their development, researchers from three institutions across Canada joined forces to conduct a national study. The overarching objectives of the study are to provide insight on how undergraduate students’ engineering identities develop through the course of their programs using the CEAB GAs as a normative framework, and enable meaningful comparisons of the GAs rankings and learning cultures at the three institutions. The objectives of this paper are to present an overview of the study development, and describe the methods used to develop the French and English codebooks for analysis of the qualitative data. We discuss the disambiguation of the codes and lexicon with particular attention to the concepts of professionalism and leadership and the emergence of three inductive codes: Engineering Work, Societal Improvement, and Personal Characteristics. We close the paper with a few words on future work.

A pilot project was conducted to study the feasibility of using electrodermal activity sensors embedded in a watch-like device to measure skin conductivity in real time. In the field of education, it may be interesting to use this technology to assess the students' cognitive engagement in the classroom. A few volunteer students as well as the professor were wearing an Empatica E4 wristband during some class periods where different activities were organized such as lectures, workshops and exams. Monitoring several individuals simultaneously makes possible to compare the collected data among students and between the students and the professor. Also, since the activities were weekly repeated, it was possible to assess to which extent the observed patterns were similar from one group to the other. In brief, the collected data is very difficult to interpret, since some external factors seem to have a significant effect on the measurements. Indeed, discrepancies are observed in the data curves representing the students’ electrodermal activity. Also, the data generated by the professor is quite different from one group to the other, even if he repeated the exact same activities at two different times of the week. It is suggested to improve the understanding of all the phenomena that could affect the electrodermal activity measurements before trying to draw conclusions related to the students’ cognitive engagement in the classroom.

The emergence of additive manufacturing has enabled the design and manufacture of lightweight parts such as lattice structures with a complex geometry. However, conducting computer simulations to predict the mechanical behavior of such structures remains a challenge, especially when the number of struts is high. Firstly, this paper presents an approach to quickly build a lattice structure made of a large number of struts. The method takes advantage of the capabilities of finite element meshers to generate the tessellation of the volume into a series of tetrahedrons whose edges define the struts of the lattice. A graded-porosity can be defined during this process. Secondly, for the numerical simulation, the struts are modeled by beam finite elements. To adequately simulate the entire range of porosity, the material stiffness can be adjusted at any point of the structure, mainly to compensate for the lack of validity of stout beam elements. A numerical validation demonstrates the validity of the method by adequately predicting the displacement distribution of a mechanically loaded lattice structure, but an experimental validation raises issues related to the manufacturing limitations of small struts.

A novel approach has been proposed for the design of porosity-graded lattice structures suitable for bone replacement applications. A MATLAB routine was developed in order to model a lattice structure and generate an STL file for additive manufacturing. With this routine, geometric properties, such as the pore size and strut thickness, can be controlled to provide the desired porosity distribution and mechanical properties of the structure.The stiffness and yield stress of three titanium structures with densities of 20, 42 and 60% were evaluated by finite element analysis and tensile testing. The experimental results diverged by up to 50% from those predicted by the finite element analysis. The geometrical deviations between the modelled and fabricated structures and the approximations made for the material modelling were considered to be at the root of these discrepancies.The experimentally evaluated Young's modulus ranged from 1.6 to 20.3 GPa for the 20 and 60% dense structures, respectively, while the yield stress ranged from 23 to 181 MPa for the same structures. These results are comparable to those for cortical and trabecular bone. Scaling relations for the stiffness and yield stress of porous structures were developed to allow the computer-assisted design of porosity-graded load-bearing implants. Keywords: Porous material, Biomaterial, Additive manufacturing, Diamond-type unit cell, Finite element analysis

Cet article présente un projet de recherche dont le but est d’étudier l’efficacité de la classe inversée implantée dans un cours obligatoire de génie mécanique. L’inversion du cours a été motivée par la passivité des étudiants durant les séances de cours magistraux et par les apprentissages en surface qu’ils réalisent. Pour remédier à cette problématique, le cours a été inversé en prenant en considération les déterminants de la motivation, certains éléments de la psychologie cognitive ainsi que la taxonomie de Bloom. Après avoir développé du nouveau matériel pédagogique, la classe inversée a été testée pour la première fois à l’hiver 2019. Les résultats préliminaires sont encourageants, car les étudiants se sont montrés satisfaits du cours lorsqu’ils se sont prononcés par un court questionnaire, par l’évaluation institutionnelle et lors d’un entretien de groupe. Les travaux se poursuivent vers une étude rigoureuse qui, à l’automne 2020, comparera l’efficacité d’un même cours offert en classe traditionnelle et en classe inversée.

