31 research outputs found

    Caracteritzaci贸 termomec脿nica d'actuadors amb mem貌ria de forma NiTiCu

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    In this thesis the thermomechanical characterization of the shape memory alloy NiTiCu working as an actuator with different heat treatment (HT) temperatures has been carried out. The results from the tests carried on resistivity changes and differential scanning calorimetry (DSC) showed the dependence of the transformation temperatures with the heat treatment temperature. There have not been identified big differences between different HT temperatures in mechanical behaviour (tensile tests until break and microhardness measurements) at martensitic state on the working range (stress/strain) of most applications. However, there has been noticed a loss of mechanical properties for high stress/strain tests values from a heat treatment temperature above 550潞C. Dynamomechanical tests (DMA) allowed the study of the martensitic transformation evolution and its relation to microstructural changes. The results of the internal friction (IF or tan d) showed correlation with the results of DSC, showing the same trend in function of the HT temperature. The characterization of the microstructure has allowed the correlation of the results obtained in the previous sections with microstructural changes. The identification of particles that were not part of the matrix (carbides, oxides and precipitates) through the scanning electron microscopy (SEM) lead to a particle quantification and distribution analysis. A list of potential precipitates present was carried out through the energy-dispersive X-ray spectroscopy (EDS) technique. The results of synchrotron X-ray diffraction (SXRD) confirmed the hypotheses done about the microstrucutural changes produced at different HT temperatures and show clear evidence of the presence of precipitates Ti2Ni. At the same time, a quantitative analysis of the texture, microstrain and presence of phase B2, B19' and Ti2Ni for all HT temperatures was also carried out analyzing the diffractograms from SXRD. The characterization of the termomechanical behaviour at different temperatures was studied through stress-strain tests at different temperatures for the whole range of working temperatures. After that, a comparative study of the main parameters for the different HT temperatures was carried out. The study of the tension/compression stress-strain asymmetry through the elastic and transformation zone was carried out on tubes with stacked rosette strain gauges. At the same time, the strain ratio (relationship between transverse and axial strains) evolution was studied. In order to study the thermomechanical cycling stability (to simulate the most common actuators working conditions) different tests conditions were applied: constant tension tests with thermal cycling at different stress levels (CS); and isothermal tests (below Mf) at a constant strain level and subsequent thermal recovery after each cycle without load (IT). Hence, constant stress with thermal cycling performed superior results for actuation purposes with high recovery strains and stabilization. Nevertheless, isothermal tests at a certain stress level showed degradation that lead to an unstable behaviour that was not reliable for actuator purposes. The results from CS tests showed that stress-temperature behaviour presented different tendencies in function of the stress level and there were significant differences between the behaviour of the initial cycle and the stabilized one at high stress levels (from 30 MPa). The microstructural changes due to thermomechanical cycling have been analyzed through microhardness increase measurements and SXRD. Hardness tests showed correlation between hardness increase and thermomechanical