121 research outputs found
Bending and twisting friction models in soft-sphere discrete element simulations for static and dynamic problems
Get PDFAbstractIn soft-sphere discrete element models of granular flow, particles may interact in a variety of ways including interactions normal to points of contact and interactions tangential to points of contact such as sliding, rolling, bending and twisting. In the majority of models normal and sliding modes are used. Rolling friction is sometimes reported but incorporation of bending and twisting effects is less common. In this paper it is shown that the precise mathematical nature of bending and twisting models in soft-sphere simulations can have significant effects on model predictions, especially for the case of dynamic granular flow problems
Life cycle assessment of gas atomised sponge nickel for use in alkaline hydrogen fuel cell applications
Get PDFThis work represents the summary of the life cycle assessment of nickel aluminide intermetallic powders as used in the anodes of hydrogen fuel cells, work done for the IMPRESS FP6 project (2004 to 2009). NiAl intermetallics have good catalytic properties making them particularly useful for numerous hydrogenation reactions in the chemical industry, as well as electro-catalysts in alkaline fuel cells.The work in this paper represents the culmination of 5 years of data gathering from all the project partners, and the presentation and interpretation of the life cycle assessment of sponge nickel produced by gas atomisation for use in industrial hydrogenation catalysis applications, as compared to the conventional manufacturing route.The results predict that there would be an overall reduction in green house gas emissions of about 10% over the lifetime of the catalyst based on improvements in catalytic activity over the industrial standard baseline, assuming the best case scenario that any technical hurdles to a wide scale adoption were to be overcome. The adoption or penetration of the improved catalysts ultimately determines the realisable environmental benefits, but the work serves as an example of responsible product development where market drive and cost can go hand in hand with environmental improvements
Mathematical framework for predicting the thermal behaviour of spectrally selective coatings within an industrial near-infrared furnace
Get PDFA transient finite difference thermal model based on the heat equations is developed, valid for spectrally selective surface coatings on any substrate material within a near-infrared (NIR) furnace. Spectral radiative heat transfer equivalent to a blackbody provides the heat source. Both radiative and natural convective cooling are accounted for. A Monte Carlo ray tracing algorithm is formulated and used to determine the radiation view factor. The variance of the algorithm in relation to mesh resolution and sample size is tested against published exact solutions. The radiative flux is divided into absorbed and reflected bands using hemispherical reflectance spectra measured within the 250–15,000 nm wavelength range, enabling the model to predict the thermal build-up of coatings with very different radiative properties. Results show that the transient temperature distribution of spectrally selective surface coatings within an NIR furnace can be modelled, with good agreement observed between experimental and simulated data. The model shows the expected relationship between colour and absorption, with darker coatings displaying greater absorption and heating rates than lighter coatings. Surprisingly, colours which appear similar to one another can display different heating rates, a result of their varied infrared reflectance properties
Apparent negative values of Young’s moduli of lattice materials under dynamic conditions
Get PDFLattice materials are characterised by their equivalent elastic moduli for analysing mechanical properties of the microstructures. The values of the elastic moduli under static forcing condition are primarily dependent on the geometric properties of the constituent unit cell and the mechanical properties of the intrinsic material. Under a static forcing condition, the equivalent elastic moduli (such as Young’s modulus) are always positive. When dynamic forcing is considered, the equivalent elastic moduli become functions of the applied frequency and they can be negative at certain frequency values. This paper, for the first time, explicitly demonstrates the occurrence of negative equivalent Young’s modulus in lattice materials experimentally. Using additively manufactured titanium-alloy lattice metastructures, it is shown that the real part of experimentally measured in-plane Young’s modulus becomes negative under a dynamic environment. In fact, we show that the onset of such negative Young’s modulus in lattice materials can be precisely determined by capturing the sub-wavelength scale dynamics of the system. Experimental confirmation of the negative Young’s moduli and the onset of the same as a function of frequency provide the necessary physical insights and confidence for its potential exploitation in various multi-functional structural systems and devices across different length scales
General investigations on the heat treatment and thermal fatigue behavior of an experimental hot work tool steel tailored for laser powder bed fusion
Get PDFLife cycle assessment of sponge nickel produced by gas atomisation for use in industrial hydrogenation catalysis applications
