Flexural fatigue of high-strength plain and fiber-reinforced concrete: influence of mesostructure and study of size effect

Equal fatigue tests in concrete, meaning those performed on exactly equal or homothetic specimens subjected to the same stress levels, present two problems yet to be solved. On the one hand, the high dispersion of the results, which causes the fatigue life in two apparently identical elements to vary by up to two or more orders of magnitude. On the other hand, the size effect, whereby fatigue strength decreases with increasing element size. The aim of this research work is to study these two issues in depth. Regarding the first one, the influence of the dispersion of concrete mesostructure on the dispersion of fatigue results will be studied; in particular, it will be evaluated whether the stochastic arrangement of fibers (in fiber concrete) or pores (in plain concrete) explains the variability of fatigue life. As for the size effect, fatigue tests will be performed on geometrically similar specimens subjected to the same equivalent stress levels. Macroscopic damage indicators, such as crack opening, will be used to determine the magnitude of the size effect and its variation according to the type of concrete (plain concrete and fiber-reinforced with different fiber contents). The results reveal that the arrangement of fibers and pores varies significantly in apparently identical specimens, and that this partly explains the dispersion of fatigue results. However, the estimation of the fatigue response of concrete from its mesostructure requires complex models, comprising several geometrical parameters of various components. In this work, a methodological approach to the problem is made, proposing mesostructure parameters that are reasonably predictive. With respect to the size effect, it is observed that the presence of fibers reduces the size effect on fatigue life, almost nullifying it. Furthermore, it is concluded that the secondary crack opening rate (dCMOD/dn) is an adequate parameter to explain the fatigue life in general, and the size effect in particular.Los ensayos de fatiga en hormigón iguales, entendiéndose como tales, los realizados en probetas exactamente iguales u homotéticas sometidas a los mismos niveles de tensiones, presentan dos problemáticas aún por resolver. Por un lado, la elevada dispersión de los resultados, que provoca que la vida a fatiga en dos elementos aparentemente idénticos pueda variar hasta en dos o más órdenes de magnitud. Por otro lado, el efecto tamaño, por el cual la resistencia a fatiga disminuye con el aumento del tamaño del elemento. En este trabajo de investigación se pretende profundizar en el estudio de estas dos cuestiones. Con respecto a la primera, se va a estudiar la influencia de la dispersión de la mesoestructura del hormigón en la dispersión de los resultados de fatiga; en particular, se evaluará si la disposición estocástica de las fibras (en hormigón con fibras) o de los poros (en hormigón en masa) explica la variabilidad de la vida a fatiga. En cuanto al efecto tamaño, se realizarán ensayos de fatiga en probetas geométricamente similares sujetas a los mismos niveles de tensión equivalente. A través de indicadores macroscópicos de daño, como la apertura de fisura, se determinará la magnitud del efecto tamaño y su variación en función del tipo de hormigón (en masa y con diferentes contenidos de fibras). Los resultados revelan que la disposición de las fibras y los poros varía significativamente en probetas aparentemente idénticas, y que esto explica en parte la dispersión de los resultados de fatiga. No obstante, la estimación de la respuesta en fatiga del hormigón a partir de su mesoestructura requiere de modelos complejos, que comprendan varios parámetros geométricos de diversos componentes. En este trabajo se realiza una aproximación metodológica al problema, proponiendo parámetros de la mesoestructura que son razonablemente predictivos. Con respecto al efecto tamaño, se observa que la presencia de fibras reduce el efecto tamaño en la vida fatiga, hasta prácticamente anularlo. Además, se concluye que la tasa de apertura de fisura secundaria (dCMOD/dn) es un parámetro adecuado para explicar la vida a fatiga en general, y el efecto tamaño en particular

Hemorragia digestiva alta secundaria a sarcoma de Kaposi gástrico y duodenal

Imágenes en patología digestiv

Influence of the Pecking Motion Frequency on the Cyclic Fatigue Resistance of Endodontic Rotary Files

Purpose: To analyze the influence of the pecking motion frequency on the cyclic fatigue resistance of endodontic rotary files. Material and Methods: Sixty PlexV 25.06 endodontic rotary files were selected and distributed into three groups: 30 movements/min (n = 20), 60 movements/min (n = 20), and 120 movements/min (n = 20). A dynamic cyclic fatigue device was designed using Computer Aided Design/ Computer Aided Engineering (CAD/CAE) technology and manufactured by 3D impressions to simulate the pecking motion performed by an operator. Failures of the endodontic rotary files were detected by a Light-Emitting Diode (LED)/Light-Dependent Resistor (LDR) system controlled by an Arduino-Driver complex and management software. Endodontic rotary files were tested on an artificial root canal manufactured by wire electrical discharge machining (EDM), with similar dimensions to those of the instrument under examination. Endodontic rotary files were used following the manufacturer’s recommendations. The results were analyzed by ANOVA and Weibull statistics. Results: All pairwise comparisons revealed statistically significant differences in all three variables, except for the difference in the number of cycles between the groups with 60 and 120 movements/min (p = 0.298). The scale distribution parameter of Weibull statistics showed statistically significant differences in all three variables, except for the differences in the number of cycles between groups with 30 and 60 movements/min (p = 0.0722). No statistically significant differences in the three variables were observed for the shape distribution parameter. Conclusion: A low frequency of pecking motion is recommended to reduce the risk of failure of endodontic rotary files associated with cyclic fatigue

