Thermo-mechanical forming of Al-Mg-Si Sheet

In warm forming of aluminum sheet, the temperature and strain rates vary considerably. In simulations, the material\ud model must be capable to predict stresses within this wide range. Here, the physically based Nes model is used to describe\ud the behavior of AA6061-T4 sheet material under warm forming conditions. A significant change of earing behavior is\ud found between room temperature and 250 ºC. Crystal plasticity calculations showed a reasonable correspondence of\ud changing r-values if extra slip systems are considered at high temperatures. Satisfactory results are obtained for simulation\ud of tensile tests and cylindrical deep drawing

Mechanical and forming properties of AA6xxx sheet from room to warm temperatures

The influence of temperature on the mechanical behaviour of the heat treatable Aluminium alloy EN AW-6061 has been investigated with a series of tensile tests. It is found that temperature has an effect on both the storage of dislocations and dynamic recovery. The results have been used to fit the dislocation based Nes work-hardening model. Simulations show that the model captures properly the dependence of yield stress and work-hardening rate with temperature and temper. The work-hardening model has been implemented into the Dieka FEM to simulate the warm deep drawing of cylindrical cups. Comparison of the simulated and experimental punch force and cup thickness reveals a good correspondence and validates the proposed modelling approach

Thermo-mechanical Forming of Al–Mg–Si Alloys: Modeling and Experiments

In an ongoing quest to realize lighter vehicles with improved fuel efficiency, deformation characteristics of the material AA 6016 is investigated. In the first part of this study, material behavior of Al–Mg–Si sheet alloy is investigated under different process (temperature and strain rate) and loading (uniaxial and biaxial) conditions experimentally. Later, warm cylindrical cup deep drawing experiments were performed to study the effect of various parameters on warm forming processes, such as the effect of punch velocity, holding time, temper and temperature on force-displacement response. The plastic anisotropy of the material which can be directly reflected by the earing behavior of the drawn cups has also been studied. Finite element simulations can be a powerful tool for the design of warm forming processes and tooling. Their accuracy will depend on the availability of material models that are capable of describing the influence of temperature and strain rate on the flow stresses. The physically based Nes model is used to describe the influence of temperature and strain rate and the Vegter yield criterion is used to describe the plastic anisotropy of the sheet. Experimental drawing test data are used to validate the modeling approaches

Effect of temperature on anisotropy in forming simulations of aluminum alloys

A combined experimental and numerical study of the effect of temperature on anisotropy in warm forming of AA 6016-T4 aluminum was performed. The anisotropy coefficients of the Vegter yield function were calculated from crystal plasticity models with an adequate combination of extra slip systems. Curve fitting was used to fit the anisotropy coefficients calculated at discrete temperatures. This temperature dependent constitutive model was successfully applied to the coupled thermo-mechanical analysis of deep drawing of aluminum sheet and results were compared with experiments

Influence of melt feeding scheme and casting parameters during direct-chill casting on microstructure of an AA7050 billet

© The Minerals, Metals & Materials Society and ASM International 2012Direct-chill (DC) casting billets of an AA7050 alloy produced with different melt feeding schemes and casting speeds were examined in order to reveal the effect of these factors on the evolution of microstructure. Experimental results show that grain size is strongly influenced by the casting speed. In addition, the distribution of grain sizes across the billet diameter is mostly determined by melt feeding scheme. Grains tend to coarsen towards the center of a billet cast with the semi-horizontal melt feeding, while upon vertical melt feeding the minimum grain size was observed in the center of the billet. Computer simulations were preformed to reveal sump profiles and flow patterns during casting under different melt feeding schemes and casting speeds. The results show that solidification front and velocity distribution of the melt in the liquid and slurry zones are very different under different melt feeding scheme. The final grain structure and the grain size distribution in a DC casting billet is a result of a combination of fragmentation effects in the slurry zone and the cooling rate in the solidification range

