Showing papers in "Advanced Engineering Materials in 2002"
TL;DR: The most common biomedical applications of shape memory alloys and SMPs are reviewed and their critical biocompatibility concerns are addressed and some engineering implications of their use as biomaterials are examined.
Abstract: Shape memory properties provide a very attractive insight into materials science, opening unexplored horizons and giving access to unconventional functions in every material class (metals, polymers, and ceramics). In this regard, the biomedical field, forever in search of materials that display unconventional properties able to satisfy the severe specifications required by their implantation, is now showing great interest in shape memory materials, whose mechanical properties make them extremely attractive for many biomedical applications. However, their biocompatibility, particularly for long-term and permanent applications, has not yet been fully established and is therefore the object of controversy. On the other hand, shape memory polymers (SMPs) show promise, although thus far, their biomedical applications have been limited to the exploration. This paper will first review the most common biomedical applications of shape memory alloys and SMPs and address their critical biocompatibility concerns. Finally, some engineering implications of their use as biomaterials will be examined.
431 citations
TL;DR: Ceramic Matrix Composites (CMC) as discussed by the authors is a type of composite material based on carbon fibres and silicon carbide matrices, which have superior tribological properties in comparison to grey cast iron or carbon/carbon.
Abstract: Ceramic Matrix Composites (CMC), based on reinforcements of carbon fibres and matrices of silicon carbide, show superior tribological properties in comparison to grey cast iron or carbon/carbon. In combination with their low density, high thermal shock resistance and good abrasive resistance, these Si-infiltrated carbon/carbon materials, called C/SiC or C/C-SiC composites, are promising candidates for advanced friction systems. Generally, the carbon fibres lead to an improved damage tolerance in comparison to monolithic SiC, whereas the silicon carbide matrix improves the wear resistance compared to carbon/carbon. In combination with new design approaches cost-efficient manufacturing processes have been developed and have lead to successfully tested prototypes of brake pads and disks, especially for passenger cars and emergency brake systems.
268 citations
TL;DR: The French company Snecma Moteurs is a leading producer of high-performance composites for operation under high mechanical stress and at high temperature, such as in jet engines, aircraft brake disks, or even rocket propulsion systems as mentioned in this paper.
Abstract: The French company Snecma Moteurs is a leading producer of high-performance composites for operation under high mechanical stress and at high temperature, such as in jet engines, aircraft brake disks, or even rocket propulsion systems. The author presents the different families and generations of carbon-carbon and ceramic-matrix composites developed by Snecma, and discusses their manufacture and characteristics.
260 citations
TL;DR: Open cell, stochastic nickel foams are widely used for the electrodes and current collectors of metal -metal hydride batteries as mentioned in this paper, but they are more costly than their periodically structured counterparts, and the average cell size, the cell size standard deviation, the relative density and the microstructure of the ligaments are all important to control.
Abstract: Open cell, stochastic nickel foams are widely used for the electrodes and current collectors of metal – metal hydride batteries. Closed cell, periodic aluminum honeycomb is extensively used for the cores of light, stiff sandwich panel structures. Interest is now growing in other cell topologies and potential applications are expanding. For example cellular metals are being evaluated for impact energy absorption, for noise and vibration damping and for novel approaches to thermal management. Numerous methods for manufacturing cellular metals are being developed. As a basic understanding of the relationships between cell topology and the performance of cellular metals in each application area begins to emerge, interest is growing in processes that enable an optimized topology to be reproducibly created. For some applications, such as acoustic attenuation, stochastic metal foams are likely to be preferred over their periodically structured counterparts. Nonetheless, the average cell s ize, the cell size standard deviation, the relative density and the microstructure of the ligaments are all important to control. The invention of more stable processes and improved methods for on-line control of the cellular structure via in-situ sensing and more sophisticated control algorithms are likely to lead to significant improvements in foam topology. For load supporting applications, sandwich panels containing honeycomb cores are much superior to those utilizing stochastic foams, but they are more costly than stochastic foam core materials. Recently, processes have begun to emerge for making open cell periodic cell materials with triangular or pyramidal truss topologies. These have been shown to match the stiffness and strength of honeycomb in sandwich panels. New cellular metals manufacturing processes that use metal textiles and deformed sheet metal are being explored as potentially low cost manufacturing processes for these applications. These topologically optimized systems are opening up new multifunctional applications for cellular metals.