cycling. SXRD analysis also showed correlation between the quantity of retained martensite (B19 (orthorhombic) and B19' (monoclinic)) at 120潞C and different thermomechanical cycling conditions.En aquesta tesi s'ha realitzat la caracteritzaci贸 termomec脿nica d'actuadors amb mem貌ria de forma NiTiCu, amb diferents temperatures de tractament t猫rmic. Els resultats dels assaigs realitzats mitjan莽ant la t猫cnica de mesura de resistivitat i per calorimetria diferencial de rastreig (DSC) mostren la depend猫ncia de les temperatures de transformaci贸 amb la temperatura del tractament t猫rmic. En el comportament mec脿nic en estat martens铆tic, s'han analitzat les difer猫ncies en el comportament mec脿nic entre els diferents HT. En el rang de treball de la majoria d'aplicacions no s'han observat grans difer猫ncies entre els HT, per貌 s'ha observat una p猫rdua de propietats mec脿niques a partir d'una temperatura de tractament t猫rmic de 550潞C. Els assaigs dinamomec脿nics (DMA) han perm猫s estudiar l'evoluci贸 de la transformaci贸 martens铆tica i els resultats mostren correlaci贸 amb els resultats de DSC, observant aix铆 la mateixa tend猫ncia en funci贸 de la temperatura del HT en els resultats de la fricci贸 interna (IF o tan d). La caracteritzaci贸 de la microestructura ha perm猫s correlacionar els resultats obtinguts en els apartats anteriors amb els canvis microestructurals. La microsc貌pia electr貌nica de rastreig (SEM) va permetre identificar les part铆cules que no formen part de la matriu i identificar els possibles precipitats presents. Els resultats de difracci贸 per raigs X de sincrotr贸 varen confirmar les hip貌tesis realitzades i mostren la pres猫ncia dels precipitats Ti2Ni i les difer猫ncies entre els HT, mitjan莽ant l'an脿lisi quantitatiu de pres猫ncia de les fases B2, B19'i Ti2Ni. El comportament tensi贸-deformaci贸 en tot el rang de temperatures de treball ha perm猫s caracteritzar el comportament tensi贸-deformaci贸 en funci贸 del HT, per a tot el rang de temperatures. El comportament de tubs amb assaigs a tracci贸 i compressi贸 mitjan莽ant l'an脿lisi de la deformaci贸 amb galgues extensom猫triques ha perm猫s identificar la asimetria de comportament tracci贸-compressi贸 i la r脿tio de deformacions transversals/axials. Un cop caracteritzades les propietats termomec脿niques dels diferents tractaments t猫rmics es va avaluar el comportament enfront al ciclatge termomec脿nic. S'han considerat dues condicions d'assaigs diferents, per una part s'avalua el comportament a tensi贸 constant amb ciclatge t猫rmic per diferents nivells de tensi贸 i cinquanta cicles en cada proveta (CS). La segona condici贸 d'assaig consta d'assaigs isot猫rmics a temperatura per sota de Mf a un nivell de deformaci贸 constant i recuperaci贸 posterior de la deformaci贸 a cada cicle sense c脿rrega (IT). En els assaigs CS, tot i la degradaci贸 observada, en tots els nivells de tensi贸 i en gaireb茅 tots els HT estudiats, s'ha aconseguit una estabilitzaci贸 del comportament Per contra, en l'avaluaci贸 del comportament en els assaigs IT, no s'ha obtingut l'estabilitzaci贸 del comportament per cap HT i, per tant, aquesta configuraci贸 de treball nom茅s 茅s v脿lida per un nombre determinat de cicles. Els gr脿fics tensi贸-temperatura realitzats amb els resultats dels assaigs CS confirmen que no es pot modelitzar el comportament amb un 煤nic tram lineal, i a m茅s a m茅s es produeixen difer猫ncies significatives entre el comportament del cicle inicial i el comportament estabilitzat en els nivells alts de tensi贸. Els canvis microestructurals soferts en els ciclatges termomec脿nics s'han analitat mitjan莽ant el canvi en la duresa del material i la difracci贸 de raigs X de sincrotr贸. Els resultats d'aquest apartat mostren que en les provetes amb ciclatge termomec脿nic s'observa l'aparici贸 de la fase B19 (ortor貌mbica), junt amb la fase B19' (monocl铆nica) com a martensita retinguda a 120潞C