This paper proposes a novel indirect assessment method to capture the voice of the students for program accreditation purposes. It consists of asking students, individually and then in teams, to draw up a list of keywords they associate with being an engineer and to write a formal definition of engineer. The raw data (list of keywords and definitions) is closed coded for the twelve graduate attributes (GAs) defined by Engineers Canada. First-year, mid-program and last-year students participated in the study in order to verify change of perception as students advance through the program. Results are compared for individual and teams, as well as for the different student populations. Sufficient insight into the program’s contribution to the development of graduate attributes in its student population (or apparent lack thereof), information that can be used for continual program improvement, was gained to warrant internal validity of the method.

This paper focuses on the development of a porous metallic biomimetic femoral stem designed to reduce stress shielding and to provide firm implant fixation through bone ingrowth. The design of this stem starts with the creation of the diagram allowing the establishment of a relationship between the bone ingrowth requirements and the metal additive manufacturing technology limitations. This diagram is then used to determine the optimum porosity (33%) that should compose the porous part of the stem. Afterward, selective laser melting is used to manufacture the porous stem altogether with its fully dense replica. Finite element analysis and numerical homogenization methods are then employed to predict the mechanical behavior of the stem. Both stems are finally tested following the ISO 7206-4 (2010) requirements under static loading conditions. The digital image correlation technique is employed to obtain the displacement and strain fields during the tests, and to validate the finite element model. While the finite element model of the dense stem has been successfully validated, that of the porous stem has shown ~40% higher stiffness than that measured experimentally. It has been proven that this discrepancy is due to the difference between the experimentally-measured (42%) and the numerically-targeted (33%) porosities. Keywords: Biomimetic femoral stem, Metallic foams, Selective laser melting, Finite element analysis, Digital image correlation, ISO 7206-4 (2010)

The fabrication of engineered lattice structures has recently gained momentum due to thedevelopment of novel additive manufacturing techniques. Interest in lattice structures resides not only in the possibility of obtaining efficient lightweight materials, but also in the functionality of pre-designed architectured structures for specific applications, such as biomimetic implants, chemical catalyzers, and heat transfer devices. The mechanical behaviour of lattice structures depends not only the composition of the base material, but also on the type and size of the unit cells, as well as on the material microstructure resulting from a specific fabrication procedure. The present work focuses on the static and fatigue behavior of diamond cell lattice structures fabricated from an AlSiMg alloy by laser powder bed fusion technology. In particular, the specimens were fabricated with three different orientations of lattice cells?[001], [011], [111]?and subjected to static tensile testing andforce-controlled pull?pull fatigue testing up to 1 107 cycles. In parallel, the mechanical behavior of dense tensile plain and notched specimens was also studied and compared to that of their lattice counterparts. Results showed a significant effect of the cell orientation on the fatigue lives: specimens oriented at [001] were ~30% more fatigue-resistant than specimens oriented at [011] and [111]. Fil: Soul, Hugo Ramon. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ecole de Technologie Superieure; Canadá Fil: Terriault, Patrick. Ecole de Technologie Superieure; Canadá Fil: Brailovski, Vladimir. Ecole de Technologie Superieure; Canadá

The objective of this work is to create a new class of porous metallic implant materials combining the biocompatibility of pure titanium with the superelasticity of Nitinol. Ti-20.8Nb-5.5Zr, Ti-22Nb-6Ta (at%) and Ti-CP foams are produced by the space-holder technique and characterized from both the pore morphology and the mechanical behavior points of view. To support these developments, a multi-scale representative volume element-based approach is proposed and experimentally validated. Using this approach, the implant's porosity can be engineered, and the base material properties adjusted, so that the implant could offer adequate pore morphology for bone ingrowth while offering high mechanical resistance.

This paper focuses on the development of an algorithm capable of generating morphologically-representative foam structures using the Representative Volume Element (RVE) approach. Stereology, a sampling method based on direct observations of the foam cross-sections, is used to characterize the pore size and shape distributions. Using the morphology generation algorithm, the smallest RVEs corresponding to the numerically-convergent foam morphologies are calculated for different foam porosities. To validate the foam generation algorithm, the pore size and shape distributions of the numerically-generated foams are compared to those of the titanium foams manufactured by the space holder method.

