Procedimiento y aparato para medir la deformación en un ensayo de tracción.

La presente invención se refiere a un procedimiento para medir la deformación en un ensayo de tracción, así como al dispositivo mediante el que se desarrolla dicho procedimiento. El método consiste en la medición de la deformación a partir del desplazamiento de dos puntos por medio de sensores láser colocados paralelamente al eje de la probeta. Estos van montados sobre un soporte articulado que se amarra a la máquina de ensayo. El dispositivo se completa con dos topes que colocados sobre la probeta sirven de diana para los sensores. El dispositivo permite: realizar medidas sin contacto con la probeta, para prevenir posibles daños en la rotura de la misma; calcular automático de la base de medida del extensómetro, sin medidas iniciales; medir de forma directa, sin calibración previa y tiene la posibilidad de medir con mucha precisión en recorridos cortos o grandes elongaciones con menor precisión.Solicitud: 200900178 (16.01.2009)Nº Pub. de Solicitud: ES2324696A1 (12.08.2009)Nº de Patente: ES2324696B2 (12.01.2010

Validation through finite element simulation of the behaviour of a polyurethane shock absorber under in-service and extreme conditions

ABSTRACT: The safety rules for the construction and installation of lifts, currently in force in Europe, include several requirements concerning the behaviour of the shock absorbers when stopping an elevator. In this paper, a finite element model simulating the behaviour of a cellular polyurethane shock absorber has been developed. The material mechanical behaviour was simulated by means of an elastomeric foam theoretical model, previously calibrated in a former paper. Several in-service and extreme condition scenarios have been analysed with this numerical model, thus verifying the fulfilment of the requirements of the standard

Characterization of mechanical properties of a shock absorber polyurethane foam for elevators. Numerical fitting of mechanical behavior models for hyperelastic and elastomeric foam materials

ABSTRACT: The elastic cellular polyurethane elastomer is widely used to manufacture shock absorbers for elevators, due to its excellent conditions for absorption of energy and vibration damping. In this paper, a complete mechanical characterization of this material was performed including the uniaxial compressive test, the planar test, and the volumetric and the simple shear test. From the experimental results, several models of behavior for hyperelastic and elastomeric foam materials have been analyzed by fitting their corresponding material parameters. The scope of this work includes the Ogden model, the Van der Waals model, and polynomial and elastomeric foam forms

Influencia del contenido de humedad en el comportamiento a fractura de poliamida 6 reforzada con fibra de vidrio corta en condiciones entalladas

Este artículo presenta el análisis de la influencia del contenido de humedad en el efecto entalla observado en poliamida 6 reforzada con fibra de vidrio corta (SGFR-PA6). El estudio se basa en los resultados experimentales obtenidos en un programa experimental compuesto por 75 probetas de fractura considerando tres contenidos de humedad (0% (seco), 2% y 5%) con un contenido de fibra del 10 wt.% y cinco radios de entalla diferentes variando entre 0 mm (fisuras) y 2.0 mm. A través del análisis de la evolución de la tenacidad aparente se observa cómo se reduce el efecto entalla al aumentar el contenido de humedad. Además, se valida el uso de la Teoría de las Distancias Críticas (TDC) en la predicción de la tenacidad. El estudio se ha completado con el análisis de la evolución de los micromecanismos de fractura al variar el contenido de humedad y el radio de entalla. Para ello se ha utilizado la Microscopía Electrónica de Barrido (SEM). Los resultados obtenidos permiten relacionar la evolución de los micromecanismos de fractura presentes con la evolución de la tenacidad aparente.Los autores de este trabajo desean agradecer al MINECO del Gobierno de España por la financiación del proyecto MAT2014-58443-P, de cuyos resultados deriva este artículo

Análisis del efecto entalla en poliamida 6 reforzada con fibra de vidrio corta

Este artículo presenta el análisis del efecto entalla en poliamida 6 reforzada con fibra de vidrio corta. El estudio se basa en los resultados obtenidos en un programa experimental compuesto por 25 probetas de fractura con un contenido de fibra del 10% y con 5 radios de entalla diferentes entre 0 mm (fisuras) y 2.0 mm. Los resultados muestran un claro efecto entalla, el cual se analiza a través de la evolución de la tenacidad aparente y la aplicación de la Teoría de las Distancias Críticas. El estudio se ha completado con el análisis de la evolución de los micromecanismos de fractura al variar el radio de entalla. Para ello se ha utilizado la Microscopía Electrónica de Barrido. Los resultados obtenidos demuestran la relación directa de esta evolución con la tenacidad aparente.This paper presents an analysis of the notch effect on short glass fibre reinforced Polyamide 6 (SGFR-PA6). The research is based on the results of obtained in an experimental programme composed of 25 fracture specimens of 10 wt. % fibre content varying the notch radius from 0 mm (crack-like defect) up to 2.0 mm. The results show a clear notch effect. The notch effect is analysed through the evolution of the apparent fracture toughness and the application of the Theory of the Critical Distances. The research is completed with the analysis of the evolution of fracture micromechanisms when the radius increases by using Scanning Electron Microscopy (SEM) fractographies. It has been revealed a direct relation between this evolution and the apparent fracture toughness observations.Los autores de este trabajo desean agradecer al MINECO del Gobierno de España por la financiación del proyecto MAT2014-58443-P: “Análisis del comportamiento en fractura de componentes estructurales con defectos en condiciones debajo confinamiento tensional”, de cuyos resultados deriva este artículo

Analysis of notch effect in load bearing capacity, apparent fracture toughness and fracture micromechanisms of ferritic–pearlitic steels

