Quantification of Kraft paper ageing in mineral oil impregnated insulation systems through mechanical characterization

Power transformers use Kraft paper, thermally upgraded Kraft and other polymeric papers (ex. Nomex) as the main solid insulation between the winding conductors. Dielectric oil used in transformers as an insulating and cooling fluid typically has an operating temperature range of 60–90 °C. These service temperatures can cause slow degradation of both the oil and the insulating paper winding, with a loss of mechanical and dielectric properties. In this sense, this work analyzes paper degradation through Young’s Modulus, yield stress, rupture strength and strain under ultimate strength. An accelerated thermal ageing of the paper in mineral oil was carried out at temperatures of 110, 130 and 150 °C over different periods of time, in order to obtain information on the kinetics of the ageing degradation of the paper. The evolution of the mechanical properties and micro mechanisms of paper failure are analysed as a function of temperature and ageing time. Finally, the results obtained are compared with the traditional method of degradation analysis, based on the degree of polymerisation measurement.The authors are grateful for the funding received to carry out this work from the State Scientific and Technical Research and Innovation Plan under the DPI2013-43897-P Grant Agreement, financed by the Government of Spain

Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

Oil-immersed transformers use paper and oil as insulation system which degrades slowly during the operation of these machines. Cellulose materials are used generally as insulation solid in power transformers. The degree of polymerization (DP), defined as number of repeating b-glucose residues in the cellulose molecule, is a critical property of cellulosic insulation material used in transformers, since it provides information about paper ageing and its mechanical strength. The fast-developing electric power industry demanding superior performance of electrical insulation materials has led to the development of new materials, as well as different drying techniques performed during transformer manufacturing and service when required. Both developments have caused some practical difficulties in the DP measurement. Moreover, the increasing interest in synthetic dielectric materials replacing cellulose materials requires measuring alternative properties to the DP to quantify the degradation of insulation solids over time. In this sense, this paper proposes the possibility of analyzing paper degradation through fracture toughness. This approach is different from the study of mechanical properties such as tensile strength or strain because it provides a tool for solving most practical problems in engineering mechanics, such as safety and life expectancy estimation of cracked structures and components which cannot to be considered through the traditional assessment of the mechanical resistance of the material. An accelerated thermal ageing of Kraft paper in mineral oil was carried out at 130 ºC during different periods of time, to obtain information on the kinetics of the ageing degradation of the paper. Double-edged notched specimens were tested in tension to study their fracture toughness. The evolution of the load-displacement curves obtained for different ageing times at the ageing temperature of 130 ºC was utilized to the determination of the stress intensity factor. Furthermore, different kinetic models based on this stress intensity factor were applied to relate its evolution over time as a function of the temperature. Finally, the correlation between the DP and stress intensity factor, which depends on the fiber angle, was also defined.The authors are grateful for the funding received to carry out this work from the State Scientific and Technical Research and Innovation Plan under the PID2019-07126RB-C22 grant agreement, financed by the Government of Spai

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

Experimental validation of an adjustable railway fastening for slab track

ABSTRACT: A railway infrastructure capable of supporting a high frequency of light and heavy traffic, sometimes at high speed, requires the implementation of a high quality track. A correct definition of all track components leads to a high degree of safety and comfort for travelers as well as reduced operating costs. One factor that determines the elastic behaviour of the track is the rail fastening system. In this paper, the mechanical, electrical, and environmental sustainability characterization tests based on European standards UNE-EN have been carried out, verifying that the TK04 fastening system with a lateral adjustment of ±1 cm, manufactured by ThyssenKrupp Gleistechnik GmbH, satisfies the conditions and requirements of European standards UNE-EN for installation on slab track systems for light rail

Machine learning algorithms for the prediction of the mechanical properties of railways' rail pads

