Centre for Mechanical Enginnering, Materials and Processes

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Organizational Unit

Publications

In search of the optimal conditions to process shape memory alloys (NiTi) using fused filament fabrication (FFF)

Publication . Carreira, Pedro; Cerejo, Fábio; Alves, Nuno; Vieira, Maria Teresa

This research was performed so as to investigate the additive manufacturing of NiTi shape memory alloys, which is associated with direct processes, such as selective laser melting. In addition to its expensive production costs, NiTi readily undergoes chemical and phase modifications, mainly as a result of Ni loss during processing as a result of high temperatures. This research explores the potential usefulness of NiTi as well as its limitations using indirect additive processes, such as fused filament fabrication (FFF). The first step was to evaluate the NiTi critical powder volume content (CPVC) needed to process high-quality filaments (via extrusion). A typical 3D printer can build a selected part/system/device layer-by-layer from the filaments, followed by debinding and sintering (SDS), in order to generate a near-net-shape object. The mixing, extruding (filament), printing (shaping), debinding, and sintering steps were extensively studied in order to optimize their parameters. Moreover, for the sintering step, two main targets should be met, namely: the reduction of contamination during the process in order to avoid the formation of secondary phases, and the decrease in sintering temperature, which also contributes to reducing the production costs. This study aims to demonstrate the possibility of using FFF as an additive manufacturing technology for processing NiTi.

2020-10-22Journal article

Open access

The Effect of Acute Physical Fatigue on Information Processing, Pain Threshold and Muscular Performance

Publication . Clemente-Suárez, Vicente Javier; Fuentes-García, Juan Pedro; Castro, Maria António; Tornero-Aguilera, Jose Francisco; Martínez-Guardado, Ismael

This study explores the multifaceted effects of acute physical fatigue on information processing, pain threshold, and muscular performance. Enrolling 28 recreational athletes, we used a high-intensity interval training (HIIT) protocol to induce fatigue and conducted pre- and post-intervention assessments. Our findings revealed significant physiological and performance adaptations following the HIIT sessions. Key observations included increased heart rate and rate of perceived exertion and an enhancement in horizontal jump performance and isometric hand strength but no significant change in cognitive processing speed. Remarkably, participants demonstrated a notable increase in pain threshold and blood lactate levels post-exercise. These results challenge traditional views of fatigue, indicating not only a physiological but also a psychological resilience to high-intensity stress. This study provides new insights into the complex interplay between physical fatigue, cognitive function, and pain perception, highlighting the comprehensive effects of HIIT on both physiological and psychological dimensions of human performance.

2024-02-29Journal article

Open access

Nugget Formation and Mechanical Behaviour of Friction Stir Welds of Three Dissimilar Aluminum Alloys

Publication . Manuel, Neves; Galvão, Ivan; Leal, Rui M.; Costa, José D.; Loureiro, Altino

The aim of this research was to investigate the influence of the properties of the base materials and welding speed on the morphology and mechanical behavior of the friction stir welds of three dissimilar aluminum alloys in a T-joint configuration. The base materials were the AA2017-T4, AA5083-H111, and AA6082-T6 alloys in 3 mm-thick sheets. The AA6082-T6 alloy was the stringer, and the other alloys were located either on the advancing or retreating sides of the skin. All the T-joint welds were produced with a constant tool rotation speed but with different welding speeds. The microstructures of the welds were analyzed using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and the electron backscatter diffraction technique. The mechanical properties were assessed according to micro-hardness, tensile, and fatigue testing. Good quality welds of the three dissimilar aluminum alloys could be achieved with friction stir welding, but a high ratio between the tool's rotational and traverse speeds was required. The welding speed influenced the weld morphology and fatigue strength. The positioning of the skin materials influenced the nugget morphology and the mechanical behavior of the joints. The joints in which the AA2017 alloy was positioned on the advancing side presented the best tensile properties and fatigue strength.

2020Journal article

Open access

Evaluation of the structural strength of anisotropic PLA components manufactured by 3D printing

Publication . Ramalho, Armando; Freitas, Dino; Amorim Almeida, Henrique

Predicting 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.

2024-02-09Conference object

Open access

Postural Control and Muscle Activity during Dual-Task in Young Adults

Publication . Saraiva, Marina; Vilas-Boas, João Paulo; Castro, Maria António

In everyday life, we recurrently perform two tasks simultaneously, which is called dual-tasking. A common dual task is smartphone use while standing or walking. According to previous studies, this task can compromise postural stability. However, few studies have analyzed lower limb muscle activity during dual-tasking using smartphones. This study aimed to assess the postural sway and muscle activity during dual-tasking in young adults. Thirty-six healthy young adults (23.08 ± 3.92 years) participated in this study. They performed a single task (ST: keeping a quiet standing posture) and a dual task (DT: keeping the ST while simultaneously performing a cognitive task on their smartphone). Postural sway was assessed through the center of pressure (CoP) analysis using a force platform: total CoP displacement, CoP displacement in the anterior–posterior and medial–lateral directions, mean total velocity of the CoP, mean velocity of the CoP in the anterior–posterior and medial–lateral directions, and 95% confidence ellipse sway area. A surface electromyography system recorded the muscle activity of the lumbar spinal erector and five muscles of the lower limb (bilaterally). The results showed an increase in postural sway from the ST to the DT in all CoP variables (p < 0.05), and muscle activity in most muscles analyzed decreased from the ST to the DT (p < 0.05). In conclusion, our results reflect a decentralization of attention from motor performance once postural sway increased and muscle activity decreased in dual-task conditions.

2024-05-13Journal article

Open access