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A systematic germanium (Ge) and vanadium (V) study on 4H-SiC epitaxial layers is presented. Electrical results of TLM structures which were fabricated on these layers revealed that highly-doped Ge and V-implanted layers showed extremely low specific contact resistivity, down to 2 x 10-7 Ω.cm2. Current flow in the conducting state of Schottky barrier diodes has been successfully suppressed in some implanted layers, with highly V doped samples showing current density values of approximately 1 x 10-5 Acm-2 at 10 V. DLTS spectra reveal the presence of germanium and vanadium centers in the respective samples as well as novel peaks which are likely related to the formation of a novel GeN center.

The review on bulk growth of SiC includes a basic overview on the widely used physical vapor transport method for processing of 4H-SiC boules as well as the discussion of three current research topics: (a) Sublimation bulk growth of large area, freestanding cubic SiC, (b) in-situ Visualization of the PVT Process using 2D and 3D X-ray based imaging and (c) prediction of dislocation formation and motion in SiC using a continuum model of dislocation dynamics (CDD).

Calcium chloride is one of the main de-icing salts for removing snow and ice from roads, infrastructures and service areas. It is well known that reinforced concrete structures, if exposed to calcium chloride, can suffer from severe damages due to both corrosion of steel reinforcement and chemical attack of the cement paste. This paper aims at evaluating the resistance to chemical attack of mortars manufactured with different low-carbon binders (alkali activated slag cements, calcium sulphoaluminate cement-based blends, high volume ultrafine fly ashes cements) in presence of CaCl2-based de-icing salts in cold weather (temperature about 4°C). Results indicated that alkali activated slag-based mortars are quasi-immune to calcium chloride attack due to their mineralogical composition. On the contrary, calcium sulphoaluminate-based blends show the total loss of binding capacity, especially when calcium sulphoaluminate cement is used with gypsum and Portland cement. Finally, the partial substitution of Portland cement with ultrafine fly ash strongly reduces the mass change and the strength loss of mortars submerged in 30 wt.% CaCl2 solutions due to the strong reduction of calcium hydroxide responsible for the calcium oxychloride formation in the cement paste.

The Oxide Precipitation Hardened (OPH) steel is a new developed group of materials from Oxide Dispersion Strengthened (ODS) alloys which are well known advanced materials for high temperature properties. Besides, the corrosion resistance of these types of material is so important regarding to their practical usage. The production of OPH alloys, the same as ODS alloys, involves mechanical alloying process to create material with ductile matrix and hard oxide dispersion. Six variants of Fe-Al base OPH steel which developed and manufactured by the authors, were prepared with different chemical composition to evaluate the role of main component on the mechanical properties and corrosion resistance of new-developed OPH steels. The corrosion tests were done using potentiodynamic polarization methods. The results show that the Aluminum content has a main role both on mechanical properties and corrosion resistance.

The material properties of SiC make SiC power devices a superior alternative to the conventional Si power devices. However, the reliability of the gate oxide has been a major concern, limiting the adoption of SiC power MOSFETs as the power semiconductor of choice in applications which demand a high reliability. The threshold voltage (VTH) shift caused by Bias Temperature Instability (BTI) has focused the attention of different researchers, with multiple publications on this topic. This paper presents a novel method for evaluating the threshold voltage shift due to negative gate bias and its recovery when the gate bias stress is removed. This method could enable gate oxide reliability assessment techniques and contribute to new qualification methods.

Masonry vaults represent one of the typical structural typologies in historical masonry buildings. The study of the ultimate behavior of masonry vaults, together with the need to design adequate retrofitting techniques, is of high relevance in the optics of the preservation of the cultural heritage. In this paper, a new approach for the limit analysis of masonry construction is applied to FRP reinforced masonry vaults. This approach relies on the representation of geometry through NURBS surfaces, upper bound formulation of limit analysis, idealization of the structure as an assembly of rigid bodies with dissipation allowed only along interfaces, and optimization by means of a mesh adaptation scheme. The presence of FRP strips can be taken into account in easy way, because they can be included simply by adding NURBS surfaces and assigning them an adequate delamination stress value. The efficient mesh adaptation is performed by means of a Prey Predator Algorithm, which has been proven to be very suited for these problems. The strength of the proposed method lies in an accurate estimation of load-bearing capacity and collapse mechanism obtained with a model which requires a very low computational effort.

