Mechanical Spectroscopy Study of CrNiCoFeMn High-Entropy Alloys

The equiatomic high-entropy alloy of composition of CrNiCoFeMn with an FCC crystal structure was prepared by either induction melting or additive manufacturing with a selective laser melting (SLM) process, starting from mechanically alloyed powders. The as-produced samples of both kinds were cold worked, and in some cases re-crystallized. Unlike induction melting, there is a second phase, which is made of fine nitride and Cr-rich σ phase precipitates, in the as-produced SLM alloy. Young’s modulus and damping measurements, as a function of temperature in the 300–800 K range, were performed on the specimens that were cold-worked and/or re-crystallized. Young’s modulus values of (140 ± 10) GPa and (90 ± 10) GPa were measured from the resonance frequency of free-clamped bar-shaped samples at 300 K for the induction-melted and SLM samples, respectively. The room temperature values increased to (160 ± 10) GPa and (170 ± 10) GPa for the re-crystallized samples. The damping measurements showed two peaks, which were attributed to dislocation bending and grain-boundary sliding. The peaks were superposed on an increasing temperature background

Parallel mesh adaptive techniques for complex flow simulation: geometry conservation

Dynamic mesh adaptation on unstructured grids, by localised refinement and derefinement, is a very efficient tool for enhancing solution accuracy and optimising computational time. One of the major drawbacks, however, resides in the projection of the new nodes created, during the refinement process, onto the boundary surfaces. This can be addressed by the introduction of a library capable of handling geometric properties given by a CAD (computer-aided design) description. This is of particular interest also to enhance the adaptation module when the mesh is being smoothed, and hence moved, to then reproject it onto the surface of the exact geometry

Parallel mesh adaptive techniques for complex flow simulation

Dynamic mesh adaptation on unstructured grids, by localised refinement and derefinement, is a very efficient tool for enhancing solution accuracy and optimise computational time. One of the major drawbacks however resides in the projection of the new nodes created, during the refinement process, onto the boundary surfaces. This can be addressed by the introduction of a library capable of handling geometric properties given by a CAD (Computer Aided Design) description. This is of particular interest also to enhance the adaptation module when the mesh is being smoothed, and hence moved, to then re-project it onto the surface of the exact geometry. However, the above procedure is not always possibly due to either faulty or too complex designs, which require a higher level of complexity in the CAD library. It is therefore paramount to have a built-in algorithm able to place the new nodes, belonging to the boundary, closer to the geometric definition of it. Such a procedure is proposed in this work, based on the idea of interpolating subdivision. In order to efficiently and effectively adapt a mesh to a solution field, the criteria used for the adaptation process needs to be as accurate as possible. Due to the nature of the solution, which is obtained by discretisation of a continuum model, numerical error is intrinsic in the calculation. A posteriori error estimation allows us to somewhat assess the accuracy by using the computed solution itself. In particular, an a posteriori error estimator based on the Zienkievicz Zhu model is introduced. This can be used in the adaptation procedure to refine the mesh in those areas where the local error exceeds a set tolerance, hence further increasing the accuracy of the solution in those regions during the next computational step. Variants of this error estimator have also been studied and implemented. One of the important aspects of this project is the fact that the algorithmic concepts are developed thinking parallel, i.e. the algorithms take into account the possibility of multiprocessor implementation. Indeed these concepts require complex programming if one tries to parallelise them, once they have been devised serially. Another important and innovative aspect of this work is the consistency of the algorithms with parallel processor execution

Al, cu and zr addition to high entropy alloys: The effect on recrystallization temperature

The equimolar Cr, Mn, Fe, Co and Ni alloy, first produced in 2004, was unexpectedly found to be single-phase. Consequently, a new concept of materials was developed: high entropy alloys (HEA) forming a single solid-solution with a near equiatomic composition of the constituting elements. In this study, an equimolar CoCrFeMnNi HEA was modified by the addition of 5 at% of either Al, Cu or Zr. The cold-rolled alloys were annealed for 30 minutes at high temperature to investigate the recrystallization kinetics. The evolution of the grain boundary and the grain size were investigated, from the as-cast to the recrystallized state. Results show that the recrystallized single phase FCC structures exhibits different twin grains density, grain size and recrystallization temperatures as a function of the at.% of modifier alloying elements added. In comparison to the equimolar CoCrFeMnNi, the addition of modifier elements increases significantly the recrystallization temperature after cold deformation. The sluggish diffusion (typical of HEA alloys), the presence of a solute in solid solution as well as the low twin boundary energy are responsible for the lower driving force for recrystallization

