1,355,075 research outputs found
Evacuation plan as a risk mitigation measure: Scenario-based time estimation of partial evacuation operation
No full textThis study concentrates on evacuation procedure as a risk mitigation measure for managing and coping with emergency due to flood hazard. Emergency Management has been known as an ever-growing area of academic research in the recent decades. Particularly, Emergency Planning ahead of threatening events is crucial for moving toward a resilient society. Effective implementation of Emergency Contingency Plans during the situation of real Risk Scenarios is mainly a matter of situation awareness, cooperation and collaboration of involved organizations, timely decision-making under stressful circumstances, and availability of resources. Having defined a plan for evacuation operations as a protective measure is necessary for reduction of risk consequences to exposed population. This paper presents partial evacuation time estimations related to vehicle movement time by two methods applied to a case study (San Rocco al Porto, Italy) due to flood event: Time is estimated as a result of modeling by Mesoscopic approach. Second, the “timeline of emergency response for flood evacuation” proposed by Steve Opper is used as a quick handy method to estimate vehicle movement time
A novel bioactive PEEK/HA composite with controlled 3D interconnected HA network
No full textPolyetheretherketone (PEEK) is a high-performance thermoplastic biomaterial which is currently used in a variety of biomedical orthopaedic applications. It has comparable tensile and compressive strength to cortical bone with favourable biocompatibility. However, natural grade PEEK-OPTIMA has shown insufficient bioactivity and limited bone integration. Bioactive PEEK composites (e.g., PEEK/calcium phosphates or Bioglass) and porous PEEK have been used to improve bone-implant interface of PEEK-based devices, but the bioactive phase distribution or porosity control is poor. In this paper, a novel method is developed to fabricate a bioactive PEEK/hydroxyapatite (PEEK/HA) composite with a unique configuration in which the HA (bioactive phase) distribution is computer-controlled within a PEEK matrix. This novel process results in complete interconnectivity of the HA network within a composite material, representing a superior advantage over alternative forms of product. The technique combines extrusion freeforming, a type of additive manufacturing (AM), and compression moulding. Compression moulding parameters, including pressure, temperature, dwelling time, and loading method together with HA microstructure were optimized by experimentation for successful biocomposite production. PEEK/HA composites with a range of HA were produced using static pressure loading to minimise air entrapment within PEEK matrix. In addition, the technique can also be employed to produce porous PEEK structures with controlled pore size and distribution
Effects of brace-viscous damper system on the dynamic response of steel frames
No full textIn this study, the effects of three different viscous damper configurations, chevron, diagonal and toggle, as well as brace stiffness on the performance of brace-viscous damper system in various steel frams under different earthquake records were investigated. A finite element software, ANSYS, is exploited to develop the numerical models. To verify the numerical simulations, their results were compared with those of the experimental studies in the literature. The results show the reduction in the base shear force given by the toggle configuration is larger than that due to the chevron and diagonal configurations. Regarding the brace stiffness (area), for a reference damping coefficient of 500 N.m/s, a 54% increase in the brace area (from 42 to 91.8 mm2) results in a 21.26, 38.61, and 17.57% reduction in the structure displacement response for the diagonal, chevron, and toggle configurations, respectively. Further, using the results of the numerical simulations, we proposed the spatially-optimized distribution of the brace-viscous damper system
3D printing of bone tissue engineering scaffolds and production of PEEK-based biocomposites
No full textIn this research work, the possibilities and limitations of using solvent-based extrusion freeforming (SEF), a type of additive manufacturing (AM) technologies, for 3D printing of bone tissue engineering scaffolds is examined. Optimised SEF technique allowing production of the highest resolution of bioceramic scaffolds has been reported so far with filament diameter as fine as 30 µm, while retaining reasonable level of detail and accuracy. In vitro tests of the 3D printed hydroxyapatite (HA) scaffolds proved cell attachment and proliferation. The spacing of 200-250 µm between adjacent HA filaments in the scaffold was identified suitable for cell survival, adhesion and proliferation while for blood vessels‟ integration the pore size should be increased to the region of 350-400 µm. In addition, feasibility of using SEF method for low-temperature 3D printing of highly uniform polylactic acid (PLA)/HA biocomposite scaffolds with varying stiffness was demonstrated and an integrated synthetic bone graft/fracture fixation system was proposed in order to minimise graft migration.A novel production technique is also outlined in this project that yields a bioactive polyether-ether-ketone (PEEK)/HA composite with a unique configuration in which the bioactive phase (i.e. HA) distribution is computer-controlled within a PEEK matrix. To this end, the relatively fragile 3D printed HA scaffolds were overmoulded with PEEK under optimised pressure, temperature, dwelling time, and loading method. The PEEK/HA biocomposites with different HA volume percentages ranging from approximately 35% to 78% were produced and analysed using computed tomography (CT). The proof of primary cell adhesion, sustained viability in contact with sample surface architecture over a 7 day period, and evidence of cell bridging were strongly supportive of biocompatibility. According to the results, incorporation of extrusion freeformed HA into PEEK eventuates in reduction in mechanical properties, although it enhances cell attachment. However, the biocomposites with HA content of 40 vol.