259 citations
TL;DR: In this paper, the truss cores are made by deformation shaping hexagonal perforated metal sheets and then bonded between thin facesheets using a transient liquid phase approach.
Abstract: Closed cell honeycomb core structures are widely used for sandwich panel construction. Periodic open cell tetrahedral truss core structures have recently been shown to possess weight specific properties that compete with those of honeycomb core designs. In contrast to honeycomb, the open cell topologies provide many opportunities for multifunctionality. Past approaches to miniature tetrahedral truss fabrication from metals have utilized investment casting routes. Material choices are then constrained by the need for high fluidity during casting. Strength knockdown due to casting defects has been observed. Here, we utilize a comparatively simple wrought metal based approach. The truss cores are made by deformation shaping hexagonal perforated metal sheets. They are then bonded between thin facesheets using a transient liquid phase approach. When designed to minimize bending of members within the core, a linear dependence of core modulus and strength upon relative density is anticipated. Core relative densities of less than two percent have been obtained. With this approach, low cost truss core structures can be made from a wide variety of heat-treatable wrought alloys. (Abstract Copyright [2002], Wiley Periodicals, Inc.)
176 citations
162 citations
TL;DR: In this paper, a strategy for selecting actuators to meet specified design requirements is described, where a number of considerations enter: the type and characteristics of the actuator, the nature of the power-source (the fuel) that is required to drive it, and the possible need of an interface between the two to convert the energy into a form that the actuators can accept.
Abstract: Actuators are controllable work-producing devices. A strategy for selecting actuators to meet specified design requirements is described here. A number of considerations enter: the type and characteristics of the actuator, the nature of the power-source (the fuel) that is required to drive it, and the possible need of an interface between the two to convert the energy into a form that the actuator can accept. The strategy is demonstrated by software that includes a database for some 220 actuators drawn from 18 families, and an advanced selection engine. Case studies are used to illustrate its use.
149 citations
TL;DR: Progress reports as mentioned in this paper are a new type of article in Advanced Engineering Materials, dealing with the hottest current topics, and providing readers with a critically selected overview of important progress in these fields.
Abstract: Progress reports are a new type of article in Advanced Engineering Materials, dealing with the hottest current topics, and providing readers with a critically selected overview of important progress in these fields. It is not intended that the articles be comprehensive, but rather insightful, selective, critical, opinionated, and even visionary. We have approached scientists we believe are at the very forefront of these fields to contribute the articles, which will appear on an annual basis. The article below describes the latest advances in Bio-inspired Materials Chemistry.
106 citations
TL;DR: A methodology for 2D and 3D characterization of different foams using X-ray microtomography with a resolution of 30 micrometer using morphological operations such as opening granulometry to separate cells when they are not perfectly closed is presented.
Abstract: The aim of this paper is to present a methodology for 2D and 3D characterization of different foams using X-ray microtomography with a resolution of 30 micrometer. 2D and 3D quantitative image analyses have been performed to obtain information about the cells. The main parameters of interest are the cell size, the cell size distribution, morphology of the cells, connectivity of the cells, and fraction of matter at the edges. We use morphological operations such as opening granulometry to separate cells when they are not perfectly closed. This characterization was performed on Alporas, IFAM, and Norsk-Hydro foam.
102 citations
TL;DR: In this article, a new processing technique for cellular aluminum, to produce net shape parts of foamed aluminum via the melt route by gas injection, is described, and the microstructure of the cell walls is presented as well as the achieved pore size and the local mass density distribution.
Abstract: This paper reports on investigations by Hutte Klein-Reichenbach and LKR in the course of the development of a new processing technique for cellular aluminum, to produce net shape parts of foamed aluminum via the melt route by gas injection. The foaming depends on the interaction between the blowing gas, the ceramic particles, and the melt. The stabilization of the foam by different particle contents in interaction with air, oxygen and nitrogen as blowing gas has been investigated for some matrix alloys with respect to the processing parameters. The resulting cell structure is characterized by computed X-ray tomography, light optical and scanning electron, as well as high resolution Auger electron microscopy. The microstructure of the cell walls is presented as well as the achieved pore size and the local mass density distribution.