A Parallel Adaptive Newton-Krylov-Schwarz Method for 3D Compressible Inviscid Flow Simulations

A parallel adaptive pseudo transient Newton-Krylov-Schwarz (αΨNKS) method for the solution of compressible flows is presented. Multidimensional upwind residual distribution schemes are used for space discretisation, while an implicit time-marching scheme is employed for the discretisation of the (pseudo)time derivative. The linear system arising from the Newton method applied to the resulting nonlinear system is solved by the means of Krylov iterations with Schwarz-type preconditioners. A scalable and efficient data structure for the αΨNKS procedure is presented. The main computational kernels are considered, and an extensive analysis is reported to compare the Krylov accelerators, the preconditioning techniques. Results, obtained on a distributed memory computer, are presented for 2D and 3D problems of aeronautical interest on unstructured grids

Magnetohydrodynamic Enhanced Entry System for Space Transportation (MEESST) as a Key Building Block for Future Exploration Missions

Aside from the launch environment, atmospheric re-entry imposes one of the most demanding environments which a spacecraft can experience. The combination of high spacecraft velocity and the presence of atmospheric particles leads to partially ionised gas forming around the vehicle, which significantly inhibits radio communications, and leads to the generation of high thermal loads on the spacecraft surface. Currently, the latter is solved using expensive, heavy, and often expendable thermal protection systems (TPS). The use of electromagnetic fields to exploit Magnetohydrodynamic (MHD) principles has long been considered as an attractive solution for this problem. By displacing the ionised gas away from the spacecraft, the thermal loads can be reduced, while also opening a magnetic window for radio waves, mitigating the blackout phenomenon. The application of this concept has to date not been possible due to the large magnetic fields required, which would necessitate the use of exceptionally massive and power-hungry copper coils. High Temperature Superconductors (HTS) have now reached industrial maturity. HTS coils can now offer the necessary low weight and compactness required for space applications. The MEESST consortium the has been awarded a grant from the EU Horizon 2020 programme for the development and demonstration of a novel HTS-based re-entry system based with its foundation on MHD principles. The project will first harmonize existing numerical codes, and then design, manufacture, and test a HTS magnet. The study shows that the use of MEESST technology can have a positive impact on the cost-effectiveness and available payload of interplanetary missions

GRAVIDADE DOS CORPOS CELESTES

Gravidade é uma aceleração que comanda o movimento dos objetos celestes, quanto maior a massa e menor o raio de um corpo maior a sua gravidade. O objetivo do nosso trabalho é dispor informações sobre a gravidade em outros planetas, e curiosidades como a altura máxima que uma pessoa alcançar ao realizar um salto em deferentes planetas, assim como o tempo que permanecerá no ar durante o salto. Como metodologia pretende-se mostrar teoricamente ao espectador e comprovar por meio de cálculos, a variação da gravidade nos diferentes planetas, fazê-los refletir que peso não é sinônimo de massa, comentar sobre os diferentes pesos para uma mesma massa em diferentes corpos celestes e de que maneira a aceleração da gravidade interfere nos saltos e tempo de permanência de não contato com a superfície. Como resultados, espera-se que ao interagir com o público, voluntários participem informando seu peso aqui na Terra, para realizar as simulações oferecidas nesse trabalho em outros corpos celestes. Assim, por meio de cálculos realizados obteremos a altura e o tempo de salto da respectiva pessoa. Esses são os respectivos dados utilizados nos cálculos durante a apresentação: Sol, 274,13m/s²; Mercúrio, 3,7m/s²; Vênus, 8,87m/s²; Terra, 9,807m/s²; Lua, 1,622m/s²; Marte, 3,711 m/s²; Júpiter, 24,79 m/s²; Europa (Lua de Júpiter), 1,315 m/s²; Saturno, 10,44 m/s²; Urano, 8,69 m/s²; Netuno, 11,15 m/s²; Plutão, 0,62m/s². Por fim, é interessante ressaltar que existe uma outra teoria que explica o movimento dos corpos celestes, a relatividade geral de Abert Einstein. No entanto essa teoria não invalida a gravitação universal de Newton, ela complementa. Para campos gravitacionais relativamente pequenos a gravitação universal funciona perfeitamente. Ou seja, não é necessário utilizar-se das equações de Einstein para lançar um objeto na orbita da terra ou pra estudar a órbita da Estação Espacial Internacional (ISS). A relatividade geral vai ser essencial onde a gravitação universal tem seus limites, por exemplo, um buraco negro. O que Einstein fez foi explicar a origem da força gravitacional e não invalidar a existência dela. Dessa maneira, a gravidade apresenta-se como um tema relevante e atraente, fato que nos levou a escolhê-lo como tema desse trabalho

