CHOOSING THE OPTIMAL COATING FOR THERMOGRAPHIC INSPECTION

Lately, the method of thermography is becoming an unavoidable method in non-destructive testing of different metal materials and constructions. The application of this method is found in testing the energy efficiency, deterioration of structural components, as well as testing the energy efficiency of housing units. Using the thermographic method it is possible to reduce the negative environmental impact and prevent a environmental incidents. Lately it finds its increasing application in testing of substructure changes in the material caused by deformation. A major impact on the measurement has a condition of samples surface, because of that the samples are prepared by applying a coating. In this paper testing were carried out on the effect of coating type on two important factors: stability in testing and factor of emissivity

Utjecaj medija i temperature na tvorbu gliotoksina u sojeva Aspergillus fumigatus

Gliotoxin is a secondary metabolite of the epipolythiodioxopiperazine family with biologically active internal disulfide bridge. It is produced by many fungal species, including Aspergillus fumigatus and A. terreus. A. fumigatus, which produces gliotoxin and more than twenty other secondary metabolites, is the leading cause of invasive aspergillosis. Gliotoxin production in situ influence the development of aspergillosis. This study investigated the in vitro production of gliotoxin in nine A. fumigatus isolates from the upper respiratory tract of immunocompromised patients. The effects of media composition and incubation temperature were studied. Gliotoxin was extracted from biomass and its concentration was semi-quantitatively analysed using thin-layer chromatography. Gliotoxin production was higher in the yeast-extract liquid medium (YES) than in the synthetic Czapek-Dox liquid medium (CZA). Incubation at 37 °C resulted in higher gliotoxin production than at 25 °C, probably because higher temperatures favour expansive growth of the mycelium. Gliotoxin could be detected after three days of incubation at concentrations 4.06 mg mL-1 (in YES at 37 °C) and 1.07 mg mL-1 (in CZA at 25 °C). YES broth as a medium containing 4 % sucrose and 2 % of yeast extract is a very rich substrate for the production of gliotoxin in vitro.Gliotoksin je sekundarni metabolit iz skupine epipolitiodioksipiperazina s biološki aktivnim internim disulfidnim mostom u molekuli, koji tvore razne plijesni i gljivica Candida albicans. Plijesan Aspergillus fumigatus vodeći je uzročnik invazivnih aspergiloza i također može tvoriti gliotoksin. Pretpostavlja se da in situ tvorba gliotoksina utječe na patogenezu aspergiloze. U ovom radu ispitali smo in vitro tvorbu gliotoksina u devet sojeva A. fumigatus vrste, izoliranih iz imunokompromitiranih pacijenata. Praćen je utjecaj medija i temperature inkubacije na tvorbu gliotoksina. Gliotoksin je ekstrahiran iz biomase i koncentracija mu je utvrđena polukvantitativno tankoslojnom kromatografijom. Tvorba gliotoksina uočena je već nakon trodnevne inkubacije u koncentracijama 4,06 mg mL-1 (u bujonu s kvaščevim ekstraktom – YES na 37 °C) i 1,07 mg mL-1 (u sintetskom Czapek-Dox bujonu – CZA na 25 °C). Tvorba gliotoksina bila je veća u YES bujonu, za razliku od sintetskog CZA bujona. Viša temperatura inkubacije (37 °C) također utječe na jaču tvorbu gliotoksina nego niža temperatura (25 °C). YES bujon s dodatkom 4 % saharoze i 2 % kvaščeva ekstrakta vrlo je bogat supstrat za in vitro tvorbu gliotoksina, kao jednog od lipofilnih sekundardnih metabolita plijesni vrste A. fumigatus

IDENTIFICATION OF LÜDERS BANDS USING DIGITAL IMAGE CORRELATION

This paper presents the characterization of Lüders bands by digital image correlation on niobium microalloyed steel during a static tensile testing.Digital image correlation with the qualitative and quantitative analysis of the Lüders bands on the microalloyed steel was proved asa very precise and suitable method for determining the strain amountin the deformation zone.In this research was determined that the strain amount is the highest in the area behind the Lüders band front and the lowest in the area in front of the Lüders band

Stress distribution at different deformation degrees in low carbon steel during cold deformation

The temperature change, i.e. stresses of low carbon steel during the cold deformation process was investigated in this study. During static tensile test, temperature changes were examined using thermography at different deformation degrees. It was found that there are temperature changes in the deformation zone during the cold deformation. The increase in temperature changes in the deformation zone during cold deformation occurs with an increase in the deformation degree. The largest localization of temperature change was measured at the moment of the test sample fracture when the maximum temperature change was 8.45 °C. A higher amount of temperature change of 5.39 °C was determined at tensile strength compared to the proportionality limit amount of -0.97 °C. It was found that there are differences between the amounts of temperature changes in the range from 0.87 °C to 1.91 °C with increasing of deformation degree of the tested steel. Calculated stress amounts proved and show the tendency that stress amounts increase as the temperature change increases in low carbon steel by increasing of deformation degree during cold deformation. It was determined deviations of the calculated stress amounts due to using the mathematical model for low carbon with niobium at the start of plastic flow

