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- International Conference on Progress in Digital and Physical Manufacturing ProDPM'19 - Book of AbstractsPublication . Almeida, Henrique; Vasco, Joel; Marto, Anabela; Capela, Carlos; Freitas, Dino; Craveiro, Flávio; Bártolo, Helena; Coelho, Luís; Correia, Mário; Vieira, Milena; Ruben, RuiThe “Progress in Digital and Physical Manufacturing” book contains keynotes and papers presented at the first International Conference on Progress in Digital and Physical Manufacturing (ProDPM'19), organized by the School of Technology and Management (ESTG) of the Polytechnic Institute of Leiria (IPLeiria), from the 2nd to the 4th of October 2019. This international conference aims to provide a major international forum for the scientific exchange of multi-disciplinary and inter-organisational aspects performed by academics, researchers and industrial partners in order to exchange ideas in the field of digital and physical manufacturing and related areas. It represents a significant contribution to the current advances in industrial digital and physical manufacturing issues as it contains topical research in this field. The ProDPM'19 conference expects to foster networking and collaboration among participants to advance the knowledge and identify major trends in the field. The conference addresses to industrial challenges focused on current market demands and actual technological trends, such as mass customization, new business and industrial models or predictive engineering. Its contribution in science and technology developments leads to more suitable, effective and efficient products, materials and processes, generating added-value for the Industry and promoting the awareness of the role and importance of the digital and physical manufacturing development in the society. This book is, therefore, an essential reading for all of those working on digital and physical manufacturing, promoting better links between the academia and the industry. The conference papers will cover a wide range of important topics like additive manufacturing, biomanufacturing, advanced and smart manufacturing technologies, rapid tooling, microfabrication, virtual environments, simulation and 3D CAD and data acquisition, materials and collaborative design.
- Analysis of the initial delamination size on the mode I interlaminar fracture of carbon/epoxy compositesPublication . Reis, P.N.B.; Ferreira, J.A.M.; Antunes, F.V.; Costa, J.D.M.; Capela, C.; Capela, Carlos;This paper describes an experimental study of the initial delamination length effects on the mode I fracture toughness using DCB tests. Delamination failure was also predicted using exponential cohesive model and a quite good agreement with experimental results was obtained. Numerical predictions showed a significant influence of initial delamination length on the force-displacement curves.
- Fracture toughness of the heat affected zone on Nd-YAG laser welded jointsPublication . Costa, J.M.; Ferreira, J.M.; Capela, C.; Capela, CarlosLaser deposit welding based on modern Nd-YAG lasers is a new mould repair process with advantages relatively to the traditional methods (Micro-plasma and TIG methods). For moulds steels there are no research studies about the laser deposit welding process effects in respect to fracture toughness, hardness and residual stresses variations in the laser-deposited layer and in the heat affected zone. These variations will have an important influence in the thermal-mechanical fatigue strength of the moulds parts. This paper is concerned on the study of the fracture toughness of transient microstructure regions in Nd-YAG laser welded joints performed in mould steels. Fracture toughness tests were performed in two hot-working tool steels: AISI H13 and AISI P20. Small welded specimens were prepared with U notches and filled with laser welding deposits. The hardness profiles were obtained at the middle cross-section of specimens against distance to the surface in order to identify the microstructures present at the crack tip region. Fracture toughness was evaluated and plotted against the Vickers hardness measured at the fatigue crack tip. Depending of the crack tip depth two very different toughness levels were observed in the H13 steel, while a lower variation of toughness was observed for the P20 steel. The values of fracture toughness observed in each specimen are consistent with the correspondent crack tip microstructure hardness.
- Mechanical Properties of Injection-Molded Glass Microsphere-Reinforced PolyamidePublication . Capela, Carlos; Ferreira, J. M.; Costa, J. M.; Mendes, N.This paper presents new studies of the physical and mechanical characterization of PA6 matrix composites with different volume fractions of glass microspheres (10, 15, 20, 25 and 30%), which have been processed in an industrial environment. The mechanical properties of different processed composites were obtained by three-point bending tests, and the influence of the time of immersion in water in the strength and modulus was analyzed. The mechanical properties obtained in static tests and DMA tests of the processed composites demonstrated significant increases with an increasing volume fraction of the glass microspheres. In fracture toughness tests, KIC values higher than 12% were obtained. On the contrary, the immersion in water for 20 days promotes a decrease in flexural strength and flexural modulus greater than 11 and 22%, respectively. Finally, the influence of the addition of glass microspheres to the polyamide matrix was analyzed, and the increase in Tg with increasing fraction of the glass microspheres was observed.
