Uvođenje tehnologije eksplozijskog platiranja u postupku izrade hidrauličkih cilindara

The microhardness, microstructure and bond strength of the interface of a bi-metallic joint on the cross-section of the testing hydraulic cylinder were investigated. Experimental findings of related to both method of cladding obtained with metallographic and mechanical investigations of the interface between the CuSn6 bronze and the TS5 (Č.1213) steel cylinder, are given.Istraživani su mikrotvrdoća, mikrostruktura i čvrstoća veze međupovršine bimetalnog spoja po poprečnom presjeku ispitivanog hidrauličnog cilindra. Na osnovi metalografskih i mehaničkih ispitivanja međupovršine između CuSn6 bronce i čeličnog cilindra TS5 (Č.1213) usporedno su prikazani odgovarajući rezultati ovih dviju tehnologija platiranja

Piezoelectric nonlinearity and frequency dispersion of the direct piezoelectric response of BiFeO3 ceramics

We report on the frequency and stress dependence of the direct piezoelectric d33 coefficient in BiFeO3 ceramics. The measurements reveal considerable piezoelectric nonlinearity, i.e., dependence of d33 on the amplitude of the dynamic stress. The nonlinear response suggests a large irreversible contribution of non-180{\deg} domain walls to the piezoelectric response of the ferrite, which, at present measurement conditions, reached a maximum of 38% of the total measured d33. In agreement with this interpretation, both types of non-180{\deg} domain walls, characteristic for the rhombohedral BiFeO3, i.e., 71{\deg} and 109{\deg}, were identified in the poled ceramics using transmission electron microscopy (TEM). In support to the link between nonlinearity and non-180{\deg} domain wall contribution, we found a correlation between nonlinearity and processes leading to deppining of domain walls from defects, such as quenching from above the Curie temperature and high-temperature sintering. In addition, the nonlinear piezoelectric response of BiFeO3 showed a frequency dependence that is qualitatively different from that measured in other nonlinear ferroelectric ceramics, such as "soft" (donor-doped) Pb(Zr,Ti)O3 (PZT); possible origins of this dispersion are discussed. Finally, we show that, once released from pinning centers, the domain walls can contribute extensively to the electromechanical response of BiFeO3; in fact, the extrinsic domain-wall contribution is relatively as large as in Pb-based ferroelectric ceramics with morphotropic phase boundary (MPB) composition, such as PZT. This finding might be important in the search of new lead-free MPB compositions based on BiFeO3 as it suggests that such compositions might also exhibit large extrinsic domain-wall contribution to the piezoelectric response.Comment: 38 pages, 11 figure

Distortion of ring type parts during fine-blanking

Distortion control is one of the most important concerns of the metal processing industry, which also includes the fine-blanking technology. Fine-blanking of sheet metal involves metal flow and shearing, which result in complex deformation. Distortion occurs during the removal of parts from the tool due to the relaxation of internal stresses. Internal stresses that are generated during fine-blanking have an important effect on the shape and size of parts after fine-blanking. The distortion of ring type products during fine-blanking was analyzed by using dimension measurements, microscopic observation and numerical simulation

Unutarnja oksidacija Cu-Se legura

The purpose of our investigation was to perform the thermodynamic calculation of all possible reactions in the Cu-Se-O system and to explain the oxidation mechanism in various conditions. For such study, a model of copper with one single inclusion and alloy with 1.65 wt. % Se were made. Depending on time, the oxidation has been taking place at two different temperatures and two oxygen partial pressures. The oxidized samples have been investigated by DTA, optical and electron microscopy (SEM).Namjena istraživanja je izraditi termodinamički proračun svih mogućih reakcija u sustavu Cu-Se-O i obrazložiti mehanizme oksidacije u različitim uvjetima. Za takovo izučavanje izrađen je model bakra sa samo jednim uključkom i legura sa 1,65 mas. % Se. U ovisnosti od vremena, oksidacija se odvijala kod različitih temperatura i kod dviju različitih djelomičnih tlakova kisika. Oksidirani uzorci su bili ispitivani metodom DTA, optičkom i elektronskom mikroskopijom (SEM)

