1,720,960 research outputs found
A direct methodology for the calibration of ductile damage models from a simple multiaxial test
No full textIn the present work a straightforward calibration procedure of ductile damage models is proposed. The direct methodology involves the use of a simple multiaxial specimen, to be tested with a universal testing machine, capable to reproduce different stress states in the material. The specimen geometry was the one proposed by Driemeier et al. [1]. In addition, a numerical-analytical procedure was devised for the identification of material strains to fracture and corresponding stress states, directly from experimental tests. This allowed to overcome the use of Finite Element Analysis and inverse methods usually adopted to retrieve the local parameters representative of the material ductility
Additive manufacturing structural redesign of hip prostheses for stress-shielding reduction and improved functionality and safety
Full text linkNowadays, the total hip arthroplasty (THA) is a widespread surgical procedure, representing the best option to restore hip joint mobility in patients suffering from trauma or joint diseases. One of the well-known possible drawbacks of THA is the stress-shielding phenomenon. Some years after the surgery, the femur starts to degrade because of its persistent unloaded condition induced by the high prosthesis stiffness, which carries the great part of the load normally taken by the bone. This condition is particularly invalidating in younger patients, with longer life expectation after the operation, requiring one or multiple additional operations to restore the proper prosthesis-bone firm connection.
The present study tries to address this issue proposing an innovative prosthesis design, taking advantage of the shape freedom ensured by Additive Manufacturing techniques. Additionally, the structural integrity of the novel prosthesis is assessed using a ductile damage numerical approach.
Different prosthesis geometries were investigated: one conventional and commercially available already, and two more innovative geometries. For each one, a bulk solution was compared to a lighter version characterized by an inner reticular structure with a body-centred cubic unit cell and by an equivalent density of about 5%, only feasible through the additive manufacturing fabrication.
Extensive Finite Element numerical simulations were carried out to compare the percentage of the induced stress shielding for the different prosthesis geometries. Pros and cons of each geometry were pointed out and eventually the most promising solution in limiting the stress shielding phenomenon was chosen. At the same time, the structural integrity of the selected design was ensured, embedding a ductile damage model in the Finite Element analysis, calibrated on a SLM Ti6Al4V, the biocompatible alloy for the prosthesis fabrication. Structural safety was evaluated under four different loading conditions: walking, stumbling, the exceptional overload due to hammering insertion during surgery and the force which induced the collapse of the implant. Additionally, the safety margin was quantified through the definition of an overall safety factor under the maximum expected load
Effects of temperature and strain rate on the ductility of an API X65 grade steel
Full text linkIn the last few decades, great effort has been spent on advanced material testing and the devel-opment of damage models intended to estimate the ductility and fracture of ductile metals. While most studies focused on static testing are applied at room temperatures only, in this paper, multi-axial tests have been executed to investigate the effects of dynamic action and temperature on the mechanical and fracture behavior of an API X65 steel. To this end, a Split Hopkinson Bar (SHB) facility for dynamic tests, and a uniaxial testing machine equipped with a high-temperature fur-nace, were used. Numerical simulations of the experiments were setup for calibration and valida-tion purposes. Based on the experimental results, the Johnson–Cook and Zerilli–Armstrong plas-ticity models were first tuned, resulting in a good experimental–numerical match. Secondly, the triaxiality and Lode angle dependent damage models proposed by Bai–Wierzbicki and Coppola–Cortese were also calibrated. The comparison of the fracture surfaces predicted by the damage models under different loading conditions showed, as expected, an overall significant increase in ductility with temperature; an appreciable increase in ductility was also observed with the increase in strain rate, in the range of low and moderate triaxialities
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fem deformation analysis of a transtibial prosthesis fed with gait analysis data. a preliminary step towards restoring proprioception in amputees
No full textThe lack of proprioception in patients with lower
limb amputation is a major impairment affecting balance and
metabolic consumption, and increases the risk of falling of
amputees. As of today, several methods have been considered to
restore this capacity, mainly involving the use of force sensing
resistors and vibrotactile feedback systems. This study explores
the possibility to use an elastomeric sensor filled with conductive
liquid as a strain sensor to obtain proprioceptive data from the
prosthesis during the gait cycle. A FEM simulation was carried
out to study the deformation of a transtibial prosthesis, in order
to identify the point of maximum deformation for the sensor
application. Both the static and the dynamic analyses identify a
frontal area in the ankle region with a maximum value of 0.02
m/m, at the intersection of leg and foot. Results are therefore
encouraging for the future application of an elastomeric strain
sensor in the indicated area
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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