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- The influence of layer height in the orthotropic elastic properties of PLA material obtained by additive processesPublication . Gonçalves, Luís; Couto, Gonçalo; Ramalho, ArmandoPolylactic acid (PLA) is a biodegradable thermoplastic polyester used extensively in 3D printing, that can be obtained from renewable resources with low production costs and low carbon emissions. The extrusion temperature of PLA is lower, and its tensile strength and elastic modulus are higher than that of other common polymeric thermoplastic materials. To assess the structural integrity of parts obtained by additive manufacturing, especially in more complex geometries, the finite element method is extensively used, being necessary, for this purpose, to characterize the constitutive model of the material. From the printer manufacturing parameters, one of the most affecting the elastic and strength properties is the layer height. The layer-by-layer slicing sequence of additive manufacturing processes can introduce anisotropy into the materials, whereby, in most applications, materials obtained by these processes are considered orthotropic. The mechanical characterization of anisotropic materials through classical tests is not always the most suitable for this purpose, given the economic aspects, the time required, precision requirements and, sometimes, the technological difficulties of the tests. The ASTM E1876-21 standard presents a method for determining the dynamic elastic properties of materials by impulse excitation of vibration, at room temperature. In this article, the influence of the layer height in the dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio obtained by impulse excitation of vibration (ASTM E1876-21 standard), of Tough PLA is analyzed.
- Recycled reinforced PLA as ecodesign solution for customized prosthesesPublication . Gaspar, Marcelo; Ferraz, Miguel; Ramalho, Armando; Vasco, Joel; Capela, CarlosAdditive manufacturing is a key technology for the digital production of customized prostheses and orthoses. Considering that such assistive devices can be designed to meet specific biomechanical needs based on the actual contours of the patients’ limbs, the ability of those having physical disabilities being able to produce their custom prostheses and orthoses at home would be groundbreaking, by current standards. To such an end, this research aims at selecting sustainable biopolymers that can be used as filaments to produce customized prosthetic sockets using low-cost additive manufacturing technology. Special focus was put into characterizing the use of recycled PLA reinforced with short carbon fibers as filaments for additive manufacturing. Numerical simulation results showed the potential of this sustainable material combination as an ecodesign solution for customized prostheses and orthoses. Such a solution should allow for patients being able to successfully produce and assemble their own customized assistive devices using fused deposition modelling.
- Evaluation of the structural strength of anisotropic PLA components manufactured by 3D printingPublication . Ramalho, Armando; Freitas, Dino; Almeida, HenriquePredicting the mechanical strength of components manufactured by additive processes is a challenging task that is difficulted by the complexity of the geometries fabricated by these processes, along with the anisotropy enhanced by the layer-by-layer manufacturing method and the difficulty in quickly obtaining the elastic and strength properties of the materials, which are strongly influenced by the manufacturing parameters. The use of 3D CAD models in the design phase of components manufactured by 3D printing facilitates the use of the finite element method in assessing their strength and simulating their in-service behavior. However, the finite element analysis of 3D printed parts using anisotropic material behaviour are rare and restricted to simple geometries. To deal with the anisotropy of materials, intense research has been carried out for the last decades in the field of evaluating the mechanical strength of composite materials, introducing several specific failure criteria. In this article, the in-service behaviour of PLA components manufactured by 3D printing is simulated, applying criteria usually used in the study of composite materials to evaluate their mechanical strength. The simulation through the finite element method was developed on the Hexagon Marc/Mentat software, using the Maximum Stress and Hoffman failure criteria.