Ponašanja tvrdoće i povećanja gustoće prahova bakra i bronce kompaktiranih procesima hladnog prešanja u matrici smjerom jedne osi

In this study hardness and densification behaviour of copper and bronze powders under wet bag cold isostatic and uniaxial die pressing processes are examined. In uniaxial pressing the specimens were compacted up to a pressure of 800 MPa. Cold isostatic pressing (CIP) resulted in better densification for both of the studied powder materials. Attained densities were 94 % for copper and 82 % for bronze powders. In uniaxial die pressing greater pressurisation was needed to attain the same densification that obtained with CIP. The microhardness of both of the studied materials were measured before and after pressing processes. Higher pressure resulted in dislocation and strain hardening and increased hardness of powders.U ovom radu se istraživala promjena tvrdoće i povećanje gustoće prahova bakra i bronce prešanih na hladno u matrici smjerom jedne osi, te izostatski pomoću fluidnog medija. Pri hladnom prešanju u matrici smjerom jedne osi uzorci su kompaktirani s tlakovima do 800 MPa. Hladno izostatsko prešanje (CIP) rezultira znatnijim povećanjem gustoće kod oba praškasta materijala. Dobivene gustoće bile su 94 % za bakarni i 82 % za brončani prah. Kod prešanja u matrici smjerom jedne osi bilo je potrebno upotrijebiti veće tlakove da bi se postigla ista gustoća kao ona dobivena CIP postupkom. Mikrotvrdoća oba proučavana materijala mjerena je prije i nakon procesa prešanja. Veći tlakovi uzrokuju očvrščavanje dislokacijama i naprezanjem, te povećavaju tvrdoću prahova

Lomna žilavost trenjem zavarenih spojeva iz AlCu4SiMg aluminijske legure

The objective of paper was to determine the fracture toughness of friction stir welding (FSW) joints of EN AW-2014 AlCu4SiMg) aluminium alloy, and to compare the fracture toughness of FSW with that of conventional metal inert gas (MIG) process. FSW of aluminium alloy was performed on a conventional semiautomatic milling machine. Defect free FSW welds were produced on alloy plates at constant tool rotation and traverse speed of 1600 rpm and 200 mm/min, respectively. The results of Vickers hardness and Charpy impact tests were used to evaluate the fracture toughness of welded joints. Low heat input, absence of melting and filler metal resulted in better fracture toughness for FSW joints

Numerical analysis of different heating systems for warm sheet metal forming

The main goal of this study is to present an analysis of different heating methods frequently used in laboratory scale and in the industrial practice to heat blanks at warm temperatures. In this context, the blank can be heated inside the forming tools (internal method) or using a heating system (external method). In order to perform this analysis, a finite element model is firstly validated with the simulation of the direct resistance system used in a Gleeble testing machine. The predicted temperature was compared with the temperature distribution recorded experimentally and a good agreement was found. Afterwards, a finite element model is used to predict the temperature distribution in the blank during the heating process, when using different heating methods. The analysis also includes the evaluation of a cooling phase associated to the transport phase for the external heating methods. The results of this analysis show that neglecting the heating phase and a transport phase could lead to inaccuracies in the simulation of the forming phase.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under project PTDC/EMS-TEC/1805/2012 and by FEDER funds through the program COMPETE—Programa Operacional Factores de Competitividade, under the project CENTRO-07-0224-FEDER-002001 (MT4MOBI). The authors would like to thank Prof. A. Andrade-Campos for helpful contributions on the development of the finite element code presented in this work.info:eu-repo/semantics/publishedVersio

Age- and region-specific hepatitis B prevalence in Turkey estimated using generalized linear mixed models: a systematic review

Toy M, Önder FO, Wörmann T, et al. Age- and region-specific hepatitis B prevalence in Turkey estimated using generalized linear mixed models: a systematic review. BMC infectious diseases. 2011;11(1): 337.BACKGROUND: To provide a clear picture of the current hepatitis B situation, the authors performed a systematic review to estimate the age- and region-specific prevalence of chronic hepatitis B (CHB) in Turkey. METHODS: A total of 339 studies with original data on the prevalence of hepatitis B surface antigen (HBsAg) in Turkey and published between 1999 and 2009 were identified through a search of electronic databases, by reviewing citations, and by writing to authors. After a critical assessment, the authors included 129 studies, divided into categories: 'age-specific'; 'region-specific'; and 'specific population group'. To account for the differences among the studies, a generalized linear mixed model was used to estimate the overall prevalence across all age groups and regions. For specific population groups, the authors calculated the weighted mean prevalence. RESULTS: The estimated overall population prevalence was 4.57, 95% confidence interval (CI): 3.58, 5.76, and the estimated total number of CHB cases was about 3.3 million. The outcomes of the age-specific groups varied from 2.84, (95% CI: 2.60, 3.10) for the 0-14-year olds to 6.36 (95% CI: 5.83, 6.90) in the 25-34-year-old group. CONCLUSION: There are large age-group and regional differences in CHB prevalence in Turkey, where CHB remains a serious health problem

