13 research outputs found
Evaluation of fatigue life of recycled opaque PET from household milk bottle wastes
Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO2 nanoparticles. The recyclability of opaque PET is an issue: whereas the recycling channels are well established for transparent PET, the presence of opaque PET in household wastes weakens those channels: opaque bottles cannot be mixed with transparent ones because the resulting blend is not transparent anymore. Many research efforts focus on the possibility to turn opaque PET into resources, as one key to a more circular economy. A recent study has demonstrated the improvement of the mechanical properties of recycled PET through reactive extrusion. In the present work, the lifespan of recycled opaque PET has been evaluated throughout tensile鈥搕ensile fatigue loading cycles at various steps of the recycling process: The specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-OPET-hom) and after reactive extrusion (Rex-r-OPET). Virgin PET is also considered as a comparison. First, tensile tests monitored by digital image correlation have been carried out to obtain the elastic modulus and ultimate tensile stress of each type of PET. The fatigue properties of reactive REx-r-OPET increase, probably associated with the rise of cross-linking and branching rates. The fatigue lifespan increases with the macromolecular weight. The fracture surface analysis of specimens brings new insight regarding the factors governing the fatigue behavior and the damaging mode of recycled PET. TiO2 nanoparticles act as stress concentrators, contributing to void formation at multiple sites and thus promoting the fracture process. Finally, the fatigue life of REx-r-OPET is comparable to those of virgin PET. Upcycling opaque PET by reactive extrusion may be a relevant new route to absorb some of the growing amounts of PET worldwide
State of railway stations before beginning the program of the revitalization on the example of Lower Silesia
Dolny 艢l膮sk jako kraina geograficzna charakteryzuje si臋 bogat膮 histori膮 zwi膮zan膮 z rozleg艂ym, jednym z najlepszych w kraju, rozwojem przestrzennym sieci kolejowej. Co si臋 z tym wi膮偶e, d艂ugo艣膰 istniej膮cych kiedykolwiek linii kolejowych wprost przek艂ada艂a si臋 na liczb臋 eksploatowanych na tym偶e obszarze punkt贸w odprawy podr贸偶nych.
Ze wzgl臋du na stale post臋puj膮cy ju偶 od kilkudziesi臋ciu lat regres d艂ugo艣ci sieci kolejowej (zwi膮zany przede wszystkim z rozwojem konkurencyjnych form transportu, ale tak偶e z zaniedbaniami w bie偶膮cym utrzymaniu infrastruktury kolejowej) zauwa偶alny jest szybki proces przekszta艂cenia pierwotnie za艂o偶onej funkcji licznych obiekt贸w dworcowych (fot. 1). W artykule przedstawione zostan膮 wyniki inwentaryzacji obiekt贸w dworcowych, kt贸ra przeprowadzono w latach 2009-2011, a wi臋c jeszcze przed rozpocz臋ciem programu rewitalizacji tych obiekt贸w
Modelowanie kompozytu w艂贸kienniczego przystosowanego do konstrukcji dachowej
3D structural components made of fibrous composite materials subjected to service loading are analysed. The laminate consists of a matrix reinforced with a ply of long and unidirectional fibres. Participation of the fibres and matrix can vary in each layer. The main goal is to create a composite roof plate transferring variable loads of wet snow or fir and to investigate its strength properties in respect of (i) the type of fibres and matrix, and (ii) the volume fraction of the matrix and fibres within each layer. Modelling of shape and mechanical properties is reduced to the final phase of structural design, omitting time-consuming, expensive experimental tests. The numerical procedure is solved using the ADINA environment and finite element method code.Analizie poddano tr贸jwymiarowe sk艂adniki konstrukcji wykonane z w艂贸knistych materia艂贸w kompozytowych, poddane obci膮偶eniu eksploatacyjnemu. Laminat sk艂ada艂 si臋 z wype艂nienia wzmocnionego przez warstw臋 d艂ugich w艂贸kien jednokierunkowych. Udzia艂 w艂贸kien i wype艂nienia mo偶e by膰 zmienny w ka偶dej z warstw. G艂贸wnym celem by艂o utworzenie kompozytowej p艂yty dachowej, kt贸ra przenosi zmienne obci膮偶enie mokrego 艣niegiem lub firnu i zbadanie jej w艂asno艣ci wytrzyma艂o艣ciowych z uwagi na (i) typ w艂贸kien i wype艂nienia, (ii) procentowy udzia艂 wype艂nienia i w艂贸kien w ka偶dej warstwie. Modelowanie kszta艂tu i w艂asno艣ci mechanicznych jest zredukowane do ko艅cowej fazy projektowania konstrukcji i pomija czasoch艂onne, kosztowne badania eksperymentalne. Przyk艂ady numeryczne zosta艂y rozwi膮zane z wykorzystaniem 艣rodowiska ADINA i kodu metody element贸w sko艅czonych
