Magnesium alloy tubes have good formability at elevated temperatures. In this study, a finite element code DEFORM 3D is used to simulate the result of T-shape hydroforming at working temperatures 150¢J and 250¢J with magnesium alloy AZ61 tubes and then conducts the hydroforming experiments. By modifying the loading paths, products with uniform thickness and branch height are obtained 49mm. The results of simulation are compared with the experimental results to verify the validity of this modeling. On the other hand, the effects of the die fillet radius on tube formability during y-shape hydroforming are discussed. With the right die fillet radius r1¡×10mm and the left die fillet radius r2¡×30mm, a better formability of the tube is obtained.

Aluminum alloys are of great interest to the automobile industry for vehicle mass reduction, which improves vehicle performance and reduces emissions. Hot forming processes, such as superplastic forming (SPF) and quick-plastic forming (QPF) have been developed to take advantage of the improved formability of certain aluminum materials at elevated temperature. Commercial fine-grained aluminum alloy AA5083 sheet is the most commonly used material in the SPF and QPF forming processes. Hot formability of AA5083 is often limited by material cavitation during forming, which makes understanding and controlling cavitation an issue of primary importance for improving hot sheet forming processes. The thermomechanical processing history of AA5083 can strongly affect superplastic performance, causing variations in formability between material lots. These variations are closely related to microstructure, and intermetallic particles are prime suspects for controlling cavitation behavior. However, there has been little more than anecdotal evidence available that these particles nucleate or influence cavitation. Interactions between intermetallic particles and cavities were, thus, analyzed using both two-dimensional (2-D) and three-dimensional (3-D) microstructure characterization techniques. Analysis of 3-D microstructures from AA5083 specimens deformed under conditions similar to the SPF and QPF processes provide conclusive proof that cavities form at specific types of intermetallic particles. Differences in cavitation between materials deformed under the SPF and QPF processes result from differences in deformation mechanisms. These differences are illustrated by the formation of filaments on fracture surfaces of superplastically deformed AA5083 specimens, which have been characterized. / text

Magnesium sheet alloys, such as wrought AZ31, have material properties that make them an attractive option for use in automotive and aircraft components. However, the low ductility of magnesium alloys at room temperature necessitates the use of high-temperature forming to manufacture complex components. Finite-element-method (FEM) simulations can assist in determining the optimum processing parameters for high-temperature forming, but only if an accurate material constitutive model is used. New material constitutive models describing the deformation behavior of AZ31 sheet at 450°C are proposed. These models account for both active deformation mechanisms at this temperature: grain-boundary-sliding creep and five-power dislocation-climb creep. Phenomena affecting these deformation mechanisms, such as material anisotropy and grain growth, are also investigated. This physics-based approach represents an improvement over previous material models, which require nonphysical parameters and can only predict forming for a limited range of conditions. Tensile tests are conducted to obtain data used in fitting constitutive models. New models are used in FEM simulations of both tensile tests and biaxial gas-pressure bulge tests. Simulation results are compared to experimental data for validation and determination of model accuracy. / text

Ansamycin natural products have historically been a rich source of new drugs for the treatment of bacterial infections and cancer. The C17-benzene ansamycins in particular have shown excellent preclinical results as potential anti-fungal and anti-cancer medicines. However, their thorough clinical evaluation has been hampered by the absence of a concise synthetic strategy. In order to address this issue, recently developed hydrogenative carbon-carbon bond forming methods were applied toward a short total synthesis of C17-benzene ansamycins. This class of natural products provides a challenging testing ground for these methods while facilitating the further development of compounds which may be used as treatments for life threatening diseases. In the first synthetic approach to the C17-benzene ansamycins key bond formations include direct iridium catalyzed carbonyl crotylation from the alcohol oxidation level followed by chelation-controlled dienylation to form the stereotriad, which is attached to the arene via Suzuki cross-coupling. The diene-containing carboxylic acid is prepared using rhodium catalyzed acetylene-aldehyde reductive C-C coupling mediated by gaseous hydrogen. Finally, ring-closing metathesis delivers the cytotrienin core. The second approach toward triene-containing C17-benzene ansamycins resulted in the syntheses of trienomycins A and F, which were prepared in 16 steps (longest linear sequence) and 28 total steps. The C11-C13 stereotriad was generated via enantioselective ruthenium-catalyzed alcohol CH syn crotylation followed by chelation-controlled carbonyl dienylation. Finally, diene-diene ring closing metathesis to form the macrocycle. The present approach is 14 steps shorter (LLS) than the prior syntheses of trienomycins A and F, and eight steps shorter than any prior synthesis of a triene-containing C17-benzene ansamycin. / text

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In sheet metal forming (SMF), the major failure reason is galling. Galling is a process of different wear stages that leads to destruction of both the forming tool and the sheet metal working piece and is, because of that, of big economic importance for the SMF industries. Therefore, investigations and researches about how tool steels microstructure affect the tool steels galling resistance is of high priority. In the present work, different carbide properties were studied to find out how their properties affected the tool materials galling resistance. The investigated carbide properties were: Shape and size of the carbides   Carbide volume fraction Carbide distribution in the microstructure The investigation included three tools, all made of the PM tool steel S390, that were heattreated differently in order to achieve different carbide properties but still maintain the same hardness. The tools were galling tested in a slider-on-flat-surface (SOFS) tribometer to determine their galling resistances. In a scanning surface electron microscope (SEM) the tools galling marks were analyzed to find explanations for the SOFS tribometer results and the connection to the tools different carbide properties.  The investigations most galling resistant tool was the tool that had the microstructure with largest carbides which were distributed at grain boundaries and the second highest carbide volume fraction among the investigated tools.

