1,721,126 research outputs found
Analysis of the welding strength in hybrid polypropylene composites as a function of the forming and overmolding parameters
No full textThis work investigates the influence of the process parameters on the welding strength in hybrid polypropylene composites manufactured by injection overmolding. A hybrid T-joint specimen was designed to evaluate the global performance of the welding by means of tensile tests. The effects of the process parameters were evaluated in accordance the design of experiments approach and the maximum strength (UTS) was assumed as response variable. The effects of melt temperature and holding pressure, combined to a variothermal mold-control system, were investigated. The residual stresses induced by the process were considered by means of coupled thermo-fluid dynamic/structural finite-element analysis. Moreover, the topography of the laminate-side surface was characterized and the process-induced surface modification was related to the performance of the welding. Results show that the melt temperature contributes to increase the welding strength; conversely, the mold temperature counteracts this effect by increasing the residual stress at the interface. POLYM. ENG. SCI., 58:592–600, 2018. © 2017 Society of Plastics Engineers
Modeling the adhesion bonding strength in injection overmolding of polypropylene parts
Full text linkIn this work, the bonding strength of overmolded polypropylene is investigated and modeled. A T-joint specimen was designed to replicate the bonding between a base and an overmolded stem made of the same polymer: a previously molded plaque was used for the base, and the stem was directly overmolded. The effect of melt temperature, holding pressure, and localized heating was investigated following the design of experiments approach. Both the melt and base temperature positively affect the welding strength. On the contrary, the holding pressure negatively contributed, as the crystallization temperature significantly increases with pressure. Then, the bonding strength of the specimens was predicted using a non-isothermal healing model. Moreover, the quadratic distance of diffusion (based on the self-diffusion model) was calculated and correlated with the bonding strength prediction. The non-isothermal healing model well predicts the bonding strength when the reptation time is calculated within the first 0.09 s of the interface temperature evolution. The prediction error ranges from 1% to 35% for the specimens overmolded at high and low melt and base temperatures, respectively
Cohesive Zone Modeling of the Interface Fracture in Full-Thermoplastic Hybrid Composites for Lightweight Application
Full text linkWith the increasing demand for lightweight and high-performance materials in the automotive and aerospace industries, full-thermoplastic hybrid composites have emerged as a pivotal solution, offering enhanced mechanical properties and design flexibility. This work aims to numerically model the fracture strength in full-thermoplastic hybrid composites made by forming and overmolding organosheets. The mode I fracture was investigated by modeling the behavior of T-joint specimens under a tensile test following the cohesive zone modeling (CZM) approach. The sample was designed to replicate the connection between the laminate and the overmolded part. Double cantilever beam (DCB) specimens were manufactured with organosheets and tested to mode I opening to determine the interlaminar fracture toughness. The fracture toughness out of the mode I test with DCB specimens was used to define the CZM parameters that describe the traction-separation law. Later, due to the particular geometry of the T-join specimens that under tensile load work close to pure mode I, the cohesive parameters were determined by inverse analysis, i.e., calibrating the theoretical models to match experimental results. The fracture resistance T-joint specimens appeared dependent on the fiber-bridging phenomenon during the delamination. In particular, the presence of fiber-bridging visible from the experimental results has been replicated by virtual analyses, and it is observed that it leads to a higher energy value before the interface’s complete breakage. Moreover, a correspondence between the mode I fracture toughness of the DCB specimen and T-joint specimens was observed
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
Health as a human right, the right to life and the freedom to choose
No full textIn a work recently published in an important international journal of medical oncology one of the most relevant names in the field of palliative care and pain therapy in Italy, reiterated once again the importance of a good end of life for cancer patients. All this in light of a recent ruling by the Italian Constitutional Court on the decriminalization decision in case of support for suicide in particular conditions, inviting the Parliament to legislate on the delicate issue concerning assisted suicide and euthanasia. By sharing the master's thought, we felt the need to make a more open reflection by putting heart and soul into it
Smart steaming: A new flexible paradigm for synchromodal logistics
Full text linkSlow steaming, i.e., the possibility to ship vessels at a significantly slower speed than their nominal one, has been widely studied and implemented to improve the sustainability of long-haul supply chains. However, to create an efficient symbiosis with the paradigm of synchromodality, an evolution of slow steaming called smart steaming is introduced. Smart steaming is about defining a medium speed execution of shipping movements and the real-time adjustment (acceleration and deceleration) of traveling speeds to pursue the entire logistic system’s overall efficiency and sustainability. For instance, congestion in handling facilities (intermodal hubs, ports, and rail stations) is often caused by the common wish to arrive as soon as possible. Therefore, smart steaming would help avoid bottlenecks, allowing better synchronization and decreasing waiting time at ports or handling facilities. This work aims to discuss the strict relationships between smart steaming and synchromodality and show the potential impact of moving from slow steaming to smart steaming in terms of sustainability and efficiency. Moreover, we will propose an analysis considering the pros, cons, opportunities, and risks of managing operations under this new policy
Automatic glass fiber length measurement for discontinuous fiber-reinforced composites
No full textSevere fiber breakage occurs in injection molding, affecting the mechanical performance of discontinuous fiber-reinforced composites. Accurate measurement of the residual fiber length distribution is crucial to experimentally investigate the physics of fiber breakage. This work proposes an automatic glass fiber length measurement method, based on the algorithm CT-FIRE for individual fiber detection. The main parameters of the algorithm were optimized to minimize the average systematic error between measurements performed with CT-FIRE and with a high-accuracy CMM. An approach to the evaluation of the measurement uncertainty based on substitution measurements was proposed and verified for a large size sample. For the scanner used in this study the uncertainty was 0.651 mm. Eventually, the developed automatic measurement method was used to investigate fiber breakage during plastication of long glass fiber-reinforced PP. The results obtained using the optimized algorithm parameters showed that significant breakage is due to the presence of the dynamic mixer
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