The fatigue crack growth modeling that based on linear fracture mechanics under the Mode I condition provided a good estimate of the stress intensity range for subsurface crack growth in α or near α-type titanium alloys. Based on the relationship between crack growth rate and stress intensity factor range, the fatigue crack propagating life was evaluated by the Paris rule. The subsurface crack initiation process consumed a large number of cycles to failure. Microstructure may strongly affect on not only subsurface crack initiation but also crack growth. The microstructural modification to prevent microcrack growth should be taken into account.
In this study, the effect of the metal salt generation bonding technique on the strength of a direct-bonded SUS304 stainless steel interface was investigated. SUS304 stainless steel surfaces were modified by boiling in 50% formic acid, and direct bonding was performed at a bonding temperature of 1023-1123K under a pressure of 147N (for a bonding time of 900 s). After direct bonding, the specimens were subjected to the peel test for evaluating their strength. As a result of the surface modification, bonded joints were obtained at bonding temperature of 30K lower than that required for the unmodified surfaces, and the peel strength was comparable to that of the maximum load. On the basis of the experimental results, it was established that metal salt generation processing is effective for removing oxide films on SUS304 stainless steel.
In order to simplify the structural integrity assessment of double cracked stainless steel piping, plastic collapse stress of asymmetric double notched pipes subjected to combined tension and bending was investigated. The experimental plastic collapse stress of the asymmetric double notched pipe is compared with the theoretical plastic collapse stress of the single notched pipe. The experimental plastic collapse points were over the theoretical collapse limit curve. The integrity of asymmetric double cracked stainless steel pipes subjected to combined tension and bending can be evaluated simply and conservatively using the theoretical plastic collapse stress of the single notched pipe.
Tensile test methodology for ceramic foams has been elaborated and test specimens of different dimensions and those containing central sharp notch (simulating a crack) were tested. Tested material was commercially available alumina based ceramic foam commonly used as filters of light metals melts. The foam cell size used within this study was 60 PPI. The main aim of the investigation has been to prove experimentally whether there is any stress concentration effect in the open cell structures. The fracture load (tensile strength) values were analysed and, in particular, the samples containing central sharp notch and comparable unbroken cross-section were compared with the unflawed samples. Specimens with central through thickness sharp notch have shown demonstrably the strength values comparably lower than the strength level of samples having the same cross-sectional area without stress concentrator. The explanation has been seen in stress concentration effect beneath the internal sharp notch root.
Numerous WWER-440 steam generators showed a very serious problem of cracking in weld joints which are connecting primary collectors to the steam generator's vessel. As a cause of this cracking was determined stress corrosion cracking mechanism. The weld is connecting austenitic steel collector to the carbon steel vessel, so it is a dissimilar metal weld. There are two approaches how to lower the possibility of stress corrosion cracking in the weld. First one is to improve the secondary water chemistry in the weld's surrounding to stop the corrosion and second one is to decrease presented stresses in weld's area. It is better to combine both approaches. This paper deals with the second approach of possibilities to decrease presented stresses. Inspired by Russian study of external cooling on WWER-1000 steam generators, it was an attempt to adapt the external cooling idea on the WWER-440 steam generators and their problem of weld cracking. It was shown that by using the external cooling it is possible not just lower the presented tensile stresses but to change the tensile stresses into compressive stresses. This will of course result in significant reduction of stress corrosion cracking possibility in the steam generator primary collector weld's area.
In order to understand the effect of the difference in chemical composition and microstructure of bond coat (BC) layer on delamination properties, pushout tests were performed on modeled air plasma-sprayed thermal barrier coatings (APS-TBCs). Nickel-platinum-aluminides (Ni-Pt-Al), hafnium modified nickel-platinum-aluminides (Ni-Pt-Al-Hf) and NiCoCrAlY alloys were used as BC alloy. Hafnium and aluminum oxide were formed in needle like shape when the Ni-Pt-Al-Hf alloy was used. Vickers hardness of BC alloy decreased up to 50hours heat exposure and then increased with increasing heat exposure time. Interfacial delamination toughness increased and then decreased with the increase in heat exposure time.
This paper deals with the optical modeling of thin hydrogenated microcrystalline silicon films grown on flexible low-cost iron-nickel alloy substrates by low-temperature (175°C) plasma-enhanced chemical vapor deposition. This material serves as the absorber in solar cells and hence it has direct impact on the resulting solar cell performance. Since the crystallinity and the material quality of hydrogenated microcrystalline silicon films evolve during the growth, the deposited film is inhomogeneous, with a rather complex structure. Real-time spectroscopic ellipsometry has been used to trace the changing composition of the films. In-situ ellipsometric data taken for photon energies from 2.8 to 4.5eV every 50seconds enabled us to study the evolution of the monocrystalline silicon fraction of the hydrogenated microcrystalline silicon films.
