1,721,042 research outputs found
A mesh morphing computational method for geometry optimization of assembled mechanical systems with flexible components
Full text linkIn this paper an interactive computational methodology was developed assuming that shape and size optimization of flexible components can significantly improve energy absorption or storage ability in assembled systems with flexible components (AS-FC). A radial basis functions mesh morphing formulation in non-linear numerical finite element analysis, including contact problems and flow interaction, was adopted as optimal design method to optimize shape and size design parameters in AS-FC. Flexible components were assembled in finite element environment according to functional ISO-ASME tolerances specification; non-linear structural analysis with flow interaction analysis was performed. The results of the study showed that the proposed method allows to optimize the shape and size of the flexible components in AS-FC maximizing the system's ability to absorb or store energy. The potentiality of the method and its forecasting capability were discussed for the case study of an automotive crash shock in which the specific energy absorption was increased by over 40%. The case studied refers to a simple flexible component geometry, but the method could be extended to systems with more complex geometries
Modeling, assessment, and design of porous cells based on schwartz primitive surface for bone scaffolds
Full text linkThe design of bone scafolds for tissue regeneration is a topic of great interest, which involves diferent issues related to geometry of architectures, mechanical behavior, and biological requirements, whose optimal combination determines the success of an implant. Additive manufacturing (AM) has widened the capability to produce structures with complex geometries, which should potentially satisfy the diferent requirements. These architectures can be obtained by means of refned methods and have to be assessed in terms of geometrical and mechanical properties. In this paper a triply periodic minimal surface (TPMS), the Schwarz's Primitive surface (P-surface), has been considered as scafold unit cell and conveniently parameterized in order to investigate the efect of modulation of analytical parameters on the P-cell geometry and on its properties. Several are the cell properties, which can afect the scafold performance. Due to the important biofunctional role that the surface curvature plays in mechanisms of cellular proliferation and diferentiation, in this paper, in addition to properties considering the cell geometry in its whole (such as volume fraction or pore size), new properties were proposed. Tese properties involve, particularly, the evaluation of local geometrical-diferential properties of the P-surface. Te results of this P-cell comprehensive characterization are very useful for the design of customized bone scafolds able to satisfy both biological and mechanical requirements. A numerical structural evaluation, by means of fnite element method (FEM), was performed in order to assess the stifness of solid P-cells as a function of the changes of the analytical parameters of outer surface and the thickness of cell. Finally, the relationship between stifness and porosity has been analyzed, given the relevance that this property has for bone scafolds design
Design and analysis of tissue engineering scaffolds based on open porous non-stochastic cells
No full textA lunar rover leg: Optimal design of a decoupling joint
No full textThe development of vehicles for the exploration in the lunar environment is a topic of great interest. In particular, recently, there has been a growing attention toward the lunar rovers for working missions since the building of lunar bases is a primary objective for the lunar exploration. However, these vehicles have peculiar requirements to be taken into account in the design of each component. In this paper a particular component of a worker rover, developed as a collaboration between two academic institutions, has been designed for an optimal functionality. Each leg of this rover comprises a mechanism for lifting weights and the component considered, a decoupling joint, is a part of this mechanism. The design optimization was performed by means of parametric modelling and numerical simulations
Uncommitted gastrointestinal stromal tumour. Case report.
