Examinando por Autor "Garrido, Miguel Ángel"

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An energetic approach to the wear behaviour of plasma-sprayed alumina-13% titania coatings
(Elsevier, 2010) Rico, Álvaro; Garrido, Miguel Ángel; Otero, Enrique; Rodríguez, Jesús
An optimisation method for the cold-spray process: On the nozzle geometry
(Elsevier Ltd., 2022-01-08) Alonso, Luis; Garrido, Miguel Ángel; Poza, Pedro
Actualmente, el proceso de proyección en frío es una técnica muy utilizada en aplicaciones de deposición de recubrimientos. La baja temperatura del proceso de deposición es la característica distintiva que lo hace adecuado para muchas actividades de fabricación aditiva, como la reparación y restauración de componentes dañados. La fiabilidad de los recubrimientos depende en gran medida de la velocidad del polvo durante su impacto sobre la superficie objetivo. Las condiciones de proyección, como la presión y la temperatura del gas portador y la geometría de la boquilla, controlan la aceleración de las partículas de polvo. En consecuencia, existe un interés creciente en la optimización de la geometría de la boquilla para maximizar la aceleración de las partículas a través de la trayectoria que siguen a lo largo de dicha boquilla. En contraste con varios enfoques existentes para lograr este objetivo (modelado de elementos finitos, enfoque experimental y métodos analíticos), en este estudio se desarrolló un modelo alternativo basado en la teoría isoentrópica unidimensional que explica la dinámica del flujo diluido de dos fases. En primer lugar, se llevó a cabo un análisis de las hipótesis habituales utilizadas para obtener la ecuación de movimiento de la partícula. Posteriormente, con los nuevos conocimientos obtenidos en el análisis anterior, se realizó un nuevo modelo teórico para la optimización de la parte divergente de la boquilla, considerando una restricción de ángulo geométrico. Este modelo se basa en la integración numérica de la ecuación de movimiento de la partícula, asegurando la maximización de la fuerza de arrastre de la partícula mediante el método del multiplicador de Lagrange. Una vez formulado el modelo analítico, se obtiene un conjunto de curvas que describen los parámetros geométricos óptimos para diferentes condiciones. Además, se presentan algunas geometrías óptimas que demuestran la baja influencia de la restricción del ángulo. Además, se muestra la relación inversamente proporcional entre la presión de proyección y la temperatura.
Influence of post cure time on the microhardness of self-adhesive resin cements inside the root canal
(Allen Press, 2012) Baena, Eugenia; Fuentes, María Victoria; Garrido, Miguel Ángel; Rodríguez, Jesús
Purpose: To compare the microhardness of several dual-cure, self-adhesive resin cements used to lute fiber posts at 24 hours and seven days after cementation. Methods: Bovine incisors were selected to lute 15 fiber posts that were 12 mm long (FRC Postec Plus size 3, Ivoclar-Vivadent). Five resin cements were tested: Multilink Automix (Ivoclar-Vivadent), without light-curing, and the self-adhesive resin cements Maxcem Elite (Kerr), RelyX Unicem (3M ESPE), G-Cem (GC), and Smartcem 2 (Dentsply), which were light-cured for 40 seconds (LED Bluephase, Ivoclar-Vivadent). Each root was embedded in chemically cured acrylic resin and stored at 37°C for 24 hours. The roots were transversally sectioned into nine specimens that were each 1 mm thick, with three specimens corresponding to each root third. Indentations (100g, 30 seconds) were performed on each section in the resin cement, at 24 hours and seven days after cementation, using a Vickers digital microdurometer (Buehler). Data were analyzed by two-way analysis of variance, Student-Newman-Keuls test, and paired t-test (p<0.05). Results: A significant influence was found (p<0.05) for the resin cement evaluated, the root third, and their interactions on microhardness values at 24 hours and seven days after post cementation. RelyX Unicem and G-Cem exhibited the highest microhardness values, whereas Multilink Automix presented the lowest. All resin cements suffered a decrease in microhardness according to root canal depth, with the exception of G-Cem and Multilink Automix at 24 hours and Smartcem 2 after seven days. After seven days, the evaluated resin cements showed a significant increase in microhardness values, with the exception of Maxcem Elite and Smartcem 2 at the coronal third. Conclusions: Microhardness of the self-adhesive resin cements when used to lute fiber posts was material-dependent and higher values were obtained in the coronal third, revealing their sensitivity to light irradiation. More information regarding the polymerization reaction of these cements is warranted. According to the current results, microhardness values were significantly higher one week after post luting.
Mechanical characterization of sclerotic occlusal dentin by nanoindentation and nanoscratch
(2010) Martín, Noelia; García, Álvaro; Vera, Vicente; Garrido, Miguel Ángel; Rodríguez, Jesús
Understanding the failure of epoxy resin U-notched samples using cohesive models
(ELSEVIER, 2019-04-02) Serrano, Ana; Garrido, Miguel Ángel; Salazar, Alicia; Rodríguez, Jesús
The critical distances theory for predicting failure loads of notched solid polymers requires assuming very high values of the characteristic stress. These values have to be much higher than the nominal tensile strength without a reasonable explanation. The use of cohesive models for linear elastic materials also requires very high cohesive stress values so that the results of the models are closer to the experimental ones. This paper has analysed the failure of a batch of three-point bending specimens with different notch radii made of epoxy resin. Numerical simulations based on a cohesive model considering the elastic-plastic material have been carried out. The results are compared with previous results obtained from experimental three-point bending tests. Additionally, the effect of triaxiality on the cohesive stress values required to get good predictions of the experimental failure loads has been also analysed.