    Controlled composite processing based on off-stoichiometric thiol-epoxy dual-curing systems with sequential heat release (SHR)

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    Control of curing rate and exothermicity during processing of thermosetting composite materials is essential in order to minimize the formation of internal stresses leading to mechanical and dimensional defects in the samples, especially in thick composite samples. It was recently proposed that sequential heat release, an approach based on the kinetic control of the curing sequence of dual-curing thermosets, would enable a step-wise release of the reaction heat and therefore a better control of conversion and temperature profiles during the crosslinking stage. In this article, it is shown experimental proof of this concept obtained by means of an instrumented mold that can be used for the processing of small samples with and without carbon fiber reinforcement. Safe processing scenarios have been defined by numerical simulation using a simplified two-dimensional heat transfer model and validated experimentally.Peer ReviewedPostprint (author's final draft

    Evaluation of the Beam-F3 method for locating the F3 position from the 10鈥20 international system

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    Electromagnetic brain transcranial stimulation techniques have emerged to treat certain pathologies that require precise anatomical localization in the scalp to access the underlying cortical targets. For example, repetitive transcranial magnetic stimulation (rTMS) is an effective treatment for major depressive disorder when targeted at the dorsolateral prefrontal cortex (DLPFC) [[1],[2]]. The 10鈥20 international system of electrode placement has been increasingly applied to locate the DLPFC, allowing the placement of a stimulation device above the F3 position. The Beam-F3 method [[3]] is commonly used by clinicians for targeting this area of the brain [[4]]. Advantages of this method include its cost-effectiveness and its ease of implementation, as it does not require neuronavigational systems for target localization.Peer ReviewedPostprint (published version

    Analysis of a new tool for electrode positioning on the scalp according to the international 10/20 system

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    The emergence of non-invasive electromagnetic brain stimulation techniques, together with the improvement of electrophysiological recordings, has led to the need to increase the precision of the localization of cranial points close to their cortical target. In the clinical practice, the most common technique for locating there points on the scalp is the International 10/20 system and tape measure and a marker pen are used to carry out the marking process, before the placement of the electrodes. In this study, we have compared the marking for different electrophysiological tests between the conventional method and a new method based on the EPlacement device. The comparison was made taking into account the time spent on each test, the mean distance error per electrode, the direction of the error using the coordinate sign and, finally, a survey of healthcare staff to get their opinions on the 1S-EP and 2S-EP variants of EPlacement. The study involved 10 healthcare workers, 5 of whom had experience in conventional marking and 5 had experience in using the EPlacement device. 90 markings on dummies and 10 markings on volunteers were performed. Once each marking was completed on the dummies, the distances between the experimental points (marked with the EPlacement and tap measure) and the reference positions from 10/20 system determined by a 3D printed template were measured. The results show that with EPlacement, marking accuracy is increased, marking time is reduced, and healthcare personnel is receptive to adopting this technology.We would like to thank the collaborating healthcare staff of the Clinical Neurophysiology Service of the Hospital Universitari Sant Joan de Reus and Ismael 脕vila for their support in the clinical research plan. This project has obtained funding from the Research to Business call (R2B2021-02), co-funded by the URV and the European Regional Development Fund (ERDF).Postprint (published version

    Comparison of electrode position marking procedures on the cranial surface

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    The study aimed to compare the conventional method of electrode marking with a new system, EPlacement, to improve accuracy and reduce the time burden on health care professionals. Ten health care professionals marked mannequin heads and adult volunteers using both methods. Time, accuracy, and usability of each method were analyzed. Three neurophysiological diagnostic tests were performed on mannequin heads: reversal pattern visual evoked potential (three electrodes required); somatosensory evoked potentials from the upper and lower extremities (five electrodes required); and standard intraoperative neurophysiological monitoring for spine surgery (nine electrodes required). Precision scanning of the mannequins with structured light and a printed hull were used to determine the actual locations of the electrodes of the 10/20 system. The new method based on the EPlacement device represents an improvement on conventional tape measure (TM) marking and may be considered within the group of advanced methods such as navigation systems since it leads to improvements of 34% (1.7 mm) for electrode positions in the Nasion-Inion and Left tragus鈥揜ight tragus lines and 77% (12.5 mm) for electrode positions using the approximate method. It reduces the time spent per test by an average of 1 min compared to the TM method. Health care staff survey results show a positive feedback regarding usability of the new method. The study showed that the EPlacement device improves accuracy, reduces time, and is easy to use compared to the conventional method of electrode marking. The EPlacement method can facilitate the complex task of electrode marking and ultimately contribute to improved patient outcomes. It has the potential to be widely accepted and implemented in clinical practice.We would like to thank the collaborating health care staff of the Clinical Neurophysiology Service at HUSJR and Ismael 脕vila for their support with the clinical research plan. The projects that led to these results received funding from 鈥渓a Caixa鈥 Foundation under grant agreements LCF/TR/CI21/52650005 and LCF/TR/CC22/52500009 and from Research to Business call R2B2021-02, co-funded by the URV and the European Regional Development Fund (ERDF).Peer ReviewedPostprint (published version

    Laboratory 3.0: manufacturing technologies laboratory virtualization with a student-centred methodology