95 citations
TL;DR: In this paper, a general overview of the Ni-Ti system and a detailed review over the NiTi-Cu system are given with special regard to the influence of heat treatments upon the phase change behavior.
Abstract: Among other special characteristics Shape Memory Alloys (SMAs) have the ability to return to a predetermined shape when heated. In fact, the phase change of an existing element can strongly be influenced by thermal and thermo-mechanical treatments. Up to now, SMEs have been discovered in various materials, which can generally be classified into noble-metal based, Cu-based, Fe-based, Ni-Ti-based alloy systems and non-metallic SMAs. In this paper a general overview of the Ni-Ti system and a detailed review over the Ni-Ti-Cu system will be given with special regard to the influence of heat treatments upon the phase change behavior.
TL;DR: In this paper, a real-time x-ray radioscopy with image frequencies ranging up to 18 Hz and spatial resolutions down to 10 μm was used to study the evolution of aluminium alloy foams.
Abstract: Aluminium alloy foams were created by expanding foamable precursors containing a gas releasing blowing agent in a dense metallic matrix. The precursors were prepared by two different ways: either by hot-compaction of powder mixtures or by thixo-casting of billets obtained by cold compaction of powder blends. Foam evolution was visualized by means of real-time x-ray radioscopy with image frequencies ranging up to 18 Hz and spatial resolutions down to 10 μm. The difference in pore formation between the two processing routes could be studied. Rupture of cell walls during foam expansion could be visualised, a critical rupture thickness measured and the time-scale of the rupture process estimated. By manufacturing foam precursors in which defects were incorporated deliberately, the question of the origin of very large pores in solid metal foams could be discussed. By forced cooling of liquid metal foams while recording their structure, the importance of solidification-induced changes of foam morphology was illustrated.
TL;DR: In this article, different empirical and physically based concepts for the integration of the elastic-plastic anisotropy into metal forming finite element simulations are reviewed. But the focus of the paper is on the discussion of the crystallographic anisotropic of polycrystalline material rather than on aspects associated with topological or morphological microstructure structures.
Abstract: Modern metal forming and crash simulations are usually based on the finite element method. Aims of such simulations are typically the prediction of the material shape, failure, and mechanical properties during deformation. Further goals lie in the computer assisted lay-out of manufacturing tools used for intricate processing steps. Any such simulation requires that the material under investigation is specified in terms of its respective constitutive behavior. Modern finite element simulations typically use three sets of material input data, covering hardening, forming limits, and anisotropy. The current article is about the latter aspect. It reviews different empirical and physically based concepts for the integration of the elastic-plastic anisotropy into metal forming finite element simulations. Particular pronunciation is placed on the discussion of the crystallographic anisotropy of polycrystalline material rather than on aspects associated with topological or morphological microstructure anisotropy. The reviewed anisotropy concepts are empirical yield surface approximations, yield surface formulations based on crystallographic homogenization theory, combinations of finite element and homogenization approaches, the crystal plasticity finite element method, and the recently introduced texture component crystal plasticity finite element method. The paper presents the basic physical approaches behind the different methods and discusses engineering aspects such as scalability, flexibility, and texture update in the course of a forming simulation.
TL;DR: In this article, a finite element-based numerical procedure was used to directly predict the stiffness and thermal expansion of several hundred multi-fiber computer models with a variety of different predefined fiber orientation states.
Abstract: It is fairly common in practice that during injection moulding, the mold filling process results in non-uniform fiber orientation distributions in the final injection molded short fiber reinforced composite part. It would be very attractive to employ an orientation averaging scheme to form predictions for the design of short fiber reinforced composite parts. Here, the authors use a finite-element-based numerical procedure developed by themselves and, for the first time, directly predict the stiffness and thermal expansion of several hundred multi-fiber computer models with a variety of different predefined fiber orientation states.
TL;DR: Progress reports as mentioned in this paper are a new type of article in Advanced Engineering Materials, dealing with the hottest current topics, and providing readers with a critically selected overview of important progress in these fields.
