Browsing by Author "Capela, Carlos"
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- Determination of dynamic elastic properties of 3D-printed nylon 12CF using impulse excitation of vibrationPublication . Garcia, Pedro F.; Ramalho, Armando; Vasco, Joel; Rubén, Rui; Capela, Carlos; MDPIMaterial Extrusion (MEX) process is increasingly used to fabricate components for structural applications, driven by the availability of advanced materials and greater industrial adoption. In these contexts, understanding the mechanical performance of printed parts is crucial. However, conventional methods for assessing anisotropic elastic behavior often rely on expensive equipment and time-consuming procedures. The aim of this study is to evaluate the applicability of the impulse excitation of vibration (IEV) in characterizing the dynamic mechanical properties of a 3D-printed composite material. Tensile tests were also performed to compare quasi-static properties with the dynamic ones obtained through IEV. The tested material, Nylon 12CF, contains 35% short carbon fibers by weight and is commercially available from Stratasys. It is used in the fused deposition modeling (FDM) process, a Material Extrusion technology, and exhibits anisotropic mechanical properties. This is further reinforced by the filament deposition process, which affects the mechanical response of printed parts. Young’s modulus obtained in the direction perpendicular to the deposition plane (E33), obtained via IEV, was 14.77% higher than the value in the technical datasheet. Comparing methods, the Young’s modulus obtained in the deposition plane, in an inclined direction of 45 degrees in relation to the deposition direction (E45), showed a 22.95% difference between IEV and tensile tests, while Poisson’s ratio in the deposition plane (v12) differed by 6.78%. This data is critical for designing parts subject to demanding service conditions, and the results obtained (orthotropic elastic properties) can be used in finite element simulation software. Ultimately, this work reinforces the potential of the IEV method as an accessible and consistent alternative for characterizing the anisotropic properties of components produced through additive manufacturing (AM).
- Development of a preliminary finite element model to assess the effects of friction on the residual limb of a transfemoral amputeePublication . Ramalho, Armando; Ferraz, Miguel; Gaspar, Marcelo; Capela, CarlosThe use of numerical modelling tools allows optimizing the development of complex anatomical artefacts, such as customized prostheses for lower limb amputees. These numerical tools make it possible to characterize the interfacial interactions taking place between different parts of the prosthesis and the residual limb. This allows for understanding which rectifications and fittings having to be made on the custom design of the artificial body part without the need for manufacturing and donning prostheses. To such end, current research focused on the development of a preliminary Finite Element Model to assess the effects of friction on the residual limb of a transfemoral amputee, as the friction on the contact between the soft tissues, the liner and the prosthesis of the amputee is of major importance for his/her health and comfort.
- Dynamic elastic properties of E-Glass randomly oriented fiber reinforced SR GreenPoxy composite - Experimental and numerical analysisPublication . Ramalho, Armando; Gaspar, Marcelo; Correia, Mário; Vasco, Joel; Capela, Carlos; Rubén, RuiIn this article, the in-plane dynamic elastic properties of an E-glass randomly oriented fiber-reinforced SR GreenPoxy 56 composite were obtained based on the procedure specified in the ASTM E1876-21 standard. The experimental frequencies and the ones predicted by the simulation of the experimental procedure using a finite element analysis developed in the Patran/Nastran 2021 package were used in an iterative algorithm using sensitivity analysis to improve the first approaches of the dynamic elastic properties obtained by the impulse excitation technique. These experimental results are compared with the ones obtained by the 2D Short Fiber Composite model of the E-glass randomly oriented fiber-reinforced SR GreenPoxy 56 composite, developed in the Patran/Nastran 2021 software.
- Efeito do atrito no membro residual numa amputação transfemoral: influência do modelo constitutivo dos materiaisPublication . Ramalho, Armando; Ferraz, Miguel; Gaspar, Marcelo; Capela, CarlosNeste artigo é avaliado o efeito das propriedades mecânicas e tribológicas dos materiais na interação entre os diversos componentes da prótese numa amputação transfemoral, através de uma análise por elementos finitos. O modelo numérico é desenvolvido sobre o software MSC.marc. O atrito vai influenciar a distribuição de tensões entre as diversas interfaces – prótese/liner, liner/tecidos moles e tecidos moles/osso cortical. A distribuição das tensões de corte junto às interfaces, influencia o conforto do paciente, sendo uma das principais causas da geração de úlceras de pressão nos pacientes amputados que usam este tipo de próteses. É analisada a influência dos modelos constitutivos utilizados na modelação dos tecidos moles e do liner, na distribuição de tensão. Em concreto são comparados os resultados obtidos com a utilização de um modelo linear elástico com os obtidos com modelos hiperelásticos.
- Enhanced reconditioning of heavy-duty pulp industry equipment: advantages of abrasive waterjet cuttingPublication . Ramalho, Armando; Silva, Agostinho; Gaspar, Marcelo; Capela, Carlos; Celorrio-Barragué, Luis; Dan, GlăvanWithin a pulp industry production process, a drop in the performance of a wood log rotary debarker was identified. Such loss of performance was due to the occurrence of excessive wear of the device’s cutting blades, requiring their regular and premature replacement. The material used to manufacture the cutting blades, Hardox 500, has characteristics considered adequate for the required use. However, it was concluded that the blade manufacturing process degraded its mechanical properties, leading to its premature wear when placed in service. The present study intends to propose, characterize, and validate an alternative cutting process to manufacture the debarker’s cutting blades. Abrasive waterjet cutting technology was proposed to produce the cutting blades. The suitability of this manufacturing process is discussed considering the specified geometry and the material characteristics of the resulting cutting blades.
- Influence of materials and their constitutive laws on the stress fields produced in the residual limb of a transfemoral amputationPublication . Ramalho, Armando; Ferraz, Miguel; Gaspar, Marcelo; Capela, CarlosCurrent research uses a finite element analysis to characterize the effect of the materials mechanical and tribological properties on the interaction between the biological tissues of a transfemoral amputation and the combined prosthesis. Considering that both friction and mechanical properties influence the stress distribution between different interfaces, these were analyzed on the contacts of the prosthesis and the liner, the liner and the soft tissues and, finally, the soft tissues and the cortical bone. This is of significant importance, as it has been acknowledged that the shear stress distribution at these interfaces significantly impacts the patients’ comfort. These shear stresses have also been reported as one of the leading causes of pressure ulcers in osteotomized patients. Finally, this research discusses the influence of the soft tissues and the liner constitutive law in the stress field generated at the biological tissues. In particular, for the liner, the results using a linear elastic model are compared with those using the Mooney-Rivlin hyperelastic model. The results using a linear elastic model are compared with the Neo-Hookean and Ogden models’ results for the soft tissues.
- 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.