- Improvement in fatigue life of Al 7475-T7351 alloy specimens by applying ultrasonic and microshot peeningPublication . Ramos, R.; Ferreira, N.; Ferreira, J.A.M.; Capela, Carlos; Batista, A.C.Shot peening and ultrasonic peening are widely used mechanical surface treatment in the automotive and aerospace industries to improve the fatigue life of metallic components. This work aims to further improve the mechanical properties of the AA7475-T7351 alloy by applying three different peening processes: Ultrasonic Peening (USP) and Microshot Peening with two different beads size (MSP). A systematic study was carried out on the roughness, surface hardening, residual stress profiles and fatigue life. Uniaxial fatigue tests were conducted. Residual stresses were evaluated by X-ray diffraction, and the fracture surface was observed and analysed with a Scanning Electron Microscope. The microstructures of the specimens were observed by optic microscope. Microhardness and roughness were also measured. All of the surface treatments enhanced the specimens fatigue lives, despite having created different superficial conditions. In addition, the experimental results and analytic predictions based on the Molski-Glinka approach were compared, and in general, agree well.
- Fatigue Crack Growth in Maraging Steel Obtained by Selective Laser MeltingPublication . Capela, Carlos; Lima Santos, Luís; Antunes, Fernando; Ferreira, José; Costa, José; Jesus, Joel; Prates, PedroThe fatigue crack growth properties of G20Mn5QT cast steel and corresponding butt welds, using compact tension specimens, were monitored and investigated via acoustic emission (AE) techniques. Fatigue crack growth is a combination of cyclic plastic deformations before the crack tip, tensile crack fractures, and shear crack fractures. The cyclic plastic deformations release the maximum amount of energy, which accounts for half of the total energy, and the second-largest number of AE signals, which are of the continuous-wave type. The tensile crack fractures release the second-largest amount of energy and the largest number of AE signals, which are of the burst-wave type. The shear crack fractures release the least amount of energy and the lowest number of AE signals, which are similar to the burst type, albeit with a relatively longer rise time and duration. Crack tip advancement can be regarded as a discontinuous process. The critical area before the crack tip brittlely ruptures when the fatigue damage caused by cyclic plastic deformations reaches critical status. The ruptures produce a large number of tensile crack fractures and rare shear crack fractures. Through fractography observation, the shear crack fractures occur probabilistically around defects caused by casting or welding, which lead to stress and strain in the local complex.
- Fatigue behaviour of selective laser melting steel componentsPublication . Santos, L.M.S.; Ferreira, J.A.M.; Jesus, J.S.; Costa, J.M.; C. CapelaSelective laser melting (SLM) is a laser based rapid manufacturing technology that builds metal parts layer-by-layer using metal powders and a computer controlled laser. Various important aspects strongly affect the mechanical properties of sintered metal components, such as: porosity, surface roughness, scan speed, layer thickness, and residual stresses. Therefore, properties of SLM manufactured parts must be carefully analysed, particularly under fatigue conditions. The purpose of this work was to study the effect of scan speed, porosity and microstructure on the mechanical properties and fatigue strength of sintered laser samples. Sintered laser parts were manufactured in maraging steel AISI 18Ni300. Fatigue behaviour is related to process parameters, such as: surface residual stresses, microstructure and porosity. The results showed that a very high scan speed (400 or 600 mm/s) causes the appearance of high percentages of porosity and a consequent drastic reduction of tensile strength and stiffness. Fatigue behaviour was assessed in terms of the traditional S-N curves and of the da/dN–DK crack propagation curves. Fatigue life predictions based on Hartman and Schijve’s equation underestimated significantly fatigue lives, particularly for low stress levels. The results of the tests performed at variable amplitude loading were well fitted by Miner’s law.
- 12º Congresso Nacional de Mecânica Experimental - Livro de ResumosPublication . Capela, Carlos; Correia, Mário Simões; Ruben, Rui
- Processamento de plásticos e materiais compósitos: comportamento mecânico de componentes em serviçoPublication . Capela, Carlos Alexandre BentoAs vantagens dos materiais plásticos, tais como facilidade de processamento, baixo custo, alta produtividade e versatilidade, permite obter plásticos e materiais compósitos de matriz polimérica para um grande número de aplicações em engenharia. Os materiais compósitos são, actualmente, muito utilizados não só na indústria aeroespacial, mas, também, num crescente número de aplicações de Engenharia Mecânica, tais como componentes de máquinas, vasos de pressão, equipamentos industriais de processos que requerem resistência à corrosão a alta temperatura, componentes sujeitos a desgaste, estruturas náuticas, equipamentos de desporto e lazer e aparelhos aplicados em biomedicina. No desenvolvimento e fabrico de peças técnicas em material plástico, processadas por injecção, é necessário ter conhecimentos de materiais plásticos, processo de moldação e bons conhecimentos de projecto e fabrico de moldes. Quando se pretende desenvolver e caracterizar materiais plásticos e plásticos reforçados é importante ter moldes específicos para processar materiais. Nesse sentido, foram desenvolvidos e fabricados dois moldes de injecção (canais