ABSTRACT: Train operations generate high impact and fatigue loads that degrade the rail infrastructure and vehicle components. Rail pads are installed between the rails and the sleepers to damp the transmission of vibrations and noise and to provide flexibility to the track. These components play a crucial role to maximize the durability of railway assets and to minimize the maintenance costs. The non-linear mechanical response of this type of materials make it extremely difficult to estimate their mechanical properties, such as the dynamic stiffness. In this work, several machine learning algorithms were used to determine the dynamic stiffness of pads depending on their in-service conditions (temperature, frequency, axle-load and toe-load). 720 experimental tests were performed under different realistic operating conditions; this information was used for the training, validation and testing of the algorithms. It was observed that the optimal algorithm was gradient boosting for EPDM (R2 of 0.995 and mean absolute percentage error of 5.08% in test dataset), TPE (0.994 and 2.32%) and EVA (0.968 and 4.91%) pads. This algorithm was implemented in an application, developed on Microsoft. Net platform, that provides the dynamic stiffness of the pads characterized in this study as function of material, temperature, frequency, axle-load and toe-load

Sistema para el ensayo de cargas de fatiga de tracción y compresión sobre los elementos de sujeción de una vía ferroviaria dentro del mismo ciclo de carga

Sistema para el ensayo de cargas de fatiga de tracción y compresión sobre los elementos de sujeción de una vía ferroviaria dentro del mismo ciclo de carga, que comprende: - una sección de carril con una abertura a lo largo del eje longitudinal de su cabeza, que presenta a su vez una porción cortada; - traviesas y elementos de sujeción característicos de una vía ferroviaria: - una barra cilíndrica situada atravesando la abertura de la cabeza, de una longitud tal que los extremos de la barra cilíndrica se sitúan fuera de la abertura, y tal que parte de la barra cilíndrica es visible debido a la porción cortada; - una horquilla que comprende un orificio, tal que la barra cilíndrica se sitúa atravesando dicho orificio: estando el sistema configurado para acoplarse a una máquina de ensayos, por medio de un aplicador permitiendo así la aplicación de fuerzas de tracción y compresión con diferentes grados de inclinación sobre la barra cilíndrica, y por ende, sobre el carril, las traviesas y los elementos de sujeción de la vía ferroviaria.Solicitud: 201700509 (31.03.2017)Nº Pub. de Solicitud: ES2665577A1 (26.04.2018)Nº de Patente: ES2665577B2 (21.08.2018

Shannon entropy as a reliable score to diagnose human fibroelastic degenerative mitral chords: a micro-ct ex-vivo study

This paper is aimed at identifying by means of micro-CT the microstructural differences between normal and degenerative mitral marginal chordae tendineae. The control group is composed of 21 normal chords excised from 14 normal mitral valves from heart transplant recipients. The experimental group comprises 22 degenerative fibroelastic chords obtained at surgery from 11 pathological valves after mitral repair or replacement. In the control group the superficial endothelial cells and spongiosa layer remained intact, covering the wavy core collagen. In contrast, in the experimental group the collagen fibers were arranged as straightened thick bundles in a parallel configuration. 100 cross-sections were examined by micro-CT from each chord. Each image was randomized through the K-means machine learning algorithm and then, the global and local Shannon entropies were obtained. The optimum number of clusters, K, was estimated to maximize the differences between normal and degenerative chords in global and local Shannon entropy; the p-value after a nested ANOVA test was chosen as the parameter to be minimized. Optimum results were obtained with global Shannon entropy and 2≤K≤7, providing p < 0.01; for K=3, p = 2.86⋅10-³. These findings open the door to novel perioperative diagnostic methods in order to avoid or reduce postoperative mitral valve regurgitation recurrences.This work is supported by the “Ministerio de Economía, Industria y Competitividad” (MINECO) and the “Instituto de Salud Carlos III” (ISCIII) of Spain, through projects INTRACARDIO (DTS17/00056) and CIBER-BBN (co-financed by FEDER funds) and IDIVAL under project DiCuTen (INNVAL16/02). The technical contributions from the members of the DICUTEN and the financial contribution from the IDIVAL are gratefully acknowledged. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. This study was approved by the Ethical Committee of Clinical Research of Cantabria – IDIVAL (Acta 02/2018)

Mechanical behavior and microstructural changes in polyurethane exposed to high doses of X rays, gamma rays or neutron irradiation