Hlavním cílem tohoto článku je popis viskozity a chování materiálu PA 6 se skelnými vlákny při plnění. Vstřikování plastů je jednou z nejčastěji používaných výrobních metod. Kvalita výsledného produktu je spojena s nastavenými parametry vstřikovacího procesu. Je nutné správně pochopit proces plnění formy a proto byl proveden tento výzkum. Spirálový test zatékavosti byl proveden, proto aby byly zjištěny vlivy různých parametrů na celkové plnění formy. Jako výsledný parametr byla srovnána celková délka spirály. Testovaný materiál byl PA6 s 15% skelných vláken (výrobní název Durethan BKV 15). Pro validaci byly provedeny virtuální simulace. Byla zjištěna lineární závislost mezi stupňem naplnění a ostatními parametry. Pro tento test byla navržena a vyrobena speciální forma. The main aim of this paper was to describe the viscosity and injection mold filling behavior of PA6 with 15% of glass fibers. Injection molding is one of the most widely used processes for polymer products. The quality of these products is directly linked to correct choice of process parameters. It is necessary to understand the filling behavior of the polymer material during the injection molding process. The spiral flow test was carried out in this study to explore the effects of several injection process parameters. The resulting lengths of spiral flow were compared. The polymer material under test was Polyamide 6 with 15% of short glass fibers (trade name: Durethan BKV 15). Virtual testing as well as real testing was performed. A predominantly linear relationship between the flow length and the mold temperature, melt temperature and injection pressure is described here. A special mold was designed for this test.

The aim of this research was to determine the influence of the short carbon fibres in nylon PA6 polymer used for fused deposition modelling (additive manufacturing) technology. Specimens from pure PA6 and PA6 with short carbon fibres were fabricated, with both main directions of the material with respect to the build orientation in a 3D printer. Experimental tensile tests of the specimens were carried out at several temperatures according to ISO standards. The strength, tensile modulus and ductility in relation to the temperature were compared. A significant influence of the short carbon fibres on the strength and heat deflection temperature of the part was found in PA6 and also for the orientation of the build in the 3D printer.

MOS Capacitors are demonstrated on 4H-SiC using an octahedral ABO3 ferroic thin-film as a dielectric prepared on several buffer layers. Five samples were prepared: ABO3 on SiC, ABO3 on SiC with a SiO2 buffer (10 nm and 40 nm) and ABO3 on SiC with an Al2O3 buffer (10nm and 40 nm). Depending on the buffer material the oxide forms in either the pyrochlore or perovskite phase. A better lattice match with the Al2O3 buffer yields a perovskite phase with internal switchable dipoles. Hysteresis polarization-voltage loops show an oxide capacitance of ~ 0.2 μF/cm2 in the accumulation region indicating a dielectric constant of ~120.

At the Alcoy Campus of the Universitat Politècnica de València, we were challenged to obtain the first double degree for our campus. This double degree was established for a Mechanical Engineering major, and our partner institution was Ostfalia Hochschule für Angewandte Wissenschaften, located in Wolfenbüttel campus. The agreement between the schools was signed in 2012, after three years of work. Students from either university could get an official diploma in Mechanical Engineering at both universities if they spent two consecutive semesters in the partner institution. This has many benefits for students and professors, which will be discussed in this paper, along with the main process followed to arrive to the final agreement.

This paper deals with the flexural stiffness of sandwich structures based on fiberglass and polymeric foams. The influence of geometrical and material parameters on the resulting effective flexural stiffness of the sandwich structure is being studied experimentally, analytically and using FEM models. The effective elasticity module of the sandwich-structured element is being studied and it’s theoretical and model dependencies on the stiffness of the foam core are being investigated. These dependencies are then compared with experimentally observed values. This study shows it is necessary to pay special attention to the issue of flexural stiffness of walls when designing sandwich shell products in order to prevent possible failures in the practical applications of these types of structures. © 2016 Trans Tech Publications, Switzerland.

This paper shows the authors experience in the implementation of cooperative learning during the fourth year of the Mechanical Engineering Grade, having involved from the second to the fourth year. Difficulties encountered are discussed.

