MECHANICAL PROPERTIES OF FORGED TUNGSTEN HEAVY ALLOYS

Tungsten heavy alloys are composite materials containing spherical tungsten particles embedded in binder matrix. Their excellent mechanical properties can be further improved by rotary forging. This paper aims to gain deeper understanding of the forging process by investigating the local elastic modulus, hardness, and residual stress of individual phases in W6Ni3Co pseudo-alloy. The resulting global properties of the composite material such as stress-strain behavior, fracture toughness and fatigue crack growth rate behavior are also studied. The results show that sintered and quenched material consists of highly textured matrix containing nearly perfect single crystal spheres of pure W. The rotary forging leads to significant lattice deformations destroying the texture and significantly increasing the hardness of both WNiCo matrix and W particles and making residual stresses in W particles anisotropic with increased compression along the longitudinal axis of the forged part

Conditions for long-term durability of dissimilar metal welds of power plants – environmental effect

Heterogenní svarové spoje v energetických zařízeních představují uzly, které mohou mít za určitých podmínek sníženou životnost. Příčiny změny užitných vlastností a způsoby poškození heterogenních svarových spojů lze rozdělit do dvou skupin podle teploty aplikace. Svarové spoje exponované při teplotách t < 300–350 °C podléhají poškození s významnějším vlivem prostředí. V příspěvku bude podána obecná charakteristika svarových spojů, s ohledem na specifické prostředí jaderných elektráren.Dissimilar metal welds in power plants equipment may have reduced service life under certain conditions. The causes of the change in utility properties and damage types of heterogeneous weld joints can be divided into two groups according to the application temperature. Welds exposed at temperatures t < 300 – 350 °C are subject to significant environmental damage. The paper will present general characteristics of dissimilar metal welds with regard to the specific environment of nuclear power plants

Characterization of dissimilar metal welds

V příspěvku je studován heterogenní svarový spoj potrubí z uhlíkové a austenitické ocele. Ve svařeném potrubí byly na rozhraní základní materiál – svarový kov nalezeny trhliny, které vznikly a šířily se mechanismem korozního praskání. Trhlina se šířila podél linie ztavení v oblasti promísení obou kovů. V této oblasti byly identifikovány změny v chemickém složení a zákalné struktury s výrazně vyšší tvrdostí oproti svařovaným kovům.TK01030108 (TA ČR)Heterogeneous dissimilar metal welds of carbon and austenitic stainless steel used in the piping systems were studied in this paper. The cracks were found in the welded pipeline at the interface between the base carbon steel and austenitic filler material. The stress corrosion cracking was identified as the cracking mechanism. The crack propagated along the fusion line in the mixing zone (area with higher diffusion) of both metals. In this area, changes in chemical composition and quenching structures with significantly higher hardness compared to the base metals were identified

Exposure of dissimilar metal welds to secondary water environment

Tento příspěvek uvádí výsledek dlouhodobé expozice heterogenních svarových spojů (HSS) teplotním cyklům v prostředí sekundárního okruhu jaderné elektrárny (JE) typu VVER. Zkoušené vzorky HSS se skládaly z uhlíkové a austenitické korozivzdorné oceli. Část vzorků byla opatřena Ni ochrannou vrstvou. Část vzorků byla v přípravcích zatížena tříbodovým ohybem pomocí speciálně vyrobených přípravků.This text presents results of long-term exposure of dissimilar metal welds (DMW) to heat cycles in VVER secondary water environment. Tested DMW were made of carbon and austenitic stainless steel. Some samples were covered by Ni protective layer. Some samples were under three-point bend load

Major Outbreak of Hepatitis A Associated with Orange Juice among Tourists, Egypt, 2004

In 2004, a major outbreak of hepatitis A among tourists returning from Egypt involved 351 case-patients from 9 European countries who were infected with a single strain (genotype 1b). The case-control study identified orange juice as the most likely infection vehicle. Vaccination against hepatitis A virus is strongly recommended before travel to disease-endemic areas

Downregulation of pyrophosphate: d-fructose-6-phosphate 1-phosphotransferase activity in sugarcane culms enhances sucrose accumulation due to elevated hexose-phosphate levels

