Diseño y validación de una máquina para ensayos a tracción de probetas de resinas poliméricas impresas en 3D

El presente proyecto técnico tuvo como objetivo presentar el diseño y validación de una máquina para ensayos a tracción de probetas de resinas poliméricas impresas en 3D. El compendio de material bibliográfico permitió presentar los principales parámetros de diseño, con una capacidad máxima establecida de 10 kN y un desplazamiento de 305 mm. Se empleó la metodología del diseño concurrente ocasionando la descomposición de cada una de las posibles alternativas mediante la aplicación y despliegue del QFD. El sistema de sujeción de probetas mediante la selección de mordazas manuales tipo cuña con capacidad de 5 kN. El sistema de conversión de carga con buena precisión y repetibilidad de tipo Xforce HP Load Cell. La medición de cuanto varia la extensión de las probetas sometidas a prueba mediante el dispositivo Clip on Extensometer 5025-1. La pantalla de un computador donde permite la visualización de resultados. Los componentes mecánicos se diseñaron mediante cálculo analítico por resistencia mecánica y rigidez, integrando la modelación en el programa SolidWorks y la aplicación del método de elementos finitos en el programa ANSYS, el cuál facilitó la validación de los valores obtenidos en el cómputo de diseño. Se realizaron cinco ensayos sobre las probetas de resina ingenieril con la geometría que establece la norma ASTM D 638 para la determinación de las principales propiedades de tracción en materiales poliméricos con un esfuerzo último de tracción equivalente a 48,561 MPa. El análisis del tipo de fractura corrobora si el material presenta un comportamiento frágil o dúctil. La simulación estática de la máquina permitió verificar que es un diseño funcional y confiable. Se recomienda caracterizar la resina polimérica utilizada mediante el método de estereolitografía ya que se carece de algunas de las propiedades mecánicas necesarias que requiere el software de simulación.The objective of this technical project was to present the design and validation of a machine for tensile testing of 3D printed polymeric resin specimens. The compendium of bibliographic material made it possible to present the main design parameters, with an established maximum capacity of 10 kN and a displacement of 305 mm. The concurrent design methodology was used, causing the decomposition of each of the possible alternatives through the application and deployment of the QFD. The specimen clamping system through the selection of wedge-type manual clamps with a capacity of 5 kN. The load conversion system with good accuracy and repeatability of the Xforce HP Load Cell type. The measurement of how much the extension of the specimens under test varies by means of the Clip on Extensometer 5025-1 device. The screen of a computer where it allows the visualization of results. The mechanical components were designed by means of analytical calculation for mechanical resistance and rigidity, integrating the modeling in the SolidWorks program and the application of the finite element method in the ANSYS program, which facilitated the validation of the values obtained in the design computation. Five tests were carried out on the engineering resin specimens with the geometry established by the ASTM D 638 standard for the determination of the main tensile properties in polymeric materials with an ultimate tensile stress equivalent to 48,561 MPa. The analysis of the type of fracture corroborates if the material presents a brittle or ductile behavior. The static simulation of the machine allowed to verify that it is a functional and reliable design. It is recommended to characterize the polymeric resin used by the stereolithography method since it lacks some of the necessary mechanical properties required by the simulation software

Evolution over Time of Ventilatory Management and Outcome of Patients with Neurologic Disease∗

OBJECTIVES: To describe the changes in ventilator management over time in patients with neurologic disease at ICU admission and to estimate factors associated with 28-day hospital mortality. DESIGN: Secondary analysis of three prospective, observational, multicenter studies. SETTING: Cohort studies conducted in 2004, 2010, and 2016. PATIENTS: Adult patients who received mechanical ventilation for more than 12 hours. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Among the 20,929 patients enrolled, we included 4,152 (20%) mechanically ventilated patients due to different neurologic diseases. Hemorrhagic stroke and brain trauma were the most common pathologies associated with the need for mechanical ventilation. Although volume-cycled ventilation remained the preferred ventilation mode, there was a significant (p < 0.001) increment in the use of pressure support ventilation. The proportion of patients receiving a protective lung ventilation strategy was increased over time: 47% in 2004, 63% in 2010, and 65% in 2016 (p < 0.001), as well as the duration of protective ventilation strategies: 406 days per 1,000 mechanical ventilation days in 2004, 523 days per 1,000 mechanical ventilation days in 2010, and 585 days per 1,000 mechanical ventilation days in 2016 (p < 0.001). There were no differences in the length of stay in the ICU, mortality in the ICU, and mortality in hospital from 2004 to 2016. Independent risk factors for 28-day mortality were age greater than 75 years, Simplified Acute Physiology Score II greater than 50, the occurrence of organ dysfunction within first 48 hours after brain injury, and specific neurologic diseases such as hemorrhagic stroke, ischemic stroke, and brain trauma. CONCLUSIONS: More lung-protective ventilatory strategies have been implemented over years in neurologic patients with no effect on pulmonary complications or on survival. We found several prognostic factors on mortality such as advanced age, the severity of the disease, organ dysfunctions, and the etiology of neurologic disease