Molecular Analysis of Microbial Communities in Endotracheal Tube Biofilms

Ventilator-associated pneumonia is the most prevalent acquired infection of patients on intensive care units and is associated with considerable morbidity and mortality. Evidence suggests that an improved understanding of the composition of the biofilm communities that form on endotracheal tubes may result in the development of improved preventative strategies for ventilator-associated pneumonia. (n = 5). DGGE profiling of the endotracheal biofilms revealed complex banding patterns containing between 3 and 22 (mean 6) bands per tube, thus demonstrating the marked complexity of the constituent biofilms. Significant inter-patient diversity was evident. The number of DGGE bands detected was not related to total viable microbial counts or the duration of intubation.Molecular profiling using DGGE demonstrated considerable biofilm compositional complexity and inter-patient diversity and provides a rapid method for the further study of biofilm composition in longitudinal and interventional studies. The presence of oral microorganisms in endotracheal tube biofilms suggests that these may be important in biofilm development and may provide a therapeutic target for the prevention of ventilator-associated pneumonia

Wpływ parametrów procesu wytwarzania na wytrzymałość na ścinanie zgrzewanego tarciowo stopu aluminium (EN AW 5005)

Aluminium and its alloys have been used in automotive technology since the first model of the car. The need for aluminium material is getting increased for weight reduction, improved fuel economy and vehicle performance. The amount of the aluminium used in a car is mainly related with joining processes of aluminium alloy. This can be achieved by developing the welding techniques for aluminium alloys. The purpose of this study was to determine the effects of friction stir spot welding parameters on tensile shear strength of friction stir spot welded lap joint EN AW 5005 Aluminium alloy. The variable parameters were tool rotation (rpm), dwell time (s) and the tool pin height (mm). Tensile shear test results indicated that the weld performance was significantly affected by the tool rotation, dwell time and the tool pin height. The results of the study indicates that there are optimum process parameters which give the highest tensile shear strength.Aluminium i jego stopy są stosowane w produkcji samochodów od pierwszego modelu. Zapotrzebowanie na aluminium rośnie z powodu dążenia do zmniejszenia masy własnej pojazdu, zmniejszeniu zużycia paliwa i poprawy osiągów pojazdu. Ilość aluminium stosowanego w samochodzie jest głównie związana z procesem łączenia stopów aluminium. To może być osiągnięte poprzez rozwój technik spawalniczych dla atopów aluminium. Celem tej pracy było określenie wpły wu parametrów zgrzewania tarciowego FSW, na wytrzymałość na ścinanie zakładkowych złączy ze stopu aluminium EN AW 5005. Zmiennymi parametrami były prędkość obrotowa narzędzia (obr/min), czas (s) i wysokość trzpienia (mm). Wyniki testów ścinania wskazują, że jakość złącza jest istotnie uzależniona od prędkości obrotowej narzędzia, czasu i wysokości trzpienia. Wyniki tej pracy wskazują, że istnieją optymalne parametry zgrzewania tarciowego FSW, które dają najwyższą wytrzymałość na ścinanie

Effects of Process Parameters on Tensile Shear Strength of Friction Stir Spot Welded Aluminium Alloy (EN AW 5005)

Aluminium and its alloys have been used in automotive technology since the first model of the car. The need for aluminium material is getting increased for weight reduction, improved fuel economy and vehicle performance. The amount of the aluminium used in a car is mainly related with joining processes of aluminium alloy. This can be achieved by developing the welding techniques for aluminium alloys. The purpose of this study was to determine the effects of friction stir spot welding parameters on tensile shear strength of friction stir spot welded lap joint EN AW 5005 Aluminium alloy. The variable parameters were tool rotation (rpm), dwell time (s) and the tool pin height (mm). Tensile shear test results indicated that the weld performance was significantly affected by the tool rotation, dwell time and the tool pin height. The results of the study indicates that there are optimum process parameters which give the highest tensile shear strength.Aluminium i jego stopy są stosowane w produkcji samochodów od pierwszego modelu. Zapotrzebowanie na aluminium rośnie z powodu dążenia do zmniejszenia masy własnej pojazdu, zmniejszeniu zużycia paliwa i poprawy osiągów pojazdu. Ilość aluminium stosowanego w samochodzie jest głównie związana z procesem łączenia stopów aluminium. To może być osiągnięte poprzez rozwój technik spawalniczych dla atopów aluminium. Celem tej pracy było określenie wpły wu parametrów zgrzewania tarciowego FSW, na wytrzymałość na ścinanie zakładkowych złączy ze stopu aluminium EN AW 5005. Zmiennymi parametrami były prędkość obrotowa narzędzia (obr/min), czas (s) i wysokość trzpienia (mm). Wyniki testów ścinania wskazują, że jakość złącza jest istotnie uzależniona od prędkości obrotowej narzędzia, czasu i wysokości trzpienia. Wyniki tej pracy wskazują, że istnieją optymalne parametry zgrzewania tarciowego FSW, które dają najwyższą wytrzymałość na ścinanie