ISEL - Eng. Mecan. - Artigos
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- Design, control, and testing of a multifunctional soft robotic GripperPublication . Correia, A.; Charters De Azevedo, Tiago; Leite, Afonso; Campos, Francisco M.; Monge, Nuno; Rocha, André; Mendes, Mário J. G. C.This paper proposes a multifunctional soft robotic gripper for a Dobot robot to handle sensitive products. The gripper is based on pneumatic network (PneuNet) bending actuators. In this study, two different models of PneuNet actuators have been studied, designed, simulated, experimentally tested, and validated using two different techniques (3D printing and molding) and three different materials: FilaFlex 60A (3D-printed), Elastosil M4601, and Dragonskin Fast 10 silicones (with molds). A new soft gripper design for the Dobot robot is presented, and a new design/production approach with molds is proposed to obtain the gripper’s PneuNet multifunctional actuators. It also describes a new control approach that is used to control the PneuNet actuators and gripper function, using compressed air generated by a small compressor/air pump, a pressure sensor, a mini valve, etc., and executing on a low-cost controller board—Arduino UNO. This paper presents the main simulation and experimental results of this research study.
- Efect of Tool Rotational Speed on Microstructure and Mechanical Properties of Friction Stir Welded Al–16Si–4Cu–10SiC Composite/ Al–4Cu–Mg Alloy JointsPublication . Aval, Hamed Jamshidi; Galvão, IvanThis study investigates the effects of different rotational speeds on the friction stir welding process of two distinct materials: an Al-16Si-4Cu-10SiC composite and an Al-4Cu-Mg alloy. The research primarily concentrates on the microstructure, mechanical properties, and corrosion resistance of the welded materials. The findings reveal that surface grooves and tunnel defects emerge at heat inputs of 1296 and 3024 J/mm, respectively. When the rotation speed decreases from 1200 to 800 rpm, the Zener parameter increases from 12.45 x 1013 to 14.78 x 1014, and the average grain size after recrystallization reduces from 3.7 +/- 0.3 to 2.1 +/- 0.4 mu m. The welding process results in the formation of theta-Al2Cu and S-Al2CuMg precipitates in the stir zones of the Al-16Si-4Cu-10SiC composite and Al-4Cu-Mg alloy, respectively. A reduction in rotational speed from 1200 to 800 rpm leads to hardness, ultimate tensile strength, and corrosion resistance values of 149.8 +/- 10.1 HV, 401.4 +/- 8.1 MPa, and 0.39 mm/year, respectively.
- Stress-Based Model for Calculating the Opening Angle of Notch Cracks in a Magnesium Alloy under Multiaxial FatiguePublication . Videira, Henrique; Anes, Vitor; Reis, LuísThis paper presents a model to calculate the opening angle of crack initiation in notched fractures subjected to multiaxial loading. To validate the proposed model, a study was performed on polished AZ31B-F magnesium alloy specimens under multiaxial high-cycle fatigue loading. The specimens exhibited a notch in the smaller cross-sectional area, which was created with a special drilling jig to promote the formation of fatigue cracks in this localized area of the specimen. The load paths used in the experiments and numerical analyses were proportional and non-proportional, resulting in different stress states in the crack front opening, which were determined by finite element analysis to validate the proposed model. To obtain more accurate numerical results for these estimates, these finite element analyses were performed using the nonlinear Chaboche plasticity model of ABAQUS (R) 2021 software. A sensitivity analysis was also performed to determine which load component-axial or torsional-has a greater influence on the fatigue strength and contributes significantly to the crack opening process. The results show that the type of load path and the stress level of each load component-axial and torsional-has a strong influence on the opening angle of the notch crack and the fatigue lifetime of the specimen. This result is confirmed not only by the experimentally determined fatigue strength, but also by a fractographic analysis performed on the surface of the specimens for both load paths. Moreover, the results show an acceptable correlation between the experimental results and the estimates obtained with the proposed model and the stresses obtained with the finite element analysis.