Unutarnja oksidacija legura srebra s telurom, selenom i sumporom

Silver alloys with tellurium, selenium and sulphur fulfil the conditions for the internal oxidation. Microstructure of these alloys consists of matrix (dilute solid solution) and particles of intermetallic compounds. Internal oxidation of ternary alloys is very similar to that of the binary alloys, but there are also distinctions in thermodynamics properties of alloying elements. At the direct oxidation of the particles of the intermetallic compound the phenomena of the selective oxidation was observed. Concentration of more reactive elements is increasing in the oxidized part of the particles of the intermetallic compound (Te in AgTeSe alloys). Therefore the precipitated oxides formed with diffusional internal oxidation are richer with less reactive alloying element (Se in AgTeSe alloy). In the precipitated oxide particles the concentration of selenium is more than twice higher than of tellurium.Legure srebra s telurom, selenom i sumporom ispunjavaju uvjete za unutarnju oksidaciju. Mirkostruktura ovih legura sastoji se od osnove (razrijeđena kruta otopina) i čestica intermetalnih spojeva. Unutarnja oksidacija ternarnih legura veoma je slična onoj za binarne legure, ali postoje i razlike u termodinamičkim svojstvima legirajućih elemenata. Kod izravne oksidacije čestica intermetalnog spoja zapažena je pojava selektivne oksidacije. Koncentracija reaktivnijih elemenata raste u oksidiranom dijelu čestica intermentalnog spoja (Te u AgTeSe leguri). Prema tome precipitirani oksidi nastali difuzijskom unutarnjom oksidacijom su bogati s manje reaktivnim legirajućim elementom (Se u AgTeSe leguri). U percipitiranim oksidnim česticama koncentracija selena je dvostruko veća nego telura

Analiza međupovršine niskougljičnog čelika/tantal nakon eksplozivnog zavarivanja

The article discusses the morphology, microstructure and chemical composition of the boundary layer in explosive welding of low-carbon steel and tantalum plates. Pools of melt composed of both metals and having a heterogeneous chemical composition appear on the boundary layer. This phenomenon is the result of incomplete mixing of both: molten metals due to rapid cooling and solidification. Within the pools of alloy, a large number of non-metallic oxide inclusions, products of deoxidation of molten alloys, can be found. The non-metal inclusions are round (0.1 to 2 µm in diameter) and vary in both: size and chemical composition. The main component of the non-metal inclusions is Ta2O5, which also contains iron, manganese, and aluminium oxides. The number of non-metal inclusions is unusually high for low-carbon steel and comparable to the number of non-metal inclusions in welds. Oxygen which causes the large number of deoxidised products does not originate in the low-carbon steel, as this steel is relatively clean. The most probable source of oxygen is the oxide scale from the surface of the low-carbon steel, which was poorly cleaned prior to welding.Članak raspravlja o morfologiji, mikrostrukturi i kemijskom sastavu pograničnog sloja pri eksplozivnom zavarivanju traka niskougljičnog čelika i tantala. Područje zone taljenja sastavljeno je od oba metala i na graničnom sloju pojavljuje se heterogeni kemijski sastav. Ova pojava je posljedica nepotpunog miješanja oba rastaljena metala, zbog naglog hlađenja i očvršćivanja. Unutar područja spajanja legure može se utvrditi veliki broj nemetalnih oksidnih uključaka, produkata dezoksidacije rastaljenih legura. Nemetalni uključci su okrugli (0.1 do 2 µm) i variraju u veličini i kemijskom sastavu. Glavna komponenta nemetalnih uključaka je Ta2O5, koji također sadrži željezne, manganove i aluminijeve okside. Broj nemetalnih uključaka je neouobičajeno velik za niskougljični čelik i usporediv je s brojem nemetalnih uključaka u zavarima. Kisik koji dovodi do nastanka velikog broja produkata dezoksidacije ne potiče iz niskougljičnog čelika jer je čelik relativno čist. Najvjerojatniji izvor kisika je površinski oksidni sloj niskougljičnog čelika koji je slabo očišćen prije procesa zavarivanja