In order to develop a new application of cast iron, high niobium cast iron has been developed as a grain refiner for stainless steel. High niobium cast iron was prepared by adding pure niobium to a commercial cast iron. Coarse primary niobium carbide crystals were observed in the microstructure of the cast iron. The effect of the high niobium cast iron as an inoculant on the grain size of austenitic and ferritic stainless steels was examined in various experimental conditions. When the amount of the cast iron inoculant more than 3 mass% was added into the steel melt, fine equiaxed grains were observed and grain size was significantly reduced to 210 μm. The results indicate that the high niobium cast iron is effective as a grain refiner for the austenitic and ferritic stainless steels. From the dissolution rate measurement, the grain refining mechanism was proposed., 9th International Symposium on Science and Processing of Cast Iron, SPCI-9; Luxor; 10 November 2010 through 13 November 2010, Key Engineering Materials, 457, pp.447-452; 2010

Practically exact solutions of stress intensity factor for several two-dimensional standard specimens were calculated and shown in numeric tables. The solutions were confirmed to converge until 6 significant figures through a systematical computation of discretization analysis. The convergence analyses were carried out by using a general purpose program based on a body force method., 9th International Conference on Fracture and Damage Mechanics, FDM 2010; Nagasaki; 20 September 2009 through 22 September 2009, Key Engineering Materials, 452-453, pp.405-408; 2010

Experiments and numerical simulations were conducted to investigate the propagation patterns of pre-existing 3-D elliptical crack in rock-like material under uniaxial tension. Research results demonstrated that as the load was increased, the wrapping wing cracks initiated near the front of long axis of crack, with the lateral growth of initial crack close to the front of short axis. A distortion surface formed from the growth of initial crack leaded to the macro fracture of samples. The distribution laws of mixed-mode stress intensity factor (SIF) along crack contour were derived with FRANC3D, and propagation process of 3-D crack under tension was simulated. It was concluded that propagation patterns of 3-D crack under tension were quite different from compressive cases, mainly in aspects of growth orientation and velocity., 9th International Conference on Fracture and Damage Mechanics, FDM 2010; Nagasaki; 20 September 2009 through 22 September 2009, Key Engineering Materials, 452-453, pp.817-820; 2010

An optimal condition of thermal stress cleaving was investigated by assuming the element-by-element temperature rise situation using finite element method. The obtained thermal stress cleaving condition is found to be optimal for the symmetrical cleaving of a rectangular plate., 9th International Conference on Fracture and Damage Mechanics, FDM 2010; Nagasaki; 20 September 2009 through 22 September 2009, Key Engineering Materials, 452-453, pp.389-392; 2010

The in-situ tests have been widely used to directly assess the strength and deformability of rock mass, along with which, various numerical approaches were proposed to give rational interpretations to the mechanical phenomenon happening during these tests. In this study, the so-called potential cracks are introduced into DEM model, leading to expanded DEM (EDEM) approach which is capable of simulating the cracking in intact rocks. The EDEM is applied to an in-situ triaixal compression test on a fractured rock sample. The simulation has well represented the failure mode, peak stress and elastic modulus obtained from tests as well as the cracking phenomenon and the slips on fracture planes during the loading process., 9th International Conference on Fracture and Damage Mechanics, FDM 2010; Nagasaki; 20 September 2009 through 22 September 2009, Key Engineering Materials, 452-453, pp.225-228; 2010

The cryogenic performance of two commercially available SiC power MOSFETs are presented in this work. The devices are characterised in static and dynamic tests at 10 K intervals from 20-320 K. Static current-voltage characterisation indicates that at low temperatures threshold voltage, turn-on voltage, on-state resistance, transconductance, and the body diode turn-on voltage all increase while saturation current decreases. Dynamic, 60 V, 3A switching tests within the cryogenic chamber are also reported and the trends of switching speed, losses, and total power losses, which rise at low temperature, are presented. Overall, both MOSFETs are fully operable down to 30 K with both positive and negative changes in behaviour.

Lattice models allow length scale dependent micro-structural features and damage mechanisms to be incorporated into analyses of mechanical behaviour. They are particularly suitable for modelling the fracture of nuclear graphite, where porosity generates local failures upon mechanical and thermal loading. Our recent 3D site-bond model is extended here by representing bonds with spring groups. Experimentally measured distributions of pore sizes in graphite are used to generate models with pores assigned to the bonds. Microscopic damage is represented by failure of normal and shear springs with different criteria based on force and pore size. Macroscopic damage is analysed for several loading cases. It is shown that, apart from uniaxial loading, the development of micro-failures yields damage-induced anisotropy in the material. This needs to be accounted for in constitutive laws for graphite behaviour in FEA of cracked reactor structures. © (2014) Trans Tech Publications.

