A Methodology For Coronary Stent Product Development: Design, Simulation And Optimization

Coronary stents are slotted tubes made of metals, alloys, or polymers. They are deployed in human arteries, which are blocked by calcified plaque, to keep the arteries open and allow the blood to flow with ease. Coronary stents have been proven as an effective treatment device for heart diseases such as acute myocardial infarction. Design plays an important role for coronary stents to perform the clinical functions properly. Various parameters such as materials, structures, dimensions, and deployment methods etc., need to be considered in the design of coronary stents. There are numerous studies on design of coronary stents and many significant manufacturing methods have been reported in the past two decades. However, there is no comprehensive methodology for the product development of coronary stents in terms of design, simulation, and manufacturing. The objective of this research is to develop a methodology for coronary stents product development that focuses on design, simulation, and manufacturing. The methodology brings together insights from numerous engineering design disciplines with the aim of making coronary stent development more flexible and more cost-efficient The product development methodology for coronary stents is executed through modeling and analyzing stent designs with details of design, simulation, and optimization methods. Three innovative stent designs are modeled using engineering design software (SolidWorks) and mechanical performances are simulated, evaluated, and optimized with the help of advanced engineering simulation software (ANSYS). In this study, the performance of stents based on stress, strain, and total deformation during deployment are analyzed and compared with commercially available optimal design i.e., Cypher (J & J Co.) stent, which acts as a benchmark design

Melt processing and characterisation of lightweight metal composites reinforced by nanocarbon

Increasing the specific strength of lightweight structural metals such as magnesium, which has two-thirds the density of aluminium, has the potential to significantly widen their application and improve the system energy efficiency and performance across transport and defence industries. Reinforcing magnesium matrices with nano-sized particles to form metal matrix nanocomposites (MMNCs) has shown promise as a way of achieving an increase in specific properties, albeit without the traditionally associated decrease in ductility. This study manufactured and characterised magnesium-based MMNCs to investigate the impact of nanoparticle reinforcements on the mechanical properties of the composites, their microstructure and the theoretical models used for the potential strengthening mechanisms. Multi-walled carbon nanotubes (MWCNTs) can be considered as the ideal reinforcing nanoparticle due to their exceptional mechanical properties, geometry and low density, which can take full advantage of the proposed strengthening mechanisms that occur when nanoparticles are added to a metal matrix. MWCNTs are however notoriously difficult to be homogenously dispersed in a metal matrix and are poorly wetted by molten metal; therefore, nickel coated MWCNTs (NiCNTs) and silicon carbide nanoparticles are also investigated as a potential solution for wettability in this study. Magnesium alloy AZ91D was used as the metal matrix material and the MMNCs were made using metal melt-stirring combined with a nanoparticle pre-dispersion technique. Melt processing and casting techniques are favoured in component manufacturing processes due their scalability and cost-effectiveness. The melt stirring processing parameters such as casting temperature, stirring time and stirring speed were thoroughly examined and modified to successfully produce MMNC samples. The compression mechanical properties of the AZ91D-MWCNT composites showed no change for a range of MWCNT concentrations for the melt stirring processing parameters tested. Theoretical studies of nanoparticle dispersion and wettability combined with electron microscopy of the cross sections of the samples showed that the pre-dispersion and melt stirring processes were insufficient to homogenously disperse the MWCNTs in the metal matrix, therefore NiCNTs were utilised. Whilst no significant differences in compression mechanical properties were seen for the AZ91D-NiCNT samples, a 13% increase in hardness was achieved. An 11% and 20% increase in hardness was achieved for samples of AZ91D composites reinforced with equal concentration of silicon carbide nanoparticles and whiskers, respectively. The poor wettability of MWCNTs by AZ91D melt, apparent from SEM imaging of the composite fracture surfaces, suggested that in order to take advantage of the superior mechanical properties of MWCNTs, a coherent interface between the MWCNT and the Mg matrix is necessary. The nickel coating and silicon carbide nanoparticles, known to wet with molten magnesium, may have provided a coherent interface that resulted in the measured increase in hardness.Open Acces

In Situ Metal Matrix Nanocomposites: Towards Understanding Formation Mechanisms and Microstructural Control