ADULTERAÇÃO DE BEBIDAS ALCOÓLICAS

A adulteração de bebidas alcoólicas é uma prática criminosa, mas que acontece rotineiramente, principalmente em bares e festas, representando um sério risco à saúde pública. Esse processo envolve a adição de substâncias químicas não seguras às bebidas, tornando-as perigosas para o consumo humano. Essa prática tem o objetivo de dopar a vítima, deixando-a desnorteada e sem consciência de seus atos, facilitando a ocorrência de abusos e crimes contra a pessoa. O álcool geralmente é a bebida mais utilizada, pois acaba potencializando o efeito da droga, além de disfarçar o golpe, pois a pessoa pensa estar embriagada, a substância mais utilizada é o "Boa noite Cinderela", essa mistura é composta por escopolamina, subprodutos da dimetiltriptamina, cetamina, flunitrazepam, gama-hidroxibutirato (GHB) e alguns anti-histamínicos. O efeito e o tempo de duração dessa droga podem diferir de pessoa para pessoa. De acordo com diversos relatos, o tempo pode variar de algumas horas até cerca de um dia. A ação dessas substâncias tem início poucos minutos após a sua ingestão e atua diretamente no sistema nervoso central, diminuindo a sua atividade e fazendo com que a pessoa perca a consciência do que está acontecendo. A mistura tem o potencial de causar danos graves à saúde das vítimas, levando à intoxicação, acidentes e a uma possível situação de vulnerabilidade a crimes, além de poder resultar em uma parada cardíaca ou cardiorrespiratória. O objetivo deste trabalho é informar sobre as drogas utilizadas e adicionadas em bebidas alcoólicas e seus principais efeitos, de uma forma que conscientize as pessoas a terem mais cuidado durante as festas para não serem vítimas deste golpe. As informações deste trabalho foram obtidas por meio de fontes confiáveis, como sites especializados e documentários de profissionais. Diante da gravidade dessa prática criminosa, é fundamental que os frequentadores de festas e locais de entretenimento estejam conscientes dos perigos envolvidos e tomem medidas preventivas para proteger sua segurança. A forma mais eficaz de se evitar o golpe do "boa noite Cinderela" é não aceitando bebidas oferecidas por estranhos em festas e bares uma vez que essas bebidas podem conter a droga utilizada no golpe, além disso, é recomendado ficar sempre atento e segurando o próprio copo enquanto se tem bebida, para evitar que substâncias sejam adicionadas em um momento de distração

A Magnetohydrodynamic enhanced entry system for space transportation: MEESST

This paper outlines the initial development of a novel magnetohydrodynamic (MHD) plasma control system which aims at mitigating shock-induced heating and the radio-frequency communication blackout typically encountered during (re-)entry into planetary atmospheres. An international consortium comprising universities, SMEs, research institutions, and industry has been formed in order to develop this technology within the MEESST project. The latter is funded by the Future and Emerging Technologies (FET) program of the European Commission’s Horizon 2020 scheme (grant no. 899298). Atmospheric entry imposes one of the harshest environments which a spacecraft can experience. The combination of hypersonic velocities and the rapid compression of atmospheric particles by the spacecraft leads to high-enthalpy, partially ionised gases forming around the vehicle. This inhibits radio communications and induces high thermal loads on the spacecraft surface. For the former problem, spacecraft can sometimes rely on satellite constellations for communicating through the plasma wake and therefore preventing the blackout. On the other hand, expensive, heavy, and non-reusable thermal protection systems (TPS) are needed to dissipate the severe thermal loads. Such TPS can represent up to 30% of an entry vehicles weight, and especially for manned missions they can reduce the cost- efficiency by sacrificing payload mass. Such systems are also prone to failure, putting the lives of astronauts at risk. The use of electromagnetic fields to exploit MHD principles has long been considered as an attractive solution for tackling the problems described above. By pushing the boundary layer of the ionized gas layer away from the spacecraft, the thermal loads can be reduced, while also opening a magnetic window for radio communications and mitigating the blackout phenomenon. The application of this MHD-enabled system has previously not been demonstrated in realistic conditions due to the required large magnetic fields (on the order of Tesla or more), which for conventional technologies would demand exceptionally heavy and power-hungry electromagnets. High-temperature superconductors (HTS) have reached a level of industrial maturity sufficient for them to act as a key enabling technology for this application. Thanks to superior current densities, HTS coils can offer the necessary low weight and compactness required for space applications, with the ability to generate the strong magnetic fields needed for entry purposes. This paper provides an overview of the MEESST project, including its goals, methodology and some preliminary design considerations