Abstract: Progress reports are a new type of article in Advanced Engineering Materials, dealing with the hottest current topics, and providing readers with a critically selected overview of important progress in these fields. It is not intended that the articles be comprehensive, but rather insightful, selective, critical, opinionated, and even visionary. We have approached scientists we believe are at the very forefront of these fields to contribute the articles, which will appear on an annual basis. The article below describes the latest advances in fluorescence and phosphorescence in organic materials.
TL;DR: In this article, important parameters in the adhesion process are reviewed, including methods to engineer these parameters in order to attain adhesion strengths ranging from complete release to irreversible bonding, and a detailed review of these parameters is presented.
Abstract: Adhesion between polymeric phases like adhesives and plastic surfaces is critical in many technological and industrial applications. In the last decades much progress has been made to understand the impact of the surface properties of both phases on the adhesive strength between them. These surface properties influence processes like wetting, molecular adsorption and inter-diffusion which determine how an interface develops into an interphase after the two materials have been brought into contact. Ultimately, the properties of this interphase determine the overall adhesion strength of an assembly. In this paper important parameters in the adhesion process will be reviewed, including methods to engineer these parameters in order to attain adhesion strengths ranging from complete release to irreversible bonding.
TL;DR: In this article, the in situ laser deposition of Ti-TiB composites using the laser engineered net-shaping (LENS™) process from a blend of elemental titanium (or titanium alloy) and boron powders is discussed.
Abstract: Due to their enhanced mechanical properties and potentially wide applicability, there is considerable interest in the development of metal-matrix composites consisting of titanium borides in a titanium alloy matrix. Despite the development of a variety of different processing routes for these composites, there are relatively few ones capable of processing a fully dense, near-net shape component with a relatively fine dispersion of boride precipitates. This paper will discuss the in situ laser deposition of Ti-TiB composites using the laser engineered net-shaping (LENS™) process from a blend of elemental titanium (or titanium alloy) and boron powders. The microstructure of the LENS™ deposited Ti-TiB composite has been compared with that of a conventionally cast in situ composite of the same composition. The conventionally cast composite exhibits a significantly coarser scale microstructure. Thus, the ability to produce a fine dispersion of TiB precipitates in dense Ti-TiB composites of near-net shape using LENS™ processing can be attributed to the rapid solidification effects during such processing.
TL;DR: In this article, the effective and potential advantages/drawbacks of Raman micro-spectrometry technique are discussed and procedures to improve the sensitivity, the legibility and the reliability are addressed.
Abstract: This paper discusses the effective and potential advantages/drawbacks of Raman micro-spectrometry technique. The procedures to improve the sensitivity, the legibility and the reliability will be addressed. Examples will be chosen among fibre-reinforced ceramic, polymer or metal matrix composites.
TL;DR: In this article, the evolution of foam microstructure is characterized by studying a series of samples representing different stages of foam expansion obtained by interrupting the foaming process for each sample at different foaming times.
Abstract: Foamed aluminium alloy containing 7 wt.-% of Si is investigated by μm-resolved X-ray computed tomography (CT) using synchrotron radiation. The foam is fabricated employing a powder metallurgical route. The evolution of foam microstructure is characterized by studying a series of samples representing different stages of foam expansion obtained by interrupting the foaming process for each sample at different foaming times. The computer tomographic reconstruction provides a 3D image of the pore structure as well as the spatial distribution of blowing agent particles. A statistical evaluation allows to determine the size distribution of the blowing agent and of the pores at different foaming stages.
TL;DR: In this article, the conditions under which aluminum foam sandwich parts may be put into series production in an economical way are described, in order to find commercially efficient applications for metal foams produced using the powder metallurgical route.
Abstract: Much work has been done to find commercially efficient applications for metal foams produced using the powder metallurgical route. Most of these efforts have not been successful, because foam quality could not be reproduced reliably and production methods were too inefficient. This article describes the conditions under which aluminum foam sandwich parts may be put into series production in an economical way.
TL;DR: In this paper, the usefulness of the CALPHAD calculations for Ni-base superalloys is evaluated by showing case study validations and examples of their use in the field of metallurgical research.
