No description available.

The effects of packaging treatments, post harvest cooling delay and storage duration on color, texture, ascorbic acid content, weight loss and glucosinolate retention in crown-cut heads of broccoli were studied. Oxygen and CO2 levels inside shrink wrap packages were also monitored. Shrink wrap packaging had a significant positive effect on hue angle (p<0.05). Packaging and post harvest cooling delay had no effect on hue difference and total color difference. While post harvest cooling delay had no effect on texture, crown-cut heads of broccoli stored in shrink wrap packaging retained firmness significantly better than ice packaged heads of broccoli (p<0.05). Ascorbic acid was retained better in broccoli held in shrink wrap packages and cooling delay had a significant negative influence on ascorbic acid content (p<0.05). Packaging and post harvest cooling delay had a significant positive effect on weight loss (p<0.05). Broccoli stored in shrink wrap film lost about 3.7% of original weight while ice packaging resulted in about 17.4% weight loss (p<0.05). No consistent trends were observed in the levels of O2 and CO2 inside shrink wrap packages. An important glucosinolate, glucoraphanin was retained significantly better in shrink wrapped heads (p<0.05). Between two cultivars, shelf life of cv.Gypsy was better than cv.Everest with respect to color, ascorbic acid retention and weight loss. But cv.Everest retained texture (firmness) better after 35 days of storage. Overall results indicate that shrink wrap packaging and shorter post harvest cooling delays protect quality of broccoli. / Master of Science

The current assembly procedure to install a trunnion and hub into a bascule bridge girder involves cooling the trunnion in liquid nitrogen and shrink fitting it into the hub. The resulting trunnion-hub assembly is then allowed to warm to room temperature. Next, the trunnion-hub assembly is cooled in the liquid nitrogen and shrunk fit into the girder. The cooling of the trunnion does not cause any problems, however, when the trunnion-hub assembly is cooled in the liquid nitrogen, the hub experiences a large thermal shock. These thermal shocks induce large stresses into the hub, which has been known to cause it to crack. This study investigates an innovative assembly procedure to install the trunnion-hub assembly into a bascule bridge girder. To avoid cooling the trunnion-hub assembly, the girder was heated instead. Laboratory testing and finite element analysis were used to determine if the girder could reasonably be heated to install the trunnion-hub assembly. An experiment was conducted to analyze the heating process that will be used. A rectangular steel plate ( 60"x60x"0.75") was used to model the girder in the lab. Inductance-heating coils were used to heat the steel plate to 350°F. The heating process was recorded using a data acquisition system with thermocouples and strain gages. ANSYS was the finite element analysis (FEA) program that was used to model the heating process of the plate. The FEA results from ANSYS were compared with the experimental results. This confirmed the parameters of the finite element analysis were correct. Those parameters were then used to model a full-scale girder. The feasibility of heating the girder was determined from the finite element analysis results. It was determined that heating the girder with 2250 BTU over min for 90 minutes, was sufficient energy for the assembly procedure to work. The girder was heated to a maximum temperature of 350°F and a 0.015" clearance was created for the assembly of the trunnion-hub. The finite element analysis of the girder showed that the placement of the heating coils on the girder was critical. Therefore this innovative assembly procedure can easily be accomplished, however, each girder must first be analyzed to determine the optimal heating configuration.

Expansive soils are a worldwide problem especially in the regions where climate is arid or semi arid. These soils swell when they are exposed to water and shrink when they dry. Cyclic swelling and shrinkage of clays and associated movements of foundations may result in cracking of structures. Several methods are used to decrease or prevent the swelling potential of such soils like prewetting, surcharge loading, chemical stabilization etc. Among these, one of the most widely used method is using chemical admixtures (chemical stabilization). Cyclic wetting and drying affects the swell &ndash / shrink behaviour of expansive soils. In this research, the effect of cyclic swell &ndash / shrink on swell percentage of a chemically stabilized expansive soil is investigated. Class C Fly Ash is used as an additive for stabilization of an expansive soil that is prepared in the laboratory environment by mixing kaolinite and bentonite. Fly ash was added to expansive soil with a predetermined percentage changing between 0 to 20 percent. Hydrated lime with percentages changing between 0 to 5 percent and sand with 5 percent were also used instead of fly ash for comparison. Firstly, consistency limits, grain size distributions and swell percentages of mixtures were determined. Then to see the effect of cyclic swell &ndash / shrink on the swelling behavior of the mixtures, swell &ndash / shrink cycles applied to samples and swell percentages were determined. Swell percentage decreased as the proportion of the fly ash increased. Cyclic swell-shrink affected the swell percentage of fly ash stabilized samples positively.

