1,720,961 research outputs found
Understanding Process-Structure-Property-Performance Relationships of Thermoplastic Olefins (TPO) Foams Through a Novel Manufacturing to Response Pathway
Full text linkThe global transportation industry is the second highest contributor to climate change. As a result, there has been a concerted effort to spearhead research in economical lightweighting technologies, as every 10 % reduction in weight will lead to to 6 – 8 % improvement in fuel efficiency. Additionally, the recent push for electrification and the emphasis on Corporate Average Fuel Economy (CAFE) standards have seen original equipment manufacturers (OEM’s) dive into lightweighting of materials to improve overall range and/or fuel-efficiency. Thermoplastic Olefins (TPOs) have in recent years carved out a niche in the automotive industry due to advantages such as increased impact resistance, lower production costs, short production times, and improving fuel efficiency on account of lower densities. TPO’s have been successfully used in interior and exterior automotive applications such as bumper fascia’s, trims, cladding, and wire insulation. Logically, the adoption of TPO foams either via conventional chemical agents or new physical blowing agents would be largely beneficial to the automotive sector given the need to drive down weight and increase efficiency.
However, conventional TPO foams have not seen widespread adoption in the automotive industry. Generally, TPO foams can be manufactured via two different approaches, viz., using either chemical or physical foaming agents in existing manufacturing processes like injection molding. TPO foams produced via chemical foaming agents are the current standard due to their low upfront costs and good molded-in color appearance but come with challenges in the form of unpredictable foaming in different cross-sections, decreased thermal stability and residual foaming agent migration induced by weather changes leading to pitting in class A painted surfaces. Alternatively, physically foamed TPO’s are yet to be adopted by a majority of the industry primarily due to higher upfront costs, splay marks on the surface that would fail the molded in color appearance requirements of almost all OEM, and the lower solubility of supercritical N2 in TPO’s making it challenging to foam. Lastly the lack of a holistic modeling pathway that couples manufacturing, microstructure, and mechanical responses pose a major impediment as they cannot be incorporated into current automotive product development cycles.
This study begins with developing a structure-property relationship for Super Critical Fluid (ScF) assisted IM TPO foams using a conventional IM tool to understand the current limitation of the process and tooling. Subsequently, a manufacturing-to-response pathway is developed to help simulate the process-structure-property relationship via the use of rheological, bubble growth, and FEA models via a mean filed homogenization approach. Furthermore, this work investigates the development of a proprietary tooling concept that can control pressure drop and cooling, both vital parameters in controlling cell nucleation and structure. Lastly, as a proof of concept, this work delves into the design and prototyping of an interior garnish part that serves as a demonstration of an industry-scaled TPO foamed product
An Investigation of Bimodal Cellular Distributions via Supercritical Fluid Assisted (SCF) Foam Injection Molding
Full text linkThe Corporate Average Fuel Economy (CAFÉ) standards for 2025 are set to introduce a fleet-wide average of 54.5 MPG for cars and thereby, prevent emissions of 6 billion metric tons of CO2 [1]. This has propelled the automotive industry to renew their focus on lightweighting cars, particularly through the use of crude oil-based structural foams. While these foams offer a unique combination of ultra-lightweighting with adequate strength, they are practically non-renewable, non-biodegradable and contribute to the growing anthropogenic carbon footprint. An alternative paradigm to such foams is the use of biosourced polymers as they offer immense advantages due to their renewable, sustainable and biodegradable nature. Currently, polylactic acid (PLA) remains the most abundant commercially consumed biopolymer, but it suffers from two major drawbacks: its inherent brittle nature and poor melt processability. Blending PLA with an inherently toughened counterpart provides an effective mechanism to overcome both these drawbacks [2]. Additionally, foaming of PLA-based blends can provide a replacement for synthetic structural foams. However, processing of such blended foams is inhibited by challenges associated with structural foam molding with regard to controlling foam microstructure – specifically, cell size and cell density. Additionally, controlled processing of bimodal cell structure has remained elusive with currently used molding parameters and chemical blowing agents. Bimodal cellular distributions are preferred for their superior properties – enhanced toughness and compressive strength, weight reduction, and insulating properties –compared to their unimodal counterparts. This study investigates the effect of material properties and processing parameters on unique cellular distributions of polylactic acid (PLA), polybutylene succinate adipate (PBSA) and their blends processed via supercritical fluid-assisted injection molding. Cell morphology, size and density were determined via scanning electron microscopy, while their influence on mechanical properties was studied using tensile testing. Thermal stability of the blends was studied via differential scanning calorimetry and thermo-gravimetric analyzer. Effect of melt rheology and viscoelastic behavior was studied in an effort to explain the bimodal cellular structure obtained
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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