Assessment of concrete strength in existing structures is a very fundamental task today, because the mechanical characteristics are strictly connected to seismic protection and performance estimation of the material. To this aim, several compression tests has been carried out on drilled core samples in conjunction with different NDT methods. The activity presented in the paper is still under development and is intended as a reference in the choice of the methods and correlations for structural survey of existing buildings.

Rice production in Brazil in 2010 was approximately 12,2 million tons, and to reach that amount several planting techniques were used with different strains of rice in different rice-growing areas. Since Rice Husk Ash (RHA) is the pozzolan of vegetable origin most studied by researchers working in the area of pozzolanic materials, the present paper evaluates the influence that the form of planting, the climate, the soil, the strain of rice and the origin/amount of nitrogen-based fertilizers used in rice cultivation has on the chemical composition and crystallographic properties of RHA. The results obtained in this paper, confirm the importance of carrying out routine chemical analysis and X-Ray diffraction to maintain the quality control of the CCAs produced, because in situations of large-scale production, husks of different origins may be used.

Rice is produced in many countries in the world, and this product permits to feed a lot of people, most of them in developing countries. Approximately one tone of rice produces 200 Kg of rice husk, and when this rice husk is burnt 20% of rice husk ash (RHA) is obtained. A very important part of rice husk is abandoned in the field producing environmental problems. RHA can be obtained by controlled combustion, when this fact occurs, a good quality RHA is produced. This RHA can be used as a pozzolanic material in mixtures with lime or Portland cement, producing good mechanical properties and durability. In this work a preliminary results about the influence of RHA/lime ratio on workability and mortars strength was studied. The results showed that mortars workability improves when RHA/lime ratio do. Compressive strength (Cs) of mortars with different RHA/lime ratios was studied, in this sense, for 28 days curing time at 20°C an increase of Cs when RHA/lime ratio do is observed. However for 90 and 180 days curing time a maximum or Cs for RHA/lime equal to 2 is obtained. The lowest and highest Cs values obtained were 6 and 18 MPa respectively, when 20°C curing temperature was used. When curing temperature increases until 65°C similar tendency of Cs respecting RHA/lime ratio was observed. A preliminary study of binders for using in mortars tiles reveals that at least low quantities of Portland cement must be included in binder composition in order to obtain short term strengths that make easy tile demoulding process.

Journal article Selective laser sintering (SLS) has the potential to fabricate bioresorbable polymer / ceramic composite scaffolds with pre-designed external and internal architecture that can be used for bone tissue engineering applications. Scaffolds were fabricated using poly-ε-caprolactone as the base material. The effect of 15 and 30 wt% of hydroxyapatite (HA) addition was investigated in terms of compressive properties, accuracy, surface topology, and wettability. Fabricated dimensions of PCL microstructures showed great deviations from their nominal values. Average surface roughness was found to be Ra=25±4 μm. Increased HA content had no statistically significant effect on accuracy and surface roughness. However the addition of HA had a significant influence on compressive properties, hydrophobicity and wettability of the samples. Addition of 30 wt% HA improved initial compressive modulus of pure PCL scaffolds from 1.31±0.08 MPa to 1.58±0.18 MPa. Yield strength values increased from 0.14±0.07 MPa to 0.17±0.01 MPa by adding 15 wt% of HA, but decreased with further HA addition. Yield strain for all compositions was over ε=0.06. Increased HA content decreased hydrophobicity and increased wettability of scaffold surfaces. The study demonstrated the ability of SLS to fabricate tissue engineering scaffolds, and the positive effect of HA particle reinforcement in terms of compressive mechanical properties and surface characteristics. peer-reviewed

A simple yet accurate macroscopic constitutive model of shape memory alloys has been developed. The features of this model are (1) energy-based phase transformation criterion, (2) one-dimensional phase transformation rule based on a micromechanical viewpoint, (3) dissipated energy with a form of a sum of two exponential functions, (4) duplication of the strain rate effect, and (5) adaptability to multi-phase transformation. This model is further improved to be able to express stress-strain relationships such that the reverse transformation starts at a higher stress than the martensitic transformation starts. Here, the ideal reversible transformation temperature is empirically described by a function of the martensite volume fraction. In this paper, an outline of our model is given, where the improvement is introduced. Then, it is shown that the model can quantitatively duplicate the major and minor hysteresis loops, strain rate effect, and asymmetry in tension and compression on the stress-strain relationship. And that it can also duplicate the stress-strain relationships having the reverse transformation start stress higher than the forward one.