The characteristics of cyclic bending deformation and fatigue fracture are studied on polycrystalline aluminum and Al-1.0mass%Mg alloy from the metallurgical point of view. It is found that the fatigue life mainly depends on grain size and the kind of materials. Cracks are preferentially formed at grain boundaries inclined 40 – 60°to the tension-compression direction, suggesting that shear stress affects the crack formation. EBSD measurements reveal the inhomogeneity of deformation. Intense development of sub-grain is seen in the grain interior close to a crack. It indicates that the work hardening close to grain boundaries triggers the crack formation.
The non-magnetic TiO2 powder and magnetically modified TiO2 powder were employed for the sorption experiments. FeSO4.7H2O was used for synthesis of magnetically responsive TiO2. The non-magnetic and prepared magnetic materials were characterized by scanning electron microscopy and X-ray diffraction methods. The particle size and specific surface area were determined. A detailed study of the adsorption process performed using batch adsorption experiments was carried out with various concentrations of lead ions and contact time. A flame atomic absorption spectrometer was used for determination of Pb2+ ions concentration in solution. Adsorption process has been modeled by the Langmuir and Freundlich isotherms using linear and non-linear regression. The results showed that the adsorption of Pb2+ ions on the magnetic and non-magnetic TiO2 particles occurred in a monolayer. Presence of magnetic iron oxides particles on the surface of sorbents increased the adsorption rate, and increased the maximum amount of adsorbed Pb2+ ions per mass in comparison with adsorption on the non-magnetic TiO2 particles. The magnetically modified TiO2 particles allow magnetic separation of the sorbents with already adsorbed ions of pollutants.
Two organic compounds (naphthalene and formaldehyde) were investigated for their sorption properties on to multiwall carbon nanotubes in original state and purified using acid treatment. Nice enhancement of sorptive ability was observed after nanotube purification. Smaller organic molecule was adsorbed in higher weight percentage (reaching 30wt.%) than naphthalene (approx.13wt.%). Molecular modeling confirmed adsorption centers of organics on carbon nanotubes being located on the outside area or close to center of nanotube, then having the lowest energy of adsorption.
In this paper, the effects of the existence of inclusion or missing cells on the overall in-plane mechanical behavior of micro-lattice plate is discussed by using the numerical finite element analysis. The micro-lattice plate can be manufactured using the selective metal laser melting technique, and various shapes of its micro-architecture can be easily produced even if there are non-uniform cells. In particular, effects of boundary condition of the plate's edges, cell's geometry and the shapes of non-uniform region on the initial stiffness and plastic collapse strength are investigated. Also, based on the numerical results, empirical equations for estimating these mechanical properties are proposed.
The paper deals with minor phase evolution in a Cu – bearing grain oriented electrical steel during the following production steps of the AlN + Cu industrial processing route: hot rolling of slabs, the 1st cold rolling + decarburization annealing and the 2nd cold rolling + slow laboratory heating to the temperature of primary recrystalization. Thermocalc calculations were used for prediction of the effect of copper additions on equilibrium phases in the temperature interval 450 – 850°C. Minor phase evolution was studied by using transmission electron microscopy. Hot rolling was accompanied by dissolution of copper rich sulfides. Slow cooling of coils after hot rolling resulted in precipitation of Fe3C along ferrite grain boundaries. Decarburization annealing after the 1st cold rolling was accompanied by dissolution of Fe3C, re-precipitation of fine Cu2S, (Mn,Cu)S and very intensive precipitation of nitrides (AlN and Si3N4). Slow laboratory heating after the 2nd cold rolling to the onset of primary recrystallization (620°C) did not cause precipitation of any other minor phase. No copper rich metallic particles (ɛ - Cu) formed during the production steps investigated. Most fine particles of inhibition phases formed during decarburization annealing.
Microstructure of the base metal, the multilayer welding seam and the two-layer cladding was characterized through the thickness of the WWER 440 reactor pressure vessel wall. Mechanical properties were determined by performing a series of instrumented indentations across the weld at room temperature. The results were treated by so-called automated ball indentation technique. Mechanical properties obtained by instrumented indentation from the local stress-strain behavior were compared with minimum values required by the standard.
