Papers by Keyword: Aluminium

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Authors: Christina Radlbeck, Mathias Rengstl, Senta Pessel, Martin Mensinger
Abstract: DIN EN 1999-1-3 presents a comprehensive framework for fatigue design of aluminum structures. Various structural details and joints are included. For safety checks against High-Cycle Fatigue, three design concepts are available: Safe-Life-Design, Damage-Tolerant-Design and Design assisted by Testing. Respective safe-life-design lines are based on a databank including results from stress controlled Wöhler fatigue tests. The phenomenon of Low-Cycle-Fatigue (<105 cycles) is treated in Annex F, giving design regulations for selected structural details. Thereby, the influence of different alloys and thus different yield strength values is not considered. In addition, plasticizing effects under high stress ranges are neglected. In general, engineers face the following questions: Which cycle numbers require (Low-Cycle-) fatigue design and thus where is the limit for static design? Furthermore, how to define the maximum allowable stress range? Respective answers are investigated in a current research project carried out by the Chair of Metal Structures, TU Munich.In this contribution, the state of the art of fatigue design according to DIN EN 1999-1-3 is presented. European design concepts are discussed in view of available data and new developments in research, quality control, fabrication of specimen as well as testing techniques. The focus is then laid on Low-Cycle Fatigue. A new concept, including the influence of alloy type and the effects of plasticizing, is worked on. To this purpose an extensive testing program has started, including a large number of strain-controlled-tests.
Authors: Hugo Biscaia, João Cardoso, Carlos Chastre
Abstract: The bonding between two different materials or between same materials is a quite popular method. Unlike fastener joints, it avoids undesirable stress concentrations and doesn't demand an intrusive application to ensure the good performance of the joint. However, depending on the configuration of the adhesively bonded joint, its performance responds differently and the choice (if possible to make) on the best configuration, i.e. the configuration that originates the highest strength and/or stiffness, may be hard to make. Within this context, several configurations of aluminium-to-aluminium bonded joints unstrengthened and strengthened with fiber reinforced polymers (FRP) were modelled using a commercial finite element code. The linearity and nonlinearity of the FRP composite and the aluminium were considered, respectively, and the adhesively bonded joints were subjected to a regular displacement that intended to simulate a tensioning load. Also, the nonlinearities of the interfaces were considered in the form of nonlinear cohesive adhesive laws. The fracture Modes I and II were defined trough a bond-slip relation with a bi-linear shape and the Mohr-Coulomb failure criterion is used for the coupling of the cohesive adhesive laws of the interface when the debonding process of the bonded joint configuration implies the interaction between both fracture modes, i.e. the joint is under a mixed-mode (Mode I+II) situation. The results are presented and discussed and the configurations of the bonded joints are all compared through bond stress distributions and load-slip responses. The study herein presented is, therefore, a contribution to the analysis of the structural integrity of bonded joints between FRP composites and aluminium substrates, helping also on the choice of the most adequate bonded joint configuration and corresponding reinforcement to be used and applied in practice.
Authors: Zhao Liu, Alexander Kraemer, Kai F. Karhausen, Holger Aretz, Marco Teller, Gerhard Hirt
Abstract: Roll bonding is a joining-by-forming process to permanently join two or more layers of different materials by hot or cold rolling. One of the typical industrial applications is aluminium sheets for heat exchangers in automobiles. During roll bonding the layers are fed into the rolling stand with parallel surfaces. Due to the plastic deformation in the roll gap metallic bonds between the layers are achieved. Several theoretical models have been published to describe the process, e.g. Zhang & Bay. These models have mostly been developed for cold rolling and describe the bond strength based on surface enlargement, contact pressure and flow stress. Since these models are developed for cold rolling, they are not temperature depending. Heat exchange is usually neglected and de-bonding after the roll gap is not accounted for. However, for hot roll bonding the above mentioned assumptions do not hold true. To understand the mechanisms of hot roll bonding industrial and laboratory scale investigations have previously been conducted. Based on the findings a FE framework for hot roll bonding was developed. This FE framework accounts for the possibility of de-bonding after the roll gap but is restricted to isothermal conditions. However, for a roll bonding simulation it is essential to take the temperature influence into consideration. Therefore, this paper presents an extended version of the FE framework which accounts for temperature dependent material flow, compatible definition of thermal & mechanical interactions and bonding status related heat exchange. To verify the new features of the extended FE framework a roll bonding test case is employed. Mechanical and thermal interactions as well as the current flow stress are calculated in subroutines in order to enable a fully coupled thermal stress simulation. The results show that with this extended FE framework the influence of non-isothermal conditions on material flow and bonding status as well as the feedback effects of bonding status to heat exchange have been successfully integrated in hot roll bonding simulations. This fully coupled thermal stress simulation is the first step towards multi-pass roll bonding simulations.
Authors: Viktor Alexandrovich Gulevskiy, Pavel Stanislavovich Golovinov, Anna Sergeevna Knyazeva, Nikolay Alexeevich Kidalov
Abstract: The article describes a technology for producing carbon-graphite-aluminium composite by non-autoclave gasless impregnation of a carbon-graphite skeleton by matrix alloy of aluminium and presents the results of testing, application areas and assessment of the properties of obtained composites as well.
