Review and Perspectives: Shape Memory Alloy Composite Systems

Following their discovery in the early 60's, there has been a continuous quest for ways to take advantage of the extraordinary properties of shape memory alloys (SMAs). These intermetallic alloys can be extremely compliant while retaining the strength of metals and can convert thermal energy to mechanical work. The unique properties of SMAs result from a reversible difussionless solid-to-solid phase transformation from austenite to martensite. The integration of SMAs into composite structures has resulted in many benefits, which include actuation, vibration control, damping, sensing, and self-healing. However, despite substantial research in this area, a comparable adoption of SMA composites by industry has not yet been realized. This discrepancy between academic research and commercial interest is largely associated with the material complexity that includes strong thermomechanical coupling, large inelastic deformations, and variable thermoelastic properties. Nonetheless, as SMAs are becoming increasingly accepted in engineering applications, a similar trend for SMA composites is expected in aerospace, automotive, and energy conversion and storage related applications. In an effort to aid in this endeavor, a comprehensive overview of advances with regard to SMA composites and devices utilizing them is pursued in this paper. Emphasis is placed on identifying the characteristic responses and properties of these material systems as well as on comparing the various modeling methodologies for describing their response. Furthermore, the paper concludes with a discussion of future research efforts that may have the greatest impact on promoting the development of SMA composites and their implementation in multifunctional structures

Characterization and Modeling of Deformation, Springback, and Failure in Advanced High Strength Steels (AHSSs)

New generations of advanced high strength steels (AHSSs), expected with tension strength exceeding 1000 MPa, sufficient cold-stamping ductility, and low-alloyed microstructure, are being highly sought for automotive lightweighting applications without compromising on neither performance nor cost standards. From the standpoint of metallurgy, the most straightforward solution is to realize complex microstructures in the new AHSSs with significant fractions of the strongest ferrous phase, martensite, in combination with the most ductile phase, austenite. Nevertheless, the preliminary-developed new AHSSs exhibit unique and complex deformation, failure, and springback characteristics compared with the conventional steel grades, which thereby bring significant challenges to the current manufacturing infrastructure in automotive sector. To thoroughly investigate this uniqueness and complexity, this research work started from a full set of mechanical experimentation on some target AHSSs to comprehensively understand their deformation, springback, and failure. In the selected AHSSs, in particular, a 980 MPa grade quenched and partitioned (QP980) steel, with tri-phase microstructure of retained austenite, martensite, and ferrite, was primarily investigated, since it would be a baseline material of the developing AHSS grades. Another highlight is that, during the entire experimental work, a stereo digital image correlation (DIC) system was widely employed to not only in-situ accurately measure the full-field material deformation and displacement, but also control the loading directions when necessary. Furthermore, based on the experimental results, a new phenomenological model was proposed to properly characterize not only anisotropy, complex hardening induced by the Bauschinger effect, but also tension-compression asymmetry and the transformation-induced plasticity (TRIP) effect. Then this new model was implemented via user material subroutine in LS-DYNA. Last but not the least, this work eventually wrapped up with a case study of component-level finite element forming and springback predictions compared with the corresponding actual panels, as an implementation and verification of the previous experimentation and modeling

Effect of Stacking Fault Energy on the mechanism of plastic deformation in Steel and CuZn alloys

Study on the mechanism of plastic deformation in AISI 304 steel and CuZn alloys with different compositions depending on the values of the Stacking Fault Energy obtained after a rolling process in different conditons of temperature and deformation