In this paper the Mueller matrix ellipsometry in the spectral range from 0.73 to 6.4eV measured using dual rotating compensator ellipsometer RC2 (Woollam company) is applied to study anisotropic crystals. First we summarize the effects of optical anisotropy to Mueller matrix spectra. As an example of an uniaxial sample we have characterized a Rutile (TiO2) tetragonal crystal. The optical axis of the sample is parallel to its surface. The sample is characterized at variable angle of incidence and variable azimuthal rotation angle. The Mueller matrix spectra are fitted to the model based on Kramers-Kronig consistent Basis spline and obtained optical functions are compared with tabulated data and ab-initio models based on first-principle calculated electronic structure.
In the present work two techniques are combined to optimize bond coat properties before thermal barrier coating (TBC) application, the cold gas dynamic spraying (CGDS) and electron beam remelting (EB). Results of the work focused on comparison of high velocity oxygen fuel (HVOF) and CGDS CoNiCrAlY bond coats are firstly presented. Than the effect of the electron beam remelting of the CoNiCrAlY coating manufactured by HVOF and CGDS deposition techniques is deeply investigated. The CoNiCrAlY bond coat to Inconel substrate interface displayed locations with very poor bonding, in larger extent for the states prepared by HVOF comparing to CGDS. The bond coats prepared by both ways being EB remelted are typically removal of the defects on the substrate to bond coat interface. The microstructure of the bond coat after this treatment is formed by Inconel fine grain layer being followed by the surface layer consisting of elongated dendritic microstructure. An increased porosity has been observed in interdendritical space in larger extent for CGDS samples.
In this study we focused on antimicrobial nanocomposites based on kaolinite, when two series of nanocomposites were prepared. In the first case, kaolinite (KAO) was used as the carrier for antibacterial drug. Secondly, kaolinite modified with dimethyl sulphoxide (DMSO) was used. In both series, chlorhexidine dihydrochloride (CH) acts as an active antimicrobial component. The resultant samples were characterized by X – ray diffraction (XRD) and infrared spectroscopy (FTIR). The antimicrobial activity of prepared composites against bacteria strains Staphylococcus aureus, Escherichia coli and against yeast Candida albicans were evaluated by finding minimum inhibitory concentration (MIC). It was found that prepared nanocomposites were very effective and they had different effect against bacteria strains and yeast. Important information was that treatment with DMSO had not significant effect on antimicrobial activity. These nanocomposites can be in future used for preparation of drugs for local treatment of oral cavity with long-acting antimicrobial activity.
The non-reciprocity of magneto-optical reflection response by surface plasmon excitation in the planar Au/Fe/Au/glass nano-systems with prism coupling is studied. In order to simulate diffraction response to external magnetic field theoretical matrix model based on rigorous coupled waves algorithm is applied that allows to simulate both the influence of metallic layer thicknesses and external magnetic field. The two new response factors related to response function are introduced and tested from the point of view of their applicability. Obtained theoretical results are compared with experiment realized using the measuring device Multiskop (Optrel GbR, Germany).
The Small Punch (SP) test technique is used for the evaluation of actual tensile, fracture and creep characteristics of materials exposed for a long period in operating plant components in order to provide data needed for plant life and integrity assessment.In the present paper the results of SP tests in the temperature range from -193 degrees C to +20 degrees C, carried out in two laboratories on low alloy steel of type 14MoV6-3 in as received state and after long term operation at 540 degrees C were compared. SP transition temperatures T-SP determined from the temperature dependences of the fracture energy were correlated with the FATT temperatures obtained using standardized Charpy V notch test specimens. (C) 2016 Published by Elsevier Ltd.
Presented paper introduces an innovative principle of fatigue life assessment suggested for WWER nuclear power plants. The subject of this work is to take into account the corrosion environment influence in actual methodology of low-cycle fatigue (LCF) assessment and prediction. The aim of this paper is to summarize the current status of the Czech proposal of corrosion fatigue assessment and prediction. The first project focused on base steel materials, which are used in primary circuit of WWER-440, started in 2010. The basic idea of Czech environmental fatigue correction factor has been introduced on international PVP conference in 2013. The new project linked to the previous one is focused on the additional area of welding joints. Theoretical base is completed by experimental verifications of proposed environmental correction factor. The subject of actually running theoretical-experimental program covers similar metal welds of austenitic stainless steel 08CH18N10T and results will be available in 2015. Moreover LCF tests in corrosion environment of dissimilar metal welds are under preparation. Experimental work is based on LCF strain-controlled tests in primary water environment of WWER-440.
If subsurface flaws are detected that are close to component free surfaces, flaw-to-surface proximity rule is used to determine whether the flaws should be treated as subsurface flaws as is, or transformed to surface flaws. However, specific factors for the proximity rules on transforming subsurface to surface flaws differ among fitness-for-service codes. The objective of the paper is to reveal the proximity factor from the stress intensity factor interaction between the subsurface flaw and the free surface.
