Browsing by Author "Santos, Telmo G."
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Item Assessment of the energetic efficiency of friction stir welding/processing(Elsevier, 2023-10-06) Inácio, Patrick L.; Ferreira, Francisco B.; Vilaça, Pedro; Oliveira, J. P.; Santos, Telmo G.; Department of Mechanical Engineering; NOVA University LisbonThis paper scrutinizes and goes beyond previously published results on the analysis of the energy flow during friction stir welding/processing (FSW/P). An in-depth scientific method was used to assess the individual energetic contribution arising from the main components within the FSW/P system. This investigation was performed during FSW/P of AA7075 with different tool rotations and travel speeds. The main contributors to energy losses during the FSW/P process include the FSW/P tool, anvil, unprocessed base material, and the surrounding environment. It was found that only about 25 % of the total energy is effectively used to perform the welding/processing, while the remaining energy dissipates through heat into the tooling and clamping system. Additionally, around 6 % of the energy is lost towards the base material, forming the heat-affected zone (HAZ). These results suggest that proper selection of the anvil material offers a promising opportunity to enhance effective energy efficiency, considering that approximately 60 % of the total energy input is lost through this component. Addressing this substantial energy loss becomes essential for achieving a more energetically sustainable industrial application of the FSW/P process.Item Contactless high-speed eddy current inspection of unidirectional carbon fiber reinforced polymer(Elsevier Limited, 2019-07-01) Machado, Miguel A.; Antin, Kim Niklas; Rosado, Luís S.; Vilaça, Pedro; Santos, Telmo G.; Department of Mechanical Engineering; Advanced Manufacturing and Materials; NOVA University Lisbon; University of LisbonThis paper presents the development and the results of a customized eddy current (EC) non-destructive testing (NDT) system for highly demanding online inspection conditions. Several planar eddy current array probes were designed, numerically simulated and experimentally compared for the inspection of low conductivity unidirectional carbon fibre reinforced polymer (CFRP) ropes. The inspections were performed using a dedicated scanner device at 4 m/s with 3 mm probe lift-off where defects under 1 mm were detected with an excellent SNR. Different defect morphologies and sizes, such as broken fibres and lateral cuts, were successful detected and compared to conventional probes.Item Double active transient thermography(ELSEVIER SCI LTD, 2022-01) Machado, Miguel A.; Silva, Maria I.; Martins, Ana P.; Carvalho, Marta S.; Santos, Telmo G.; Department of Mechanical Engineering; Advanced Manufacturing and Materials; NOVA University LisbonThis paper presents an innovative variant of the Active Transient Thermography (ATT), designated Double Active Transient Thermography (DATT), where the component inspected is excited by one heat and one cold sources. The goal is to speed up and improve the temperature contrast, namely for polymer matrix composites parts produced by Additive Manufacturing. Finite element analysis of the thermal phenomena involved in DATT were performed to assist the definition of the experimental set-ups and confirm the high potential of the technique. Experimental results prove that the introduction of the cold flow increases the temperature contrast up to 100%, comparing with ATT, and mid thickness defects are the ones that benefits the most from this technique. Therefore, the improvement of the inspection procedure is achieved by two means: enhancing the thermal contrast of the defects, and/or anticipating the instant when the maximum contrasts occur.Item Eddy Current Testing of Unidirectional Carbon Fibre Reinforced Polymer Composites Using Advanced Probe(2015) Antin, Kim-Niklas; Santos, Telmo G.; Vilaça, Pedro; Department of Engineering Design and ProductionItem Effect of processing temperatures on the properties of a high-strength steel welded by FSW(2018-11-01) Sorger, Gonçalo; Sarikka, Teemu; Vilaça, Pedro; Santos, Telmo G.; Department of Mechanical Engineering; Engineering Materials; NOVA University LisbonThe need for weight reduction without compromising load-bearing capacity has driven the development of modern high-strength steels (HSS). The ability to take full advantage of these modern HSS is limited by their weldability. Friction stir welding (FSW) can join HSS at low peak temperatures, better preserving the properties of the base material. This work evaluates the influence of different FSW peak temperatures and cooling rates on the properties of a modern HSS. A HSS produced by a thermo-mechanically controlled process was welded by FSW with peak temperatures, measured within the processed zone, ranging from about 900 to 650 °C. Temperatures were measured using thermocouples positioned at the mid-thickness of the workpiece, at 5 to 10 mm from the joint line. The effect of the different peak temperatures was evaluated by mechanical testing, including bending, tensile testing with digital imaging correlation, Charpy impact test, and hardness measurements. Microscopic analyses, including optical microscopy and electron backscatter diffraction, were used to evaluate the microstructure. Results show that FSW enables welding HSS within the intercritical temperature domain. The impact