Advanced Materials Research Vols. 83-86

Abstract: For the possibility of easy disassembly of a joint assisted by strain recovery, the joint is fabricated with a cold rolled circular polycarbonate (PC) disk embedded in the center of an aluminium or a PC disk. Also, a shaft and a hollow circular disk are assembled by compressing or press fitting a cold rolled PC ring into the gap between them. First, the cold rolled polycarbonate disk is heat treated and the change in geometry is examined. Secondly, in order to evaluate joint strength, shear force and torque of the assembled joints are discussed with regard to reduction in thickness, tool clearance and interference. Lastly, joints are heat treated and the disassembly is checked. The cold rolled disk is recovered with the temperature 190°C for 20min. In embedding, disk compression in addition to rolling reduction is effective in increasing joint strength. In fabricating the shaft/disk joint, deformation of polycarbonate was not effective due to the recovery in room temperature after joining, while press fitting of the polycarbonate ring could fabricate the assembly. Heat treatment helped the joint to be automatically disassembled. The directly joined parts became completely apart, but the shaft/disk joint was disassembled only between the ring and the disk.

Abstract: The paper deals with the structure features of Fe-C alloys quenched by means of laser, electron beam and plasma arc. The martensite and residual austenite obtained are highly inhomogeneous. Their morphology and distribution depend both on the initial state before quenching and on the kinetics of the temperature changes. Four different structures of martensite are observed – package, lamellar isothermal, lamellar thermo-kinetic and “feathery nest-like”. The new martensite structure observed, called by us “feathery nest-like”, is a result of explosive austenite-martensite transformation in pearlitic irons. It differs from the classic modification in its specific morphology. Low-carbon package martensite occupies the regions of the former ferrite grains. Its hardness reaches 1050-1150 HV0.1. In the regions of microstructure with increased carbon concentration lamellar martensite is observed. The residual austenite is with different proportion in relation to the martensite. In particular regions its quantity could reach 100%. It is characterized by a high quantity of imperfections and high mechanical properties. Its hardness reaches 450-500 HV0.1. The higher the power density and the lower the energy density of the concentrated energy flux, the higher the residual austenite quantity.

Abstract: The present paper deals with the structure and properties of two types of tool steels with high chromium content (12% Cr) hardened by means of Concentrated Energy Fluxes (CEF). The treatment conditions are chosen to ensure liquid state transformations. The melted zone of the surface layer features a quasi-ledeburite structure, consisting of inhomogeneous residual austenite and Cr-containing carbides of MmCn type. This austenite is strongly cold hardened and over-saturated with Cr and carbon. The micro-hardness of this region varies from 400 up to 800 HV0.1. The higher the energy density, the lower the hardness and the wider the modified layers. The lower hardness is due to the presence of nearly 100% austenite. Higher hardness was obtained in the heat affected zone. Carbides of M23C6, M7C3, M6C, M3C and МС types were identified. A scheme of carbide changes after treatment with CEF is given.

Abstract: Capacity analysis of signalized intersections basically consists of estimating saturation flow and delay. Pre-timed signals are most commonly used in developing countries. This research deals with development of saturation flow and delay models for pre-timed signalized intersections with reference to non-lane based traffic condition prevailing in Bangladesh. In order to account non-uniformity in the static and dynamic characteristics of the vehicles passenger car unit (PCU) values for each vehicle is found out using synchronous regression technique and a range of site-specific PCU values were obtained. From this study, it has been observed that unified PCU concept does not hold good for non-lane based traffic condition and it has been recommended that the analysis should be site specific for non-lane based traffic condition. The saturation flow for each study approach was calculated using the average PCU values and multiple linear regression techniques were then used to derive predictive saturation flow models. Field delay for each approach is calculated based on HCM 2000 guidelines. It has been observed that HCM 2000 delay model consistently over estimate delay at degree of saturation more than 1.0. It has been suggested from the analysis that theoretical incremental delay (due to random arrival and over saturated queues) in HCM 2000 delay model be reduced by 70 % to better reflect field conditions in capacity analysis for non lane based traffic condition.

Abstract: The geometry of bone scaffolds plays a crucial role in bone tissue regeneration. This architecture, especially pore size and shape, determines the mechanical strength of the scaffold. A number of previous workers have indicated the parameters which are believed to be the main stimulus in the adaptive bone remodelling process. An ideal bone manufacturing system would deliver bone morphogenetic proteins (BMP) and provide adequate mechanical properties. The aim of this study was to design a highly osteoconductive and mechanically strong bone regeneration scaffold which can be successfully manufactured. Three porous architectures of scaffold were designed using Solid EdgeTM 3D solid modelling software. The equivalent trabecular structure model consisted of repeatable unit cells arranged in layers to fill the chosen scaffold volume. The three different unit cell structures examined include cubic, triangular, and hexagonal polyhedral. Designed scaffold’s pores were varied in this study to 120, 340 and 600µm. This range was selected to meet one of the requirements of the scaffold design – the macropores must be at least 100µm in diameter, so the cells can penetrate and proliferate within the structure. The strengths of each scaffold were determined using ANSYSTM finite element software. Trabecular scaffold designs were analysed independently and in connection with simulated cortical bone in order to investigate their stress-strain response. As well as providing useful information on strengths developed from these topologies, the models developed indicated geometric constraints in order to tailor scaffolds to specific patient needs.