% could survive in one million compression-compression cyclic loading at 30% of their compressive strength without any degradation in compressive properties. The application of these composites can be extended into porous PEEK scaffold, or PEEK microfluidic device, when the interconnected HA phase is removed by socking the composites in hydrochloric acid (HCl).Direct low-cost extrusion freeforming of biomimetic porous PEEK parts with complicated external geometry and controlled pore size was also demonstrated for the first time in this project. The findings of this study suggest that 3D printed PEEK structures have promising compressive properties with potential for both load bearing and non-load bearing applications. According to the results, the 3D printed solid PEEK specimens with 100% infill rate had 14% porosity and ultimate tensile strength (UTS) of 75.06 MPa that is 33% less than solid injection moulded PEEK. The air gap between infill pattern and entrapped micro-bubbles inside filaments were identified as the main source of mechanical properties degradation. The 3D printed PEEK samples had flexural modulus and strength significantly higher than those various polymers/composites printed using other AM technique
Creep life prediction of IN738 gas turbine blade
No full textThe aim of this study is life prediction of IN738 LC gas turbine blade via Larson- Miller parameter method and fulfilment of some systematic metallographic, creep and hardness tests. Various calculative methods of remaining life prediction have been considered and Larson-Miller parameter method is used in order to predict remaining life of ABB-130 gas turbine blade. By investigation of the metallographic images it was observed that the hardening phase (γ’) becomes bigger after passing of a long time and under high temperature (780 °C) and has been converted from cubic to almost spherical status. It results in a decrease in the strength of the matrix and degradation of alloy’s metallurgical properties and eventually generation of continuous carbides in the grain boundaries, bigness and joining of γ’ particles, grain boundary refining and generation of creep voids, all of which resulted in satisfactorily calculation of remaining life time
Extrusion-based additive manufacturing of PEEK for biomedical applications
No full textThere has been a trend in recent years to develop polyetheretherketone (PEEK)-based medical devices due to the excellent cell biocompatibility and desirable mechanical properties of PEEK, which has elastic modulus comparable to cortical bone. Different manufacturing techniques such as injection moulding, particulate leaching, compression moulding, and selective laser sintering (SLS) have been used to produce porous PEEK for biomedical applications. Despite a large number of publications on extrusion-based additive manufacturing (AM) of porous structures using various materials, there have been very few general reports on extrusion AM of low quality small PEEK parts without defects such as warpage and delamination and no further assessment of mechanical properties. Successful low-cost 3D printing of PEEK structures using filament-based extrusion AM process is reported in this paper for the first time. Hot extrusion head design, extrusion temperature, and ambient temperature were identified as important factors need to be taken into consideration for printing PEEK structures without warpage, delamination, and polymer degradation. Compression and tensile tests were conducted to investigate mechanical properties of these new 3D printed PEEK structures. The air gap between infill pattern and entrapped micro-bubbles inside filaments were identified as the main source of mechanical properties reduction. In addition, three-point flexural test was performed on the 3D printed PEEK and compared with flexural specimens printed using other AM materials and techniques
Investigation of process parameters in extrusion freeforming to make high resolution bioceramic lattice structures
No full textVarious fabrication methods including traditional chemical engineering methods and advanced Additive Manufacturing (AM) techniques are currently used for construction of tissue engineering (TE) scaffolds. Traditional techniques have several limitations as they usually can’t control pore size, pore geometry and spatial distribution of pores properly. In contrast, AM advanced techniques can simply control the internal and external structure of scaffolds and overcome some intrinsic limitations of conventional methods such as shape restrictions, manual intervention, inconsistent and inflexible processing procedures. In order to these advantages, there has been trend in recent years on fabrication of TE scaffolds using AM processes directly or indirectly. In particular, extrusion freeforming systems such as fused deposition modelling (FDM), bioplotting, robocasting, and solvent-based extrusion freeforming have been widely investigated for producing TE scaffolds and bioactive constructs due to their ability of processing different biomaterials, their possibility of manufacturing scaffolds in a cell-friendly environment, their high reproducibility and flexibility, and their simple process control in comparison with other AM techniques. Despite the daily progress in the use of extrusion freeforming methods in regenerative medicine there are still some aspects such as process resolution need to be improved to meet the requirement in different biomedical applications.A solvent-based extrusion freeforming device was designed and set up to print 3D bioceramic lattice structures with highly uniform interconnected pores (as fine as 30 µm) for different application. Filaments can be delivered with high precision with diameters down to 60mm thanks to our unique nozzle design and the equipment built in-house at Southampton. The effect of nozzle die land on extrusion pressure was investigated and used as a guide to optimize the nozzle design to make high resolution bioceramic lattice structures with decrease extrusion pressure. In this talk, the effects of process parameters including nozzle size and die land, paste rheology, and bioceramic particle size on extrusion pressure, uniformity and resolution of the 3D printed lattice structures will be discussed in detail<br/
