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  • Blackwell Publishing Ltd  (11)
  • American Institute of Physics (AIP)  (10)
  • 11
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 18 (1995), S. 0 
    ISSN: 1460-2695
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau
    Notizen: Abstract— The influence of Al2O3 particle reinforcement on the fatigue crack growth properties of 6061-T6 aluminium alloy in the near threshold regime has been investigated at a load ratio of R=– 1 using an alloy with 15 vol.% fine particles (6061/Al2O3/15p) and one with 21 vol.% coarser particles (6061/Al2O3/21p). The Al2O3 particles act as obstacles for fatigue crack growth and are especially effective at very low cyclic loads. For the reinforced alloy with fine particles the threshold of the stress intensity amplitude is higher than that for the alloy containing coarse particles, and the lowest threshold value of Kmax was obtained for pure 6061-T6. Fracture of ceramic particles and interfaces between matrix and Al2O3 particles, both more frequent for coarser particles, may serve as an explanation for the more effective improvement of fatigue crack growth properties by fine particles. At maximum stress intensity factors above 6.5 MPa√m, fatigue crack growth in the particle reinforced alloys is faster than in the unreinforced alloy 6061-T6, which is attributed to more frequent particle and interface fracturing.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 16 (1993), S. 0 
    ISSN: 1460-2695
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau
    Notizen: Rough fracture surfaces usually influence substantially the fatigue growth properties of materials in the regime of low growth rates. Friction, abrasion, interlocking of fracture surface asperites and fretting debris reduce the applied load amplitude to a smaller effective value at the crack tip (“sliding crack closure”, or “crack surface interaction” or “crack surface interference”). The influence of these phenomena on the fatigue crack growth properties of structural steel is discussed and compared for the two kinds of mixed mode loading employed in this work. Mixed mode loading was performed by (A): cyclic mode III + superimposed static mode I and (B): cyclic mode I + superimposed static mode III loading. Such loading cases frequently occur in rotating load-transmission devices.Several differences are typical for these two mixed-mode loading cases. A superimposed static mode I load increases the crack propagation rate under cyclic mode III loading whereas cyclic mode I fatigue crack propagation is retarded when a static mode III load is superimposed. Increase of the R -ratio (of the cyclic mode III load) leads to an insignificant increase of fracture surface interaction and subsequently to a small decrease of the crack growth rate for cyclic mode III loading, whereas higher R -values during cyclic mode I+ superimposed static mode III loading lead to a significant reduction of the crack growth rates.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 13
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 15 (1992), S. 0 
    ISSN: 1460-2695
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau
    Notizen: Abstract— The significance of interaction effects has been studied in tests with a continuous repetition of blocks with low and high amplitude cycles under conditions characteristic for ultrasound fatigue. Significant retardation effects were observed. However, low-intensity cycles, which according to a previous investigation might be harmless, did contribute to crack growth. Delayed retardation explains this observation. A fractographic analysis indicated the significance of surface roughness. Low-amplitude cycles may induce a smoother fracture surface, and thus increase the crack growth rate at higher amplitudes. Accurate predictions are therefore problematic. For similar reasons, omitting numerous low-amplitude cycles in random load experiments should be done with great care.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 14
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 18 (1995), S. 0 
    ISSN: 1460-2695
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau
    Notizen: Abstract Fatigue crack growth under constant and random loading conditions was investigated for a metastable austenitic-bainitic steel in comparison with a ferritic chromium steel at very low crack growth rates. Experimentally determined random crack growth was compared with linear Miner calculations on the basis of constant amplitude results. It was found that the measured crack growth rates in transforming material are a factor of 10 lower than the calculated values, whereas the difference is only a factor of 2 for the ferritic steel. The reason for the pronounced crack growth retardation in the metastable alloy is transformation of part of the austenitic phase into martensite in the stress field of the crack tip, accompanied by a volume increase and, consequently, residual compressive stresses. Rare high load cycles in the random sequence increase the closure level, which then leads to pronounced retardation of fatigue crack growth for the numerous successive low amplitude cycles.