Search

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.

Inconel 625 coupons were manufactured via laser powder bed fusion with different levels of intentionally-seeded porosity (up to 2.7%). The processing-induced porosities, morphologies and distributions were measured via Archimedes method and computed tomography. Tensile tests were performed, followed by fatigue crack propagation characterization. The static strength characteristics were not strongly affected by the levels of porosity, but the elongation at break was severely impacted. In the near threshold region of the Paris diagram, porous specimens were unaffected by porosity and build orientation. However, under higher stress intensity factors, the effect of porosity was found to be significant and build orientation-dependent.

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.

In this paper, the room temperature fatigue crack propagation behavior of Inconel 625 alloy processed by laser powder bed fusion was studied and compared to that of a wrought alloy of the same composition. First, the processing-induced defects distribution and the build orientation-dependent tensile properties of the laser powder bed-processed specimens were analysed. Next, crack propagation testing specimens were manufactured with four build orientations, half were subjected to stress relief annealing, while the other half were subjected to stress relief annealing followed by hot isostatic pressing. The impact of the build orientation and the post-processing conditions on the long fatigue crack propagation behavior at low R ratio (R = 0.1) was evaluated. The resistance to crack propagation of the laser powder bed-processed IN625 specimens was found to be similar to that of a wrought alloy.

Shape memory alloys are used in ever-increasing numbers of applications, such as implants made of porous shape memory alloys, where the material is subjected to complex loading conditions with various loading paths. Finite element simulation of such parts requires utilizing a constitutive model that is able to capture the multiaxial and path-dependent behavior of shape memory alloys. The main objective of this article is to investigate the accuracy of the constitutive model implemented in current commercial finite element software such as Ansys in predicting the shape memory alloys mechanical response under different multiaxial loading paths. To this end, several isothermal tests were conducted on thin-walled NiTi tubes with uniaxial, as well as multiaxial, path-varying loadings. The performance of the material model within Ansys was then investigated by finite element modeling of the sample tubes and performing simulations of the tests. Comparing the finite element results with experimental data, it was observed that while this model provided a close prediction of the uniaxial tensile superelastic response, it was not able to reproduce the multiaxial and path-dependent behavior of the shape memory alloy samples with sufficient accuracy. A brief discussion of the reasons behind the inaccuracy of the current model and potentially promising models for future investigation are provided.

Background Dense and stiff metallic femoral stems implanted into femurs for total hip arthroplasties produce a stress shielding effect since they modify the original load sharing path in the bony structure. Consequently, in the long term, the strain adaptive nature of bones leads to bone resorption, implant loosening, and the need for arthroplasty revision. The design of new cementless femoral stems integrating open porous structures can reduce the global stiffness of the stems, allowing them a better match with that of bones and provide their firm fixation via bone ingrowth, and, thus reduce the risk of implantation failure. Methods This paper aims to develop and validate a simplified numerical model of stress shielding, which calculates the levels of bone resorption or formation by comparing strain distributions on the surface of the intact and the implanted femurs subjected to a simulated biological loading. Two femoral stems produced by laser powder-bed fusion using Ti-6Al-4V alloy are employed: the first is fully dense, while the second features a diamond cubic lattice structure in its core. The validation consists of a comparison of the numerically calculated force-displacement diagrams, and displacement and strain fields with their experimental equivalents obtained using the digital image correlation technique. Results and conclusions The numerical models showed reasonable agreement between the force-displacement diagrams. Also, satisfactory results for the correlation analyses of the total displacement and equivalent strain fields were obtained. The stress shielding effect of the implant was assessed by comparing the equivalent strain fields of the implanted and intact femurs. The results obtained predicted less bone resorption in the femur implanted with the porous stem than with its dense counterpart.

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)

In this communication, a new methodological approach is proposed to develop a biomimetic metallic femoral stem. The design of this stem starts with the definition of an outer skin by reproducing the shape and overall dimensions of a Stryker® femoral stem to be implanted in an artificial femur model from Sawbones®. In-house algorithms are then used to generate two types of porous structures inside the outer skin: either a stochastic cubic-based porous structure or an ordered diamond-type porous structure. Next, a model of the femur-stem assembly is developed using the finite element method. The fully dense Stryker stem replica and two porous stems are fabricated using selective laser melting technology. Then, comparative mechanical testing is carried out using the ISO 7206-4 (2010) guidelines. These tests are conducted on an intact artificial femur (reference case) and on the identical femurs, but now implanted with the fully dense and porous stems. Using digital image correlation tools, the results of four series of tests are compared to assess which implant design leads to the lowest stress shielding in the implanted femur. Finally, the experimentally measured strain fields are compared to the numerical predictions to validate the numerical models.