Quality control of quick response products by used of reverse engineering technologies
No full textError comparisons of fabricated parts and original CAD design is often a difficult yet important issue in product quality control. In this study, an integrated technique of 3D scanning with reverse engineering and rapid prototyping technologies proposed. This will be applied to the entire quality control phase of quick response products during the manufacturing process. For evaluation of presented approach, an automotive test model was made using the layered manufacturing process RP fabricator, a 3D Printing RP system. Then non-contact laser 3D scanner with RE software employed to evaluate dimensional deviations of manufactured RP model. Regarding to the result of inspection, maximum deviation was ?0.306 mm. So, with the virtue of the 3D laser scanning system and RE software, the proposed method could be used during the entire quality control phase of the manufacturing process
Host defence peptides: mechanisms of membrane perturbation and target cell selectivity
No full textHost defence peptides (HDPs) are effector molecules of the innate immune system. They show broad activity against bacteria and cancer cells, usually by perturbing the permeability of cell membranes, leading to the death of pathogens by collapse of transmembrane electrochemical gradients and loss of important metabolites and cellular components. Due to this mechanism of action, development of resistance is unlikely. For this reason, HDPs are excellent candidates as a new class of therapeutics to address the problem of drugresistance pathogens. Pore formation in the pathogen membranes requires a significant accumulation of peptide molecules on the cell surface. Therefore, it is conceivable that other effects, in addition to permeabilization, might take place. In this thesis, the effects on membrane dynamics of four peptides (magainin, melittin, LAH4 and killer-FLIP) were analysed. In all cases, a peptide-induced reduction in lipid mobility and lateral diffusion was observed. These effects appeared to be independent of peptide electrostatic charge. A significant hindering of lipid dynamics might lead to inhibition of the function of membrane proteins, contributing to the bactericidal activity of the peptides. Cell selectivity of HDPs is due to the different composition of pathogen and host membranes, and particularly to the negatively charged lipids present in the membranes of bacteria and cancer cells. As a consequence, the cationic charge of most HDPs is an essential determinant of selectivity. However, it is not sufficient: extensive structure-activity relationship studies with a number of HDPs have revealed that a delicate balance between net charge, amphipathicity, hydrophobicity, and structural propensity is critically important to ensure antimicrobial potency and target cell selectivity. An immediate consequence of HDP amphipathicity is the tendency of several of these peptides to aggregate in water. In this thesis, the role of this phenomenon in cell-selectivity has been investigated, focusing on the cationic peptide killer-FLIP, which is strongly selective for cancer cells. We observed that this property is linked to the formation of aggregates. Notwithstanding the cationic charge, the monomeric peptide has a significant affinity towards all membrane compositions, because the water-exposed apolar residues provide a hydrophobic driving force for binding and insertion into neutral membranes of normal cells. By contrast, in the aggregates the hydrophobic sidechains are buried, thus reducing the affinity towards neutral membranes. At the same time, the aggregates still tend to associate to the anionic membranes of cancer cells, driven by electrostatic attraction. Overall, these findings provide a better understanding of the structural determinants of the membrane-perturbing activity and selectivity of HDPs, which is essential for the development of novel HDP-inspired drugs to effectively fight resistant infections and cancer, with minimum toxicity to eukaryotic cells
A review on 3D micro-additive manufacturing technologies
No full textNew microproducts need the utilization of a diversity of materials and have complicated three-dimensional (3D) microstructures with high aspect ratios. To date, many micromanufacturing processes have been developed but specific class of such processes are applicable for fabrication of functional and true 3D microcomponents/assemblies. The aptitude to process a broad range of materials and the ability to fabricate functional and geometrically complicated 3D microstructures provides the additive manufacturing (AM) processes some profits over traditional methods, such as lithography-based or micromachining approaches investigated widely in the past. In this paper, 3D micro-AM processes have been classified into three main groups, including scalable micro-AM systems, 3D direct writing, and hybrid processes, and the key processes have been reviewed comprehensively. Principle and recent progress of each 3D micro-AM process has been described, and the advantages and disadvantages of each process have been presented
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