No description available.

Pressverbindungen gehören zu den klassischen Maschinenelementen und werden insbesondere in der Antriebstechnik häufig eingesetzt. Zur sicheren und zugleich wirtschaftlichen Auslegung derartiger Verbindungen unter zyklischen Lasten fehlen generell gültige sowie abgesicherte normative Vorgaben bzw. Richtlinien für den Anwender. Insbesondere ist dies dann zutreffend, wenn Geometrien vorkommen, für welche keine Tabellen- bzw. Erfahrungswerte existieren. In dieser Arbeit werden ausführliche experimentelle Untersuchungen zur Ermüdungsfestigkeit von Pressverbindungen einer Standardgeometrie vorgestellt. Im Fokus der Untersuchungen steht die Dauer-, Zeit- und Betriebsfestigkeit der biege- sowie torsionsbelasteten Verbindung. Auf Basis der erzielten Festigkeiten und Lebensdauerwerte erfolgt die Ableitung normspezifischer Kennwerte für die Praxis. Weiterhin steht die Übertragung der erzielten Ergebnisse auf andere Pressverbindungs-Geometrien, wie beispielsweise die Verbindung mit Wellenabsatz, im Vordergrund. Hierbei wird das Verhalten hinsichtlich der Kerbwirkung im Vergleich zu gekerbten Wellen sowie zu anderen reibdauerbeanspruchten Verbindungen untersucht. Zudem erfolgt eine ausführliche Analyse simulationsspezifischer Einflussgrößen auf die Beanspruchungshöhe der Pressverbindung. Auf Grundlage dieser Erkenntnisse wird ein neues Auslegungskonzept erarbeitet und an Ergebnissen aus der Literatur gespiegelt.

The McTronX research group at the North–West University designs and develops Active Magnetic Bearings (AMBs). The group’s focus shifted to the design and development of AMB supported drive systems. This includes the electromagnetic and mechanical design of the electric machine, AMBs, auxiliary bearings as well as the development of the control system. The research group is currently developing an AMB supported high speed Induction Machine (IM) drive system that will facilitate tests in order to verify the design capability of the group. The research presented in this thesis describes the mechanical design and manufacturing of a high speed IM rotor section. The design includes; selecting the IM rotor topology, material selection, detail stress analysis and selecting appropriate manufacturing and assembly procedures. A comprehensive literature study identifies six main design considerations during the mechanical design of a high speed IM rotor section. These considerations include; magnetic core selection, rotor cage design, shaft design, shaft/magnetic core connection, stress due to operation at elevated temperatures and design for manufacture and assemble (DFMA). A critical overview of the literature leads to some design decisions being made and is used as a starting point for the detail design. The design choices include using a laminated cage rotor with a shrink fit for the shaft/magnetic core connection. Throughout the detail design an iterative process was followed incorporating both electromagnetic and mechanical considerations to deliver a good design solution. The first step of the iterative design process was, roughly calculating the material strengths required for first iteration material selection followed by more detailed interference fit calculations. From the detail stress analysis it became apparent that the stress in the IM rotor section cannot be calculated accurately using analytical methods. Consequently, a systematically verified and validated Finite Element Analysis (FEA) model was used to calculate the interferences required for each component. The detail stress analysis of the assembly also determined the allowable manufacturing dimensional tolerances. From the detail stress analysis it was found that the available lamination and squirrel cage material strengths were inadequate for the design speed specification of 27,000 r/min. The analysis showed that a maximum operating speed of 19,000 r/min can be achieved while complying with the minimum factor of safety (FOS) of 2. Each component was manufactured to the prescribed dimensional tolerances and the IM rotor section was assembled. With the failure of the first assembly process, machine experts were consulted and a revised process was implemented. The revised process entailed manufacturing five small lamination stacks and assembling the stack and squirrel cage afterwards. The end ring/conductive bar connection utilises interference fits due to the fact that the materials could not be welded. The process was successful and the IM rotor section was shrink fitted onto the shaft. However, after final machining of the rotor’s outer diameter (OD), inspections revealed axial displacement of the end rings and a revised FEA was implemented to simulate the effect. The results indicated a minimum FOS 0.6 at very small sections and with further analytical investigation it was shown that the minimum FOS was reduced to only 1.34. Although the calculations indicated the FOS was below the minimum prescribed FOS ? 2, the rotor spin tests were scheduled to continue as planned. The main reasons being that the lowest FOS is at very small areas and is located at non critical structural positions. The fact that the rotor speed was incrementally increased and multiple parameters were monitored, which could detect early signs of failure, further supported the decision. In testing the rotor was successfully spun up to 19,000 r/min and 27 rotor delevitation test were conducted at speeds of up to 10,000 r/min. After continuous testing a secondary rotor inspection was conducted and no visible changes could be detected. The lessons learnt leads to mechanical design and manufacturing recommendations and the research required to realise a 27,000 r/min rotor design. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2011.

