Influence of ECAPressing temperature on crystallinity and mechanical behaviour of polypropylene and high-density polyethylene / Influência da temperatura de ECAPressing na cristalinidade e comportamento mecânico do polipropileno e do polietileno de alta densidade

In this paper, the influence of single equal channel angular pressing, ECAPressing, pass and processing temperature on crystallinity evolution and mechanical behaviour of the polymers polypropylene, PP, and high-density polyethylene, HDPE was investigated. ECAPressing tests were performed at the temperatures of 25, 50, 75 and 100°C for HPDE and 25, 90 and 120ºC for PP. The materials mechanical behaviour before and after ECAPressing tests was evaluated from room temperature compression tests while their crystallinity changings were analyzed through differential scanning calorimetry, DSC, experiments. In terms of strengthening and by comparison with as-received materials, it was observed an interesting efficiency of ECAPressing performed at 100°C for HDPE and 120°C for PP. In relation to crystallinity evolution, the results obtained from DSC tests showed its considerable increasing for higher pressing temperatures also by comparing either to as-received conditions or after single pass of equal channel angular pressing at room temperature

Evaluation of s355nl Steel Welded by Flux Cored Arc Welding Using Different Tubular Wires

High strength low alloy (HSLA) steels are used in several industrial sectors, as they have good mechanical strength and easy weldability. This HSLA is present in several areas, such as naval, petrochemical, piping, and civil construction. S355 NL steel is HSLA grade and has its application in the manufacture of the Brazilian submarine. For the manufacture and finishing of a Brazilian submarine, countless welds are performed during the assembly steps. The welding process currently applied is FCAW (Flux Cored Arc Welding), and the currently applied filler metal is of French origin. However, this import, from France to Brazil, makes manufacturing costs high and the waiting time for the imported product to arrive is long. Thus, in this work, the idea was to characterize a national filler metal (Brazilian) that similarly maintained the microstructure and consequently its mechanical and electrochemical properties concerning the imported filler metal (French). Therefore, the present work aimed at the microstructural, mechanical, and electrochemical characterization of S355NL structural steel welded by the FCAW process with national tubular wire (Brazilian) and imported tubular wire (French). We performed microstructural characterization with the aid of optical microscopy (OM) and scanning electron microscopy (SEM). For the mechanical characterization, we performed the following tests: tensile test, Vickers hardness, and impact at room temperature and -40ºC. In the electrochemical characterization, it generated polarization curves where the samples were exposed to a 3.5% NaCl solution to test the behavior in corrosive media. The results showed that the wires, national and imported, behaved homogeneously and uniformly concerning the mechanical properties. In the electrochemical part, the national material presented in the weld metal a corrosion current density interesting. Therefore, the national tubular wire is a promising filler metal for the welding application of this Brazilian submarine

On the mechanical behavior of an Al 7075 alloy deformed by asymmetrical and conventional rolling

Samples of the Al 7075 naturally and artificially aged were processed by conventional and asymmetricalrolling with 5% of thickness reduction. The rolling processes were evaluated under room temperature andunder warm condition (130°C). Mechanical properties were evaluated by uniaxial tensile and Vickersmicrohardness tests. Microstructure evolutions were followed by optical microscopy analysis. Naturally agedsamples showed better yield strengthening under warm processing. Greater ultimate stress and ductility underroom temperature processing was also noticed in naturally aged specimens. Artificially aged samples showedbetter mechanical properties under room temperature, softening under warm processing due to grain recoveryprocess. Microhardness tests showed expected results for both rolling types, especially on asymmetricalrolling with the higher predictions were observed. Micrographs have shown no expressive grain changes orrefinement although its flattening was observed. Precipitates were analyzed by EDS/SEM revealing thepresence of MgZn2 and CuMgAl along the matrix that provides plastic strengthening.Keywords: Aging, asymmetrical rolling, conventional rolling, mechanical behavior, Al 7075 alloy

Estimulação cerebral profunda na Doença de Parkinson: evidências de estudos de longa duração