Get PDFThis paper presented results from a complete lifecycle assesment of various sponge nickel catalysts, produced in two different ways, namely either by gas atomisation or by the industrial standard techniques of cast and crush. The application considered was for the industrial hydrogentation of butyraldehyde to butanol. The paper describes the LCA methodology adopted which conformed to the ISO14040 standards, looking at various production scenarios and the impact on the emissions.The results indicated that the energy usage and emissions during the operation phase of the catalyst outweighed the primary production, manufacturing and recycling. It was shown that the increase in activity of gas atomised catalysts by doping with various metals, such as iron, molybdenum and tin, led to a significant reduction in emissions over the lifetime of the catalysts, which greatly outweighed the small increase in emissions at the primary extraction and manufacturing stages
Combinatorial development and high throughput materials characterisation of steels
Get PDFA series of small iron specimens with minor additions of C, Si and Mn were manufactured via induction melting and characterised using a high throughput methodology. The aim was to analyse the high throughput approach itself, not the effects of minor additions to steel. Despite their small size, the trends in measured standard mechanical properties were consistent with published data, and target alloy compositions were achieved to a sufficient degree of accuracy. This is most encouraging as the experimental approaches described here delivered results in a very short time frame, with time per composition estimated to be < 2 h per sample. Such an approach would appear to be an excellent precursor to more traditional, expensive and time consuming alloy development methods used by industry. Limitations of the methodology are described, and key bottlenecks are identified. However, the use of small specimens to quantify trends in properties of steels and identify possible new alloys is potentially a valuable addition to the development of new steels
Rapid Alloy Prototyping for a range of strip related advanced steel grades
Get PDFOver many decades, the traditional route for material product developments, especially in the steel industry has been the laboratory VIM cast route at scale of 25 to 60kg, followed by through-processing of steel ingots involving hot rolling and cooling as well as further downstream processes to simulate finished cold annealed rolled and coated products. This traditional route has so far delivered value for optimising current grades and process routes as well as developing new products prior to production implementation. However, in order to accelerate process and grade developments even smaller scale and faster laboratory synthesis and processing is desired. The AccMet project [1] developed strategies for new alloy development [2,3] and this needs to be further developed to account for the complex processing route for strip steel production. Strategies combining small scale laboratory alloy processing routes, together with mechanical/thermal testing and modelling are being developed, ranging from 20-30g to 4.5 kg [4-8].This paper summarises current Rapid Alloy Prototyping (RAP) approaches and rationale developed under a new UK Engineering and Physical Sciences Research Council (EPSRC) Prosperity project between Tata Steel and the Universities of Swansea and Warwick (WMG). Specific attention is paid to the overall experimental methodology as well as benefits (throughput) of small-scale manufacturing and testing, the generation of representative microstructures for a range of strip grades as well as ways of integrating new concepts which bridge the physical length scale. A range of experimental facilities (20-40g) based on a powder route and induction melting (IM)/heat treatments is being developed to provide material for hot/cold rolling/annealing prior to mechanical testing. Modelling and testing to account for mechanical test specimen size effects for small scale RAP samples is being carried out to ensure consistent mechanical properties are obtained. This small-scale RAP is also being complemented with an intermediate material route operating between 200g and 4.5kg using centrifugal casting and small size ingot vacuum induction melting respectively to provide additional material and throughput sitting alongside the more traditional pilot-scale 25-30kg route. Finally, the 25-30kg standard route is being reviewed to provide a bridge to the laboratory routes through various innovative concepts. This paper concludes with a review of future activities and challenges for effective development and implementation of a range of small scale experimental and pilot manufacturing lines
Computational modeling of creep-based fatigue as a means of selecting lead-free solder alloys
Get PDFThe primary aim of this investigation was to understand the effect of temperature fluctuations on a number of various solder materials namely SAC105, SAC305, SAC405 and Sn–36Pb–2Ag. To achieve this objective, three different classic joint assemblies (a ball joint, a test specimen joint and finger lead joint) were modeled which provided the foundation for the creep and fatigue behaviors simulation. Anand’s viscoplasticity as a constitutive equation was employed to characterize the behavior of solders numerically under the influence of thermal power cycles (80–150 °C) and thermal shock cycles (−40 to 125 °C). To extend the research outcome for industrial use, two additional research activities were carried out. One of them was to obtain lifetime-predictions of solder joints based on Coffin Manson concept. The other one focused on parameterization to obtain the ideal solder thickness under the consideration of plastic strain and economic benefit
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