Cellular solid materials and, more specifically, foams are increasingly common in many industrial applications due to their attractive characteristics. The tetrakaidecahedral foam microstructure, which can be observed in many types of foams, is studied in the present work in association with shape memory alloys (SMA) material. SMA foams are of particular interest as they associate both the shape memory effect and the superelasticity with the characteristics of foam. A Unit Cell Finite Element Method approach is used, an approach that allows accurate predicting of the macroscale response of the foam with a highly reduced numerical effort. The tetrakaidecahedral foam’s responses, both in the elastic and in the superelastic stages, are then extracted and compared with results from the literature. The tetrakaidecahedral geometry is found to be of particular interest when associated with SMA as it takes more advantage of the superelastic property of the material than foams with randomly distributed porosity.

Recent studies were dedicated to the realization of measurements on stay-cable samples of different geometry and static conditions as available at several facilities. The elaboration of the acquired data showed a a satisfactory efficacy of the dampers made of NiTi wires in smoothing the cable oscillations. A further attempt to investigate the applicability of the achieved results beyond the specific case-studies represented by the tested cable-stayed samples is herein pursued. Comparative studies are carried out by varying the diameter of the NiTi wire so that similar measurements can be taken also from laboratory steel cables of reduced size. Details of the preparation of the Ni-Ti wires are discussed with particular attention being paid to the suppression of the creep phenomenon. The resulting shape of the hysteretic cycle differs according to the wire diameter, which affects the order of the fitting polynomial to be used when trying to retrieve the experimental results by numerical analyses. For a NiTi wire of given diameter, an estimate of the amount of dissipated energy per cycle is given at low levels of maximum strain, which correspond to a fatigue fracture life of the order of millions of cycles. The dissipative capability is affected by both the temperature and the cycling frequency at which the tests are performed. Such effects are quantified and an ageing process is proposed in order to extend the working temperature range of the damper to cold weathers typical of the winter season in Northern Europe and Canada. A procedure for the simulation of the shape memory alloy behavior in lengthy cables by finite element analysis is eventually outlined.

This paper presents a study of the effect of stitched reinforcements on impact-induced damage and damage propagation under flexural load. TiNi and Kevlar threads were used as the superelastic element and the reference thread, respectively. Unstitched carbon/epoxy laminates were also produced. Embedded damage (matrix cracks, fiber rupture and delamination) was induced by low velocity impact testing. The performance of the unstitched and stitched specimens was assessed in terms of the energy per unit volume of damage created during impact testing, and the energy to failure of the impacted specimens during their three-point bending testing. A finite element model was used for simulating the propagation of damage, and particularly delamination, in stitched and unstitched structures during the bending test, and, depending on the mechanical properties of the stitching threads, different propagation schemes were predicted with this model.

In this study, a numerical model is developed especially for tracking the propagation of the impact-induced delamination under subsequent flexural loading. The progressive damage modeling technique is used to simulate the quasi-static three-point bending test. The numerical model is validated with experimental bending tests on impacted carbon/epoxy specimens. The specimens contain embedded delamination caused by low velocity impact prior to applying the flexural load. The impact-induced delaminated zone and the delamination propagation during the bending test are assessed using ultrasonic inspection. The force–displacement response and the delamination propagation obtained from the model and the experiments are compared for validation, with satisfactory results.

Shape memory alloys (SMAs) are used as active elements in novel actuation devices. Two generic types of SMA actuators can be distinguished according to the type of bias passive-bias actuators where an elastic component serves as a bias and active-bias actuators where two SMA elements are connected together. This paper describes an experimental testing bench developed for the characterization of SMA active elements and their testing in a real actuation environment. The characterization of SMA active elements is performed under three complementary testing modes: (a) constant-stress, (b) fixed-support, and (c) elastic-bias recovery modes. Force, displacement and temperature data acquired during testing of a given SMA active element are then used to assess the mechanical work-generation potential of this active element and, ultimately, for the design of an SMA actuator containing this element. Finally, a case study is presented to illustrate the experimental design methodology and results.

Guaranteeing the use of Shape Memory Alloys (SMA) in mitigation of extreme load effects requires a deep study of the SMA behavior according to the specific requirements of the applications in damping. The damper was defined according the expected requirements (length of SMA and number of SMA wires). It is applied to two types of alloys (CuAlBe and NiTi) in the diagonals of a realistic steel portico (2.47 m x 4.10 m). The measurements establish that the used SMA reduces the oscillation amplitude to a less than a half.