In this master’s paper there are analyzed various theoretical and practical marketing strategy forming steps, given by Lithuanian and foreign authors; there is made full analysis of factors of marketing environment. You can find analysis of target market, positioning and strategy of marketing complex elements when strategy of such companies is formed. There is given customer and expert research. According results of customer research, document analysis and interview results of companies’ managers, the marketing strategy was formed. Using received data, specific singularities of marketing strategy forming for building materials retailers were generalized.

All over the world researches of youth life, value orientation, attitudes are important because at that time main social person psyche changes happen, which results are important for all his further life.To learn in vocational schools, which has specific features due to meaning of vocational training, the young people gather from different regions (rural and urban). According to research, in vocational school most of pupils are from rural, so their behaviour, habits, interests and intercourse with urban pupils have its peculiarity. Although at present lithuanian scientists are interested in youth life, culture, but in their works there is still not much attention to vocational schools. There schools’ system is located in both urban and rural territory, that is why children identification is important (sex, age, social group ). From here comes the problem of our research. While trying to signify not conflict interaction among urban and rural pupils educational environment of vocational school, it is necessary to identify possibilities, which have influence on these cultures’ expression, which is multicultural. The goal of research is to do the survey of urban and rural cultural conflict possibilities in vocational school and provide the dimensions in preventive program. For realizing the goal, the work had these tasks, it is based theoretically urban and rural cultures conflict main point and preconditions for multicultural interaction in vocational school, to do an empirical... [to full text]

The discovery of the pore-forming toxins produced by Bacillus thuringiensis, which are toxic to insects but not to mammalians, has provided a new successful means to control harmful plant-feeding insects biologically. The toxins are also used on insects that don’t feed on plants, for example on Anopheles. The Bacillus thuringiensis toxins fall into two structural families, named cry and cyt. All of these toxins act by damaging the cell membranes in the mid gut of the insect. In this study, a reliable system for expression and purification of the recombinant Cyt2Aa1 toxin has been developed. The recombinant Cyt2Aa1 toxin has been produced, characterized, followed by the construction of the cysteine mutants V186C and L189C by site directed mutagenesis. The new expression system yields 0.4 g of protein per litre of culture. The activated Cyt2Aa1 toxin is active in the hemolysis assay. Of note, the hemolytic activity of the V186C mutant exceeds that of wild type Cyt2Aa1 toxin and of the L189C mutant. Calcein release assay experiments have been done to examine the activity of the toxin with different artificial liposomes. It was found that Cyt2Aa1 toxin is very active with DMPC, DMPC+DMPG unilamellar liposomes. Surprisingly, however, Cyt2Aa1 toxin showed no activity with liposomes containing cholesterol. With both erythrocytes and sensitive liposomes, the toxin shows a “pro-zone effect”, that is the activity decreases at very high concentrations. The findings are discussed in the context of the toxin’s putative mode of action.

Warm forming of aluminum alloys of has shown promising results for increasing the formability of aluminum alloy sheet. Warm forming is a term that is generally used to describe a sheet metal forming process, where part or all of the blank is formed at an elevated temperature of less than one half of the material’s melting temperature. The focus of this work is to study the effects of warm forming on Novelis X926 clad aluminum brazing sheet. Warm forming of clad aluminum brazing sheet, which is commonly used in automotive heat exchangers has not been studied. This work can be split into three main goals: i) to characterize the material behavior and develop a constitutive model, ii) to experimentally determine the effects of warm forming on deep drawing; and, iii) to create and validate a finite element model for warm forming of Novelis X926. For an accurate warm forming material model to be created, a temperature and rate dependant hardening law as well as an anisotropic yield function are required. Uniaxial isothermal tensile tests were performed on 0.5mm thick Novelis X926at 25°C (room temperature), 100°C, 150°C, 200°C, and 250°C. At each temperature, tests were performed with various strain rates between 7.0 E -4 /sec and 7.0 E -2 /sec to determine the strain rate sensitivity. Tensile tests were also performed at 0° (longitudinal), 45° (diagonal), and 90° (transverse) with respect to the material rolling direction in order to assess the anisotropy of the material. It was found that increasing forming temperature increases elongation to failure by 200%, decreases flow stress by 35%, and increases strain rate sensitivity. Barlat’s Yield 2000 yield function (Barlat et al., 2003a) and the Bergström work hardening law (van den Boogaard and Huétink , 2006) were found to accurately method model the material behavior. Warm deep drawing of 101.6 mm (4”) diameter cylindrical cups was performed using specially designed tooling with heated dies and a cooled punch. Deep drawing was performed on 228.6 mm (9“) and 203.2 mm (8”) diameter blanks of 0.5 mm thick Novelis X926. Deep drawing was performed with die temperatures ranging from 25°C to 300°C with a cooled punch. Teflon sheet and Dasco Cast 1200 lubricants were used in experiments. Different punch velocities were also investigated. 228.6 mm diameter blanks, which could not be drawn successfully at room temperature, were drawn successfully using 200°C dies. Increasing the die temperature further to 250°C and 300°C provided additional improvement in formability and reduced tooling loads. Increasing the punch velocity, increases the punch load when forming at elevated temperatures, reflecting the strong material rate sensitivity at elevated temperatures. A coupled thermal mechanical finite element model was developed using the Bergström hardening rule and the Yield 2000 yield surface using LS-DYNA. The model was found to accurately predict punch force for warm deep drawing using Teflon sheet as a lubricant. Results for Dasco Cast 1200 were not as accurate, due to the difficulties in modeling the lubricant’s behavior. Finite element simulations demonstrated that warm forming can be used to reduce thinning at critical locations, compared to parts formed at room temperature.