An outstanding feature of shape memory alloys (SMAs) is their potential to produce different functional effects like thermal shape memory or superelasticity in one component. The purpose of the present study is to find a way to create a universal component with properties adjustable for various applications solely by modifying the local material properties. We refer to this process as in-situ configuration. The basis of in-situ configuration of the materials’ properties is generated by first deactivating the shape memory effect in the whole element and then local activation of the shape memory effect by use of local heat treatment. The NiTi-elements presented in this study offer various options, since they do not feature perceptible thermal shape memory or superelasticity due to a high dislocation density. Instead, to achieve a specific local function, the elements are subjected to in-situ heat treatment carried out by a local resistive heating element. There is a need to adjust the duration and intensity of the heat input in order to obtain different functional properties.

A thick film anemometer for in situ control of the flow rate in fluidic systems was designed, manufactured and characterized. The sensor is integrated in a retention modulus consisting of Low Temperature Cofired Ceramics (LTCC). These materials allow the cost-effective realisation of fluidic microsystems with integrated electronics. The challenge of the work is to design an anemometer under the exclusive use of thick film technologies. The necessity to trim resistors causes the external use of relevant pastes. Therefore, the use inside of a closed fluidic system requires the leak of process gases and, at the same time, a maximal heat-insulating of the sensor element from the substrate. Free-standing elements necessitate the control of stress due to shrinking mismatch, TCE mismatch, density gradients and deformation during the lamination. In the presented solution, embossed flue channels prevent blow forming on a free-standing bridge. The anemometer has a linear sensor characteristic for flow rates up to 0.1 ml/min. The layout guarantees that the fluid gets only in contact with the basic ceramic material, which is compatible with a wide range of biological substances. Therefore the sensor is applicable in contact with cell fluids or PCRreagents.

IPMCs are one of the most promising smart actuators to replace traditional actuators for some specific applications particularly in the micro-nano scales. IPMC actuator’s shape and configuration have a dramatic effect on the actuation parameters. While the behaviour of IPMCs as a single fixed end strip actuator (cantilever) has been widely studied since the early 80’s, its behaviour in other configurations is relatively unknown. This paper presents work carried out in order to reconfigure these actuators for some new applications. The first configuration is when both ends of an IPMC actuator strip are fully constrained, in both the actuator plane and the normal direction. In this case the displacement and force measurements at the mid point of the strip are presented. The results of a series of experiments show the behaviour of the actuator in this configuration and using these results some models have been proposed. The second configuration is when only one end of the strip is fixed and the other end is constrained in the normal direction with respect to the plane of the actuator strip. A series of experiments were also carried out to explore the IPMC actuator behaviour in terms of maximum displacement and force generated in this configuration. The behaviour of the IPMC actuator in these two configurations is also investigated by studying the internal stresses in the IPMC structure.

Shape Memory Alloys (SMA) show particular properties associated to their martensitic transformation between metastable phases. Their use in dampers requires a deep knowledge of the SMA behavior and its coherence with the application requirements. In earthquakes engineering standard conditions require that, after several years or decades at rest, an excellent performance is necessary for one or two minutes, i.e., nearly 200 working oscillations. When the target is the damping of stayed cables in bridges under the wind or rain actions, a larger number of oscillations is expected per each working day. This contribution analyzes the fatigue behavior of a CuAlBe alloy (appropriate for earthquakes) and discusses the results of some available experiments on a NiTi alloy for their eventual application to stayed cables..

Aging structures need repairing if their lifetime is to be extended. If the structure has been monitored before and after repair, the information from both configurations can be utilized. The data before repair include the environmental or operational influences, whereas the data after repair represent the current structural condition. Also, if damage is proportional to the worked modifications, its extent can be assessed solely from the measurement data; no finite element model is needed. The proposed method is verified with a numerical model of a vehicle crane.

Shape memory materials represent a promising class of dual-shape materials that can move from one shape to another in response to a stimulus such as light, heat, electricity or magnetism. In this regard, the biomedical field is showing large interest in this class of materials, especially in shape memory polymers (SMPs), whose mechanical properties make them extremely attractive for many biomedical applications. However, diverse characteristics including also the mechanical behaviour are still part of research. In this contribution the shape memory properties of polymers will be quantified by cyclic thermomechanical investigations. One cycle includes the "programming" of the sample and the recovery of its permanent shape. To describe this phenomenon, a three-dimensional thermomechanical coupled model is proposed. This macromechanical constitutive model is based on the physical understanding of the material behaviour and a mechanical interpretation of the stress-strain-temperature changes observed during thermomechanical loading. The main focus of this work is the influence of both, the material constants and heat transfer boundary conditions on the response of shape memory polymers. Therefore we illustrate different general simulations as well as examples of application.