The McTronX research group at the North–West University designs and develops Active Magnetic Bearings (AMBs). The group’s focus shifted to the design and development of AMB supported drive systems. This includes the electromagnetic and mechanical design of the electric machine, AMBs, auxiliary bearings as well as the development of the control system. The research group is currently developing an AMB supported high speed Induction Machine (IM) drive system that will facilitate tests in order to verify the design capability of the group. The research presented in this thesis describes the mechanical design and manufacturing of a high speed IM rotor section. The design includes; selecting the IM rotor topology, material selection, detail stress analysis and selecting appropriate manufacturing and assembly procedures. A comprehensive literature study identifies six main design considerations during the mechanical design of a high speed IM rotor section. These considerations include; magnetic core selection, rotor cage design, shaft design, shaft/magnetic core connection, stress due to operation at elevated temperatures and design for manufacture and assemble (DFMA). A critical overview of the literature leads to some design decisions being made and is used as a starting point for the detail design. The design choices include using a laminated cage rotor with a shrink fit for the shaft/magnetic core connection. Throughout the detail design an iterative process was followed incorporating both electromagnetic and mechanical considerations to deliver a good design solution. The first step of the iterative design process was, roughly calculating the material strengths required for first iteration material selection followed by more detailed interference fit calculations. From the detail stress analysis it became apparent that the stress in the IM rotor section cannot be calculated accurately using analytical methods. Consequently, a systematically verified and validated Finite Element Analysis (FEA) model was used to calculate the interferences required for each component. The detail stress analysis of the assembly also determined the allowable manufacturing dimensional tolerances. From the detail stress analysis it was found that the available lamination and squirrel cage material strengths were inadequate for the design speed specification of 27,000 r/min. The analysis showed that a maximum operating speed of 19,000 r/min can be achieved while complying with the minimum factor of safety (FOS) of 2. Each component was manufactured to the prescribed dimensional tolerances and the IM rotor section was assembled. With the failure of the first assembly process, machine experts were consulted and a revised process was implemented. The revised process entailed manufacturing five small lamination stacks and assembling the stack and squirrel cage afterwards. The end ring/conductive bar connection utilises interference fits due to the fact that the materials could not be welded. The process was successful and the IM rotor section was shrink fitted onto the shaft. However, after final machining of the rotor’s outer diameter (OD), inspections revealed axial displacement of the end rings and a revised FEA was implemented to simulate the effect. The results indicated a minimum FOS 0.6 at very small sections and with further analytical investigation it was shown that the minimum FOS was reduced to only 1.34. Although the calculations indicated the FOS was below the minimum prescribed FOS ? 2, the rotor spin tests were scheduled to continue as planned. The main reasons being that the lowest FOS is at very small areas and is located at non critical structural positions. The fact that the rotor speed was incrementally increased and multiple parameters were monitored, which could detect early signs of failure, further supported the decision. In testing the rotor was successfully spun up to 19,000 r/min and 27 rotor delevitation test were conducted at speeds of up to 10,000 r/min. After continuous testing a secondary rotor inspection was conducted and no visible changes could be detected. The lessons learnt leads to mechanical design and manufacturing recommendations and the research required to realise a 27,000 r/min rotor design. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2011.