toughness of the best weld condition overmatched the base material by over 37%, at both − 40 and − 60 °C. The yield strength efficiency was about 70%.Item Effect of processing temperatures on the properties of high strength steel welded by FSW(2017) Lourenco Sorger, Goncalo; Sarikka, Teemu; Santos Vilaca da Silva, Pedro; Santos, Telmo G.; Department of Mechanical Engineering; Engineering Materials; NOVA University LisbonItem Evaluation of Different Non-destructive Testing Methods to Detect Imperfections in Unidirectional Carbon Fiber Composite Ropes(Springer New York, 2019-03-01) Antin, Kim Niklas; Machado, Miguel A.; Santos, Telmo G.; Vilaça, Pedro; Department of Mechanical Engineering; Advanced Manufacturing and Materials; NOVA University LisbonOnline monitoring of carbon fiber reinforced plastic (CFRP) ropes requires non-destructive testing (NDT) methods capable of detecting multiple damage types at high inspection speeds. Three NDT methods are evaluated on artificial and realistic imperfections in order to assess their suitability for online monitoring of CFRP ropes. To support testing, the microstructure and electrical conductivity of a carbon fiber rope is characterized. The compared methods are thermography via thermoelastic stress analysis, ultrasonic testing with commercial phased array transducers, and eddy current testing, supported by tailor-made probes. While thermoelastic stress analysis and ultrasonics proved to be accurate methods for detecting damage size and the shape of defects, they were found to be unsuitable for high-speed inspection of a CFRP rope. Instead, contactless inspection using eddy currents is a promising solution for real-time online monitoring of CFRP ropes at high inspection speeds.Item FSW of Aluminium AA5754 to Steel DX54 with Innovative Overlap Joint(2017) Sorger, Gonçalo; Wang, Hao; Vilaça, Pedro; Santos, Telmo G.; Department of Mechanical Engineering; Engineering Materials; Aalto University; NOVA University LisbonAn innovative overlap joint concept was tested to evaluate the quality improvement of welds between aluminum alloy AA5754-H22 (2 mm) and steel DX54 (1.5 mm). The innovation is a wave-shaped interface produced on the steel being directly processed by the tip of the probe, generating localized heat, extensive chemically active surfaces, and additional mechanical interlocking. Welds with different parameters were evaluated by metallographic analysis and mechanical tests. The best set of parameters was then implemented in a conventional overlap joint, plus in two- and three-passes welding, with the innovative overlap joint concept, to evaluate the effect on microstructure and mechanical efficiency. With a single-pass weld, the new concept presented lower strength in tensile shear tests, but higher strength in peeling tests. The main mechanism governing this behavior was the reduction of effective thickness in the aluminum alloy sheet, due to the flow of steel into the aluminum alloy. The characterization and distribution of the intermetallic compounds were evaluated via SEM-EDX. The two-passes weld resulted in the best strength values in tensile shear tests, reaching about 50% of the ultimate tensile strength of the aluminum alloy base material.Item Functionalized material production via multi-stack Upward Friction Stir Processing (UFSP)(TAYLOR & FRANCIS, 2022) Inácio, Patrick L.; Nogueira, Fábio; Ferreira, Francisco B.; Vidal, C.; Schell, Norbert; Tero, Teemu; Vilaça, Pedro; Oliveira, J. P.; Santos, Telmo G.; Department of Mechanical Engineering; Advanced Manufacturing and Materials; NOVA University Lisbon; Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research; Department of Mechanical EngineeringAn innovative friction stir processing variant, named Upward Friction Stir Processing (UFSP), for producing customized materials with multifunctional particles is presented. In the UFSP, an upward flow is used to disperse these functional particles in a metallic matrix, in opposition to the widely used downward flow. As a proof of concept, SiC particles were introduced and dispersed into an aluminum alloy AA7075-T651 matrix to study different process parameters and to validate this novel material processing technology. Six different small-sized ingots were produced and compared to the conventional FSP technology. The microstructural evolution is studied by means of light microscopy, eddy current testing, microhardness mapping and advanced characterization techniques, such as high-energy synchrotron X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction. The number of passes was seen to greatly impact the particle distribution. Additionally, UFSP promotes a more uniform particle distribution over a larger processed area, when the lateral tool offset progress along the retreating side.Item Innovative Concept and Application of EC Probe For Inspection of Friction Stir Welds(2013) Vilaça, Pedro; Santos, Telmo G.; Rosado, Luis; Miranda, Rosa M.; Department of Engineering Design and ProductionItem Local magnetic flux density measurements for temperature control of transient and non-homogeneous processing of steels(NATURE PUBLISHING GROUP, 2019-11-29) Sorger, Goncalo; Vilaca, Pedro; Santos, Telmo G.; Department of Mechanical Engineering; Advanced Manufacturing and Materials; Universidade Nova de LisboaMeasuring temperatures during high-temperature processing of steels is usually limited to surface measurements that cannot directly assess the internal temperature