A current challenge of physical, chemical and engineering sciences is to develop theoretical tools for predicting structure and physical properties of hybrid organic inorganic nanocomposite from the knowledge of a few input parameters. However, despite all efforts, progress in the prediction of macroscopic physical properties from structure has been slow. Major difficulties relate to the fact that (a) the microstructural elements in multiphase material are not shaped or oriented as in the idealizations of computer simulations, and more than one type can coexist; (b) multiple length and time scales are generally involved and must be taken into account, when overall thermodynamic and mechanical properties wish to be determined, and finally (c) the effect of the interphases/interfaces on the physical properties is often not well understood and characterized. As a consequence, their role is often neglected in the development of new theoretical tools or they are treated in a very empirical way. In this work, we focused on issues (b) and (c) in a multiscale molecular simulation framework, with the ultimate goal of developing a computationally-based nanocomposite designing tool. In particular, we developed a hierarchical procedure in which lower scale (i.e., QM, MD and /or MC) simulations are performed to obtain parameters for higher scale (i.e., mesoscopic and/or finite element) calculations, from which the bulk properties of the hybrid nanocomposite material can be ultimately estimated.

Compliant mechanisms fulfil a desired force and displacement characteristic. The development of such structures having a defined kinematical motion and subjected to several constraints, like deformability, stiffness and activation force is highly challenging. The present work deals with a methodology for analysing compliant mechanisms considering geometrically nonlinear deformations. By assembling pre-calculated nonlinear beam elements a new beam truss approach is introduced. The accuracy and quality of the mechanical model are verified by selected examples and compared to existing methods.

In order to better understand the unique functional responses of shape memory alloys, improve the currently existing SMA modeling tools and used them beneficially in smart structure applications, it is desirable to investigate the deformation/transformation processes in these materials in action – i.e. under stress and temperature variation. In this work, an overview is presented on the applications of various recently developed or originally employed in-situ experimental methods and approaches to martensitic transformations in SMAs.

Shape memory alloy (SMA) films enable the development of novel mechanically active microsystems as they provide large force and stroke in restricted space. The performance of SMA film actuators and sensors does not only depend on SMA material properties, but also requires a mechanically and thermally optimized design as well as a suitable fabrication technology being compatible to existing microsystems technologies. The paper gives an overview on the engineering aspects of SMA film actuators and sensors. These aspects are illustrated by selected examples such as bridge microactuators, microvalves and microscanners. The examples demonstrate the ongoing progress in the field, current limitations as well as existing opportunities for emerging new applications.

The experimental conditions chosen as a reference for the 2007 edition of the extrusion benchmark that was held in Bologna, Italy, and the corresponding main results are sum-marized in this work. The die design stage is first explained in order to address the main features of the experiment and its objectives. The die is a flat one with multiple holes; four angular profiles were produced with different pocket geometries, the experimental plan being entirely described. The initial temperatures for the billet and the die set, together with the temperature development during the process strokes, are also reported. The results are shown, for each profile, in terms of final profile length, mean exit speed, global process load, profile exit temperature.

The present work deals with the preparation and characterization of ceramic composites for the substitution of load-bearing bone portions, made of hydroxyapatite (HA) and bioactive β- calcium silicate (β-Ca2SiO4) as a reinforcing phase. The composite materials were prepared by Fast Hot-Pressing technique (FHP), which allowed the rapid sintering of monolithic ceramics at temperatures up to 1500 °C, well above the commonly adopted temperatures for sintering of hydroxyapatite (1200-1300 °C), in order to achieve the densification of the reinforcing phase also. XRD analysis reported no formation of secondary phases other than HA and β-Ca2SiO4, after FHP cycles. Flexural strength tests were performed on selected samples sintered at different temperatures: the composite materials exhibited increased mechanical resistance compared to samples constituted of HA only. These preliminary results confirmed that composites of HA and β- Ca2SiO4 are promising for the development of bioactive load-bearing ceramic bone substitutes.