This paper presents the analysis of the notch effect in two ferritc–pearlitic steels: S275JR and S355J2. The research is based on the development and analysis of an experimental programme composed of 336 CT specimens, combining 6 different notch radii, and testing temperatures from the lower shelf up to the upper shelf of the two materials. The notch effect is analysed through the evolution of both the load bearing capacity and the apparent fracture toughness, and also through the relation between these two variables and the failure micromechanisms. The results reveal a clear notch effect in both materials. In the case of the load bearing capacity, this notch effect has its maximum at lower shelf temperatures. The notch effect in the apparent fracture presents a maximum at the lower temperatures of the ductileto-brittle transition zone. Finally, the Scanning Electron Microscopy fractographies have justified the previous observations

Degradation of the compression strength of spacers made of high-density pressboard used in power transformers under the influence of thermal ageing

The structural components inside power transformers are commonly made of high-density pressboard, due to its suitable mechanical and dielectric properties. Among these components are the spacers used in the windings of transformers, which are subjected to compressive loading during operation. The spacers are immersed in dielectric liquid and subjected to high temperatures and chemical reactions during the lifespan of the transformer, which result in the degradation of their dielectric and mechanical properties. The performance and reliability of the power transformer greatly depends on its mechanical integrity, so it is necessary to understand how ageing degrades the mechanical response of the high-density pressboard. In this study, spacers made of high-density pressboard and pieces of copper conductor were immersed in uninhibited paraffinic oil and aged at 150 °C for different periods of time, trying to realistically represent the process suffered by a power transformer during its whole lifespan. The evolution caused by the thermal ageing over some chemical parameters (acidity and moisture content) and dielectric properties (AC breakdown voltage, dielectric dissipation factor, resistivity and degree of polymerisation) of the oil and the pressboard was studied experimentally. Compressive mechanical tests were performed on samples of the aged high-density pressboard, and the compressive stiffness during the ageing process was related with other chemical and dielectric parameters

Predicción del módulo de elasticidad de la poliamida reciclada reforzada con fibra de vidrio

Este trabajo plantea un modelo para predecir el módulo de elasticidad de la poliamida 6.6 reforzada con un 35% en peso de fibra corta de vidrio reciclada, en estado seco, en función del número de reinyecciones. El estudio se basa en una modificación del modelo analítico simplificado de Templeton. La aproximación planteada propone la incorporación de dos nuevos coeficientes que consideran la degradación sufrida por la matriz termoplástica. El modelo analítico desarrollado mantiene los efectos asociados a la fibra como su desorientación y acortamiento durante la reinyección así como la eficacia del agente adherente en la interfase fibra-matriz, ya evaluado por otros autores. La novedad de este estudio radica en aportar el efecto añadido de la degradación de la matriz polimérica, medida a través de la variación de su viscosidad y temperatura de transición vítrea sobre el comportamiento mecánico del compuesto.This work proposes a model to predict the modulus of elasticity of recycled polyamide 6.6 reinforced with 35% by weight of short fiberglass, in the dry as moulded (DAM) conditions, which is based on the number of reinjections. The study is a modification of the simplified analytical model of Templeton. The proposed approach incorporates two new coefficients that consider the degradation suffered by the thermoplastic matrix. The developed analytical model maintains the effects associated to the fiber as its disorientation and shortening during reinjection as well as the effectiveness of the adherent agent in the fiber - matrix interface, already evaluated by other authors. The novelty of this study is that provides the added effect of degradation of the polymer matrix, measured through the variation of its viscosity and glass transition temperature,on the mechanical behavior of the compound

Effect of temperature on fatigue behaviour of self-compacting recycled aggregate concrete

ABSTRACT: The most recommendable frequency range for concrete fatigue tests is between 1 and 15 Hz. It has been clearly established that performing the tests at low frequency (<1 Hz) reduces the fatigue limit because it increases test time and therefore, creep damage. On the other hand, there are not enough studies analysing tests above 15 Hz, which could greatly reduce test time. In this work, three recycled concretes were characterized, starting with the comparison between tests at moderate frequency (10 Hz) with tests at very high frequency (90 Hz). From these tests it was observed that, in all cases, the fatigue limit or fatigue life was notably lower in the case of performing the tests at high frequency. The test results show that, in the case of tests performed over the fatigue limit, the temperature of the specimens rises up to approximately 100 °C, while, in the case of tests performed with strength lower the fatigue limit, the temperature stabilises at around 65 °C. In order to analyse whether the temperature was the cause of the reduction in the fatigue limit, creep tests were carried out at 3 temperatures: 20, 65 and 100 °C, and it was possible to verify that creep damage became significantly greater as temperature was increased, and that this effect was emphasized in those cases where the concretes were made with recycled crushed concrete aggregates.The authors would like to thank the Spanish Ministry of Economy and Competitiveness of Spain for financing the project MAT2014- 57544-R

A modification of the Norris failure criterion for the prediction of the mechanical failure of the aged paper insulation in the windings of a power transformer

The deterioration of the insulation in the windings of power transformers affects their lifespan. A commercial insulated Continuously Transposed Conductor (CTC) was studied experimentally, numerically and analytically. The purpose was to understand the mechanisms governing the mechanical failure of the insulating paper, and to achieve a criterion for predicting failure under different conditions. Samples of that insulated CTC were extracted from a coil and aged at 150∘C for different durations inside vessels filled with naphthenic oil. Then the degree of polymerisation and tensile, compressive and shear mechanical properties of the insulation were measured/estimated. Aged insulated CTC samples were subjected to three-point bending tests, producing deformations compatible with a short circuit, and the fractures in the insulation were analysed. The bending test over a CTC sample was simulated by means of a FEM Program. The Norris failure model, applicable to a lamina, was adapted to the studied insulation materials. The predictions of that failure criterion agreed with experimental observations