Properties of continuously casted Cu-Al alloy

In this work are shown properties of continuously casted Cu – 9.1Al alloy before and after heat treatment. The continuously cast cylindrical bar with 8 mm diameter was produced using the device for the vertical continuous casting which is connected with the vacuum induction furnace. Heat treatment was consisted of annealing at 900 °C/30 minutes and water quenching. Microstructural analysis was performed by optical microscopy (OM), scanning electron microscopy (SEM) equipped by device for energy dispersive spectroscopy (EDS) and using differential scanning calorimeter (DSC). Also, hardness and mechanical properties were measured. EDS analysis confirmed that as-cast state of Cu – 9.1Al alloy is successfully done and alloy with homogeneous composition was produced. Optical and scanning electron microscopy showed existence of dual-phase α+β microstructure, which keeps after heat treatment but with certain sporadic changes of α - phase shape. DSC analysis on all samples presented one endothermic change of the heat flow during the heating, which probably represents α→β transformation and one exothermic change of the heat flow during the cooling which probably represents β→α transformation. The effect of heat treatment on the hardness and yield strength values is insignificant, while the tensile strength decreases with annealing

The stress distribution in the deformation zone of niobium microalloyed steel

U ovom doktorskom radu provedena su usporedna istraživanja na čeliku mikrolegiranom niobijem koji ima sitne precipitate niobija, čeliku istog baznog kemijskog sastava bez dodatka niobija i niobijem mikrolegiranom čeliku s krupnim precipitatima niobija. Uz statički vlačni pokus istovremeno su primijenjene metode termografije i digitalne korelacije slike, koje omogućuju konstantno mjerenje promjena temperature i deformacije. Primjenom programskih paketa IRBIS3 Professional i MatchID 2D omogućena je kvalitativna i kvantitativna analiza rezultata mjerenja promjena temperature i pomaka tijekom deformacije. Provedena istraživanja su pokazala da se čelik mikrolegiran niobijem značajno različito ponaša pri deformaciji u odnosu na čelik istog baznog sastava bez niobija. Utjecaj sitnih niobijevih precipitata naročito je izražen na početku plastičnog toka materijala. Nakon granice proporcionalnosti, niobijem mikrolegirani čelik ima reološki kompleksno ponašanje. Istraživanja su pokazala da je to ponašanje povezano s pojavom Lüdersovih linija. Lüdersova linija se formira na način da plastična deformacija započinje na jednom kraju uzorka, pri čemu se ostvari deformacija od 0,004 mm/mm. Nakon toga, Lüdersova linija propagira pod kutom od 45. Utvrđeno je da na fronti Lüdersove linije dolazi do porasta temperature od 4,5 do 6C, što je povezano s porastom naprezanja. Iza fronte linije ostvaruje se Lüdersova deformacija od 0,05 mm/mm. Nakon toga, u formiranoj zoni deformacije nastavlja se daljnja plastična deformacija, a naprezanja se koncentriraju u sredini zone deformacije, kao kod niskougljičnog čelika. Predložen je matematički model koji povezuje naprezanja i deformaciju s izmjerenim promjenama temperatura, s kojim je moguće iz izmjerenih vrijednosti deformacije i temperature odrediti iznose naprezanja u promatranim točkama. Usporedbom rezultata istraživanja i rezultata dobivenih razvijenim modelom, pokazalo se kako se vrijednosti podudaraju sve do brzine 30 mm/min, gdje su zabilježena značajna odstupanja.In this doctoral thesis a comparative research were conducted on niobium microalloyed steel which has fine niobium precipitates, steel with same base chemical composition but without the addition of niobium and on niobium microalloyed steel with large precipitates of niobium. With the tensile testing, at the same time the methods of thermography and digital image correlation were applied, which enables the continuous measurement of temperature changes and strain. By using software packages IRBIS 3 Professional and MatchID 2D is enabled a quantitative and qualitative analysis of measured changes in temperature and strain. Research results have shown that microalloyed niobium steel has a significantly different behavior upon deformation in relation to the steel of the same base composition without niobium. Effect of the fine precipitates of niobium is especially pronounced at the beginning of plastic flow of material. After yielding the niobium microalloyed steel has rheological complex behavior. Research has shown that this behavior is associated with the occurrence of Lüders bands. Lüders band is formed in such way that plastic deformation starts at the one end of sample, in doing so the strain of 0,004 mm/mm is carried out. After that Lüders band propagates at the angle of 45°. It was found that on the Lüders band front there is increase in temperature of about 4.5 to 6 °C, which is associated with increases in stress. Behind the Lüders front the strain of 0.05 mm/mm is achieved, Lüders deformation. After that, in the formed deformation zone, further plastic deformation continues and stresses are concentrated in the centre of the deformation zone, as in the low-carbon steel. Proposed mathematical model links measured stress and deformation with the measured temperature changes, with which is possible from the measured values of deformation and temperature changes determine the amount of stress in the observed points of deformation zone. By comparing the results of the research and the results obtained by the developed model, it was shown that the values match up to the speed of 30 mm / min, where is shown a significant discrepancies