The development of innovative ceramic scaffolds for bone substitution with superior biomechanical features and smart anisotropic performances was performed through chemical and physical transformations of natural hierarchic structures, as trees, shrubs, palms, etc. These final structures will be highly organized from the molecular to nano, micro and macro-scales, with extremely functional architectures able to constantly adapt to ever changing mechanical and biofunctional needs. This study reports the preliminary results of the ceramisation process: starting from suitable vegetal raw materials pyrolysed to produce carbon templates characterized by complex pore structure, then infiltrated by vapour phase calcium to produce calcium carbide and finally transformed into porous ceramic of calcium carbonate by multi-step thermic and hydrothermal treatment in controlled environment.

Pulsed laser deposition was used to obtain functionally graded bioactive glass coatings on titanium substrates. An UV KrF* (lambda=248 nm, tau GT 7 ns) excimer laser was used for the multi-pulse irradiation of the targets. The depositions were performed in oxygen while keeping substrate temperature at 400 degrees C. We used sintered glass targets in the system SiO2-Na2O-K2O-CaO-MgO-P2O5 that differed in SiO2 content, which was either 57 wt.% (6P57) or 61 wt.% (6P61). A glass 6P61 was used as the first layer in direct contact with the metallic substrate, while the outer bioactive layer was made of glass 6P57. Both the bioactive coatings and the bulk glasses were analyzed by Fourier transform infrared spectrometry (FTIR), grazing incidence X-ray diffraction (GIXRD), and scanning electron microscopy (SEM). The FTIR spectra of the glass powders and glass coatings showed the main vibration modes of the Si-O-Si groups. GIXRD analysis confirmed that the glass coatings had an amorphous structure. The SEM micrographs of the glass coatings showed the films to consist of droplets with diameters ranging from 0.2 to 5 Pm. SEM was used to determine the rate of apatite formation on the coating when exposed to simulated body fluid (SBF) solution for 7 days. We demonstrated that pulsed laser deposition leads to good glass-metal adhesion on the substrate and well attached bioactive particles on the surface. We consider therefore this method appropriate for forming implants that can develop an apatite layer after immersion in SBF. 20th International Symposium on Ceramics in Medicine, Oct 24-26, 2007, Nantes, France

A 2D cellular automaton model developed for the simulation of grain growth in hexagonal metals is presented here. It allows the direct use of experimental measurement as input data. Texture evolution of a titanium alloy and a zirconium alloy are simulated on the basis of simple hypothesis and compared with experimental evolution as well as the results from a 3D Monte Carlo model. Results from both models are discussed with regards to their characteristics.

International audience; The development of a digital material framework is presented, allowing to build virtual microstructures in agreement with experimental data. The construction of the virtual material consists in building a multi-level Voronoï tessellation. A polycrystalline microstructure made of grains and sub-grains can be obtained in a random or deterministic way. A corresponding finite element mesh can be generated automatically in 3D, and used for the simulation of mechanical testing under large strain. In the examples shown in this work, the initial mesh was non uniform and anisotropic, taking into account the presence of interfaces between grains and sub-grains. Automatic remeshing was performed due to the large strains, and maintained the non uniform and anisotropic character of the mesh. A level set approach was used to follow the grain boundaries during the deformation. The grain constitutive law was either a viscoplastic power law, or a crystallographic formulation based on crystal plasticity. Stored energies and precise grain boundary network geometries were obtained directly from the deformed digital sample. This information was used for subsequent modelling of grain growth with the level set approach, on the same mesh.

A hierarchical multiscale procedure for softening materials is proposed in this paper. A standard multiscale model has been analysed with respect to macro-level mesh dependence and meso-level cell size dependence. In order to eliminate spurious macro-level mesh dependence and meso-level cell size dependence a coupled-volume approach has been proposed. A discussion on the various interacting length scales in the model is included.

The paper presents an experimental application of the Proper Orthogonal Decomposition (POD) to damage detection in steel beams. A damaged beam has been excited with a sinusoidal force, the acceleration response at points regularly spaced along the structure has been recorded and the relevant Proper Orthogonal Modes calculated. In this way it is possible to locate damage by comparing the measured dominant Proper Orthogonal Mode with a smoothed version of it which does not exhibit apparent peaks in correspondence with the damage. One of the principal advantages of the proposed damage detection technique is that it does not require vibration measurements to be performed on the undamaged structure. Moreover the ‘optimality’ of the proper orthogonal modes only requires the use of a few (one-two) of them which can be computed in real time during lab experiments or while the structure is functioning in the field.