An aerostructural numerical model of a two-dimensional morphing laminar wing prototype is built and validated for different flight conditions: Mach numbers ranging from 0.2 to 0.3 and angles of attack ranging from-1 to 2°. The active structure of the wing is modeled using the ANSYS commercial finite element software. The aerostructural interaction is achieved by coupling the XFoil free-license aerodynamic solver to ANSYS. This model is used to minimize the drag force under constant-lift conditions during wind-tunnel testing using a two-step optimization algorithm (global and local search). The wake pressure wind-tunnel measurements show that extrados morphing results in an average 18.5% drag reduction for eight flow cases covering the flow condition range of interest. Simultaneously, the infrared thermography measurements record an average laminar flow extension of 25% of the wing chord over the upper wing surface. The experimental and numerical results are in good agreement, thus validating the use of an aerostructural model to efficiently manage the shape of a morphing laminar wing. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

This paper focuses on the design of an active extrados structure for an experimental morphing laminar wing, which has been tested in a subsonic wind tunnel. Actuators localized inside the wing box apply individually controlled displacements over the flexible structure, made from laminate composite, to modify the airfoil profile in accordance with the database, which is built using XFoil aerodynamic solver. This database contains a set of wing profiles, which maximize laminar flow under a given set of cruise flight conditions: Mach number 0.2 to 0.35 and attack angles −1 to 2 ° . A finite elements structural model of the active extrados has been developed with ANSYS software. Two main design parameters were identified: the number of plies in the composite laminate of the flexible extrados and the number of actuators. To balance the tradeoff between stiffness and flexibility of the active extrados structure, aerodynamic (laminar flow regime enhancement) and mechanical (low strain energy) performance criteria were considered simultaneously. Using the multi-objective optimization technique, the designer's preferences led to the selection of the 4-ply 2-actuator active extrados structure configuration.

An experimental morphing laminar wing was developed to prove the feasibility of aircraft fuel consumption reduction through enhancement of the laminar flow regime over the wing extrados. The morphing wing prototype designed for subsonic cruise flight conditions (Mach 0.2 … 0.3 ; angle of attack − 1 … + 2 ∘ ), combines three principal subsystems: (1) flexible extrados, (2) rigid intrados and (3) an actuator group located inside the wing box. The morphing capability of the wing relies on controlled deformation of the wing extrados under the action of shape memory alloys (SMA) actuators. A coupled fluid-structure model of the morphing wing was used to evaluate its mechanical and aerodynamic performances in different flight conditions. A 0.5 m chord and 1 m span prototype of the morphing wing was tested in a subsonic wind tunnel. In this work, SMA actuators for morphing wings were modeled using a coupled thermo-mechanical finite element model and they were windtunnel validated. If the thermo-mechanical model of SMA actuators presented in this work is coupled with the previously developed structureaerodynamic model of the morphing wing, it could serve for the optimization of the entire morphing wing system.

For shape memory alloys (SMA) to be usable in engineering applications, it must be possible to simulate the degradation of the material when subjected to cyclic loading. This paper presents an adaptation of Likhachev’s micromechanical model capable of such a degradation, concentrating on strain accumulation. The proposed model, based on a cellular automata algorithm and on the Ramberg–Osgood theory of plasticity, is easy to characterize, with the material constants reduced to a minimum. Further, a thermal model is coupled to the micromechanical formulation in order to allow the thermal exchanges with the surroundings to be taken into account. A series of numerical validations demonstrate the potential of the model to reproduce SMA-related effects: superelasticity, thermal cycling and shape-memory effect. An experimental validation is carried out using a superelastic NiTi wire and a good agreement with experimental data is found.

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.

Shape memory alloys (SMA) are good candidates for solid state dampers because of their large recoverable strain and hysteresis. In this work, experimental analysis and modeling of the thermomechanical behavior for two SMAs is done. The SMA models are developed and included in a finite element simulation environment (ANSYS). Using these developing tools, a complete damping solution for a family house is outlined. The paper presents the design and optimization methodology for the dampers, analyzes their performance, and quantifies the relevant physical effects from the experimental measurements. The simulation results show that the SMA dampers are capable of reducing the maximum oscillation amplitude induced by “El Centro” accelerations by a factor 2 and that they dissipate 50% of the energy transmitted to the structure. Furthermore, SMA dampers constitute a passive, unsupervised damping solution appropriate for family houses.