Le procédé de rétreint fait partie de la famille des techniques de mise en forme sans enlèvement de matière. La déformation du lopin est obtenue par chocs successifs d'un ensemble de matrices disposées autour de la pièce. Ce procédé est généralement utilisé pour la réduction de section de tubes ou de barres. Dans un contexte industriel, la maîtrise des paramètres procédé et la compréhension des phénomènes sous-jacents est indispensable pour non seulement limiter le temps de développement de nouveaux produits mais aussi diminuer le nombre de rebus des références qui posent problème. L'objectif de la thèse est de répondre à ces attentes en exploitant les possibilités offertes par la simulation numérique. Dans un premier temps, les alliages étudiés ont été caractérisés mécaniquement. En effet grâce à des essais de traction et d'impact de Taylor et à l'emploi d'une méthode d'identification par analyse inverse, les paramètres de la loi d'écoulement de Johnson-Cook ont été déterminés. Dès lors différents modèles, utilisant le code Abaqus/Explicit, ont été mis en place (du 2D axisymétrique au 3D en passant des modèles en reprenant que le quart de la pièce) et la validation s'est faite grâce à des campagnes d'essais réalisés sur site. Enfin, un progiciel développé en C++ sera livré à l'industrie. Il intègre différentes fonctionnalités comme la prédiction des efforts de forge par calcul analytique. Tous ces outils numériques et analytiques ont permis de mieux comprendre le procédé en termes de chemin d'écoulement de la matière, de distribution des contraintes et déformations et de profil d'évolution d'évolution de l'effort tout au long de la mise en forme. ABSTRACT : The shrinking process is part of the family of formatting techniques without removing material. / The shrinking process is part of the family of formatting techniques without removing material.

Vor allem in gasisolierten Schaltanlagen und Leitungen werden zylindrische Leiter aus Aluminium mit großen Durchmessern für den Energietransport eingesetzt. Um die Leiter mit anderen Bauteilen zu verbinden, werden i. d. R. lösbare Steckverbindungen mit federnden Kontaktelementen genutzt. Es ist zu prüfen, ob die Steckverbindungen in vielen Fällen durch nicht lösbare stromführende Verbindungen ersetzt werden können. Dadurch soll vorrangig die Kosten- aber auch die Energieeffizienz sowie die Zuverlässigkeit der gasisolierten Anlagen erhöht werden. Betriebserfahrungen lagen für diese Verbindungen bisher nicht vor. Deshalb ist zuerst sicherzustellen, dass diese, über die Lebenszeit der Anlagen von mehreren Jahrzehnten Dauerströme im Kiloampere-Bereich langzeitstabil führen können. Um nicht lösbare stromführende Verbindungen mit zylindrischen Leitern aus Aluminium herzustellen, können verschiedene Fügetechnologien eingesetzt werden. Im Rahmen der Arbeit werden das Längs- und Querpressen sowie das elektromagnetische Umformen zum Herstellen nicht lösbarer Verbindungen betrachtet. Das elektrische Kontakt- und Langzeitverhalten, der mit diesen Fügetechnologien hergestellten Verbindungen, wurde bisher nur unzureichend untersucht. Es wurde daher das elektrische Kontaktverhalten der zylindrischen Verbindungen abhängig von verschiedenen Fügeparametern experimentell ermittelt. Aus den Ergebnissen wurden Empfehlungen zur Vorbehandlung und zum Fügevorgang beim Längs- und Querpressen sowie zur Form der Innenteile beim elektromagnetischen Umformen erarbeitet. Mit mechanischen Modellen auf Basis der Finite-Elemente-Methode wurde der Fügevorgang beim Längs- und Querpressen nachgebildet. Ein Zusammenhang zwischen dem Kraftschluss in den Verbindungen und dem ermittelten Kontaktverhalten der Verbindungen konnte damit hergestellt werden. Um das elektrische Langzeitverhalten der Verbindungen zu