The adequate choice of different target materials for X-ray generators is a very important subject of engineers practice and research. In the present work we analyze theoretically the transport of electrons through the anode material and the production of the corresponding bremsstrahlung radiation. In our analysis we simulate the particle transport with the help of the FOTELP code, which is based on the Monte Carlo simulation. Our main aim is to develop an efficient and handy method, which could be helpful in improving the design of the X-ray tube components and in reducing of the patient dose, while keeping the image quality. The obtained results are encouraging. Research Trends in Contemporary Materials Science, 8th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 04-08, 2006, Herceg Novi, Montenegro

Neutral beam processing has evolved into one of the most promising methods for overcoming plasma process induced damage. Surface treatment by neutrals avoids problems with surface charging effects, frequently encountered when using common ion treatment, especially for low k-materials. In this paper, the influence of various parameters on the neutralization of ion beams in Ar-CF4 mixture based on a Particle in Cell with Monte Carlo collisions (PIC/MCC) simulation is studied. The efficiency of neutralization has been treated by considering both surface neutralization of ions and collisions of ions in the gas. Research Trends in Contemporary Materials Science, 8th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 04-08, 2006, Herceg Novi, Montenegro

In this paper the fatigue behaviour of Ti-6Al-4V alloy coated with a TiN arc-deposited PVD film was studied. Rotating bending tests (R = -1) were carried out on standard “hourglass” specimens to evaluate the fatigue limit at 200000 load cycles. Conventional and notched (120° Vnotch transversal to the rotating axis at the minimum cross section area) specimens were tested, both coated and uncoated, to investigate the effect of the coating on the fatigue limit of the titanium alloy, with and without the surface notch. Fracture surfaces were observed by SEM. The coating did not improve the titanium alloy fatigue life.

International audience; 6H and 4H-SiC epilayers were Al-implanted at room temperature with multiple energies (ranging from 25 to 300 keV) in order to form p-type layers with an Al plateau concentration of 4.5×1019 cm-3 and 9×1019 cm-3. Post-implantation annealing were performed at 1700 or 1800 °C up to 30 min in Ar ambient. During this process, some samples were encapsulated with a graphite (C) cap obtained by thermal conversion of a spin-coated AZ5214E photoresist. From Atomic Force Microscope measurements, the roughness is found to increase drastically with annealing temperature for unprotected samples while the C capped samples show a preservation of their surface states even for the highest annealing temperature. After 1800°C/30 min annealing, the RMS roughness is 0.46 nm for the lower fluence implanted samples, slightly higher than for unimplanted samples (0.31 nm). Secondary Ion Mass Spectroscopy measurements confirm that the C cap was totally removed from the SiC surface. The total Al-implanted fluence is preserved during postimplantation annealing. A redistribution of the Al dopants is observed at the surface which might be attributed to Si vacancy-enhanced diffusion. An accumulation peak is also observed after annealing at 0.29 9m, depth corresponding to the amorphous/crystalline interface that was determined on the as-implanted samples by Rutherford Backscattering Spectroscopy in channeling mode. The redistribution of the dopants has an impact on their electrical activation. A lower sheet resistance (Rsh= 8 k_) is obtained for samples annealed without capping than for samples annealed with C capping (Rsh= 15 k_ ).

The research into the stress state of gear rim has been based on the developed model of pinion-wheel system and the finite element application. For a spur gear structure of middle web position, the assumption of load distribution in the contact area that reflects, first of all, the tooth support deformation, has been not required for the imposed boundary conditions. To study the influence of web thickness stiffening effect on the inner rim surface stress, the ranges of rim and web thickness values have been considered. The area of stress along the rim circle and tooth facewidth has been shaped and discussed in relation to maximum rim stress appearance.

Copolymer poly(D,L-lactide-co-glycolide) is used for obtaining the systems for controlled delivery of medicaments. Its specific characteristics make it suitable for various researches where its synthesis is performed in different ways. Using the system for controlled delivery of medicaments, an equal concentration of the medicament is achieved in the body throughout an extended period of time and it has advantages over the conventional methods. In this paper we present a new solvent/non-solvent chemical method for obtaining DLPLG nanospheres. In the experiment various stabilizers were used in order to examine their influence on morphological characteristics of DLPLG particles. The samples were characterized by Infrared Spectroscopy (IR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Stereological analysis. Research Trends in Contemporary Materials Science, 8th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 04-08, 2006, Herceg Novi, Montenegro