Formation of hot tear under controlled solidification conditions

Aluminum alloy 7050 is known for its superior mechanical properties, and thus finds its application in aerospace industry. Vertical direct-chill (DC) casting process is typically employed for producing such an alloy. Despite its advantages, AA7050 is considered as a "hard-to-cast" alloy because of its propensity to cold cracking. This type of cracks occurs catastrophically and is difficult to predict. Previous research suggested that such a crack could be initiated by undeveloped hot tears (microscopic hot tear) formed during the DC casting process if they reach a certain critical size. However, validation of such a hypothesis has not been done yet. Therefore, a method to produce a hot tear with a controlled size is needed as part of the verification studies. In the current study, we demonstrate a method that has a potential to control the size of the created hot tear in a small-scale solidification process. We found that by changing two variables, cooling rate and displacement compensation rate, the size of the hot tear during solidification can be modified in a controlled way. An X-ray microtomography characterization technique is utilized to quantify the created hot tear. We suggest that feeding and strain rate during DC casting are more important compared with the exerted force on the sample for the formation of a hot tear. In addition, we show that there are four different domains of hot-tear development in the explored experimental window-compression, microscopic hot tear, macroscopic hot tear, and failure. The samples produced in the current study will be used for subsequent experiments that simulate cold-cracking conditions to confirm the earlier proposed model.This research was carried out within the Materials innovation institute (www.m2i.nl) research framework, project no. M42.5.09340

Microtubules in Bacteria: Ancient Tubulins Build a Five-Protofilament Homolog of the Eukaryotic Cytoskeleton

Microtubules play crucial roles in cytokinesis, transport, and motility, and are therefore superb targets for anti-cancer drugs. All tubulins evolved from a common ancestor they share with the distantly related bacterial cell division protein FtsZ, but while eukaryotic tubulins evolved into highly conserved microtubule-forming heterodimers, bacterial FtsZ presumably continued to function as single homopolymeric protofilaments as it does today. Microtubules have not previously been found in bacteria, and we lack insight into their evolution from the tubulin/FtsZ ancestor. Using electron cryomicroscopy, here we show that the tubulin homologs BtubA and BtubB form microtubules in bacteria and suggest these be referred to as “bacterial microtubules” (bMTs). bMTs share important features with their eukaryotic counterparts, such as straight protofilaments and similar protofilament interactions. bMTs are composed of only five protofilaments, however, instead of the 13 typical in eukaryotes. These and other results suggest that rather than being derived from modern eukaryotic tubulin, BtubA and BtubB arose from early tubulin intermediates that formed small microtubules. Since we show that bacterial microtubules can be produced in abundance in vitro without chaperones, they should be useful tools for tubulin research and drug screening

Tesla Inc. : an equity valuation

The purpose of this dissertation is to determine the value of one Tesla, Inc. share as of 31 December 2018. An analysis of the automotive and energy generation and storage industry is presented, together with a detailed analysis of Tesla’s business and financial performance. For Tesla’s valuation purposes, the financial items are forecasted for a period of 10 years, i.e. from 2018 to 2027. In order to determine Tesla’s value, it is used the DCF approach, with the WACC as the discount rate. Additionally, the multiples method is also prepared as a complementary valuation to DCF. Based on the DCF approach, the achieved Tesla’s price target is $229.95, with a downside of 27.62$317.69, on 31 December 2018. Therefore, it is considered that Tesla is overvalued. In addition, a sensitivity analysis was completed to variations on WACC, terminal growth rate and total operating costs. Finally, the estimated Tesla’s share price is compared to the valuation done by J.P.Morgan, which recommended price target is $216 on 31 December 2018. To conclude, both valuations yield to a sell recommendation.O objetivo da presente dissertação é determinar o valor de uma ação da Tesla, Inc. a 31 de dezembro de 2018. É apresentada uma análise da indústria automóvel, produção e armazenamento de energia, juntamente com uma análise detalhada do negócio e do desempenho financeiro da Tesla. Para fins de avaliação da Tesla, são efetuadas previsões das contas financeiras para um período 10 anos, i.e., de 2018 a 2027. Por forma a determinar o valor da Tesla é usado o método DCF com WACC como a taxa de desconto. Adicionalmente, também é usado o método dos múltiplos, como um método de avaliação complementar do DCF. Com base no modelo DCF, o preço target estimado da Tesla é$229.95, o qual representa um valor de 27.62% abaixo do preço de mercado da ação $317.69, a 31 de dezembro de 2018. Neste sentido, considera-se que a Tesla está sobrevalorizada. Adicionalmente, uma análise de sensibilidade é efetuada relativamente às variações na taxa WACC, na taxa de crescimento a longo prazo e nos custos operacionais. Por fim, o preço estimado da Tesla é comparado com a avaliação feita pela J.P.Morgan, que recomendou um preço target de$216 a 31 de dezembro de 2018. Concluindo, ambas as avaliações recomendam uma decisão de venda