This article focuses on the development of a shape morphing composite skin representing a wing extrados. The objective is to design and manufacture a skin capable of changing its geometry in order to improve its aerodynamic efficiency. One geometry is considered to be the nominal geometry and a deformed geometry is identified. It is obtained upon application of a displacement at the aftmost boundary of the active portion of the wing profile. The displacement is imposed on the skin by shape memory alloy wires. These actuators are combined with a self-locking transmission mechanism that maintains the deformed geometry without any further energy consumption. The lay-up of the composite skin is optimised such that the deformed profile approaches the desired geometry as closely as possible. This lay-up selection routine is done through an ANSYS Parametric Design Language sub-routine. The finite element model is validated experimentally by conducting mechanical testing on the composite skin.

An original methodology was proposed to design, manufacture and test stochastic porous open-cell structures for medical applications. The first phase of the design procedure consisted in the numerical determination of the minimum representative size of the porous gauge section of testing specimens. Next, porosity gradients between the porous gauge section and the fully dense grip extremities of the specimens were created. The tensile specimens with porosities of 0.30, 0.40 and 0.50 were then produced using cobalt–chromium alloy powders and the Selective Laser Melting (SLM) technology. Finally, the specimens were subjected to uniaxial tension to failure to allow the determination of their stiffness and mechanical strength. The elastic response of these specimens in the central gauge section and the porosity gradient zones were in line with our numerical predictions and the literature data.

Inconel 625 fatigue testing specimens with different levels of intentionally-seeded porosity in their gauge section (≤0.1, 0.3, 0.9 and 2.7%) were manufactured by laser powder bed fusion and subjected to stress relief annealing. The morphology, number and distribution of seeded defects were characterized using the micro-computed tomography technique. The effect of the different levels of porosity on the high cycle fatigue behavior of these specimens was studied using room temperature force-controlled fatigue testing according to the ASTM E466 standard (frequency of 30 Hz; R = 0.1) with a runout at 107 cycles. The fatigue strength of specimens with the lowest level of porosity (≤0.1%) was found to be 590 MPa. Next, using El-Haddad’s formulation of the Kitagawa-Takahashi model defining the limiting conditions for fatigue failure in the presence of defects and Murakami’s parameter for defect size rating, the fatigue strengths of specimens with 0.3, 0.9 and 2.7% porosity were predicted at 280, 190 and 160 MPa, respectively. The predicted values were found to deviate by less than 8% from the experimental results, which were, respectively, 288, 207 and 170 MPa.

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.

Background The current total hip prostheses with dense femoral stems are considerably stiffer than the host bones, which leads to such long-term complications as aseptic loosening, and eventually, the need for a revision. Consequently, the lifetime of the implantation does not match the lifetime expectation of young patients. Method A femoral stem design featuring a porous structure is proposed to lower its stiffness and allow bone tissue ingrowth. The porous structure is based on a diamond cubic lattice in which the pore size and the strut thickness are selected to meet the biomechanical requirements of the strength and the bone ingrowth. A porous stem and its fully dense counterpart are produced by laser powder-bed fusion using Ti-6Al-4V alloy. To evaluate the stiffness reduction, static testing based on the ISO standard 7206-4 is performed. The experimental results recorded by digital image correlation are analyzed and compared to the numerical model. Results & conclusions The numerical and experimental force-displacement characteristics of the porous stem show a 31% lower stiffness as compared to that of its dense counterpart. Moreover, the correlation analysis of the total displacement and equivalent strain fields allows the preliminary validation of the numerical model of the porous stem. Finally, the analysis of the surface-to-volume and the strength-to-stiffness ratios of diamond lattice structures allow the assessment of their potential as biomimetic constructs for load-bearing orthopaedic implants.

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.

This article presents a novel design procedure leading to fabrication of a composite adaptive panel prototype with an embedded array of linear shape memory alloy actuators. This procedure allows determination of the panel’s radius of curvature as a function of the shape memory alloy actuators’ actuation temperature and panel configuration (number and orientation of plies, number and location of actuators, the materials’ properties, and the geometric arrangement). This design procedure integrates properties of the host structure (composite laminate) and of the actuators (shape memory alloy wires) in the framework of a unique design diagram. The performances of shape memory alloy actuators are obtained by experimental manipulations, whereas the rigidity of the host structure is calculated using the finite element numerical modeling approach. To validate the developed design procedure, a [90/90/90/wire/90] 425 × 425 × 5-mm adaptive panel prototype is fabricated using the vacuum-assisted resin transfer molding method. The results obtained from experimental tests are used to monitor the global performance of the adaptive panel and to validate the developed design procedure.

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 article focuses on the development of a finite elements model of an adaptive composite panel with embedded shape memory alloy actuators. It is firstly shown that a combination of shell, beam and link elements could be employed to model the panel. A simplified version of the Likhachev model is then employed as the constitutive relation for the actuators. Several experimental tests were successfully carried out on a prototype to validate the model and to demonstrate the possibility of controlling the panel shape. Further works should consider improving the technique employed for reading the actuators’ temperature during experimental tests.