A Doença de Parkinson (DP) é uma condição neurodegenerativa crônica que afeta principalmente idosos, mas pode ocorrer em adultos jovens. É a segunda doença neurodegenerativa mais comum, após o Alzheimer. A DP afeta 1% dos indivíduos acima de 60 anos em países industrializados. Sua causa envolve fatores genéticos e ambientais, como exposição a pesticidas e envelhecimento. A Estimulação Cerebral Profunda (DBS) é um tratamento que simula lesões cerebrais, melhorando sintomas motores e não motores. O presente estudo tem como objetivo analisar evidências de estudos sobre a eficácia da DBS no tratamento da DP. Trata-se de uma revisão sistemática de estudos quantitativos que utiliza as bases de dados PubMed (Medline), Cochrane Library e Scientific Electronic Library Online (SciELO) para selecionar artigos científicos. Os estudos incluídos abrangem o período de 2013 a 2023 e estão em inglês, abordando a DBS no tratamento da DP. A DBS melhora diversos sintomas motores e não motores, resultando em uma melhor qualidade de vida para os pacientes. Tais benefícios são sustentados mesmo em estágios avançados da Doença de Parkinson, a qual consiste em fornecer pulsos de corrente elétrica a áreas cerebrais profundas através de eletrodos implantados cirurgicamente, geralmente quando a terapia medicamentosa já não é eficaz. Em um estudo com 82 pacientes, a terapia com DBS resultou em uma redução de ± 52% nos sintomas motores do UPDRS sob medicação antes da cirurgia. A melhora nos sintomas motores com a estimulação, em comparação com a ausência de estimulação e medicação, foi de ± 61% no primeiro ano e ± 39% de 8 a 15 anos após a cirurgia (antes da reprogramação). A medicação foi reduzida em ± 55% após 1 ano e ± 44% após 8 a 15 anos, com a maioria dos pacientes mostrando melhorias após a reprogramação. De acordo com as literaturas analisadas, a DBS é uma terapia eficaz para a DP. Enfatiza-se a importância da inovação contínua e dos novos estudos para explorar as facetas não investigadas desse campo. Com a abordagem dos aspectos clínicos, cirúrgicos, tecnológicos e científicos, destacam-se os benefícios, limitações e desafios a serem superados. Ademais, inovações tecnológicas na DBS, como a estimulação direcional, adaptativa e a telemedicina estão sendo exploradas. Em suma, este artigo fornece evidências sobre os benefícios da DBS na DP, ressaltando a necessidade de pesquisas adicionais para otimizar tal intervenção terapêutica e melhorar a qualidade de vida dos pacientes

A influência de precipitados Al6Mn no crescimento de grão de uma liga Al-1% massa Mn

Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorO ancoramento dos contornos de grão é estudado numa liga Al-1% peso Mn contendo precipitados Al6Mn. As amostras da liga foram laminadas 40% e 80% e tratadas termicamente entre 500ºC e 620ºC a cada 20ºC, por um tempo de 1 hora (3600 s). As amostras foram lixadas, polidas eletroliticamente e anodizadas. Realizaram-se medidas de metalografia quantitativa: fração volumétrica dos precipitados, VV, área interfacial dos precipitados por unidade de volumes, Svp, comprimento médio dos interceptos dos grãos, l e área dos contornos dos grãos por unidade de volume, Sv. Os resultados experimentais mostram uma excelente concordância com a fórmula alternativa proposta por Rios: Svc = 3Svp, onde Svc é área dos contornos dos grãos por unidade de volume quando o raio médio dos grãos é igual ao raio crítico. Essa expressão é mais fácil de verificar experimentalmente que a forma equivalente: Rc = r/6f, onde r é o raio da partícula, f é a fração volumétrica das partículas e Rc é o raio crítico do grão

O estudo do crescimento de grão em uma liga Al-1 % massa Mn

Grain growth was studied in detail in a high purity Al-1mass% Mn alloy containing particles. This thesis contains an introduction, a literature survey, materials and methods and five chapters about: grain geometry, precipitate characterization, influence of the precipitates in the grain boundary pinning, abnormal grain growth and the effect of thickness on grain growth. In chapter 4, grain geometry, the measures of the three grain curvatures are presented. Geometrical models relating these three quantities to the mean intercept length of the grains, l, were derived. The models showed good agreement with experimental data. After precipitate characterization done in chapter 5, the influence of the precipitates on grain boundary pinning was studied in chapter 6. The usual expression to calculate the limiting or critical grain radius due to the pinning by precipitates uses quantities that are not very convenient for comparison with experimental results. In this work two alternative expressions are proposed. Good agreement is obtained between theory and experiments. The relative merits and shortcomings of each expression are discussed in detail from a fundamental and experimental point of view. During abnormal grain growth, in contrast with the normal grain growth, only few large grains dominate the grain growth process. Chapter 7 deals with the evolution of the abnormal grains and the influence of these grains in the normal grains geometry. In chapter 8, the effect of thickness on grain growth and on the geometry of grains was studied. Finally the work was summarized and its main conclusions were presented.Conselho Nacional de Desenvolvimento Cientifico e TecnológicoO crescimento de grão é estudado detalhadamente em uma liga Al-1% massa Mn de alta pureza com a presença de partículas. A tese contém: uma introdução, uma revisão bibliográfica, materiais e métodos e cinco capítulos sobre: geometria dos grãos, caracterização dos precipitados, influência dos precipitados no ancoramento dos contornos de grão, crescimento anormal de grão e o efeito da espessura no crescimento de grão. No capítulo 4, geometria dos grãos, as medidas das três curvaturas são apresentadas. Modelos geométricos são derivados relatando essas três quantidades com o comprimento médio das intersecções dos grãos, l. Os modelos apresentam uma boa concordância com os dados experimentais. Após a caracterização dos precipitados, discutida no capítulo 5, a influência desses precipitados no ancoramento dos contornos de grão foi estudada no capítulo 6. A expressão usual para calcular o raio limite ou crítico do grão devido ao ancoramento de partícula utiliza uma formulação não muito conveniente para comparação com resultados experimentais. Neste trabalho duas expressões alternativas são propostas. Boa concordância é obtida entre teoria e os experimentos Os méritos e deméritos de cada expressão são discutidos em detalhe tanto do ponto de vista fundamental quanto experimental. Durante o crescimento anormal de grão, em contraste com o crescimento normal de grão, somente poucos grãos grandes dominam o processo de crescimento. O capítulo 7 trata da evolução dos grãos anormais e a influência desses grãos na geometria dos grãos normais. No capítulo 8, o efeito da espessura no crescimento de grão e na geometria desses grãos foi estudado. Ao final do trabalho, as suas principais conclusões são apresentadas