Abstract: While the world growth in PVC consumption continues (currently ~35 million tonnes per annum), its poor thermal stability, remains an issue due to restrictions on the use of stabilizers containing heavy metals such as lead. Monitoring degradation in PVC is important, and this work is concerned with the detection of PVC degradation using UV and Raman spectroscopies. The bands which appear in the Raman spectra of PVC samples after thermal degradation at around 1100 and 1500 cm-1, are the result of a resonance Raman effect. Optimization of the PVC degradation assessment process using laser-Raman is crucial to minimize the effects of additive interference and the fluorescent background. The most important factor is the wavelength of the exciting laser source, as it should fall within the absorption range for polyene sequences in degraded PVC. Laser-Raman spectroscopy has been shown to be an appropriate method for the quantitative determination of the polyene length distribution in lightly degraded PVC samples. The application of this method for various degraded PVC samples is reported. Ageing of compounds containing various heat stabilizers were considered, in order to assess their effectiveness. Additives studied included calcium zinc stabilizers and two commercial grades of hydrotalcite (Sorbacid 911 and Alcamizer P93).

Abstract: Microfluidics is a technology where application span the biomedical field and beyond. Single cell analysis, tissue engineering, capillary electrophoresis, cancer detection, and immunoassays are just some of the applications within the medical field where microfluidics have excelled. The development of microfluidic technology has lead to novel research into fuel cells, ink jet printing, microreactors and electronic component cooling areas as diverse as food, pharmaceutics, cosmetics, medicine and biotechnology have benefited from these developments. Since laminar flow is prevailing at most flow regimes in the micro-scale, thorough mixing is a challenge within microfluidics. Therefore, understanding the flow fields on the micro-scale is key to the development of methods for successfully microfluidic mixing applications.

Abstract: Mechanical alloying technique was used to produce an intermetallic based composite powder. Mechanical activation of aluminum and nickel oxide powder mixture using a high energy ball mill resulted in a self-propagating high temperature synthesis through which nickel oxide was reduced by metallic aluminum and produced nickel aluminide and alumina composite powder. Effect of milling time on crystallite sizes of the product phases was investigated. The synthesized product was characterized by scanning electron microscope and X-ray diffraction. It was shown that increased milling time resulted in crystallite size reduction and peak broadening in XRD patterns. Calculation of the mean crystallite sizes of the product phases indicated that they are in nano scale. The results were further confirmed by transmission electron microscopy.

Abstract: This paper presents the rheological properties of SS316L water atomized MIM feedstock. Coarse and fine SS316L water atomized powder is mixed with a composite binder consisting of PMMA and PEG to form a homogenous paste, termed as feedstock. The feedstock is loaded with SS316L water atomized powder ranging 62 v/o, 62.5 v/o, 63 v/o, 63.5 v/o and 64 v/o. However, due to the morphology of the water atomized powder which is not spherical compared to the gas atomized ones, fine powder feedstock is unable to produce any significant rheological result due to the powder loading being more than 63.5 v/o. Results show that the fine powder feedstock demonstrates a higher viscosity if compared to the coarse powder feedstock. It can be established that binder separations are likely to occur in the coarse powder feedstock, especially, at high temperatures. The investigation concludes that the fine powder feedstock has its best rheological properties at 62 v/o while the coarse powder feedstock lies between 63 v/o and 63.5 v/o.

Abstract: Nanometer-sized particles possess characteristic physical and chemical properties different from those of bulk materials due to an increase in surface-to-volume ratios as well as of confinement of electrons, excitons, and photons into small volumes. Therefore it is worthwhile to discuss the thermal behaviours of powders constituted by nanometer-sized particles. The heat transfer in the powder composed of nanoparticles is experimentally investigated in this paper. The understanding for thermal properties of the powder is advantageous to the advancement of the processing technologies such as laser cladding, laser sintering, powder metallurgy and its other applications. The powder is wrapped up in the slender tube made of insulating material. One end of the slender tube filled with powder is maintained at temperature 0°C and the other end is kept at room temperature. The temperature histories at two different locations in the slender tube are recorded using thermal couples. The results show that the thermal diffusivity in the powder composed of nanoparticles is larger than that in bulk material. The pressure on the Al powders enhances the rate of heat transport due to the increase of contact area for thermal conduction.