172 research outputs found
Mathematical simulation of pultrusion processes: A review
No full textA review of computational modelling and simulation of pultrusion processes is presented including such aspects as: resin flow and pressure distribution in a forming die; impregnation of reinforcing fibers; heat transfer and resin reaction; pulling force, stresses and strains development; methods for numerical optimization of the process. Development of models provides deeper knowledge concerning the mechanisms behind the process as well as the influence of constituent materials’ properties and manufacturing parameters. Consequently, accelerated development of pultrusion process, allowing for the manufacturing of geometrically complex profiles is promoted
Modeling spring-in of l-shaped structural profiles pultruded at different pulling speeds
No full textCure-induced deformations are inevitable in pultruded composite profiles due to the peculiarities of the pultrusion process and usually require the use of costly shimming operations at the assembly stage for their compensation. Residual stresses formed at the production and assembly stages impair the mechanical performance of pultruded elements. A numerical technique that would allow the prediction and reduction of cure-induced deformations is essential for the optimization of the pultrusion process. This study is aimed at the development of a numerical model that is able to predict spring-in in pultruded L-shaped profiles. The model was developed in the ABAQUS software suite with user subroutines UMAT, FILM, USDFLD, HETVAL, and UEXPAN. The authors used the 2D approach to describe the thermochemical and mechanical behavior via the modified Cure Hardening Instantaneous Linear Elastic (CHILE) model. The developed model was validated in two experiments conducted with a 6-month interval using glass fiber/vinyl ester resin L-shaped profiles manufactured at pulling speeds of 200, 400, and 600 mm/min. Spring-in predictions obtained with the proposed numerical model fall within the experimental data range. The validated model has allowed authors to establish that the increase in spring-in values observed at higher pulling speeds can be attributed to a higher fraction of uncured material in the composite exiting the die block and the subsequent increase in chemical shrinkage that occurs under unconstrained conditions. This study is the first one to isolate and evaluate the contributions of thermal and chemical shrinkage into spring-in evolution in pultruded profiles. Based on this model, the authors demonstrate the possibility of achieving the same level of spring-in at increased pulling speeds from 200 to 900 m/min, either by using a post-die cooling tool or by reducing the chemical shrinkage of the resin. The study provides insight into the factors significantly affecting the spring-in, and it analyzes the methods of spring-in reduction that can be used by scholars to minimize the spring-in in the pultrusion process
Analysis of spring-in deformation in L-shaped profiles pultruded at different pulling speeds: Mathematical simulation and experimental results
No full textPeculiarities of the pultrusionmanufacturing process lead to the occurrence of spring-in deformations, whereas their value depends on the pulling speed. In this article experimental and numerical analysis was carried out for glass fiber/vinyl ester resin 75 × 75 × 6mmL-shaped profiles pultruded at pulling speeds of 200 and 600 mm/min. Spring-in angles of produced profiles were determined on the same day of manufacturing when profiles cooled down to room temperature. Higher pulling speeds provoked increased values of spring-in. 2D numerical model accounting for thermo-chemical and mechanical composite’s behavior during pultrusion was implemented in ABAQUS software. Cure Hardening Instantaneous Linear Elastic (CHILE) constitutive law was used to describe matrix resin Young’s modulus evolution. Since both unidirectional (UD) rovings and fabric material were utilized, effective mechanical properties of UD and fabric layers were calculated in accordance with Self-Consistent Field Micromechanics (SCFM) approach. Spring-in angles determined within experimental and numerical studies were compared and a good correlation was found: the errors were 12.6% and 6% for the pulling speed of 200 and 600 mm/min, respectively
Pultruded materials and structures: A review
No full textCurrently, the application of pultruded profiles is increasing owing to their advantages, such as light weight, high strength, improved durability, corrosion resistance, ease of transportation, speed of assembly, and nonmagnetic/nonconductive characteristics. This review analyzes the main application fields of elements produced by pultrusion manufacturing processes: bridges and bridge decks, cooling towers, building elements and complete building systems, marine construction, transportation, and energy systems. Analysis of the scientific literature in relation to the mechanical behavior of pultruded elements is presented as well. Finally, this review outlines the future study possibilities, giving the researchers and practitioners the directions for deeper investigation of specific features and exploration of new ones concerning the mentioned aspects of pultruded fiber-reinforced polymer composites
Effects of pulling speed on structural performance of L-shaped pultruded profiles
No full textPultrusion is a highly automated process for manufacturing structural composite elements, wherein the produc-tion rate depends on the pulling speed. This study analyzed the influence of pulling speed on the structuralcharacteristics of pultruded glassfiber/epoxy‐vinyl resin 75 × 75 × 6 mm L‐shaped profiles. The profiles werepultruded at three pulling speeds: 200, 400, and 600 mm/min. After fabrication, the spring‐in values of thefabricated profiles were measured; the profiles were examined under a microscope to identify and study theircracking; and the mechanical properties of the pultruded composite were determined. The spring‐in was mea-sured immediately after fabrication and then at intervals of two to three days over a 90‐day period. The spring‐in angle was found to increase with increments in the pulling speed. The profiles produced at the lower pullingspeeds (200 and 400 mm/min) exhibited no significant differences in matrix cracking or mechanical charac-teristics. By comparison, at the high pulling speed (600 mm/min), wherein a large part of the profile is poly-merized after exiting the die, the formation of delamination perpendicular to the matrix cracks was observed.Furthermore, at this pulling speed, there were increased variations in the strength and Young’s modulus valuesand decreased interlaminar shear strength
Investigation on the shape distortions of pultruded profiles at different pulling speed