Nickel-titanium shape-memory alloy reinforced aluminum composites

The purpose of the study is to create an NiTi/aluminum metal matrix composite (MMC) material which will have mechanical properties superior to those of the aluminum matrix. The goal is to fabricate a composite material by dispersing a shape memory alloy (NiTi) in the form of a powder, into an aluminum matrix, using isostatic or hot pressing, powder-metallurgy processing techniques. The author wishes to obtain a composite material with a satisfactory density (\u3e 97% of theoretical density), greater strength, and improved fatigue resistance, relative to the aluminum matrix. When the shape-memory alloy particles are embedded in the matrix, the shape memory effect is utilized by deforming the composite material below the Mg temperature, (around -20°C or -4°F), which will also deform each NiTi particle within the matrix (since the martensitic phase of NiTi has a much lower yield strength than aluminum at that temperature). Upon reheating to the austenite phase, the NiTi will return to it’s original shape, (within 8-9% of deformation), embedded within the aluminum matrix which has a much lesser degree of thermal strain. This action will create residual, internal stresses around each NiTi particle, tensile stresses in the longitudinal and transverse directions, and compressive stresses in the through-thickness direction, which will strengthen the material m a similar fashion as thermal stresses strengthen a ceramic particle reinforced metal matrix composite upon cooling from the manufacturing temperature. In order to accomplish the objective, the NiTi powder may first be reduced in size to enhance bonding and deformation characteristics. This is done through a tedious and time-consuming mechanical milling process. Also, since the shape-memory effect is so strongly dependent on the composition of the NiTi, the powder must first be treated with a coating to resist the diffusion of the matrix into the NiTi particles during pressing. Oxide and nitride coatings have been investigated with moderate success. The process of hot pressing also lends difficulty because the time at elevated pressures and temperatures results in further diffusion. However, without a sufficient pressure and temperature in hot pressing, a good density cannot be achieved. Internal voids due to poor densification may become sites for crack initiation upon loading, thus weakening the material. Several different NiTi/Al composites have been studied. The NiTi powders have been treated in a couple different manners. One method reduces the particle sizes and roughens their shape. A heat-treatment procedure has been developed in order to produce a surface oxide coating, which helps prevent diffusion during hot pressing. Different aluminum powders have been investigated also. The size of the aluminum particles has proved to be very influential in affecting the quality of composite materials produced. This finding is important because the failure of this kind of composite has been shown to be matrix-dominated. Some physical and mechanical properties of the NiTi/Al composite material have been characterized by Digital Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), and through tensile and fatigue testing. There is a considerable increase in the yield strength, the ultimate strength, and the fatigue resistance due to the addition of the NiTi powder into the matrix. However, the elastic modulus drops slightly in some materials, perhaps due to a phenomenon called stress-induced martensite, which is common in the NiTi shape-memory alloy

Launch vehicle flight control augmentation using smart materials and advanced composites (CDDF Project 93-05)

The Marshall Space Flight Center has a rich heritage of launch vehicles that have used aerodynamic surfaces for flight stability such as the Saturn vehicles and flight control such as on the Redstone. Recently, due to aft center-of-gravity locations on launch vehicles currently being studied, the need has arisen for the vehicle control augmentation that is provided by these flight controls. Aerodynamic flight control can also reduce engine gimbaling requirements, provide actuator failure protection, enhance crew safety, and increase vehicle reliability, and payload capability. In the Saturn era, NASA went to the Moon with 300 sq ft of aerodynamic surfaces on the Saturn V. Since those days, the wealth of smart materials and advanced composites that have been developed allow for the design of very lightweight, strong, and innovative launch vehicle flight control surfaces. This paper presents an overview of the advanced composites and smart materials that are directly applicable to launch vehicle control surfaces

The thermoelastic martensite transformation in copper-aluminium-nickel alloys

Imperial Users onl

Advances in Low-carbon and Stainless Steels

This Special Issue of Metals was dedicated to recent advances in low-carbon and stainless steels. Although these types of steels are not new, they are still receiving considerable attention from both research and industry sectors due to their wide range of applications and their complex microstructure and behavior under different conditions. The microstructure of low-carbon and stainless steels resulting from solidification, phase transformation, and hot working is complex, which, in turn, affect their performance under different working conditions. A detailed understanding of the microstructure, properties, and performance for these steels has been the aim of steel scientists for a long time. This Issue received quality papers on different aspects of these steels including their solidification, thermomechanical processing, phase transformation, texture, etc., and their mechanical and corrosion behaviors