distribution. Here, we demonstrate the feasibility of using a magnetic flux density measurement system to assess transient and non-homogeneous temperature fields in a modern high-strength steel, within the intercritical temperature range where microstructural evolution defines their key mechanical properties. The system accurately detects the Curie temperature and distinguishes temperature change rates within the processed volume. The magnetic measurements are also sensitive to the volume above Curie temperature and its shape, as revealed when integrated with thermal computational simulations. The electromagnetic signal provides real-time qualitative and quantitative information relevant to the metallurgical conditions enabling future intelligent control systems for the production and processing of steels. Contactless measurements of temperature-dependent electromagnetic properties can enable through-thickness temperature monitoring solutions, opening up opportunities for non-destructive full-field imaging of steels during thermal and thermomechanical processing.Item Microscale channels produced by micro friction stir channeling (μFSC)(Elsevier, 2024-09-01) Sabor, Wagner C.; Damásio, Daniel F.B.; Tasnicenco, Rúben S.; Sorger, Goncalo; Santos, Telmo G.; Machado, Miguel A.; Vidal, Catarina I.S.; Department of Mechanical Engineering; Materials to Products; NOVA University LisbonThe current literature lacks comprehensive research on the processing limits of the Friction Stir Channeling process (FSC) for creating the smallest continuous and integral channels, using tools with threaded probes 2 mm in diameter or smaller. This study pioneers the exploration of the extreme limits of the microscale FSC process, with potential applications in the development of ultra-compact heat exchangers, seeking to enhance the efficiency and sustainability of these systems. Customized tools were designed and manufactured, with predefined dimensions and geometries to establish a set of parameters that consistently produce continuous microchannels, maximizing the hydraulic diameter within the constraints of each tool's specifications and geometry. Comprehensive evaluations—including continuity, watertightness, micro-computed tomography, neutron computed tomography, microhardness testing, and thermal measurements—were conducted to ensure the channels' structural integrity and suitability for super-compact heating and cooling applications. Internal channels were successfully created using tools with threaded probes measuring 2.0, 1.0, and 0.5 mm in diameter, and corresponding shoulder diameters of 5, 4, and 3.5 mm, within 5 mm thick AW1050-H111 aluminum alloy plates. The smallest channel achieved a hydraulic diameter of 191 μm, using a 0.5 mm diameter threaded probe, thus qualifying it as a microchannel. The thermal performance of a compact heat exchanger model was also tested, demonstrating that despite the high cost associated with tool production, particularly due to the specialized manufacturing processes required, the FSC process remains viable, reliable, and repeatable for the production of mini- and micro-channels.Item Process Developments and Materials Characterization in FSW/P(2014) Miranda, Rosa M.; Gandra, João; Santos, Telmo G.; Quintino, Luísa; Santos Vilaca da Silva, Pedro; Department of Engineering Design and ProductionItem Recent developments in FSW assisted by electrical current hybrid process(2017) Santos, Pedro; Oliveira, J. P.; Inácio, Patrik L.; Chen, Yingchun; Santos Vilaca da Silva, Pedro; Miranda, R.M.; Santos, Telmo G.; Department of Mechanical Engineering; Engineering Materials; NOVA University Lisbon; Ohio State UniversityItem Review of conventional and advanced non-destructive testing techniques for detection and characterization of small-scale defects(Elsevier Ltd, 2023-09) Santos Silva, Maria; Malitckii, Evgenii; Santos, Telmo G.; Vilaça, Pedro; Department of Mechanical Engineering; Materials to Products; Universidade Nova de LisboaInspection reliability of small-scale defects, targeting dimensions below 100 µm, is crucial for structural safety of critical components in high-value applications. Early defects are often possible to repair, contributing for the circular economy and sustainability by allowing extended life and reuse of components. During in-service operation, the small-scale defects are typically originated from creep, fatigue, thermal cycles, and environmental damage, or any combination of these multiphysical loading conditions. What are thresholds in Non-Destructive Testing (NDT) techniques to detect and reliably characterise small-scale defects? What is the state of the art of NDT-based solutions, in terms of small-scale defects located at surface, and interior of materials? Examples of small-scale defects in engineering materials are established, and a holistic review is composed on the detectability in terms of sensitivity and resolution. Distinguishable high detection accuracy and resolution is provided by computed tomography paired with computer laminography, scanning thermal microscopy paired with Raman spectroscopy, and NDT techniques paired with machine learning and advanced post-processing signal algorithms. Other promising techniques are time-of-flight diffraction, thermoreflectance thermal imaging, advanced eddy currents probes, like the IOnic probe, micro magnetic bridge probe used in magnetic flux leakage, driven-bacterial cells, Quantum dots and hydrogen-as-a-probe.
