1,721,055 research outputs found
The effect of microstructure on the tensile and impact behaviour of short-glass fibre-reinforced polyamide 6.6 as assessed by micro-computed tomography
Full text linkInjection moulding of short-fibre-reinforced thermoplastics opens a new dimension in the field of mass production of complicated net-shaped parts with accurate dimensions and the new challenge is to produce parts with tailored properties. However, the layered structure frequently observed in these composites strongly affects their mechanical behaviour and constitutes the main difficulty in transferring the results of tests performed on standard specimens to actual components and parts. In addition, to use injection-moulded composite materials safely, their mechanical behaviour under different loading conditions must be well understood. In the present work, the effect of microstructure, in terms of fibre length and orientation, on the tensile and impact behaviour of injection-moulded short-glass fibre-reinforced polyamide 6.6 was investigated. Digital reconstruction of the three-dimensional structure of samples, differently oriented with respect to the melt flow path, was obtained by the high-spatial-resolution non-destructive technique of synchrotron radiation micro-computed tomography (micro-CT). Automatic evaluation of the fibre length distribution was developed by a global method based on the mean fibre length distribution, computed from the star length distribution (SLD). The results of uniaxial tensile tests and Izod impact experiments were successfully correlated with morphological analysis of fractured surfaces and the results of SLD. These studies revealed important changes in fibre orientation distribution when the sample orientation is changed with respect to melt flow direction, which also strongly influenced the composite mechanical response.Fil: Rosic, N.. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Mollo, M.. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Bernal, Celina Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnología en Polímeros y Nanotecnología. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnología en Polímeros y Nanotecnología; ArgentinaFil: Cosmi, F.. Università degli Studi di Trieste; Itali
BES TESTTM accuracy evaluation by means of 3D-printed phantoms
No full textThe BES TEST (TM) (Bone Elastic Structure Test), is a recently developed software medical device that detects pathological changes of bone trabecular architecture by measuring its elastic characteristics, known to be directly related to its resistance. The results are expressed by the Bone Structure Index (BSI) or by its T-score, that is the number of standard deviations from the healthy population average. Purpose: Evaluate the precision of BES TEST (TM) under reproducibility conditions, defined as repeated measurements on the same or similar objects which include different locations, operators, and measuring systems. Methods: A total of 5 I replicate measurements were performed by four different operators on five different phantoms. Each phantom was 3D printed using Stereolithography (SLA) and Fused Deposition Modeling (FDM) and has a unique internal structure that mimics trabecular bone. ISO 5725 guidelines were followed for the interpretation of results. Results: The 3D-printed phantoms performed like real bones when analyzed with BES TEST (TM). The reproducibility 95% Confidence Interval expressed in BSI is CIR = +/- 11.1, which corresponds in T-score to CIR,Tscore = +/- 0.49. The Least Significant Change in BSI is LSCR = +/- 7.9, which corresponds to LSCR,Tscore = +/- 0.35. Conclusion: The reproducibility of BES TEST (TM) within the admissible range is not inferior to that of gold standard tests for osteoporosis. 3D printing proved a valuable tool to perform reliable replicate measurements without having patients undergo unnecessary tests
MODELLING ELASTICITY OF INJECTION MOULDED SHORT FIBRE REINFORCED POLYMERS: COMPARISON BETWEEN EXPERIMENTAL AND ANALYTICAL APPROACHES
Full text linkIn this work we analysed a sample of short fibre reinforced polyamide extracted from an injection moulded plate. We derived local values of the elastic constants by two different numerical methods, one based on simulation and one based on the reconstruction of the sample's microstructure by micro - CT. Results were compared in terms of moduli of elasticity, assuming an orthotropic material model. Fibre orientation was first simulated by process simulation and results were checked against experimental data obtained by the optical section method. Then, fibre orientation data were used for micro-mechanical modelling of the elastic behaviour by means of mean field homogenisation tools. The experimentally based approach was based on micro computed tomography reconstructions of the inner structure of samples extracted from the injection moulded plate. Using numerical models based on the Cell Method, the elastic behaviour of the reconstructed volume was simulated and results were compared with analytical models based on process simulations and homogenization
A mechanical and clinical evaluation of the Helix Wire for subcapital humerus fracture ostheosynthesis
No full textThe aim of this paper is the investigation of the mechanical properties the Helix Wire, a device that
has been employed for subcapital humerus fracture ostheosynthesis in recent years. There are
several potential clinical advantages associated with its use, but clinical results reported in literature
are controversial.
The Helix Wire has been assimilated to a helical spring, and several analytical solutions for
displacements and stresses have been compared and experimentally validated, showing the
importance of the pitch angle contribution.
Based on the results, the main factor for the clinical indication of this fixation device was found to
be the patient age. In fact, the use of the Helix Wire should be avoided in case of young patients or
of patients with well-developed muscular masses, where the forces may easily lead to critical
stresses in the spring and separation of the fracture surfaces. The clinical results obtained on 30
elderly patients confirmed these findings
Bone structure and fragility fracture risk factors: a population analysis
Full text linkOsteoporosis (OP) is a silent disease, characterized by a decreasing bone strength, which leads to a progressive increase in fracture risk. Mechanical properties of bone depend on both its composition and its trabecular component micro-architectural arrangement. OP diagnosis is made on the basis of bone mineral density (BMD), possibly combined with algorithms based on the clinical risk factors, e.g. FRAX®, but about half of those at risk of OP still go undetected, since their OP risk is linked to alterations of the trabecular architecture. The BESTEST® is a test based on the simulated application of loads on a virtual biopsy of the patient. Briefly, the test uses planar X-rays projections to assess the mechanical properties of the patient’s trabecular bone tissue. In this work, we aim to identify the distributions of fragility fracture risk factors in a population of female volunteers
La difficile equazione sull'identità castellana: recupero e conservazione tra luogo e società
No full textLo studio analizza la problematica edilizia legata al recupero dell’architettura fortificata. In particolare vengono esaminati i rapporti tra valore della permanenza storica e contesto. La possibilità di un futuro recupero della stessa viene valutata nella più generale prospettiva del dibattito culturale attuale
Sono ancora attuali i fondamenti della casa operaia?
No full textQuesta pubblicazione riporta i risultati di un lungo lavoro di ricerca relativo all’analisi tipologica e sociale del villaggio Crespi d’Adda. Tale lavoro si colloca in un più ampio quadro di ricerca interdisciplinare, tendente ad analizzare i fondamentali elementi caratterizzazione della casa operaia, anche in un quadro di confronto con gli attuali requisiti socio-funzionali che caratterizzano la residenza economico e popolare.
Il caso studio considerato, pur nella sua unicità architettonica, ha consentito di evidenziare alcune soglie di riferimento per quanto riguarda le prestazioni funzionali, che potranno costituire utili indicazioni per la formulazione di future linee guida di carattere progettuale
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Catecholamines plasma levels and haemodynamic changes induced by nifedipine in chronic severe heart failure.
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