bewerten, wurden diese bei thermischer und elektrisch-thermischer Belastung unter normaler Atmosphäre für eine Zeit von mindestens 20.000 h untersucht. Dabei zeigten die Verbindungen mit unbeschichteten Kontaktpartnern, im Gegensatz zu Verbindungen mit einem silberbeschichteten und einem unbeschichteten Kontaktpartner, ein sehr stabiles Langzeitverhalten. Die sehr große scheinbare Kontaktfläche und die relativ geringe mittlere mechanische Spannung sind für die untersuchten zylindrischen Verbindungen charakteristisch. Mit dem Kontaktwiderstandsbelag wurde ein elektrisches Vergleichs- und Bewertungskriterium für kraftschlüssige Flächenkontakte eingeführt. Es konnte gezeigt werden, dass das Kontaktverhalten quergepresster Verbindungen mit dem von Stromschienen mit deutlich kleinerer Kontaktfläche bei homogener Verteilung der Kontaktkraft vergleichbar und somit skalierbar ist.:1 Einleitung 2 Theorie zum stromführenden Verbinden von zylindrischen Leitern 2.1 Lösbares Verbinden 2.2 Nicht lösbares Verbinden 2.3 Kontakt- und Langzeitverhalten 3 Fügetechnologien für zylindrische Leiter 3.1 Pressen 3.1.1 Längspressen 3.1.2 Querpressen 3.1.3 Auslegen von längs- und quergepressten Verbindungen nach DIN 7190-1 3.2 Elektromagnetisches Umformen 4 Aufgabenstellung 5 Elektrisches Kontaktverhalten von Verbindungen mit zylindrischen Leitern 5.1 Vorbetrachtungen 5.1.1 Messen der Kontakt- und Verbindungswiderstände 5.1.2 Genauigkeit der Widerstandsmessung mit dem Mikroohmmeter 5.2 Fügen der Verbindungen 5.2.1 Längspressen 5.2.2 Querpressen 5.2.3 Elektromagnetisches Umformen 5.3 Experimentelle Untersuchungen 5.3.1 Einfluss der Vorbehandlung beim Längs- und Querpressen auf den Widerstand 5.3.2 Anfangswert des Widerstands nach dem Fügen 5.3.3 Charakterisieren der Eigenschaften der Kontaktflächen 5.4 Berechnen des Fügevorgangs von längs- und quergepressten Verbindungen 5.4.1 FE-Modell der Fügeprozesse 5.4.2 Materialmodell und Materialverhalten der eingesetzten Leiterwerkstoffe 5.4.3 Qualitatives Verifizieren der FEM-Berechnungen 5.4.4 Kontaktkraft und mechanische Spannung in der Kontaktfläche 5.5 Metallographische Untersuchungen 6 Langzeitverhalten von Verbindungen mit zylindrischen Leitern 6.1 Versuche im Wärmeschrank 6.1.1 Versuchsaufbau und -durchführung 6.1.2 Versuchsergebnisse 6.2 Versuche bei Belastung mit Wechselstrom 6.2.1 Versuchsaufbau und -durchführung 6.2.2 Versuchsergebnisse 6.3 Zusammenfassung der Untersuchungen zum Kontakt- und Langzeitverhalten von Verbindungen mit zylindrischen Leitern 7 Verbindungen mit zylindrischen Leitern im Vergleich zu anderen Flächenkontakten 7.1 Bestimmen eines Bewertungs- und Vergleichskriteriums 7.2 Einfluss der erhöhten mechanischen Spannungen im Randbereich auf das elektrische Kontaktverhalten zylindrischer Verbindungen 7.3 Versuche bei flächiger Krafteinwirkung 8 Zusammenfassung und Ausblick 9 Literaturverzeichnis 10 Bildverzeichnis 11 Tabellenverzeichnis Anhang / Especially in Gas Insulated Switchgears and Gas Insulated Lines (GIS/GIL), cylindrical aluminum conductors with huge diameters are used for transportation of energy. To connect the conductors with other parts of the system, separable connections with contact elements are the common and most used solution. In many cases, the separable connections can be replaced with permanent connections in order to reduce costs as well as operating power losses and to increase the reliability. Until now, there had been no data of operating experience for these connections. Therefore a stable long-term behavior of the connections during the projected lifetime of the assets needs to be ensured. Different joining technologies can be used to set up these permanent electrical connections with cylindrical aluminum conductors. This work focuses on the press- and shrink-fit