No full textGastrointestinal Stromal Tumours (GIST) are mesenchymal tumours with uncertain prognosis. Malignant variety represents about 2.0% of malignant gastroenteric tumours. The Authors report a clinical case of malignant gastric and duodenojejunal GIST, in which the only surgical treatment seems to be definitive. R. S., a 69-year-old female, was admitted for asthenia and fever in January 1997. Endoscopic exploration, ultrasonography and CT-scan of the abdomen demonstrated an exophytic tumour in the greater gastric curvature and one tumour of 5.5 cm of diameter in the Treitz's angle. We performed a resection of the gastric tumour and the duodenojejunal angle. Postoperative course was uneventful and the patient was discharged after 14 postoperative hospital days. Histological analysis showed two spindle cells stromal tumours with mitotic rate > 20/10 HPF. The immunohistochemistry demonstrated the uncommitted origin of tumour cells. The patient refused the chemotherapy treatment. There was no local recurrence or metastasis at a follow up of 47 months, in spite the high malignancy degree. For this reason and because of the uncertain behaviour of benign GIST, the authors propose a lifelong follow up of the patients managed with potentially curative surgical resection
Neck orthosis design for 3D printing with user enhanced comfort features
Full text linkAn area of interest in orthopaedics is the development of efficient customized neck orthoses, considered that pathologies which affect the neck area are widespread. Advanced acquisition and modelling approaches combined with Additive Manufacturing (AM) can potentially provide customized orthoses with improved performance and complexity. However, in the design of these devices, besides functional and structural requirements, benefit and comfort of the patient should be a main concern, in particular, at the early stage of design during the acquisition of the body’s part, and while using the printed orthosis. In this paper, a scanning system with three sensors was developed which allows a fast, about 5 s, and accurate acquisition of the neck area with minimum discomfort for the patient. A neck orthosis with a ventilation pattern obtained by Topology Optimization (TO), lightened by about 35%, was also established. In fact, a main role for comfort is played by the ventilation pattern which contributes both to lightness and breathability. Its structural and comfort performance was evaluated in comparison with an orthosis with a ventilation pattern configured by Voronoi cells. Structural assessment was carried out by means of finite element analysis under main loading conditions. An evaluation of neck temperatures in relation to wearing 3D printed prototypes, manufactured with Hemp Bio-Plastic® filament, was finally conducted by means of a thermal imaging camera. TO orthosis prototype showed a better performance regarding thermal comfort, with a maximum increase of neck temperature less than 1 °C, which makes the proposed configuration very promising for user's comfort
Assessment of High Porosity Lattice Structures for Lightweight Applications
Full text linkAdditive manufacturing (AM) methods have a growing application in
different fields such as aeronautical, automotive, biomedical, and there is a huge
interest towards the extension of their use. In this paper, lattice structures for AM
are analysed with regards to stiffness and printability in order to verify the suitability for applications where the main requirement of efficiency in terms of stiffness
has to be balanced with other needs such as weight saving, ease of manufacturing
and recycling of the material. At this aim, lattice structures with high porosity
unit cells and large cell size made of a recyclable material were considered with a
geometrical configuration allowing 3D printing without any supports. The lattice
structures considered were based on body-centred cubic (BCC) and face centred
cubic (FCC) unit cell combined with cubic cell. Finally, a multi-morphology lattice structure obtained by mixing different unit cells is also proposed. The lattice
structures were modelled and structurally analysed by means of finite element
method (FEM), manufactured with a Fusion deposition modelling (FDM) printer
and evaluated in relation to printability and dimensional accuracy. The results
show that the proposed structure with mixed cells is potentially advantageous in
terms of weight saving in relation to the mechanical properties
Design of a prototype system operant in lunar environment
No full textIn this paper, the design of a prototype system developed for a rover intended for the removal and transport of rocks on lunar soil is reported. The part of the rover dedicated to some of the main tasks, i.e. the lifting of objects and moving on rugged terrain, while controlling of the balance of the vehicle, is considered. These tasks are accomplished through the mechanical components assembled in a column connected to wheels. The study has been conducted with the aim of obtaining a simple and lightweight structure satisfying the requirements necessary to operate on the lunar soil. After a description of the architecture of the rover, the layout of the components of the column is detailed. A compliant, spiral-spring wheel is proposed to complete the mobility system. The primary components of the column are then structurally assessed by means of FEM numerical simulations. A numerical model of the wheel has also been implemented, in order to define in detail the wheel geometry and performance. The proposed layout could be promising for lunar applications since it has a configuration suitable for the specific characteristics of the environment it has to operate
Design and assessment of functionally graded lattices
No full textLattice structures are architectures of interest for lightweight applications in different fields such as aerospace, biomedical, automotive and structural engineering. Their properties, such as strength to weight ratio, specific strength and energy absorption can be potentially tailored or generally improved by functionally grading. In this study differently graded lattice structures based on Body Centered Cubic (BCC) unit cell, which has a simple basic geometry that can be advantageous for easier 3D printing and a wider use in industry were considered. Linearly graded and symmetrically linearly graded geometries were modelled with a similar value of average relative density in order to compare their structural behaviour with a uniform BCC lattice structure. The different geometries of the graded lattices were 3D printed with stereolithography (SLA), which allowed to obtain a good geometrical accuracy and superficial finish. The printed models were subjected to compression tests and main parameters, specifically, stiffness and energy absorption capability were evaluated. The results obtained showed that, in particular, the proposed symmetrical functional grading allowed a moderate increase of stiffness and a more noticeable improvement of energy absorption capability with respect to a uniform structure, which was higher when the load was applied perpendicularly to the grading direction
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