frios) para processar provetes para a realização de ensaios de tracção, impacto, flexão em três pontos e ensaios de fractura. São apresentados casos de estudo realizados no âmbito do desenvolvimento e caracterização de materiais. O projecto de moldes de injecção de plásticos envolve o dimensionamento do sistema de injecção, refrigeração, selecção de materiais, análises estruturais e reológicas e dimensionamento do sistema de extracção. O dimensionamento de um sistema de extracção de um molde de injecção envolve, naturalmente, conhecimentos relativos aos materiais a processar, complexidade das peças plásticas, aspectos relacionados com o projecto e fabrico dos moldes e controlo das variáveis do processo de injecção. Com o objectivo de avaliar experimentalmente as forças envolvidas na extracção de peças plásticas, foi desenvolvido e fabricado um molde com a possibilidade de processar peças com diferentes geometrias, em função dos elementos moldantes considerados para o efeito. Na determinação das forças de extracção foram utilizadas técnicas de extensometria. Os valores relativos às forças de extracção, para diferentes materiais e diferentes condições de processamento, foram comparados com os valores de modelos disponíveis na literatura. O desenvolvimento e fabrico de materiais compósitos, bem como as técnicas de projecto e tecnologias de produção a eles associados, constituíram um dos mais importantes avanços na história dos materiais. Os plásticos e os compósitos são materiais que podem ser processados de forma a satisfazerem necessidades específicas. Os materiais compósitos podem possuir grande resistência a temperaturas superiores à temperatura ambiente, à corrosão, à oxidação e ao desgaste. Por outro lado, os processos de fabrico de compósitos estão hoje bem adaptados à fabricação de estruturas complexas, o que permite a consolidação das peças com custos de fabrico relativamente baixos. Estas características permitem a sua utilização em muitas aplicações, com vantagem em relação aos materiais monolíticos. Os materiais estudados no Capitulo 4 são compósitos de partículas muito utilizados em equipamentos de cozinha e sanitários. Estes materiais são constituídos por uma matriz polimetil-metacrilato (PMMA) com enchimento de partículas de sílica com diferentes granulometrias. Os equipamentos fabricados com estes materiais compósitos eram comercializados pela empresa Sanitana, pertencente ao Grupo KeramiK. Fazia, também, parte deste Grupo o Grupo Cinca. Estes materiais compósitos, quando utilizados em lava-louças de cozinha, podem ser submetidos a fluxos de água fria e quente que podem originar variações severas de temperatura, na zona envolvente do furo de escoamento de águas. Foram observadas roturas que parecem ser originadas pelas tensões de origem térmica desenvolvidas junto ao furo de escoamento de águas. Consequentemente, pretendeu-se estudar a sensibilidade do material à presença de defeitos de modo a compreender a ocorrência de roturas observadas em serviço. Foram obtidas as propriedades mecânicas destes materiais compósitos (Asterite, Amatis e Ultra-quartz, marcas registados pela ICI) na gama de temperaturas compreendidas entre 0° e 80° C. Estes materiais foram, também, sujeitos a estudos de tenacidade à fractura (gama de temperaturas entre 0° e 80° C) e fadiga de amplitude de carga constante e variável. Os ensaios de fadiga foram realizados em provetes de furo central onde foi analisada a influência da temperatura e da razão de tensão na resistência à fadiga. O objectivo deste estudo foi o de estabelecer o risco de falha, por fadiga, e analisar a tolerância de defeitos em condições de serviço. As tensões de origem térmica, devidas aos fluxos alternados de água fria e quente, foram determinadas experimentalmente em lava-louças instrumentados de Asterite e Ultra-quartz. Foi realizada uma análise numérica de forma a estudar a influência das temperaturas da água fria e quente nas tensões de origem térmica. Foi realizado um estudo de previsão de vida de fadiga em provetes de furo central, considerando as tensões residuais originadas pelo processo de fabrico, a solução de K obtida numericamente e as velocidades de propagação determinadas experimentalmente. Para além disso, considerando os mesmos resultados, foi realizada uma análise de fadiga térmica em lava-louças em que foi considerada a influência do ciclo térmico.
- Fracture Toughness of Hybrid Components with Selective Laser Melting 18Ni300 Steel PartsPublication . Santos, Luis M. S.; Jesus, Joel De; Ferreira, José M.; Costa, José D.; Capela, CarlosSelective Laser Melting (SLM) is currently one of the more advanced manufacturing and prototyping processes, allowing the 3D-printing of complex parts through the layer-by-layer deposition of powder materials melted by laser. This work concerns the study of the fracture toughness of maraging AISI 18Ni300 steel implants by SLM built over two different conventional steels, AISI H13 and AISI 420, ranging the scan rate between 200 mm/s and 400 mm/s. The SLM process creates an interface zone between the conventional steel and the laser melted implant in the final form of compact tension (CT) samples, where the hardness is higher than the 3D-printed material but lower than the conventional steel. Both fully 3D-printed series and 3D-printed implants series produced at 200 mm/s of scan rate showed higher fracture toughness than the other series built at 400 mm/s of scan rate due to a lower level of internal defects. An inexpressive variation of fracture toughness was observed between the implanted series with the same parameters. The crack growth path for all samples occurred in the limit of interface/3D-printed material zone and occurred between laser melted layers.