28 research outputs found

    effect of porosity and cell topology on elastic plastic behavior of cellular structures

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    Abstract In this work we study the mechanical behavior of Ti6Al4V cellular structures by varying the randomness in the cell topology from regular cubic to completely random and the porosity of the structure. The porosity of the structure is altered by changing the strut thickness and the pore size to obtain a stiffness value between 0.5-12Gpa. The geometrical deviation in the structures from the as-designed values is studied by morphological characterization. The samples are subjected to compression and tensile loading to obtain the stiffness and the elastic-plastic behavior of the samples. Finite element modelling (FEM) is carried out on the as-designed structures for both tensile and compressive loading to study the effect of deviation between the as-designed and as-built structures. FEM is also carried out for as-built regular structures, by introducing the geometrical deviation to match the porosity of the as-built structures. Comparison of FEM and experimental results indicated that the effect of cell topology depends on the porosity values. Simulation results of as-built structures demonstrated the importance of defects in the structure

    Tensile and compression properties of variously arranged porous Ti-6Al-4V additively manufactured structures via SLM

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    Abstract Additively manufactured porous structures find increasing applications in the biomedical context to produce orthopedic prosthesis and devices. In comparison with traditional bulk metallic implants, they permit to tailor the stiffness of the prosthesis to that of the surrounding bony tissues, thus limiting the onset of stress shielding and resulting implant loosening, and to favor the bone in-growth through the interconnected pores. Mechanical and biological properties of these structures are strongly influenced by the size and spatial arrangement of pores and struts. In the present work irregular and regular cellular as well as fully random porous structures are investigated through tensile and compression uniaxial tests. Specific point of novelty of this work is that, beside classical compressive tests, which are standard characterization methods for porous/ cellular materials, tensile tests are carried out. Mechanical tests are complemented with morphological analysis and porosity measurements. An attempt is made to find correlations between cell arrangements, porosity and mechanical properties

    A forecasting model for waste being disposed of in landfills

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    The purpose of this paper is to propose a model capable to provide, by the analysis of the historical series of municipal solid waste disposed of in landfills, sufficiently reliable forecast of the quantity of this type of waste being disposed of in landfills in the future. The forecasting model proposed draws from the consideration that a landfill facility could be placed only in an area satisfying specific requirements, for example with regard to geological, hygienic, landscape and urban matters. Since eligible areas are limited, a natural limit to the exploitation of dumping ground exists. The main assumption of this study is that the quantity of waste disposed of in landfills follows a trend that can be described with the mathematical model of the Logistic function. The values of the historical series describing the streams of municipal solid waste landfilled in Italy are used as input data. The proposed model allows to perform forecasts that could be useful to governments for the definition of environmental policies and for a timely and adequate planning of the waste management system

    Performance analysis of energy recovery in an Italian municipal solid waste landfill

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    The objective of this paper is to assess the techno-economic viability of the use of fuel cell as an alternative technology for landfill gas energy recovery. The case of an Italian municipal solid waste landfill is analyzed. The landfill was opened in 1998 and in 2001 the energy recovery facility started operation. The current landfill gas conversion system is based on internal combustion engine technology. However, the drawbacks of internal combustion engine in terms of conversion efficiency and air emissions are widely acknowledged. Some authors have proposed molten carbonate fuel cell as one of the most interesting solution for landfill gas energy recovery for the near future. Fuel cells have proven capable of providing superior energy efficiency and environmental performance, but their widespread use is constrained by the capital cost required. Using actual data from the landfill, a comparison between the current energy recovery system and a hypothetical alternative solution based on molten carbonate fuel cell is performed. The analysis assesses the cost-effectiveness of the two solutions, considering also some environmental externalities usually not included in traditional economic assessment. The main strengths and weaknesses of the two landfill gas energy recovery systems are highlighted and some new insights into molten carbonate fuel cell overall sustainability are provided

