1,723,203 research outputs found
Multiphysics simulation of thermoplastic polymer crystallization
Full text linkThe main goal of the presented work is to implement a robust framework for the computation of the crystallization kinetics of semi-crystalline thermoplastics by using a multiscale approach. The purpose of multiscale modeling is to assess parameters influencing microstructure formation that would otherwise require very time-consuming analysis with experiments. The numerical method, crystallization kinetics and their implementation into numerical software operating at macro- and micro-scale are described as well as the experimental data needed to prepare and validate numerical results
Multiscale simulation to predict microstructure dependent effective elastic properties of an injection molded polypropylene component
Full text linkIndustrial plastic parts, made of semi-crystalline polymers, are often produced by injection molding. In this process the melt undergoes a complex deformation and cooling history which results in an inho- mogeneous distribution of spherulites in the component. The different size and shape of the spherulites induce local variations of the elastic properties in the final part. To evaluate these inhomogeneities in an isotactic polypropylene (α-iPP) component accurately, a 3D multi-scale, integrated simulation approach has been developed. At first, a coupled mold filling and heat transfer analysis is achieved at the macro- scale and the predicted velocity and temperature fields are transferred to the micromodel. Then, a 3-D microstructure evolution model is developed, where the nucleation of spherulite germs and their growth are described. To evaluate their effective mechanical properties a two-level homogenization scheme has been adopted. At the nano-scale, the effective properties of the lamella build of crystalline and amor- phous phases are determined. In this study, not only the radial growing lamella of amorphous and crys- talline phases is homogenized, but also its “cross hatched” lamellar structure. At the micro-scale, the spherulite microstructure is homogenized via a 3D radial distribution of equivalent lamellae around its mono-crystal center. Finally, the application of the developed homogenization scheme allows the pre- diction of the distribution of effective mechanical properties over the component thickness in different sections of the staggered component
Simulation of crystallization of isotactic polypropylene with different shear regimes
Full text linkFlow induced crystallization is an important process during polymer solidification because it strongly influences the material morphology and properties. The melt of isotactic polypropylene crystallizes slowly in isothermal conditions whereas shear conditions speed up the crystallization process. The main objective of the presented research is the investigation of the shear-induced crystallization of isotactic polypropylene through a comparative analysis between isothermal and non-isothermal conditions in different shear regimes. A numerical simulation of crystallization kinetics of semicrystalline thermoplastics with a multiscale model is proposed to evaluate the nucleation and growth of spherulites, after identifying the material parameters needed to connect crystallization kinetics to the molecular material properties. This model is validated by using data from differential scanning calorimetry (DSC) and a rotational rheometry (RHEO)
Analysis of polymer crystallization with a multiscale modeling approach
No full textThe main objective of the presented work is to describe the crystallization kinetics of semi-crystalline thermoplastics with a multiscale model implemented into the COMSOL software and the in-house developed code SphäroSim. The filling and cooling simulations, implemented by using the computational fluid dynamics (CFD) and heat transfer (HT) modules of COMSOL, require the simultaneous solution of non-Newtonian multi-phase flow (polymer/air) and thermal fields in non-isothermal condition and transient regime. The simulation results are collected, converted into the OpenSource file format VTK (Visualization Toolkit) and transferred to the SphäroSim code after a matching operation with the COMSOL mesh. The SphäroSim code uses COMSOL results as input data to compute crystallization kinetics, using the COMSOL data as boundary conditions in the microstructure simulation. This allows the time resolved calculation of the crystallization process and a prediction of the final microstructure in the part which can be used in further simulations such as a structural analysis. The analytical parameters needed to connect crystallization kinetics with molecular material properties and applying the analytical scheme to the numerical simulation during filling and cooling in an injection moulding process are identified
Thermal simulation of polymer crystallization during post-filling
No full textCrystallization from polymer melt is one of the most fundamental phenomena of material phase transformations. The possibility of controlling crystallization kinetics is essential to achieve the proper polymer microstructure and consequently obtain desired material properties, reducing undesired effects such as excessive anisotropy of shrinkage, warpage and insufficient dimensional accuracy. Due to the high transformation rate, the experimental analysis of crystallization is critical. For this reason, it is more convenient to evaluate this phenomenon by using a finite element commercial software under several testing and processing conditions. The work investigates the crystallization evolution in post-filling, mainly induced by thermal gradients, and its effect on the final properties of an injection molding part. The numerical scheme, crystallization models and their implementation into commercial software are described as well as the experimental data for isotactic Polypropylene
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
Crystallization of isotactic polypropylene in different shear regimes
No full textThe investigation of the shear-induced crystallization of isotactic polypropylene in isothermal conditions in different shear regimes is the aim of the present research. A multiscale framework is developed and implemented to compute the nucleation and growth of spherulites, based on material parameters needed to connect crystallization kinetics to the molecular material properties. The framework consists of a macro-model based on a Finite Element Method linked to a micro-model based on Cellular Automata. The main results are the evolution of the crystallization degree and spherulite space filling as a function of imposed temperature ash shear rate
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
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