Trip steels as smart sensor alloys.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.Upon deformation, TRIP steels undergo progressive irreversible transformation from paramagnetic austenite to more thermodynamically stable, ferromagnetic αʹ-martensite. The change in magnetic permeability is readily detectable, and since TRIP steels also have excellent mechanical properties, this presents the opportunity for implementing cheap, robust structural health monitoring systems. However, the extent of martensitic transformation in TRIP steels is affected not only by the degree of deformation, but by environmental temperature at the time of deformation and strain rate. This creates inherent inaccuracy when implementing TRIP steels as sensor materials. In this thesis it has been demonstrated that it is possible to design TRIP steels that are less susceptible to these factors, show good deformation induced transformation, and can function simultaneously as sensors and structural elements. As-cast alloys were tested in compression, while annealed, hot-rolled and warm-rolled alloys were tested primarily in tension. There was considerable variation between alloys in rate of transformation with deformation. Martensitic transformation was evaluated magnetically and correlated with optical and scanning electron microscopy and X-ray diffraction results. Changes in magnetisation and magnetic permeability curves with deformation were characterised to ensure optimal electronic monitoring. Equations from literature for determining characteristic transformation temperatures, Ms and Md30 were evaluated experimentally for the alloy range of interest, and the best equations were selected to aid in the design of high alloy TRIP steels exhibiting strong transformation and low temperature sensitivity. Temperature sensitivity between alloys was found to vary as predicted. Temperature sensitivity was also compared in annealed, hot rolled and warm rolled conditions; the annealed condition showed the lowest sensitivity, and this is thought to be related to lower dislocation densities. Mining was targeted as a primary industry for application of these sensor systems because of the pressing need for greater safety and more efficient structural support at low cost. Two distinct devices for monitoring the structural health of mines were designed, built and tested, and a third was developed for the aerospace industry. Better understanding and control of the temperature sensitivity of martensitic transformation in TRIP steels is expected to aid not only structural health monitoring, but also the application of such materials to other areas of technology, such as sheet forming and high impact resistance applications. Although there are limitations on the extent to which TRIP steel transformation characteristics can be controlled, it was shown that they can be manipulated to enable successful implementation of new alloys for smart load or damage sensors. Practical, robust, low cost structural health monitoring sensors based on the smart properties of TRIP steels were shown to be feasible