- Mechanical and thermal processing of wire-arc additively deposited stainless steelPublication . Silva, Carlos; Pragana, João; Bragança, Ivo; Martins, PauloMechanical and thermal processing of wire-arc additively deposited stainless steel is investigated with the purpose of improving its microstructure, surface morphology, formability, and stress response. Microscopy helps identifying the processing conditions that permit full recrystallization of the as-built columnar microstructure. Combination with strain loading paths, topography and fractography in tensile tests show that mechanical processing consisting of 20 % thickness reduction followed by annealing at 1100 °C under 4 h eliminates anisotropy and increases the fracture forming limits by 30 %. The work is a step forward to consolidate the hybridization of wire-arc additive manufacturing with metal forming as an alternative to conventional manufacturing.
- On the Enhancement of Material Formability in Hybrid Wire Arc Additive ManufacturingPublication . Pragana, João; Brito, Beatriz; Bragança, Ivo; Silva, Carlos; Martins, PauloThis paper is focused on improving material formability in hybrid wire-arc additive manufacturing comprising metal forming stages to produce small-to-medium batches of customized parts. The methodology involves fabricating wire arc additive manufactured AISI 316L stainless steel parts subjected to mechanical and thermal processing (MTP), followed by microhardness measurements, tensile testing with digital image correlation, as well as microstructure and microscopic observations. Results show that mechanical processing by pre-straining followed by thermal processing by annealing can reduce material hardness and strength, increase ductility, and eliminate anisotropy by recrystallizing the as-built dendritic-based columnar grain microstructure into an equiaxed grain microstructure.
- Evaluation of tool rotational speed effect in Al-16Si-4Cu-10SiC composite/Al-4Cu-Mg alloy jointPublication . Jamshidi Aval, Hamed; Galvão, IvanThis study investigated the influence of the rotational speed of the tool with a cylindrical threaded pin on the microstructure, mechanical properties and corrosion resistance of the Al-16Si-4Cu-10SiC composite/Al-4Cu-Mg alloy joint. The results show tunnel defects are formed on the advancing side in the heat input less than 121 J/mm and more than 342 J/mm. With the increase of rotational speed from 800 to 1000 rpm, the silicon particle size and the aspect ratio have decreased and increased from 5.6 ±1.2 to 3.5±1.4 µm and 0.6 to 0.8, respectively. By decreasing rotational speed from 1000 to 800 rpm, the maximum hardness (152.3 ±0.6 HV0.1), yield strength (383±6 MPa), ultimate tensile strength (469±9 MPa) and corrosion rate (1.03 mm/year) were achieved.
- A strain acceleration method to identify the onset of diffuse neckingPublication . Sampaio, Rui F. V.; Pragana, João; Bragança, Ivo; Silva, Carlos; Martins, PauloThis paper presents an innovative ‘strain acceleration method’ for determining the onset of diffuse necking in sheet forming tests using data obtained from digital image correlation (DIC). The method identifies the onset time of diffuse necking and provides the corresponding in-plane principal strain values by detecting a local extreme in the second derivative of the minor principal in-plane strain with respect to time at the edges of the sheet surface region where diffuse necking occurs. Results obtained from applying the method to tensile testing on two different materials and comparisons with available methods based on force-time or principal strain rate evolutions confirm its accuracy and validity. The new method was implemented in a computer software to be used for research and education that also enables determination of localized necking and fracture and plotting the strain loading paths in principal strain space.