Analyses of transgenic sugarcane clones with 45–95% reduced cytosolic pyrophosphate: d-fructose-6-phosphate 1-phosphotransferase (PFP, EC 2.7.1.90) activity displayed no visual phenotypical change, but significant changes were evident in in vivo metabolite levels and fluxes during internode development. In three independent transgenic lines, sucrose concentrations increased between three- and sixfold in immature internodes, compared to the levels in the wildtype control. There was an eightfold increase in the hexose-phosphate:triose-phosphate ratio in immature internodes, a significant restriction in the triose phosphate to hexose phosphate cycle and significant increase in sucrose cycling as monitored by 13C nuclear magnetic resonance. This suggests that an increase in the hexose-phosphate concentrations resulting from a restriction in the conversion of hexose phosphates to triose phosphates drive sucrose synthesis in the young internodes. These effects became less pronounced as the tissue matured. Decreased expression of PFP also resulted in an increase of the ATP/ADP and UTP/UDP ratios, and an increase of the total uridine nucleotide and, at a later stage, the total adenine nucleotide pool, revealing strong interactions between PPi metabolism and general energy metabolism. Finally, decreased PFP leads to a reduction of PPi levels in older internodes indicating that in these developmental stages PFP acts in the gluconeogenic direction. The lowered PPi levels might also contribute to the absence of increases in sucrose contents in the more mature tissues of transgenic sugarcane with reduced PFP activity

Synthetic biology to access and expand nature's chemical diversity

Bacterial genomes encode the biosynthetic potential to produce hundreds of thousands of complex molecules with diverse applications, from medicine to agriculture and materials. Accessing these natural products promises to reinvigorate drug discovery pipelines and provide novel routes to synthesize complex chemicals. The pathways leading to the production of these molecules often comprise dozens of genes spanning large areas of the genome and are controlled by complex regulatory networks with some of the most interesting molecules being produced by non-model organisms. In this Review, we discuss how advances in synthetic biology — including novel DNA construction technologies, the use of genetic parts for the precise control of expression and for synthetic regulatory circuits — and multiplexed genome engineering can be used to optimize the design and synthesis of pathways that produce natural products

Analýza součástí příznivého podnikatelského prostředí Pardubického kraje

The entrepreneur environment is the complex of the factors and parts which can influence the entrepreneurs and their activities in some region. We can suppose that only positive entrepreneur surrounding enables to entrepreneurs to reach their goals most effectively. This paper deals with the research results presentation and provides information about evaluation of the entrepreneur surrounding made by the investors (they have came to the Czech Republic with the CzechInvest support) and by public administration representatives. The paper conclusion deals with the generalization of the results obtained

Quantitative Fractography - Well Spring of Intimate Knowledge in Fatigue Crack Growth History

Quantitative fractography of fatigued structure parts can offer very useful and valuable information on the fatigue process. One of main contribution of this experimental method is a detailed description of fatigue crack growth in time and in space. The fractographic reconstitution of fatigue process history is conditioned by the existence and detectability of a fractographic feature characteristics of which is correlated with the fatigue crack growth rate. In the paper presented, three various fractographic features are used for the fractographic reconstitution - striations (in the case of constant amplitude loading), beach marks (for simple program loading) and special inserted fracture marks (for complex program loading). All three methods described are illustrated on case studies, all from the area of testing and development of aircraft structure parts

Microstructure and Failure Processes of Reactor Pressure Vessel Austenitic Cladding

This paper is dedicated to an experimental program focused on the evaluation of microstructure and failure mechanisms of WWER 440 type nuclear reactor pressure vessel cladding made from Sv 08Kh19N10G2B stainless steel. Static fracture toughness tests performed on standard precracked single edge bend specimens revealed extreme variations in fracture toughness values, J0.2. Fractured halves of test specimens were subject to detailed fractographic and metallographic analyses in order to identify the causes of this behavior and to determine the relationship between local microstructure, failure mode and fracture toughness. Results indicated that fracture toughness of the cladding was adversely affected by the brittle cracking of sigma particles which caused a considerable decrease in local ductile tearing resistance. Extreme variations in relative amounts of sigma phase, as well as the extreme overall structural heterogeneity of the cladding determined in individual specimens, provided a reasonable explanation for variations in fracture toughness values