ADVANCED CERAMIC MATERIALS FOR DENTAL APPLICATIONS SINTERED BY MICROWAVE HEATING

[EN] Zirconia has become a widely utilized structural ceramic material with important applications in dentistry due to its superb mechanical properties, biocompatibility, aesthetic characteristics and durability. Zirconia needs to be stabilized in the t-phase to obtain improved mechanical properties such as hardness and fracture toughness. Fully dense yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) materials are normally consolidated through the energy-intensive processing of powders at very high temperatures (>1000 °C). Innovative non-conventional approaches are being developed to reduce time and energy consumption and, consequently, environmental impact in ceramic powder processing. Microwave sintering is one such approach aimed at fully-densifying ceramics by using a different heating mechanism based on the material's inherent dielectric properties. The main purpose of this work is to obtain highly dense Y-TZP dental materials from commercial and lab-prepared sources via microwave sintering with mechanical and microstructural qualities that are similar or even improved with respect to their conventionally sintered counterparts. Therefore, its effect on important aspects related to dental applications has been studied. First, Y-TZP ceramics have been characterized upon sintering to determine whether the resulting properties meet the minimum mechanical requirements for structural dental applications. Second, the influence of microwave sintering on hydrothermal degradation, a spontaneous ageing phenomenon that affects zirconia materials in wet conditions, has been investigated. And third, the behavior under fretting wear conditions of microwave and conventionally sintered materials has been assessed to evaluate their durability and performance. The main conclusions indicate that microwave sintering allows proper consolidation of dental Y-TZP materials resulting in a finer microstructure due to shorter processing time and mechanical properties comparable, and in some cases enhanced, to those obtained in conventional sintered materials at lower dwell temperatures. Additionally, a higher resistance to hydrothermal degradation has been determined for microwave sintered materials due to a finer grain size and lower sintering temperatures that reduce the presence of cubic phase, which is responsible for destabilizing neighboring tetragonal phase grains. Finally, a similar wear rate has been obtained between microwave and conventional sintering of zirconia materials under fretting wear conditions. In addition, humidity can reduce the wear volume loss due to the lubricative effect of water and wear of degraded materials might increase the resistance due to the formation of a protective debris layer. In general, microwave sintering can be an interesting alternative for obtaining fully-densified Y-TZP dental materials providing certain advantages over conventional methods. Nonetheless, more studies are still necessary to have a better understanding of the advantages and disadvantages of microwave sintering of zirconia ceramics.[ES] La circona es un material ampliamente utilizado como cerámica estructural con aplicaciones en el ámbito dental debido a sus propiedades mecánicas, biocompatibilidad, características estéticas y durabilidad. Para poder aprovechar las altas propiedades mecánicas de la circona, es necesario estabilizarla en su fase tetragonal. Los materiales de circona policristalina estabilizada con itria (Y-TZP) se consolidan normalmente a través de polvos mediante procesos energéticamente intensivos a altas temperaturas (>1000 °C). Actualmente, se están desarrollando técnicas basadas en métodos no convencionales para reducir el tiempo y el consumo energético en el procesado de polvos cerámicos. La sinterización por microondas tiene por objetivo la densificación completa mediante la utilización de mecanismos de calentamiento basados en las propiedades dieléctricas del material. El objetivo principal es la obtención de materiales dentales de Y-TZP altamente densos mediante la sinterización por microondas con propiedades mecánicas y microestructurales similares, o incluso por encima de las obtenidas por el método convencional. Para ello, se estudian aspectos relevantes al ámbito dental. En primer lugar, los materiales son caracterizados con el fin de determinar si las propiedades finales cumplen con los requisitos mecánicos para aplicaciones dentales. Además, se ha investigado la influencia de la sinterización por microondas en la degradación hidrotérmica, un fenómeno espontáneo de envejecimiento que afecta a los materiales de circona en condiciones de humedad. Finalmente, se ha evaluado el comportamiento en condiciones de desgaste fretting de los materiales sinterizados para determinar su durabilidad. Las conclusiones principales indican que la sinterización por microondas permite la consolidación adecuada de estos materiales, resultando en una microestructura más fina debido a los tiempos más cortos de procesado y en propiedades mecánicas comparables a las de materiales obtenidos mediante el método convencional, incluso a temperaturas más bajas. Una mayor resistencia a la degradación hidrotérmica se ha determinado en materiales sinterizados por microondas. Al emplear temperaturas más bajas se reduce la presencia de fase cúbica, la cual es responsable por la desestabilización de granos adyacentes de fase tetragonal. Tasas de desgaste similares han sido observadas entre materiales sinterizados por microondas y convencionalmente bajo condiciones de desgaste fretting. Adicionalmente, la humedad puede reducir sustancialmente la pérdida de volumen de desgaste debido al efecto lubricante del agua y los materiales degradados pueden aumentar la resistencia a este tipo de desgaste como consecuencia de la formación de una capa protectora de material que se desprende más fácil. En general, la sinterización por microondas es una alternativa interesante para obtener materiales dentales de Y-TZP altamente densos con ciertas ventajas sobre los métodos convencionales pero deben considerarse también las desventajas de esta técnica.[CA] La circona és un material àmpliament utilitzat com a ceràmica estructural amb aplicacions en l'àmbit dental a causa de les seues propietats mecàniques, biocompatibilidad, característiques estètiques i durabilitat. Per a poder aprofitar les altes propietats mecàniques de la circona, és necessari estabilitzar-la en la seua fase tetragonal. Els materials de circona policristalina estabilitzada amb itria (Y-TZP) es consoliden normalment mitjançant processos energèticament intensius a altes temperatures (>1000 °C). Actualment, s'estan desenvolupant tècniques basades en mètodes no convencionals per a reduir el temps i el consum energètic en el processament de la pols ceràmicas. La sinterització per microones té per objectiu la densificació completa mitjançant la utilització de mecanismes d'escalfament basats en les propietats dielèctriques del material. L'objectiu principal d'aquesta tesi és l'obtenció de materials dentals de Y-TZP altament densos mitjançant la sinterització per microones amb propietats mecàniques i microestructurals superiors a les obtingudes per mètodes convencionals. En primer lloc, els materials seràn caracteritzats per a determinar si les propietats finals compleixen amb els requisits mecànics per a aplicacions dentals. En segon lloc, s'investigarà la influència de la sinterització per microones en la degradació hidrotèrmica, un fenomen espontani d'envelliment que afecta als materials de circona en condicions d'humitat. I en tercer lloc, s'avaluarà el comportament en condicions de desgast fretting dels materials sinteritzats per a determinar la seua durabilitat. Les conclusions principals indiquen que la sinterització per microones permet la consolidació adequada i millorada de materials de Y-TZP, amb una microestructura més fina a causa dels temps més curts de processament i propietats mecàniques comparables a les de materials obtinguts mitjançant el mètode convencional, fins i tot a temperatures més baixes. Un factor positiu ha sigut la major resistència a la degradació hidrotèrmica en materials sinteritzats per microones. A més, al emprar temperatures més baixes es redueix la presència de fase cúbica, la qual és la responsable de la desestabilització de grans adjacents de fase tetragonal. Finalment, sota condicions de desgast fretting, s'han observat taxes de desgast similars entre materials sinteritzats per microones i via convencional. Addicionalment, en condicions de 100% d'humitat es pot reduir substancialment la pèrdua de volum de desgast a causa de l'efecte lubrificant de l'aigua i materials degradats, els quals poden augmentar la resistència a aquest tipus de desgast com a conseqüència de la formació d'una capa protectora de material que es desprèn amb més facilitat. En general, la sinterització per microones és una alternativa molt interessant per a obtindre materials dentals Y-TZP òptims i amb certes avantatges sobre els mètodes convencionals, però han de considerar-se també algunes desavantatges d'aquesta tècnica.Presenda Barrera, Á. (2016). ADVANCED CERAMIC MATERIALS FOR DENTAL APPLICATIONS SINTERED BY MICROWAVE HEATING [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68510TESI