technology as well as the electromagnetic forming. Until now the electrical contact- and long-term behavior of connections joined through these technologies had not yet been sufficiently investigated. Therefore, the electrical contact behavior of the cylindrical connections was determined experimentally regarding different joining parameters. From these results, recommendations for the pretreatment and the joining processes when using press- and shrink-fit technologies as well as suggestions regarding the shape of the inserts when using electromagnetic forming were derived. Mechanical models based on the finite element method were used to calculate the joining processes of the press- and shrink-fit technologies. Through these models, a relation between the contact force and the contact behavior of the connections could be established. To evaluate the electrical long-term behavior, the connections were investigated under thermal- and electrical-thermal load for a minimum of 20,000 h within normal atmosphere. As a result, the connections with uncoated contact partners showed very stable long-term behavior compared to those connections with one silver-plated and one uncoated contact partner. Typical for the investigated cylindrical connections are the very large apparent contact area and the comparatively low average mechanical stress. The resistance of contact layer was established as an electrical criteria to compare and evaluate force closure based connections. It could be shown that the contact behavior of shrink-fit connections is comparable to that of joints with busbars, loaded with a homogenous distributed contact force, which have much smaller contact areas. The contact behavior is therefore scalable.:1 Einleitung 2 Theorie zum stromführenden Verbinden von zylindrischen Leitern 2.1 Lösbares Verbinden 2.2 Nicht lösbares Verbinden 2.3 Kontakt- und Langzeitverhalten 3 Fügetechnologien für zylindrische Leiter 3.1 Pressen 3.1.1 Längspressen 3.1.2 Querpressen 3.1.3 Auslegen von längs- und quergepressten Verbindungen nach DIN 7190-1 3.2 Elektromagnetisches Umformen 4 Aufgabenstellung 5 Elektrisches Kontaktverhalten von Verbindungen mit zylindrischen Leitern 5.1 Vorbetrachtungen 5.1.1 Messen der Kontakt- und Verbindungswiderstände 5.1.2 Genauigkeit der Widerstandsmessung mit dem Mikroohmmeter 5.2 Fügen der Verbindungen 5.2.1 Längspressen 5.2.2 Querpressen 5.2.3 Elektromagnetisches Umformen 5.3 Experimentelle Untersuchungen 5.3.1 Einfluss der Vorbehandlung beim Längs- und Querpressen auf den Widerstand 5.3.2 Anfangswert des Widerstands nach dem Fügen 5.3.3 Charakterisieren der Eigenschaften der Kontaktflächen 5.4 Berechnen des Fügevorgangs von längs- und quergepressten Verbindungen 5.4.1 FE-Modell der Fügeprozesse 5.4.2 Materialmodell und Materialverhalten der eingesetzten Leiterwerkstoffe 5.4.3 Qualitatives Verifizieren der FEM-Berechnungen 5.4.4 Kontaktkraft und mechanische Spannung in der Kontaktfläche 5.5 Metallographische Untersuchungen 6 Langzeitverhalten von Verbindungen mit zylindrischen Leitern 6.1 Versuche im Wärmeschrank 6.1.1 Versuchsaufbau und -durchführung 6.1.2 Versuchsergebnisse 6.2 Versuche bei Belastung mit Wechselstrom 6.2.1 Versuchsaufbau und -durchführung 6.2.2 Versuchsergebnisse 6.3 Zusammenfassung der Untersuchungen zum Kontakt- und Langzeitverhalten von Verbindungen mit zylindrischen Leitern 7 Verbindungen mit zylindrischen Leitern im Vergleich zu anderen Flächenkontakten 7.1 Bestimmen eines Bewertungs- und Vergleichskriteriums 7.2 Einfluss der erhöhten mechanischen Spannungen im Randbereich auf das elektrische Kontaktverhalten zylindrischer Verbindungen 7.3 Versuche bei flächiger Krafteinwirkung 8 Zusammenfassung und Ausblick 9 Literaturverzeichnis 10 Bildverzeichnis 11 Tabellenverzeichnis Anhang