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 84 (1991), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract A 3-deoxy-2-heptulosaric acid (DHA), very probably with the lyxo-configuration, was identified in the R-core region of lipopolysaccharides from modulating strains of Rhizobium leguminosarum, Rhizobium meliloti and from all three biovars of the phytopathogenic Agrobacterium tumefaciens. Its structure could be deduced from the fragmentation pattern of the corresponding alditol acetates obtained after reduction of the 2-keto and the 1,7-carboxy groups by sodium borohydride or sodium borodeuteride. DHA in lipopolysaccharide was not destroyed by periodate and is therefore not in a terminal position. Two DHA-containing oligosaccharides, namely glucosyl (1 → 4)-3-deoxy-2-heptulosaric acid and rhamnosyl-rhamnosyl-(1 → 5)-3-deoxy-2-heptulosaric acid could be tentatively identified by mass spectrometric methods amongst the products of mild acidic hydrolysis of lipopolysaccharides of Rhizobium leguminosarum strain 24. The two types of non-nodulating mutants of Rhizobium leguminosarum included in this study did not contain 3-deoxy-2-heptulosaric acid.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 16
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 73 (1990), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract Exposure of dry oxic paddy sol to submerged anoxic conditions resulted in a decrease of the soil redox potential and initiation of CH4 production. However, the most probable numbers (MPN) of hydrogenotrophic and acetotrophic methanogens did not change upon flooding the soil and upon initiation of CH4 production, and stayed constant at 105−106 and 104−105 g−1 d.w. soil, respectively. Cells of Methanobacterium strain Bab1 added to anoxic soil suspensions mostly survived drying and storage under an air atmosphere. Initiation of CH4 production was not affected by storage of dry soil under N2, air, or O2 atmosphere. However, it was negatively affected by storage under the air at high negatively affected by storage under air at high relative humidities, under moist conditions, or by using only the small (〈 100 μ m) soil particle fraction. All these treatments also resulted in decreased contents of dissolved organic carbon (DOC). The soil's capacity for initiation of CH4 production could be regenerated either by addition of glucose or by exposure to H2 and addition of reducing agents. The establishment of decreased redox potentials and the provision of methanogenic substrates by heterotrophic bacteria, but not the number of methanogenic bacteria, seemed to be the essential factors for initiation of CH4 production after submergence of oxic paddy soil. CH4 production could also be initiated in forest and arable soils. Here, however, the population of methanogenic bacteria (MPN) increased from about 103 to 105−106 g−1 d.w. when methanogenesis started.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 17
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 14 (1982), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 18
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 47 (1988), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract Pseudomonas aeruginosa strains isolated from cystic fibrosis patients agglutinate in antisera against anti-polyagglutinable antigen (PA). Anti-PA antibodies were formed in rabbits when immunization was carried out with bacteria possessing core-bound PA, independently of whether the strains were of S or R phenotype. For bacterial agglutination with anti-PA antibodies two prerequisites are essential: the bacterial cell must be of R phenotype and must possess the core-linked PA. In contrast, the PA in the isolated LPS's can be demonstrated in passive haemagglutination for both (S or R) phenotypes, provided the PA is core-linked. Two PA forms have been recognized, one found only in P. aeruginosa species, both in free and bound form. The other one is shared by all members of Pseudomonas genus but is present only in a free, unbound form.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 19
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 60 (1989), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract The presence and the relative amount of 4-amino-l-arabinose in lipopolysaccharides of members of the Enterobacteriaceae family and in a single strain of Chromobacterium violaceum has been studied with regard to growth-temperature dependent variations. Changes in the presence and the amount of 4-amino-l-arabinose (4-AA) were observed in almost all cases, but the variations observed were not consistent among different species. While Salmonella minnesota and Proteus mirabilis showed higher levels of incorporation at higher temperatures, the S- and R-forms of Yersinia enterocolitica showed the opposite effect, i.e. only marginal incorporation by growth at 37°C, in contrast to rather high values by growth at 10°C. Chromobacterium violaceum, however, showed no significant alteration in the 4-amino-l-arabinose content when growth either at 14 or at 37°C. DOC-PAGE pattern of isolated lipopolysaccharides showed characteristic profiles indicating that the O-chain-synthesis of distinct Enterobacteriaceae is also differently influenced by changes in growth temperature.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 20
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 17 (1983), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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