Numerical analysis of metallographic preparation effect on the hardness of titanium alloy

Titanium alloys due to their good properties are increasingly used in biomedicine. However, in order to improve certain properties, titanium- based alloys with new chemical compositions are designed. In order to be characterized in a satisfactory manner, they must first be adequately prepared. In this paper the two most influential parameters were varied: grinding time and force, while the speed of rotation of the grinding wheel was constant. After grinding with the highest gradation of grind paper, the samples were observed under a light microscope to determine the condition of the surface. Then their hardness was determined by the Vickers method with different indenter loads. After that, the samples were polished under the same conditions, and their hardness was determined again. The obtained hardness values were numerically analyzed and the corresponding functional dependences of the measured hardness on the grinding parameters (time and force) and on the indentation force were determined

Hidrometalurška proizvodnja iz perspektive holističkog environmentalizma

Analiza hidrometalurške proizvodnje iz perspektive holističkog environmentalizma zahtjeva interdisciplinarni pristup jer je nužno sagledavanje ne samo tehnoloških mogućnosti provedbe određenog hidrometalurškog procesa, već i preispitivanje društvene opravdanosti gradnje ili održavanja tehnološkog postrojenja koje onečišćuje materijalni okoliš. Hidrometalurška proizvodnja iz perspektive holističkog environmentalizma promatra se dvojako: s jedne strane kao mogućnost, a s druge strane kao prijetnja. Hidrometalurška proizvodnja suvremenom čovječanstvu omogućava korištenje niza proizvoda bez kojih bi bilo nemoguće zamisliti našu tehničku civilizaciju, no ona može postati ozbiljna prijetnja ukoliko se tijekom proizvodnog procesa zanemaruje važnost očuvanja čistoće vode, zraka i tla. Za opravdanost funkcioniranja hidrometalurških postrojenja, iz pozicije holističkog environmentalizma, potrebna je socijalna odgovornost hidrometalurških poduzeća

Influence of Niobium Content on Strain Amount in Lüders Bands in Niobium Microalloyed Steel

In this paper, the influence of niobium content on strain amounts in various areas of Lüders bands propagation was investigated. The tests were simultaneously performed by a static tensile test and a digital image correlation in microalloyed steel with the same base chemical composition but with different addition of 0.035% and 0.06% of niobium. Strain changes were determined by a qualitative and quantitative analysis using a digital image correlation in the area of maximum strain amount behind the Lüders band front (position 1), on the Lüders band front (position 2) and in front of the Lüders band front (position 3). Different deformation behavior of Lüders bands was found in the examined samples with different addition of microalloying element niobium. The area behind the Lüders band front (position 1) showed the highest strain amounts in relation to the other two examined areas. The steel with 0.035% of niobium indicates higher strain amounts in the area of maximum strain behind the Lüders band front (position 1) compared to the steel with 0.06% of niobium which is associated with dislocation density and grain size. This difference is lower on the Lüders band front (position 2) and in front of the Lüders band front (position 3). There were no significant changes in the strain amount with the change of niobium content

Evaluation of Sample Preparation Importance for Digital Image Correlation during Cold Deformation

In this paper, tests were performed by monitoring changes of strain amounts and their distribution by digital image correlation during static tensile testing of steel. The influence of different combination of speckles application on the sample surface (white speckles on the black sample surface and black speckles on the white sample surface) during cold deformation of steel was tested with the non-contacting digital image correlation. Strain amounts obtained by digital image correlation analysis of tested samples, with white on black and black on white painted speckle patterns, were compared. Different analysis for determining and monitoring strain amounts, provided by digital image correlation software, were used in this paper. The strain amounts were compared during cold deformation until the occurrence of sample fracture in both combinations of speckles application on the sample surface. Research has shown the importance of proper sample preparation for determination strain amounts and insignificant minor differences of strain amounts, between different sample preparations for digital image correlation, during cold deformation of tested steel