Abstract: Thermodynamic calculations on complex, multi-component alloys are becoming more common in metallurgical research. They are now used on a daily basis in industrial laboratories such as the GE Research Center. They have proven to be of great assistance in the development of new alloys, and in the selection of processing conditions for existing or new alloys. This paper presents an evaluation of the usefulness of the CALPHAD calculations for Ni-base superalloys by showing case study validations and examples of their use.
TL;DR: In this paper, the authors describe several applications of powder densification maps to advance solutions in direct selective laser sintering of metallic and ceramic powders, which is a manufacturing process in which a part is produced without the need for part-specific tooling.
Abstract: Selective Laser Sintering (SLS) is a manufacturing process in which a part is produced without the need for part-specific tooling. It competes effectively with other manufacturing processes when part geometry is complex and the production run is not large. Traditionally, this was limited to prototype production, although tooling applications are now appearing. This paper describes several applications of powder densification maps to advance solutions in direct SLS of metallic and ceramic powders. Time-dependent plasticity issues arise in pre-processing of powder to make it suitable for SLS and in post-processing of SLS parts to obtain desired density.
TL;DR: In this paper, the formation and decay of foams produced by gas bubble expansion in a molten metal is numerically simulated with the Lattice Boltzmann Method (LBM) which belongs to the cellular automaton techniques.
Abstract: The formation and decay of foams produced by gas bubble expansion in a molten metal is numerically simulated with the Lattice Boltzmann Method (LBM) which belongs to the cellular automaton techniques. The present state of the two dimensional model allows the investigation of the foam evolution process comprising bubble expansion, bubble coalescence, drainage, and eventually foam collapse. Examples demonstrate the influence of the surface tension, viscosity and gravity on the foaming process and the resulting cell structure. In addition, the potential of the LBM to solve problems with complex boundary conditions is illustrated by means of a foam developing within the constraints of a mould as well as a foaming droplet exposed to gravity.
TL;DR: In this article, two different approaches were studied in order to strengthen copper-based conductor materials for applications such as pulsed high magnetic field coils, where the increase of strength coincides with a decrease of conductivity.
Abstract: There is a need for high-strength and highly-conducting materials for applications such as pulsed high magnetic field coils. Two different approaches were studied in order to strengthen copper-based conductor materials. On the one hand, microcomposite Cu-Ag alloys yield high strength as a consequence of their nanoscale microstructure and, on the other hand, a Cu-based macrocomposite can be strengthened by the use of a steel jacket. In both cases the increase of strength coincides with a decrease of conductivity. Thus, the ideal material balances between these two competing properties.
TL;DR: In this paper, the authors focus on the overall elastic constants and use the finite-element-based numerical procedure developed by them to assess the adequacy of two of the most widely used micromechanics-based models.
Abstract: Predicting the overall, effective properties of short fiber composites with fully aligned fibers from the properties of the individual phases and the composite's morphology has attracted a great deal of attention during the last decades In this work, the authors focus on the overall elastic constants and use the finite-element-based numerical procedure developed by them to assess the adequacy of two of the most widely used micromechanics-based models
TL;DR: Progress reports as discussed by the authors are a new type of article in Advanced Engineering Materials, dealing with the hottest current topics, and providing readers with a critically selected overview of important progress in these fields.
Abstract: Progress reports are a new type of article in Advanced Engineering Materials, dealing with the hottest current topics, and providing readers with a critically selected overview of important progress in these fields. It is not intended that the articles be comprehensive, but rather insightful, selective, critical, opinionated, and even visionary. We have approached scientists we believe are at the very forefront of these fields to contribute the articles, which will appear on an annual basis. The article below describes the latest advances in Advanced Engineering Ceramics.
TL;DR: In this article, tensile tests were performed on PET films coated with Al doped zinc oxide films by RF magnetron sputtering, and the electrical resistance of the oxide was evaluated in situ.
Abstract: Tensile tests were performed on PET films coated with Al doped zinc oxide films by RF magnetron sputtering. During the tensile elongation, the electrical resistanceof the oxide was evaluated in situ. The results indicate that the increase in the electrical resistance is related to the crack debsity and crack width, which also depends on the film thickness.