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- Crack growth in simulated residual stress fields on tungsten inert gas dressed welded joints: a 2d approachPublication . Ramalho, Armando; Antunes, F.V.; Ferreira, J.A.M.In this paper is presented a 2D finite element model to predict the residual stresses generated by Tungsten Inert Gas (TIG) dressing at the weld toe of a T-joint. The welded T-joints, made of S355AR steel, are obtained by covered electrode process and improved with TIG dressing. The analysis was developed with the MSC.Marc finite element code. The estimated stress field is validated with experimental stress results obtained using X-ray diffraction. Over the estimated residual stress field is simulated the growth of fatigue cracks. The simulation is performed with the virtual crack closure technique, implemented in the MSC.Marc software. The obtained results are compared with the integration solutions of the Paris-Erdogan law, without influence of residual stresses, where the stress intensity factor is obtained using the Mk factor proposed by Bowness and Lee, included in BS 7910 standard. The numerical predictions are also compared with experimental results.
- Measuring the dynamic elastic properties of anisotropic materials to characterize the mechanical behaviour of products manufactured by additive processesPublication . Ramalho, ArmandoThe use of additive processes in the manufacture of prototypes and structural components, or machine parts, had a great growth in the last decade. The use of new materials adapted to the requirements of use, with environmental sustainability and enabling the production of complex geometries, has leveraged additive manufacturing processes. The layer-by-layer slicing sequence of these manufacturing processes are prone to introducing anisotropy into the materials. 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 E 1876 – 01 standard presents a method for determining the dynamic elastic properties of materials by impulse excitation of vibration, at room temperature. Although the presented methodology is specifically suitable for isotropic materials, it is also mentioned that the methodology can be adopted for the use of anisotropic and non-homogeneous materials, requiring in this case additional care in the interpretation of the results. This speech will present the methodology adopted to obtain the dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio by impulse excitation of vibration, of materials obtained by 3D printing. The obtained properties are used in the simulation of the mechanical behaviour of components under in-service conditions, through the finite element method.
- Magnetoresistive sensors and piezoresistive accelerometers for vibration measurements: a comparative studyPublication . Dionísio, Rogério Pais; Torres, Pedro; Ramalho, Armando; Ferreira, Ricardohis experimental study focuses on the comparison between two different sensors for vibration signals: a magnetoresistive sensor and an accelerometer as a calibrated reference. The vibrations are collected from a variable speed inductor motor setup, coupled to a ball bearing load with adjustable misalignments. To evaluate the performance of the magnetoresistive sensor against the accelerometer, several vibration measurements are performed in three different axes: axial, horizontal and vertical. Vibration velocity measurements from both sensors were collected and analyzed based on spectral decomposition of the signals. The high cross-correlation coefficient between spectrum vibration signatures in all experimental measurements shows good agreement between the proposed magnetoresistive sensor and the reference accelerometer performances. The results demonstrate the potential of this type of innovative and non-contact approach to vibration data collection and a prospective use of magnetoresistive sensors for predictive maintenance models for inductive motors in Industry 4.0 applications.
- 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.
- 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.
- Simulação do crescimento de fendas em juntas soldadas: influência de campos de tensões residuaisPublication . Ramalho, Armando; Antunes, F.V.; Ferreira, J.A.M.Neste artigo é apresentado um modelo de elementos finitos tridimensional para prever o crescimento de fendas no pé do cordão de juntas soldadas em T. O modelo é desenvolvido sobre o software MSC.marc. A vida de fadiga é estimada por integração da lei de Paris-Erdogan. Os fatores de intensidade de tensão são obtidos pela técnica do fecho virtual de fenda (“virtual crack closure technique”), VCCT, implementada no software MSC.marc. É analisada a influência das tensões residuais geradas por deformação plástica no pé do cordão, na velocidade de propagação da fenda. Observou-se que a existência de campos de tensões residuais de compressão provoca um retardamento do crescimento de fenda.
- Retrofitting of welded structures by TIG and Plasma DressingPublication . Ramalho, Armando; Antunes, F.V.; Ferreira, J.A.M.Due to economic and environmental constrains, the currently trend is to use the welded structures beyond their design lives. The predominant cause of in service failure of these aged structures is the fatigue of the welded joints. The use of improvement techniques in welded joints, as a repair technique, has been suggested by several authors. TIG dressing is one of the most promising of these repair techniques. However, the effectiveness of TIG remelting is closely linked to the depth of the repaired crack. The use of strain gauges can be effective to detect the presence of fatigue cracks in their initial phase of propagation, however their effectiveness in inspection programs on jobsite needs to be proven. Some TIG variants associated to recent technological innovations of fusion arc welding, are appointed to improve the penetration and the sustainability of the remelting process. In this article are presented some results of the work developed by the authors in the last years, relevant to assess the efficiency of sustainable repair, by TIG and plasma dressing, of welded structures. Relevance is given to the repair, complete or defective, of deep cracks, as well as the possible advantage of using TIG variants.
- 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.
- 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.