- Characterization of friction stir welded Al-4Cu-Mg alloy / Al-16Si-4Cu-10SiC composite jointPublication . Aval, Hamed Jamshidi; Galvão, IvanThis study investigated the tool’s rotational speed effect during dissimilar friction stir welding of A390–10 wt.% SiC composite-AA2024 aluminum alloy on microstructure, mechanical properties, and corrosion resistance. The results show that the tunnel defect is created on the advancing side at low rotational speeds of 400 and 600 rpm due to insufficient material flow and a high rotational speed of 1200 rpm due to turbulent material flow in the stir zone. Finely equiaxed recrystallized grains are formed in the stir zone under a high plastic strain rate and particle-stimulated nucleation mechanism. The minimum hardness occurs in the TMAZ of the AA2024 aluminum alloy side, and by increasing the rotational speed from 800 to 1000 rpm, the average hardness in the stir zone decreases from 146.06±8.67 to 137.86±3.98 HV0.1. Also, by increasing the rotational speed from 800 to 1000 rpm, the stir zone’s yield strength and ultimate tensile strength decrease by 4.9 and 5.2%, respectively. With the increased rotational speed from 800 to 1000 rpm, corrosion current increases from 0.0213 to 0.0225 mA.cm_2 and corrosion resistance decreases by 17 %. After friction stir welding with a rotational speed of 800 rpm and traverse speed of 20 mm/min, the corrosion resistance of the joint increases and decreases compared to the composite base metal and AA2024 aluminum alloy base metal, respectively.
- Microstructural characterization and corrosion-resistance behavior of friction stir-welded A390/10 wt% SiC composites-AA2024 Al alloy jointsPublication . Aval, Hamed Jamshidi; Galvão, IvanThis study examined the effect of traverse speed on the mechanical properties, corrosion-resistance behavior, and microstructure of friction stir-welded A390/10 wt% SiC composites AA2024 Al alloy joints. The laminar flow of both materials was found to diminish in the stir zone (SZ) when the traverse speed of the tool increased from 40 to 80 mm/min, lowering their mixing rate. Large aspect ratio Si particles are broken by the tool pin-induced applied plastic strain, which turns them into refined equiaxed particles. Their aspect ratio remains unchanged in the SZ, despite their decreasing size. SiC and Si particles progressively come into view when moving from the AA2024 alloy’s SZ to the composite workpieces. These changes happen abruptly as traverse speed increases due to the lack of an interfacial layer structure. The advancing side (AS)’s SZ grain size drops from 4.2 ± 0.3 μm to 1.2 ± 0.2 μm as the traverse speed drops from 80 to 40 mm/min. Increased traverse speed from 40 to 80 mm/min will result in a 5.8% decrease in elongation percentage (EP) and 8.4%, 36%, and 10.3% increases in the ultimate tensile strength (UTS), corrosion resistance, and yield strength, respectively.
- Microstructure and corrosion behavior of A390-10 wt% SiC composite-AA2024-T6 aluminum alloy dissimilar joint: Effect of post-weld heat treatmentPublication . Aval, Hamed Jamshidi; Galvão, IvanThe weldability of aluminum matrix composites to other materials, such as aluminum alloys, is an essential point in expanding the use of these materials. This study investigated the effect of rotational speed and post-weld heat treatment on the microstructure, mechanical properties, and corrosion behavior of A390-10 wt% SiC composite/ AA2024-T6 aluminum alloy dissimilar joint. Friction stir welding is performed using a square frustum pyramid pin tool with a rotational speed of 400–1200 rpm and a traverse speed of 40 mm/min. Results found that a surface groove formed on the weld crown at a rotational speed lower than 800 rpm due to insufficient material flow. Also, the tunnel defect formed on the advancing side at a rotational speed higher than 1000 rpm due to the turbulent flow of material. By increasing rotational speed from 800 to 1200 rpm, the average grain size of the advancing and retreating sides increased by 41.1 and 46.3 %, respectively. Compared to AA2024-T6 and A390-10 wt% SiC composite base metals, the average hardness of the stir zone of the joint fabricated by the rotational speed of 800 rpm increased by 8.4 and 38.2 %, respectively. By increasing the rotation speed from 800 to 1000 rpm, the yield strength and ultimate tensile strength decreased by 6.8 and 6.5 %, respectively. By decreasing rotational speed from 1000 to 800 rpm, the elongation and corrosion resistance decreased by 5.4 % and 34.7 %, respectively. After post-weld heat treatment, the hardness, yield strength, ultimate tensile strength, and corrosion resistance increase 15.9, 12.7, 7.8, and 28.9 %, respectively.