Size effect of steel fiber–reinforced concrete cylinders under compressive fatigue loading: Influence of the mesostructure

This study deals with the influence of the fiber concrete mesostructure on the size effect under compressive fatigue loading. For this purpose, three series of cylindrical specimens of steel fiber–reinforced concrete were fabricated. Before fatigue testing, all the cylinders were scanned and the main morphological, orientation, and distribution parameters of the pores and fibers were checked. The images reveal that, near the cylinders’ walls, the porosity is lower than that in the cores and is even lower for large sizes. Additionally, larger specimens are more vulnerable to compressive fatigue loading, resulting in a reduction in fatigue life.The authors are grateful for the financial support from the Ministerio de Economía y Competitividad, Spain with grant nos. PID2019-110928RBC32, PID2019–110928RB–C31, and RTC–2017–6736–3, and from the Junta de Comunidades de Castilla-La Mancha, Spain through grant no. SBPLY/19/180501/000220

Conexión inteligente para la gestión turística desde el aula al destino (CIGTAD)

Fac. de Comercio y TurismoFac. de Trabajo SocialFALSEsubmitte

Influence of the Pecking Motion Frequency on the Cyclic Fatigue Resistance of Endodontic Rotary Files

This article belongs to the Special Issue Innovations in Endodontic Dentistry.[Purpose] To analyze the influence of the pecking motion frequency on the cyclic fatigue resistance of endodontic rotary files.[Material and Methods] Sixty PlexV 25.06 endodontic rotary files were selected and distributed into three groups: 30 movements/min (n = 20), 60 movements/min (n = 20), and 120 movements/min (n = 20). A dynamic cyclic fatigue device was designed using Computer Aided Design/ Computer Aided Engineering (CAD/CAE) technology and manufactured by 3D impressions to simulate the pecking motion performed by an operator. Failures of the endodontic rotary files were detected by a Light-Emitting Diode (LED)/Light-Dependent Resistor (LDR) system controlled by an Arduino-Driver complex and management software. Endodontic rotary files were tested on an artificial root canal manufactured by wire electrical discharge machining (EDM), with similar dimensions to those of the instrument under examination. Endodontic rotary files were used following the manufacturer’s recommendations. The results were analyzed by ANOVA and Weibull statistics.[Results] All pairwise comparisons revealed statistically significant differences in all three variables, except for the difference in the number of cycles between the groups with 60 and 120 movements/min (p = 0.298). The scale distribution parameter of Weibull statistics showed statistically significant differences in all three variables, except for the differences in the number of cycles between groups with 30 and 60 movements/min (p = 0.0722). No statistically significant differences in the three variables were observed for the shape distribution parameter.[Conclusion] A low frequency of pecking motion is recommended to reduce the risk of failure of endodontic rotary files associated with cyclic fatigue

Novel Electronic Device to Quantify the Cyclic Fatigue Resistance of Endodontic Reciprocating Files after Using and Sterilization

Background: The aim of this study was to analyze the effects of the time of use (TU) and sterilization cycles (SC) of endodontic reciprocating files on cyclic fatigue resistance. Methods: One-hundred-and-twenty (120) Procodile NiTi endodontic reciprocating instruments were selected at random and distributed into the following study groups: A: 0 sterilization cycles/0s time of use (n = 10); B: 0/60 (n = 10); C: 0/120 (n = 10); D: 1/0 (n = 10); E: 1/60 (n = 10); F: 1/120 (n = 10); G: 5/0 (n = 10); H: 5/60 (n = 10); I: 5/120 (n = 10); J: 10/0 (n = 10); K: 10/60 (n = 10); and L: 10/120 (n = 10). A dynamic cyclic fatigue device was designed using computer-aided design/computer-aided engineering (CAD/CAE) technology and created with a 3D printer to simulate the pecking motion performed by the clinician. Failure of the endodontic rotary instrument was detected by a light-emitting diode-light-dependent resistor (LED-LDR) system controlled by an Arduino driver complex and management software. The results were analyzed using the ANOVA test. Results: All pairwise comparisons presented statistically significant differences between the time to failure, number of cycles to failure and number of cycles of in-and-out movement for the time of use study groups (p < 0.001), but not in the number of sterilization cycles (p > 0.05). Conclusions: The time of use of NiTi endodontic reciprocating files negatively affects dynamic cyclic fatigue resistance. Dynamic cyclic resistance is not affected by the number of sterilization cycles

Incorporación de las competencias específicas de los certificados EuroPsy en el practicum de la facultad de psicología: fase II

Memoria sobre la ejecución del proyecto de Innovación y Mejora de la Calidad Docente 2023, Incorporación de las competencias específicas de los certificados EuroPsy en el practicum de la facultad de psicología: fase iiDepto. de Psicología Social, del Trabajo y DiferencialFac. de PsicologíaFALSEsubmitte