Authors: Roberta Nipoti, Alberto Carnera, Giovanni Alfieri, Lukas Kranz
Abstract: The electrical activation of 1×1020 cm-3 implanted Al in 4H-SiC has been studied in the temperature range 1500 - 1950 °C by the analysis of the sheet resistance of the Al implanted layers, as measured at room temperature. The minimum annealing time for reaching stationary electrical at fixed annealing temperature has been found. The samples with stationary electrical activation have been used to estimate the thermal activation energy for the electrical activation of the implanted Al.
Authors: Muhammad Tayyab Naqash, Antonio Formisano, Gianfranco De Matteis
Abstract: Curtain wall systems are considered as envelop of a building, generally made of a lightweight material such as aluminium. The curtain wall façade does not carry any weight from the building, rather it transfers loads that are incident upon it to the main building structure through connections with floors or columns. This paper addresses some key issues in satisfying the respective limit state design checks. Two mullion profiles 85mm and 125mm deep of three manufacturers are analysed showing that the different extrusions of mullion profiles does not have any drastic effect on its structural behavior. Due to the versatility and lightweight, aluminum has many advantages when used as a curtain wall framing material, but it has the distinct disadvantage of being three times more deformable than steel. Therefore, the fulfillment of serviceability limits is an important issue when designing the framing members, in order to avoid damage of connected glasses. Also, the importance of connections and steel insert are highlighted. Finally, some completed and in-progress ALUTEC projects with different curtain wall systems are presented. The paper is therefore interesting for the Façade Engineers involved in the design of curtain walls.
Authors: Vasiliki Ntaskagianni
Abstract: Offshore lifts can be performed by platform cranes, crane vessels, helicopters or modular structures. The challenge of an offshore lift lies in performing it in inaccessible locations on the platform and minimizing the cost and the offshore time. Platform cranes often cannot reach the lifting object, and crane vessels and helicopters provide solutions which increase the operation costs. On the contrary, aluminium modular structures provide solutions which can make a challenging lift efficient and successful without incurring high costs.
Authors: Jean Brice Mandatsy Moungomo, Donatien Nganga Kouya, Victor Songmene
Abstract: The recycling of alumium alloys has been growing in interest and applications during the last fourthy years and has become a cost effective, ecological and reliable way to produce aluminium parts. The aluminium scraps that can be recycled include cans and machining chips. The machining processes produce chips of various sizes and shapes, wet or dry, oxidised or not, depending on type of process and the machining conditions, parameters and tools used. Some processes produce metallic dusts and fine chips while other produce large or medium size chips. In some industries such as mould making and aeronautic industries, the chip removal can easily represent 80% of the initial workpiece mass. The type of chips produced during machining can have a great impact on chip management, on part quality, on machine and tool reliability and on part manufacturing costs. The machining chips can be recycled using casting, sintering or pressing and extrusion processes depending on the goal targeted. The selection of the recycling process must take into account the targeted applications, the chip (composition, sizes and cleanliness) and its mechanical properties. Depending on the nature of process to be used and the machining chip generation conditions, some treatments might be necessary prior to transportation and recycling. Parts made with recycled chips can either be bi-phase metal matrix composites materials or usual one phase material with mechanical properties and wear properties comparable or not to the parent alloys. Over the last decades, several chip recycling processes have been proposed for aluminium alloys. This article review the aluminium chips formation, treatement methods, the recycling processes and their impact on recomposed parts’ performance: strength, ductility, corosion and wear resistances.
Authors: Cyriel Clauwaert
Abstract: In the past five years a number of master’s theses have been conducted at Belgian Technical Colleges and Universities to (re)introduce knowledge of aluminium as a structural material, given that courses offered in Belgium are oriented towards steel and concrete design and no specific course on aluminium exists. The present contribution highlights the different subjects covered in these theses and illustrates the results obtained. Emphasis is placed on the methodology used to design and innovate with aluminium, taking into account the Eurocode rules that apply to the design of specific aluminium structures. For this, appropriate use was made of existing software that allows for the detailed calculation of section reduction and unity checks.
Authors: Petr Urban, Eduardo Sanchez Caballero, Fatima Ternero, Francisco Javier Viña Reina, Francisco Gomez Cuevas
Abstract: This paper focuses on the microstructural characterization of Al25Ti75, Al37Ti63, Al50Ti50, Al63Ti37 and Al75Ti25 powders mixtures prepared by mechanical alloying (MA). The high-energy ball-milling, up to 75 h, of aluminium and titanium powders leads to a nanocrystalline or an amorphous structure. It is showed that a stable amorphous Al–Ti phase with uniform elemental distribution forms after 50 h of milling in Al50Ti50 alloy. Heat treatment of the different alloys leads to the crystallization of AlTi3, AlTi, Al2Ti and Al3Ti intermetallic compounds. A comprehensive study by laser granulometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) was carried out on the structure, surface morphology and thermal behaviour of the MA Al-Ti mixtures, both of milled and heat treated powders.
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