No full textPultrusion is a continuous technique for manufacturing of polymer composites which combines automation and versatility. The main factors behind the wide application of the process are the enhanced productivity and the remarkable mechanical properties achievable. Nevertheless, the quality of pultruded products dramatically depends on the choice of the process parameters. As a matter of fact, pultrusion presents numerous tunable parameters, such as the temperature of the heating plates or the pulling speed, because most of the polymerization reaction of the resin occurs within the curing-forming die in a short time. Resin shrinkage, thermal contraction and residual internal stresses change the geometry of the profiles after their production. Process related stresses typically result in distortions evolving for months after the process, which can lead to out of geometrical tolerances. The present paper discusses an experimental/numerical investigation of the shape distortions of L-shaped profiles made of epoxy-based resin reinforced with E-glass rovings and unidirectional glass fabrics. The samples were pultruded at three different pulling speeds, namely 200, 400 and 600 mm/min. For each of them, the spring-in angle was periodically measured for the 90 days following production. The results show the dependence of the shape distortions on pulling speed and on time
Fine Line Metallization of Silicon Heterojunction Solar Cells via Collimated Aerosol Beam Direct Write
No full textSolar energy has come to the forefront as a scalable and largely underutilized renewable energy resource. The current cost of solar electricity, namely from photovoltaics, along with other logistics factors, has prevented the widespread adaptation of the technology. A key determinant of efficiency and cost for a solar cell is the current collector grid. This work presents the Collimated Aerosol Beam Direct Write (CAB-DW) system as a non-contact printing method that can achieve current collector grid finger widths of less than 10 ?m which are amenable to decreasing both resistive and optical losses. The ability to produce high aspect ratio grid fingers, and deposit optimized grid structures on high efficiency SHJ solar cells using silver nanoparticle inks is also demonstrated. A decrease in shadowing and via profile modification of the grid fingers is presented, along with a study of aging and degradation of electrical properties within silver nanoparticle inks
Les études in Ising field theory and related problems
No full textThe main subject of this thesis is the Ising field theory, the field theory describing the scaling limit of the two-dimensional Ising model near its critical point. We study the Ising field theory in low- and high-temperature regimes.
In the low-temperature regime we address questions related to the mass spectrum of the bound states that exist in the theory. The overall goal is to study analytic properties of the masses taken as functions of the scaling variable in the theory. At this stage, we are primarily interested in the asymptotic series in the coupling parameter. We describe methods used for developing expansions in the coupling parameter when this parameter is sufficiently small. This gives rise to the low-energy and semiclassical series. Methods developed are then applied to a different model, a model that has many things in common with the Ising field theory, the two-dimensional quantum chromodynamics with infinite number of colors, also known as the ‘t Hooft model.
In the second part of the thesis we turn to the Ising field theory in the high- temperature regime. Here we study the problem of scattering in a weak magnetic field. We compute the leading perturbative correction to the scattering amplitude for the 2 -> 2 process. This is done first by means of standard methods based on the direct intermediate-state decomposition and dispersion relations. Then we compute the large energy asymptotic of the amplitude for this process directly using a known relation between the Ising field theory at zero magnetic field and classical sinh-Gordon equation. We obtain consistent results that show the logarithmic growth of the amplitude with energy at this order in magnetic field. Going beyond the leading order we argue that at large energies for a sufficiently weak magnetic field the amplitude exhibits a power-like decay.Ph.D.Includes bibliographical referencesIncludes vitaby Iskander Ziyatdino
The goatibex constellation of Fazil Iskander: translation and commentary
No full textFazil Iskander (1929- ) é um dos mais representativos escritores soviéticos remanescentes da geração do degelo. Devido ao desconhecimento deste autor no Brasil, este trabalho consiste na tradução da novela que lhe deu notoriedade, precedida por uma apresentação e comentário: Sozvezdie Kozlotura, em português, A constelação do capriuro, de 1966. Apesar de pertencer à tradição satírica russa, junto a nomes como Nikolai Gógol e Mikhail Bulgákov, a prosa de Iskander carrega as singularidades da sua origem não-russa. A sua terra natal, a Abkházia, com a sua história e costumes, além de reverberarem na obra do autor, entrecruzam-se com a cultura russo-soviética numa relação complexa que dá às suas narrativas um caráter único. Neste trabalho, foram analisados os elementos que tornam a sátira de Iskander tão inovadora.Fazil Iskander (1929- ) is one of the most representative remaining writers of the Thaw Generation. Due to the lack of recognition of this author in Brazil, the present dissertation consists in the translation of the short-novel that has made him internationally renowned, preceded by a presentation and commentary: Sozvezdie Kozlotura from 1966, or A constelação do Capriuro in Portuguese. Though the prose of Iskander belongs to the Russian satire tradition, along with names like Nikolai Gogol and Mikhail Bulgakov, it carries the singularities of his non-Russian origin. His motherland, Abkhazia, with its proper history and customs, besides reverberating on his works, entwines itself with the Russian-soviet culture in a complex and tense relationship that gives these narratives their unique nature. In this research, it is analyzed the characteristics that make the satire of Iskander so innovative
COMPARATIVE ANALYSIS OF THE STORIES "YESTERDAY" BY NURALI KABUL AND "THE POET" BY FAZIL ISKANDER
No full textThe article provides a comparative analysis of the stories of the Uzbek writer Nurali Kabul "Yesterday" and the Abkhaz author Fazil Iskander "The Poet". The research is aimed at identifying common and different artistic principles of the two writers, belonging to different national literatures, but united by a common humanistic worldview. moral choice and the role of the individual in the socio-cultural context. The author comes to the conclusion that the works of Kabul and Iskander demonstrate similarities in the desire to assert the value of spiritual freedom and moral purity of a person
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