Many applications involve actuated devices made of shape memory alloys, but the lack of efficient numerical tools hinders the development of such technologies. Software using a finite element method like ANSYS allows the user to predict complex responses of a system without extensive programming. In this paper, a homemade phenomenological 1D bilinear model is programmed through the USERMAT procedure in ANSYS. The model allows the representation of both mechanical and thermal hystereses. The martensitic transformation is controlled by transformation criteria similar to those used in conventional plasticity, and subcycles are modeled by a simple elastic return through the hysteresis. The model is validated through isothermal tensile testing, assisted two-way shape memory testing and stress generation testing, and a good agreement with experimental results is shown. Finally, thermomechanical response of a single-degree-of-freedom actuator is simulated as a typical application and a case study involving the shape change of a radio controlled aircraft wing shows the potential of the numerical simulations.

The necessary physical properties for CuAlBe and, also tentatively, for NiTi alloys are analyzed at mesoscopic scale via static and dynamic contributions. The long time scale of the civil engineering (more than 10 or 20 years) requires analysis of the diffusion effects acting on microscopic scales. Simplified models for CuAlBe and NiTi dampers are built inside the ANSYS software scheme ensuring faster simulation for a three arch (or portico) in a family house. The dynamic simulation using accelerations of actual quakes (i.e., El Centro) shows that the SMA dampers reduce the amplitude of free oscillations by, at least, a factor two.

Shape memory alloys (SMA) suffer from the same impairing mechanisms experienced during cycling loading by classic alloys. Moreover, SMA fatigue behavior is greatly influenced by thermomechanical cycling through the zone of thermoelastic phase transformation, which is the basis of shape memory and superelasticity effects. Since the fatigue resistance of any material can be improved by an appropriate thermomechanical treatment, in the present work combined differential scanning calorimetry and microhardness testing were used to determine an optimum annealing temperature for the cold-worked Ni-50.1%Ti alloy. The optimization is based on the assumption that latent heat of transformation is proportional to the mechanical work generated by SMA upon heating, while material hardness is related to the yield stress of the material. It is supposed that an optimum trade-off in these two properties guarantees the best dimensional and functional stability of SMA devices. The level and stability of the mechanical work generated by the material during low-cycle fatigue testing are considered criteria for the material performance and thus of the validity of the proposed optimization procedure.

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.

In this paper, the properties of shape memory alloy (SMA) wires relevant for their application as passive elements to mitigate the vibrations of stayed cables in bridges are discussed. These properties are investigated by carrying out experimental tests on samples of diameter 2.46 mm. Future research will address the scalability issues.

Shape Memory Alloys (SMAs) are good candidates for solid-state dampers appropriate for the oscillations of bridge stay cables because of their large recoverable strain, hysteresis and reasonable fatigue-life. This work experimentally analyzes the relevant properties of NiTi SMA and conducts facility measurements, frequency analyzes and simulations of the effects of SMA on stay cables. Appropriate phenomenological SMA models were developed and included in a Finite Element (FE) simulation environment. A complete damping solution for bridge stay cables was developed from these experimental analyzes. This paper detail the required properties for a NiTi SMA and analyzes their performance. For instance, the fatigue-life and several of the thermo-mechanical effects influencing the application of NiTi SMAs are outlined. The damping effect of the SMA was studied in two facilities. The first series of measurements was performed using cable 1 of the ELSA facility (JRC-EU, Ispra, Italy). The second was completed in two campaigns at IFSTTAR (Bouguenais, near Nantes in France). The numeric analyzes and simulated results were completely coherent with these experiments: the SMA dampers also drastically reduce the maximum oscillation amplitude induced by the simulated action. The frequency evolution of the damped cable was studied using direct calculations on the signals, the windowed Fourier transform and Morlet wavelets.

Porous Shape Memory Alloys (SMAs) are of particular interest for many industrial applications, as they combine intrinsic SMA (shape memory effect and superelasticity) and foam characteristics. The computational cost of direct porous material modeling is however extremely high, and so designing porous SMA structure poses a considerable challenge. In this study, an attempt is made to simulate the superelastic behavior of porous materials via the modeling of fully dense structures with material properties modified using a porous/bulk density ratio scaling relation. Using this approach, direct modeling of the porous microstructure is avoided, and only the macroscale response of the model is considered which contributes to a drastic reduction of the computational cost. Foam structures with a gradient of porosity are also studied, and the prediction made using the fully dense material model is shown to be in agreement with the mesoscale porous material model.