A cooling system for s.m.a. (shape memory alloy)based on the use of peltier cells

The aim of this thesis has been the study and the implementation of an innovative cooling system for S.M.A. (Shape Memory Alloy) material by using a Peltier cell. This system has demonstrated a consistent cooling time reduction during the application and so that the solution adopted has confirmed that it can be used for a better operability of the S.M.A. material during the cooling phase. After an accurate selection of possible cooling system to be adopted on these materials the better choice in terms of efficiency and energy consumption reduction has converged on Peltier cell design development. In this context for our research three investigation have been conducted. The first one has concerned an analytic investigation in order to understand the phenomenology and the terms involved during the heat exchange. After this study a numerical investigation through a Finite Element approach by commercial software has been carried out. Also an experimental investigation has been conducted, at the CIRA Smart Structure Laboratory, in order to verify the results obtained by the numerical prediction. The set-up with the Peltier cell used as heater and cooler of the S.M.A. has confirmed the soundness of the solution adopted. Finally, a correlation between numerical and experimental results have been presented demonstrating the validity of the obtained results through the developed investigations. This system, composed of Peltier cell has confirmed also an energy consumption reduction because the cell has been used for heating and cooling phase without additional system as resistive system (Joule effect). This project shall be also industrial involvement in a new cost cut down point of vie