Sigma Phase: Nucleation and Growth

Duplex stainless steels (DSS) and superduplex stainless steels (SDSS) are important classes of stainless steels, because they combine the benefits of austenite and ferrite phases. This results in steels with better mechanical properties and higher corrosion resistance. Owing to these characteristics, DSS and SDSS are widely employed in industry. However, the appearance of undesirable intermetallic phases in their microstructure impairs the properties of DSS and SDSS. Among the undesirable intermetallic phases, the main one is the sigma phase (σ), which can be nucleated when the steel is exposed to the temperature range between 650 °C and 900 °C, reducing the steel’s toughness and resistance to corrosion. In a previous work, Fonseca and collaborators used two descriptors of the microstructural path to analyze the formation of sigma phase (σ), the interfacial area per unit volume between sigma phase and austenite (SV), and the mean chord length of sigma (<λ>), both as a function of VV, the volume fraction of sigma, known in the literature as the microstructural partial path (MP). In this work, the contiguity ratio is applied for the first time to describe the microstructural path in the study of sigma phase precipitation in SDSS. The contiguity ratio shows that the distribution of the ferrite/sigma boundaries is homogeneous. Thus, it is reasonable to infer that one has a uniform distribution of sigma phase nuclei within the ferrite. About the kinetics of sigma phase formation, the DSS can be described by the classical Johnson-Mehl, Avrami, and Kolmogorov (JMAK) equation, whereas for the SDSS, the kinetics tend to follow the Cahn model for grain edge nucleation. Finally, we present the three-dimensional (3D) reconstruction of the sigma phase in SDSS. The results demonstrate that the sigma phase nucleates at the edges of the ferrite/austenite interfaces. Moreover, the sigma phase grows and consumes the ferrite, but is not fully interconnected

The Feasibility of Structural Health Monitoring Using the Fundamental Shear Horizontal Guided Wave in a Thin Aluminum Plate

Structural health monitoring (SHM) is emerging as an essential tool for constant monitoring of safety-critical engineering components. Ultrasonic guided waves stand out because of their ability to propagate over long distances and because they can offer good estimates of location, severity, and type of damage. The unique properties of the fundamental shear horizontal guided wave (SH0) mode have recently generated great interest among the SHM community. The aim of this paper is to demonstrate the feasibility of omnidirectional SH0 SHM in a thin aluminum plate using a three-transducer sparse array. Descriptions of the transducer, the finite element model, and the imaging algorithm are presented. The image localization maps show a good agreement between the simulations and experimental results. The SH0 SHM method proposed in this paper is shown to have a high resolution and to be able to locate defects within 5% of the true location. The short input signal as well the non-dispersive nature of SH0 leads to high resolution in the reconstructed images. The defect diameter estimated using the full width at half maximum was 10 mm or twice the size of the true diameter

Stereological analysis of the microstructure of pure iron with random nucleation

Microstructural characterization of metallic materials is of paramount importance in the qualification and quantification of their desired final properties. Metallic materials have often been characterized by means of optical and electronic microscopy. Results from these techniques are in most of the cases based on 2D analysis. Stereological methods are then employed to obtain 3D information. However, such methods are based on assumptions and approximations of the real material structure. Therefore, it is essential to know the limitations of these methods. A further complication arises when one wishes to compare real materials with computer simulation results and stereological analytical techniques. In this paper, methods normally applied to real microstructure are applied to microstructures simulated by cellular automata (CA) simulation. Experimental results from microstructural characterization of polycrystalline pure iron were used as the starting point for the simulation. Consequently, we could apply analytical formulae of stereology to experimental data from pure iron and to computer generated microstructures from cellular automata simulation. Comparison of analytical formulae, experimental results and computer simulation provided useful insights on limits of applicability and on the meaning of the stereological analysis