Several solutions have been proposed to mitigate the vibrations of stay cables in bridges, which are subjected to wind, rain and traffic loads. One possible solution relates to the use of semi-active devices, such as the ones based on magneto-rheologic fluids. These devices need guaranteed electrical power, together with computational effort and technical attention. In contrast, shape memory alloy (SMA) wires were studied for application as passive elements. In the present work, the properties of SMA that are required to realize dampers provided with an appropriate reliability are discussed. In particular, the fatigue/fracture life of the SMA wires and the thermal effects induced by both external temperature and the self-heating process are studied. The SMA dampers were applied to stayed cables of realistic size and tested in "facilities." Namely, the cables No 1 of 45 m length available at the ELSA-JRC in Ispra, Italy, and the 50 m cable of IFSTTAR near Nantes, in France, were considered. The experimental results establish a reduction of the vibration amplitude to one half or less than the one observed in the un-damped case. Furthermore, the installation of the SMA dampers causes an increase of the cable frequency. Performing a Windowed Fourier Transform or a Wavelet Transform analysis the evolution of frequency with the signal amplitude was studied. The change of amplitude produces a change of stiffness in the SMA. The adoption of an appropriate phenomenological model of the hysteresis cycle permits to perform numerical simulations using standard Finite Elements Analysis tools such as, for instance, the ANSYS software.

There have been published many papers and several reviews on the application of SMA's as damping devices in civil engineering by using the pseudo-elastic effect, but they are difficult to apply because the behaviour of the alloys is not carefully analyzed. In particular, the summer-winter temperature effects, aging long time at low temperature, self-heating or residual strains requirements for the given applications are rarely well established. In this work, we analyze and compare two cases, the damping of earthquake effects on relatively small structures as family homes, and the damping of stayed cables in large bridges. The requirements for the materials are different, and in each case a different commercial alloy with appropriate conditioning might provide acceptable answers. To confirm the usefulness of the dampers, the hysteretic behaviour of two SMAs (CuAlBe and NiTi) has been analyzed, and later modelled and introduced in finite element codes for the simulation of structures. The behaviour of the structures without and with dampers have been analyzed and compared. Also, some realistic experiments with cable 1 in the ELSA Joint Research Centre of the EU in Ispra have been done with NiTi wire of 2.46 mm diameter as damper, to compare with simulations.

One of the classical applications of the SMA is based on the used of the hysteresis cycle associated to the martensitic transformation (classically, described as a first order phase transition) for damping devices. For each application a detailed knowledge of the conditions to be accomplished by the material is absolutely necessary. For the stayed cables in bridges of the Iroise bridge, the oscillation frequencies are 1 and 3 Hz; and the peak to peak oscillation amplitude is close to 10 cm and, also, the SMA works in close contact with the external ambient temperature. In fact, the bridge is a 2*2 lanes free highway situated between Brest and Plougastel (France). The main requirement is related to several days of intense winds or rain associated to strong storms. The conditions imposed to the samples suggest appropriate behavior for, at least, 500000 cycles of working. The experimental analysis, centered in NiTi, is focused in 1) the fatigue life of the samples, 2) the evaluation of the Clausius-Clapeyron coefficient, 3) assuring that the degradation of the material properties remains below a safety limit in the expected time scale of application, 4) modeling the cable behavior to show the positive damping capacity of SMA and 5) studying the applications in semi-realistic scale in the ELSA-JRC (a civil engineering facility in Ispra, Italy) demonstrating the positive effect of the SMA.

The properties of SMA (Shape Memory Alloys, smart materials) are associated to a first order phase transition named martensitic transformation that occurs between metastable phases: austenite and martensite. At higher temperature phase or at lower stress the austenite is the metastable phase. The martensite appears at lower temperature phase or higher stresses. The hysteresis of the transformation permits different levels of applications, i.e., in their use as a damper. Two types of applications can be considered in damping of structures in Civil Engineering. The first one is related to diminishing the damage induced by earthquakes. The second one is a reduction of oscillation amplitude associate to an increase of the lifetime for the stayed cables in bridges. Different fundamental behavior of the SMA needs to be guaranteed in each case.