Polymeric materials are widely used in applications where the environmental conditions entail their exposure to different sources of irradiation (in most cases ultraviolet or low dose of electromagnetic irradiation for sterilization). In contrast, in this study we have assessed the modifications undergone by a series of polyurethane joints exposed to high radioactive doses of either X-rays or gamma rays (with doses of 20.5, 100, 300 and 900?kGy) or neutron irradiation (with a fluence of 7.23·1010 n/cm2) which are typical of the environment of nuclear reactors. Tensile tests were carried out to assess the change in mechanical properties derived from the radioactive exposure. Three mechanical parameters were used to monitor the evolution of strength, ductility and toughness: the tensile strength (?max), the strain corresponding to ?max (??max) and the density of energy absorbed prior to maximum load (U?max). With regards to X and gamma rays, a negative impact of radiation on strength, ductility and toughness was observed. The detailed statistical analysis of the results has shown that a threshold dose of 300?kGy must be overcome to trigger the damage process. For the fluence employed in this study, neutron irradiation produced very little change in the mechanical properties. The SEM fractographic study has allowed the influence of irradiation on the material failure mechanisms to be identified. Thus, the fracture surface of unirradiated samples shows evidence of plastic deformation and ductile tearing. In contrast, the fracture surface of those samples exposed to a dose of 900?kGy corresponds to brittle fracture. In a consistent way, samples exposed to neutron irradiation have a fracture surface similar to that of the non-irradiated material. In summary, electromagnetic radiation for doses above the threshold leads to the embrittlement of polyurethane. Raman spectroscopy was employed to identify the microstructural changes induced by the different sources of radiation at the molecular level. The band corresponding to the vibration of the C-H bending bonds present in the polyurethane was measured as a function of the dose, finding a strong correlation between its vibration frequency and the dose of exposure to electromagnetic radiation. This shift is more sensitive than the mechanical material response since the frequency is affected at doses of 100?kGy, below the threshold previously identified for any of the mechanical properties. This correlation opens the door for the use of Raman spectroscopy as a novel non-destructive tool to characterize the microstructural effect of irradiation on polyurethane

Determination of the optimum amount of superplasticizer additive for self-compacting concrete

ABSTRACT: Self-compacting concrete modifies its workability with small variations in the amount of superplasticizer additive. For this reason, large number of tests are required to monitor its workability. In order to determine the appropriate amount of additive for a single mix, the evolution of the power consumption of the concrete mixer during the addition of small amounts of additive to the concrete was analyzed. These results were compared both with typical workability characterization for self-compacting concrete and with the saturation point results, determined by the Marsh cone method. After this comparison, a good correlation was obtained between the results from the traditional tests and the proposed ?concrete mixer method?Funding: This research was funded by Spanish Ministry of Economy and Competitiveness of Spain, grant number MAT2014-57544-R”

Recycled polyethylene fibres for structural concrete

Modern society demands more sustainable and economical construction elements. One of the available options for manufacturing this type of element is the valorisation of end-of-life waste, such as, for example, the recycling of polymers used in industry. The valorisation of these wastes reduces costs and avoids the pollution generated by their landfill disposal. With the aim of helping to obtain this type of material, this work describes a methodology for recycling polyethylene for the manufacture of fibres that will later be used as reinforcement for structural concrete. These fibres are manufactured using an injection moulding machine. Subsequently, their physical and mechanical properties are measured and compared with those of the material before it is crushed and injected. The aim of this comparison is to evaluate the recycling process and analyse the reduction of the physical-mechanical properties of the recycled polyethylene in the process. Finally, to determine the properties of the fibre concrete, three types of concrete were produced: a control concrete, a reinforced concrete with 2 kg/m³ of fibres, and a reinforced concrete with 4 kg/m³ of fibres. The results show an enhancement of mechanical properties when the fibres are incorporated, particularly the tensile strength; and they also show excellent performance controlling cracking in concrete.This research was funded by the LADICIM (Laboratory of Materials Science and Engineering), Universidad de Cantabria. E.T.S. de Ingenieros de Caminos, Canales y Puertos, Av./Los Castros 44, 39005 Santander, Spain