Modulacija eksperimentalnog autoimunog encefalomijelitisa (EAE) DA pacova levamizolom

We investigated the influence of an antiparasitic drug, levamisole (2,3,5,6 - tetrahydro - 6- phenyl-imidazo (2,1 - b) thiazole -hydrochloride) with potent immunomodulatory properties on the course and development of experimental autoimmune encepha-lomyelitis (EAE). EAE was induced in female Dark Agouti (DA) rats aged two months by immunization with guinea pig spinal cord in complete Freunds adjuvant. Following immunization animals were subcutaneously treated every other day with 2.2 mg/kg levamisole. The course, development and characteristics of this autoimmune process were monitored as indirect indicators of immune system activity. Our results indicate that in EAE levamisole exerts immunosuppressive effects when administered every other day from the moment of immunization until the end of the disease. This application regime and dose postponed the onset of the first clinical signs, shortened the duration of the disease, abrogated the severity of clinical symptoms and accelerated the recovery of sick animals. In the period of induction and during EAE, levamisole also decreased the severity of changes in the cerebral perivascular spaces. In the peripheral blood of levamisole treated animals with induced EAE, a significant increase of CD4-CD8+ T cells was demonstrated. Furthermore, all rats with induced EAE had decreased numbers of CD4+CD8- T cells in their blood. These changes were in correlation with clinical signs of EAE.U ovom radu su prikazani rezultati ispitivanja anthelmintika levamizola (2,3,5,6 tetrahidro - 6 - fenil - imidazo (2,1 - b) tiazol hidrohlorida) sa snažnim imunomodulatornim svojstvima na tok i razvoj eksperimentalnog autoimunog encefalomijelitisa (EAE). EAE je indukovan imunizacijom ženki pacova soja DA (Dark Agouti) starih dva meseca pomoću homogenata kičmene moždine zamorčeta u kompletnom Freundovom adjuvansu. Posle imunizacije, životinje su tretirane subkutanim injekcijama levamizola (2.2 mg/kg) svaki drugi dan a praćeni su tok, razvoj i karakteristike ovog autoimunog oboljenja kao indirektni indikatori aktivnosti imunološkog sistema. Postignuti rezultati ukazuju dalevamizol ispoljava imunosupresivno delovanje u modelu EAE ako se aplikuje svaki drugi dan od momenta imunizacije do kraja bolesti. Primenjena doza i režim aplikacije odložili su momenat pojavljivanja prvih kliničkih simptoma, skratili trajanje bolesti, ublažili ispoljavanje simptoma i ubrzali oporavak bolesnih životinja. U periodu indukcije i tokom EAE-a levamizol je smanjio stepen promena u cerebralnim perivaskularnim prostorima. U ženskoj krvi ženki pacova sa indukovanim EAE i tretiranim levamizolom uočeno je značajno povećanje broja CD4-CD8+ T ćelija. Osim toga, u obe imunizovane grupe životinja zapaženo je smanjenje broja CD4+CD8- ćelija. Ove promene su bile u skladu sa kliničkom slikom bolesti

Heat stress increases long-term human migration in rural Pakistan

Human migration attributable to climate events has recently received significant attention from the academic and policy communities (1-2). Quantitative evidence on the relationship between individual, permanent migration and natural disasters is limited (3-9). A 21-year longitudinal survey conducted in rural Pakistan (1991-2012) provides a unique opportunity to understand the relationship between weather and long-term migration. We link individual-level information from this survey to satellite-derived measures of climate variability and control for potential confounders using a multivariate approach. We find that flooding—a climate shock associated with large relief efforts—has modest to insignificant impacts on migration. Heat stress, however—which has attracted relatively little relief—consistently increases the long-term migration of men, driven by a negative effect on farm and non-farm income. Addressing weather-related displacement will require policies that both enhance resilience to climate shocks and lower barriers to welfare-enhancing population movements