    Wear of ten dental restorative materials in five wear simulators-results of a round robin test

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    OBJECTIVE: The purpose of the present study was to prove the hypothesis that different wear measurement methods generate different material rankings. METHODS: Ten restorative materials, eight composites (BelleGlass, Chromasit, Estenia, Heliomolar RO, SureFil, Targis cured at 95 and 130 degrees C, Tetric Ceram) an amalgam (Amalcap) and a ceramic (Empress) have been evaluated with regard to the wear with five different wear methods (IVOCLAR, ZURICH, MUNICH, OHSU, ACTA). Every center received specimens, which Ivoclar Vivadent had made using the same batch. The test centers did not know which brand they were testing. After completion of the wear test, the raw data were sent to IVOCLAR for further analysis. The statistical analysis of the data included logarithmic transformation of the data, the calculation of relative ranks of each material within each test center, measures of agreement between methods, the discrimination power and coefficient of variation of each method as well as measures of the consistency and global performance for each material. RESULTS: Relative ranks of the materials varied tremendously between the test centers. When all materials were taken into account and the test methods compared with each other, only ACTA agreed reasonably well with two other methods, i.e. OHSU and ZURICH. On the other hand, MUNICH did not agree with the other methods at all. The ZURICH method showed the lowest discrimination power, ACTA and IVOCLAR the highest. Materialwise, the best global performance was achieved by Empress, which was clearly ahead of BelleGlass, SureFil and Estenia. In contrast, Heliomolar RO, Tetric Ceram and especially Chromasit demonstrated a poor global performance. The best consistency was achieved by BelleGlass and SureFil, whereas the consistency of Amalcap and Heliomolar RO was poor. SIGNIFICANCE: As the different wear simulator settings measure different wear mechanisms, it seems reasonable to combine at least two different wear settings to assess the wear resistance of a new material

    Pearls & Oy-sters: An unusual case of varicella-zoster virus cerebellitis and vasculopathy.

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    CNS complications of varicella-zoster virus (VZV) occur mainly in immunocompromised or elderly patients and include meningitis, myelitis, acute encephalitis, vasculopathy, and, rarely, cerebellitis.(1-8.

    Comparative metrological characterization of Ti6Al4V lattice structures produced by laser powder bed fusion

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    The advancement of Additive Manufacturing (AM) technologies, such as Laser Powder Bed Fusion (LPBF), enables the fabrication of metallic lattice materials with a wide range of topologies and size scales. The possibility to manufacture these materials into complex shapes with good property-to-weight ratio stimulates a growing interest in several industrial sectors, including biomedical, aerospace, and automotive. Nevertheless, such structural features printed at a small-scale often suffer from a wide range of morphological defects that can lead to a marked deviation from the nominal geometry and consequently impact the mechanical, transport and thermal properties. An accurate metrological characterization of the lattice is thus of paramount importance for a more reliable prediction of the properties of the lattice. The most common characterization techniques used for as-built lattice materials are scanning electron microscopy (SEM), optical microscopy (OM) and X-ray computed tomography (CT). CT, contrary to the other methods, provides full 3D data including inaccessible geometries and features, in a non-destructive way, but it requires expensive equipment and considerable expertise. SEM and OM can be faster and less expensive, but can be non-destructive only when limited to the outer surface of the lattice. When combined with metallographic analysis, instead, they require destructive, careful and time-consuming specimen preparation, and the analysis is confined to selected sections. In this work, the three above-mentioned techniques are applied to the metrological characterization of LBPF Ti6Al4V regular cubic lattices of 4 mm unit cell size and struts with circular cross-section of diameter 0.760 mm. The results in terms of strut cross-section parameters and junction fillet radius are compared and the effect of the size of the analysis domain on the accuracy of the results is investigated by comparing lattice sub-volumes of different size. Via a thorough statistical analysis it is shown that CT and metallographic characterization are compatible, while microscope imaging can lead to an overestimation of the strut thickness
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