Przepi臋cia 艂膮czeniowe i piorunowe a wymagany poziom wytrzyma艂o艣ci otwartych styk贸w wy艂膮cznik贸w 245 KV
Przedstawiono spos贸b oceny warto艣ci przepi臋膰 generowanych w sieci pomi臋dzy otwartymi stykami wy艂膮cznika podczas operacji 艂膮czeniowych i wy艂adowa艅 piorunowych. Warto艣ci przepi臋膰 por贸wnano z warto艣ciami napi臋膰 probierczych wy艂膮cznik贸w. Zaproponowano spos贸b doboru ogranicznik贸w napi臋cia. Wy艂膮czanie pr膮d贸w zwarciowych mo偶e powodowa膰 os艂abienie izolacji komory wy艂膮cznika zmniejszaj膮c jego wytrzyma艂o艣膰 elektryczn膮 i trwa艂o艣膰 艂膮czeniow膮. W energetyce zg艂aszano przypadki zap艂on贸w 艂uku na otwartych stykach wy艂膮cznik贸w, tego rodzaju awarie mog膮 by膰 bardzo gro藕ne w skutkach. Problem ten dotyczy przede wszystkim wy艂膮cznik贸w jednoprzerwowych, w kt贸rych napr臋偶enia elektryczne izolacji przerwy pomi臋dzy stykowej wy艂膮cznika s膮 bardzo du偶e. Z tego powodu pojawiaj膮 si臋 postulaty zwi臋kszenia liczby 艂膮cze艅 podczas bada艅 typu wy艂膮cznika, jakie nale偶y wykonywa膰 bez wymiany jakichkolwiek cz臋艣ci komory wy艂膮cznika, czy te偶 nap臋du.This paper deals with the surges generated in the network during switching operations and lightning surges. The level of both kinds of surge was compared with the required dielectric strength between the open contacts of 245 kV circuit breakers. Overvoltages greater than the electrical withstand voltage of the circuit breaker can cause arc ignition between the circuit breaker鈥檚 open contacts and power engineering service s have reported such cases. The results of such failures can be very serious. This is a problem especially for single-break circuit breakers, in which the stresses on the electrical insulation between the open contacts of the breaker are very high. A method for selecting lightning arresters to lower the overvoltages is proposed. The switching of short-circuit currents by a circuit breaker may cause a weakening of the circuit breaker chamber鈥檚 insulation and reduce its electrical withstand and durability
Uncertainty and Local Sensitivity Analysis of View Factors for Transient Conjugate Heat Transfer Problems
The anticipatory politics of homophobia: explaining constitutional bans on same-sex marriage in post-communist Europe
Active Learning Embedded in聽Incremental Decision Trees
As technology evolves and electronic devices become widespread, the amount of data produced in the form of stream increases in enormous proportions. Data streams are an online source of data, meaning that it keeps producing data continuously. This creates the need for fast and reliable methods to analyse and extract information from these sources. Stream mining algorithms exist for this purpose, but the use of supervised machine learning is extremely limited in the stream domain since it is unfeasible to label every data instance requested to be processed. Tackling this problem, our paper proposes the use of active learning techniques for stream mining algorithms, specifically incremental Hoeffding trees-based. It is important to mention that the active learning techniques were implemented to match the stream mining constraints regarding low computational cost. We took advantage of the incremental tree original structure to avoid overburdening the original computational cost when selecting a label. In other words, the statistical strategy to grow each incremental tree has supported the execution of active learning. Using techniques of uncertainty sampling, we were able to drastically reduce the number of labels required at the cost of a very small reduction in accuracy. Particularly with Budget Entropy there was an average negative impact of accuracy about using only of samples labelled