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    This paper presents a blended-learning strategy for improving the teaching method applied in the laboratory subject Manufacturing Technologies. The teaching method has been changed from a predominantly teacher-centred to an active learning system with a student-centred focus and e-learning activities. In face-to-face classes, a game-based learning platform has been used. This methodology ensured engaging classes at the same time that provided a useful live feedback for students and teachers. The virtualization of the laboratory was achieved by two different e-learning activities, self-assessment tasks and video clips. These e-learning tools have been used not only to improve the students鈥 learning but also to enhance their motivation. The results from academic outputs show a significant improvement after the new blended learning method is applied. Moreover, a student satisfaction survey shows the positive impact of the methodology on the students鈥 engagement and motivationPeer Reviewe

    Laboratori 3.0: virtualitzaci贸 del laboratori amb una metodologia centrada en l'estudiant

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    This paper presents an improvement introduced to a laboratory subject by means of a student - centered blended - learning teaching strategy. The implemented virtual tools (videos and questionnaires) help to prepare the practical sessions and allow the sel f - assessment before and after each practical session. Students have shown a great satisfaction with the method. The analysis of the qualifications obtained has allowed an assessment of the degree of correlation between the different techniques used.Postprint (published version

    脷s de Kahoot! com a eina de ludificaci贸 per a la retroalimentaci贸 a temps

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    Es presenta l鈥檃ctuaci贸 duta a terme en les pr脿ctiques de Teoria de M脿quines i Mecanismes de l鈥橢TSEIB. S鈥檌ntrodueix una retroalimentaci贸 a temps mitjan莽ant l鈥檃plicaci贸 Kahoot! la qual cosa permet estimular l鈥檌nter猫s de l鈥檃lumnat i ajudar a adquirir els coneixements de l鈥檃ssignatura amb les metodologies t铆piques de l鈥檃prenentatge basat en jocs. Els resultats mostren millores significatives en els grups on s鈥檋a dut a terme l鈥檃ctuaci贸 i aporten evid猫ncies en favor de la ludificaci贸.Postprint (published version

    Aplication of a gamification learning system in mechanical engineering studies

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    The purpose of this study is to examine the effects of using a gamification tool as a new teaching strategy. Specifically, Kahoot! is evaluated as a tool for enhancing student learning. We test the tool empirically in a university class setting in an engineering degree, namely as part of the laboratory sessions of the subject Mechanism and Machine Theory during two consecutive academic years. The students were randomly divided into three different groups (control group, gamification group and writing group) and their results were evaluated depending on the learning method applied during the class. In terms of gamification, this project introduces real-time feedback to stimulate the interest of students and help them use the typical tools and methodologies of game-based learning. The analysis of their performance in the laboratory exam shows significant differences between the group that used gamification and the groups that did not. The study concludes that gamebased elements and competitive activities enhanced student performance and recommend their use in educational environments to support the learning process

    Cost-effectively 3d-printed rigid and versatile interpenetrating polymer networks

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    Versatile acrylate鈥揺poxy hybrid formulations are becoming widespread in photo/thermal dual-processing scenarios, especially in 3D printing applications. Usually, parts are printed in a stereolithography or digital light processing (DLP) 3D printer, after which a thermal treatment would bestow the final material with superior mechanical properties. We report the successful formulation of such a hybrid system, consisting of a commercial 3D printing acrylate resin modified by an epoxy鈥 anhydride mixture. In the final polymeric network, we observed segregation of an epoxy-rich phase as nano-domains, similar to what was observed in a previous work. However, in the current work, we show the effectiveness of a coupling agent added to the formulation to mitigate this segregation for when such phase separation is undesired. The hybrid materials showed significant improvement of Young鈥檚 modulus over the neat acrylate. Once the flexible, partially-cured material was printed with a minimal number of layers, it could be molded into a complex form and thermally cured. Temporary shapes were readily programmable on this final material, with easy shape recovery under mild temperatures. Inspired by repairable 3D printed materials described recently, we manufactured a large object by printing its two halves, and then joined them covalently at the thermal cure stage with an apparently seamless unionPeer ReviewedPostprint (author's final draft
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