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Centre for Mechanical Enginnering, Materials and Processes
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Fatigue fracture morphology of AISI H13 steel obtained by additive manufacturing
Publication . Macek, Wojciech; Martins, Rui F.; Branco, Ricardo; Marciniak, Zbigniew; Szala, Mirosław; Wroński, Sebastian; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; Springer Verlag
The paper focuses on researching the effect of fatigue loading on metallic structure, lifetime, and fracture surface topographies in AISI H13 steel specimens obtained by selective laser melting (SLM). The topography of the fracture surfaces was measured over their entire area, according to the entire total area method, with an optical three-dimensional surface measurement system. The fatigue results of the SLM 3D printed steel specimens were compared with those reported for conventionally manufactured 13H steel. The investigation also considers the roughness of the specimens’ side surface. Moreover, the fractographic evaluation conducted using scanning electron microscopy confirms that the predominant fracture mechanism is transgranular fracture. Microtomography done after mechanical loading also showed the influence of the stress level on the porosity distribution. Both fractographic and Micro-CT investigations confirm that higher stresses result in coarser and much more uniform porosity observed in fractured samples. These comprehensive quantitative and qualitative fracture analyses are beneficial to predict the failure conditions of SLM steel parts, especially in the case of fatigue damage. From the quantitative analysis of the H13 SLM-manufactured fracture surface topography, it was possible to conclude that the larger the loadings acting on the specimen, the rougher the fracture surface because the ductile fracture mode dominates. It has also been proven that the porosity degree changes along the length of the sample for the most stressed specimens.
Mechanical Properties of Additively Manufactured Polymeric Materials—PLA and PETG—For Biomechanical Applications
Publication . Martins, Rui F.; Branco, Ricardo; Martins, Miguel; Macek, Wojciech; Marciniak, Zbigniew; Silva, Rui; Trindade, Daniela; Moura, Carla; Franco, Margarida; Malça, Cândida; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; DEMI - Departamento de Engenharia Mecânica e Industrial; MDPI - Multidisciplinary Digital Publishing Institute
The study presented herein concerns the mechanical properties of two common polymers for potential biomedical applications, PLA and PETG, processed through fused filament fabrication (FFF)—Material Extrusion (ME). For the uniaxial tension tests carried out, two printing orientations—XY (Horizontal, H) and YZ (Vertical, V)—were considered according to the general principles for part positioning, coordinates, and orientation typically used in additive manufacturing (AM). In addition, six specimens were tested for each printing orientation and material, providing insights into mechanical properties such as Tensile Strength, Young’s Modulus, and Ultimate Strain, suggesting the materials’ potential for biomedical applications. The experimental results were then compared with correspondent mechanical properties obtained from the literature for other polymers like ASA, PC, PP, ULTEM 9085, Copolyester, and Nylon. Thereafter, fatigue resistance curves (S-N curves) for PLA and PETG, printed along 45°, were determined at room temperature for a load ratio, R, of 0.2. Scanning electron microscope observations revealed fibre arrangements, compression/adhesion between layers, and fracture zones, shedding light on the failure mechanisms involved in the fatigue crack propagation of such materials and giving design reference values for future applications. In addition, fractographic analyses of the fatigue fracture surfaces were carried out, as well as X-ray Computed Tomography (XCT) and Thermogravimetric (TGA)/Differential Scanning Calorimetric (DSC) tests.
Development of a gas metal arc based prototype for direct energy deposition with micrometric wire
Publication . Dornelas, Paulo Henrique Grossi; Oliveira, J. P.; Silva, Tadeu Castro da; Ramos, A. S.; Santos, Telmo G.; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); Elsevier Editora Ltda
In recent years, efforts have been focused on the development of metal additive manufacturing (AM) processes to address the growing trend of miniaturization in industries such as aerospace and electronics. Thus, new technologies have been developed based on a downscaled approach using direct energy deposition (DED) processes, now referred to as μ-DED. In this context, the development of a downscaled DED prototype based on gas metal arc (GMA) working with micrometric wires (μ-GMA) has the potential to unify the positive characteristics of GMA-based DED, increasing the complexity of the design and resolution of the produced parts. Therefore, this work focuses on developing a μ-GMA prototype and assessing its technical feasibility. This paper describes the development of the μ-GMA prototype, characterizes the metallic transfer mode, and statistically analyzes the effect of deposition parameters on bead width and height. Additionally, microstructural analysis, Vickers microhardness, and reduced Young's modulus tests were performed. The μ-GMA prototype demonstrated the capability to deposit beads with an approximate width of 1 mm, nearly 5 times thinner than standard GMA-based DED deposition, with a build rate of 30 cm3/h, which is lower than GMA-based DED but higher than other μ-DED processes. Furthermore, the mechanical properties of the μ-GMA depositions are comparable to regular GMA-based DED parts.
Structural integrity of polymeric components produced by additive manufacturing (Am)—polymer applications
Publication . Martins, Rui F.; Branco, Ricardo; Berto, Filippo; Soares, Nuno; Bandeira, Sebastião; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; MDPI - Multidisciplinary Digital Publishing Institute
In the work presented herein, the structural integrity of polymeric functional components made of Nylon-645 and Polylactic acid (PLA) produced by additive manufacturing (Fused Deposition Modelling, FDM) is studied. The PLA component under study was selected from the production line of a brewing company, and it was redesigned and analyzed using the Finite Element Method, 3D printed, and installed under real service. The results obtained indicated that, even though the durability of the 3D printed part was lower than the original, savings of about EUR 7000 a year could be achieved for the component studied. Moreover, it was shown that widespread use of AM with other specific PLA components could result in even more significant savings. Additionally, a metallic hanger (2700 kg/m3 ) from the cockpit of an airplane ATR 70 series 500 was successfully redesigned and additively manufactured in Nylon 645, resulting in a mass reduction of approximately 60% while maintaining its fit-for-purpose. Therefore, the components produced by FDM were used as fully functional components rather than prototype models, which is frequently stated as a major constraint of the FDM process.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UIDB/00285/2020