Digital replicas of three types of SiSiC ceramic foams (10, 30, and 60 pores per inch, PPI) were obtained by means of X-ray computed tomography. Equivalent pore diameters were determined using a combination of the 3D Watershed analysis (VG Studio Max software) and an analytical tetrakaidecahedron model of a cellular structure and compared to those provided by the manufacturer. Upon investigation, it was found that pore diameters provided by the manufacturer were underestimated and the discrepancies between them and the CT-measured values were 10% for 10 PPI, 60% for 30 PPI and 120% for 60 PPI specimens. Next, diamond lattice structures equivalent to 10, 30, and 60 PPI foams in terms of their porosity and permeability were designed and some of them 3D-printed from metallic CoCr alloy. A two-section porous medium burner test bench was then used to measure the temperature, pollutant emissions and pressure drop for six different setups containing, in the upstream and downstream sections, different arrangements of the foam and lattice structures made of either ceramic or metal materials. In all the setups, pollutant emissions were low and at the detection limit of the equipment, which agrees with previous research. The application of CoCr alloy in the upstream section was determined to be advantageous, ensuring higher flame stability and structural strength. The diamond lattice was found to be a good candidate for replacement of the foam geometry by providing both the better control of porosity and higher structural stiffness. Further research with ordered porous materials is recommended for a broad range of lean combustion regimes with metallic alloys in the upstream section, and ceramic materials in the downstream section.

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.

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 metastables est a l’origine des proprietes particulieres des Alliages a Memoire de Forme (AMF). L’utilisation des AMF necessite une connaissance approfondie de leur comportement associe aux exigences de l’appli...

Shape memory alloys have become very popular over the past few decades, mainly as actuators or superelastic devices. Their complex behavior complicates the design process of these applications, and several models have been developed to assist design engineers in this endeavor. One of these models, the structure-analytical theory proposed by Likhachev, is particularly attractive because it is physically grounded and capable of dealing with tensorial stress and strain states. Unfortunately, its stress-controlled formulation has hindered its implementation in displacement-based finite element programs. This paper presents an adaptation of Likhachev’s model leading to a strain-controlled formulation based on an iterative algorithm and a proportional controller. The resulting model is implemented in ANSYS and a simple finite element analysis is carried out to illustrate its appropriate functioning.

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.

morphing structures are expected to play an increasingly important role in aeronautic applications, among others. Shape memory alloys (SMA) are one of the most promising candidates to date. However, work remains to be done before these structures meet the stringent requirements of their successful integration in an aeronautic context. Research has shown that SMA/Polymer interface strength can be a limiting factor in active deformable structure performance. In this study, the effect on the SMA/Polymer interface strength of various surface treatments, wire geometries and resin types are evaluated. SMA wire geometry is modified through a specific combination of cold rolling and post-deformation annealing, which is capable of maintaining SMA actuating properties while achieving required cross-section area reductions. The most promising thermomechanical processing is finally proposed but results show that further work is required before SMA active elements can safely be used in an active structure.

Shape Memory Alloys (SMAs) can provide compact and effective actuation for a variety of mechanical systems. Generally speaking, SMA-driven actuator systems can be divided into three subsystems: a) SMA active element, b) the transmission and c) a bias element. In respect to the type of bias, two actuator configurations can be distinguished: passive bias actuators where the SMA active element is coupled with an elastic bias element (spring), and active bias actuators in which two SMA active elements are connected together. This work is focused on designing an SMA actuator using active bias elements for morphing wing applications. Keywords: SMA actuator, active bias, antagonist, design, morphing wing

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.

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.

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.

The properties of SMA (or smart materials), are associated with a first order phase transition named martensitic transformation, that occurs between metastable phases from the upper temperature phase (austenite) to the lower temperature phase (martensite). The first order transformation (in stress, deformation and temperature coordinates) has a hysteresis and provides different kinds of applications, i.e., actuators and dampers. Two types of applications can be considered in the damping of structures in civil engineering. The first one is related to the reduction of the damage produced by earthquakes. The second one is the increase of the lifetime of cables in bridges. A completely different behaviour of the SMA is required in each case. Several years or decades without any action (except for the effects of summer-winter room temperature evolution) followed by one or two minutes of sudden oscillations is the characteristic pattern in an earthquake. Large numbers of oscillations per day (a half mil...

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.

This work presents a combined performance evaluation approach for SMAs as actuator material – an approach based on the combination of three testing modes: a) stress-free thermal recovery mode, b) fixed-support stress generation mode and c) constant (or variable) bias-stress recovery mode. Based on this testing, a so-called “design diagram” can be constructed. This diagram demonstrates the mechanical work generation potential of an SMA and therefore represents a must-have tool for the application engineer. Given that the working envelope depends on the material composition, microstructure and number of actuation cycles, this approach allows the selection of an appropriate material and the processing technique that will meet the functional requirements of a specific application. To illustrate the proposed performance evaluation technique, we show how it can be applied to the design of an SMA actuator for a morphing wing.

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.

In the past two decades, a number of porous materials for implant applications have been developed. In this review article, the functional requirements for this class of materials, their manufacturability, morphology and mechanical properties are discussed. A special section is also devoted to modern trends in numerical modeling of these structures. This review article is not meant to be comprehensive; rather, it concentrates on some selected aspects related to the manufacture, characterization and modeling of metallic foams for orthopedic applications.

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.