Lightweight materials are critical to meet the ever-increasing demands for improved fuel economy in the automotive, aerospace and defense industries. Consequently, aluminum alloys have been employed extensively in these industries for structural applications owing to their high strength-to-weight ratio. However, Al alloys suffer from several shortcomings, such as poor thermal stability of mechanical properties, limiting their usage for components operating in elevated temperature environments. Recently, the incorporation of nano-scale particles in the Al matrix, termed metal matrix nanocomposites (MMNCs), has been identified as a promising approach to improved ambient and elevated temperature mechanical properties, while still retaining the lightweight benefits of Al. MMNCs manufactured through typical ex situ incorporation methods, wherein pre-made particles are mixed into the matrix, can suffer from precursor contamination and undesirable particle/matrix interfacial reactions, making incorporation and large-scale processing difficult. In situ processing alternatives, where particles are created directly in the melt via direct reaction, have been demonstrated to exhibit improved particle/matrix interface stability and easier incorporation within the matrix. However, the ability to reliably control critical mechanical property-dependent particle characteristics (i.e., particle size, volume fraction, and dispersion) remains a barrier to large-scale processing of in situ MMNCs. The research for this dissertation is aimed at elucidating the mechanisms governing formation of the particles and provide guidance to controlling the resulting microstructure of MMNCs processed via in situ methods, for the purposes of informing large-scale processing efforts. In this work, we investigate the processing-microstructure-mechanical property relationships for two in situ processing methods, namely: in situ gas-liquid reaction (ISGR) for Al-AlN MMNCs and thermite-assisted self-propagating high-temperature synthesis (SHS) for Al-TiC MMNCs. We find that the SHS process is more capable of readily producing nano-scale TiC particles in a wide variety of volume fractions and dispersions dependent on processing conditions. Additionally, we report on successful SHS processing, at our industry partner, of commercial pilot-scale quantities of in situ Al-TiC MMNCs exhibiting enhanced mechanical properties for relatively low amounts of particle addition. The preliminary results are a promising demonstration of the potential for commercial-scale processing of in situ MMNCs. Building upon our study of large-scale processing of MMNCs, we then perform a more detailed investigation into understanding the formation mechanisms and microstructural control of the thermite-assisted SHS process. By leveraging 2D and 3D microstructural quantification techniques with a thermodynamic-based analysis, we identify three potential direct- and indirect- reaction pathways governing TiC formation and the conditions under which they are active. We also demonstrate an approach for correlating processing-property relationships via multivariate statistical analysis (i.e., canonical correlation analysis (CCA)). Using CCA, we report on the dominant processing variables affecting final MMNC microstructure and particle characteristics and discuss the link between processing variables, reaction pathways, and resultant microstructural signatures. Our results and analysis are expected to inform a more rational approach to process control of in situ SHS MMNCs, as well as being applicable to other in situ processing methods.PHDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163192/1/reesecw_1.pd

Magnesium Alloys Structure and Properties

Magnesium Alloys Structure and Properties is a comprehensive overview of the latest knowledge in the field of magnesium alloys engineering. Modern magnesium alloys are promising for a variety of applications in many branches of the industry due to their excellent mechanical properties, high vibration, damping capacity, and high dimensional stability. This book discusses the production, processing, and application of magnesium alloys. It includes detailed information on the impact of alloying additives and selected casting technologies, as well as modern manufacturing technologies based on powder metallurgy, the production of composites and nano-composites with metal matrixes, and methods for improving alloy properties

Metallurgy: A compilation

A technology utilization program is presented for the dissemination of information on technological developments which have potential utility outside the aerospace and nuclear communities. Discussion is restricted to the effects of hydrogen on a variety of metal alloys, and the mechanical properties of some recently developed alloys. Hydrogen at both low and high pressure is shown to have adverse effects on alloys such as ultrahigh-strength steels, irradiated steels, columbium, inconel alloys, titanium alloys, and certain stainless steels. The mechanical and physical properties of a wide range of alloys, their performance at elevated temperatures, and some of the processes involved in their development are also considered

Critical analysis of accumulated experimental data on filament-reinforced metal matric composites

Data analysis on filament reinforced metal matrix composite

Clinching of inductively heated aluminum die casting

The aim of the investigations described in this article is to improve the clinching of aluminum die casting. The focus is on clinching an aluminum die casting alloy by local heat treatment and hence to join them in a process-safe manner. For this purpose, a heating strategy is used to warm up the die casting alloys to reduce temporarily and reversibly the elongation and the yield strength in the material. In preliminary investigations, three different heating strategies (heating plate, resistance heating and inductive heating) have been investigated. Induction heating has been selected as the most suitable method due to the short heating time and the production of crack-free clinch points. In this paper, two clinching tool systems (one with a flexible die, one with a rigid die) were used. For these tools, two inductors with different diameter were manufactured. The effects of each inductor and clinching tool on an aluminum die casting alloy, such as heating time and crack behavior, were investigated. Surface images of the clinch points in regard to the heat treatment temperature were analyzed. Furthermore, the characteristic parameters of the joints such as interlock, bottom thickness and neck thickness were examined. In addition, the strength of the joined parts was investigated by head tension tests. The results of the developed method showed that it is possible to produce crack-free clinching joints below 6 s. Furthermore, the local heating led to an increasing interlock resulting in a 26% increase of the head tensile strength