Fatigue fracture toughness and crack propagation rate

Fatigue crack growth rate, da/dN, of two high strength steels were examined in a laboratory air at different stress ratios, covering almost the entire range of stress intensity, K, from nearly threshold value, Kth, to final fracture. The fatigue fracture toughness, Kfc, corresponding to the final fracture in fatigue, was also determined. The lower the Kfc, the higher da/dN and reduced Kth are revealed.This correlation was analyzed quantitatively based on the four parameter Weibull function. And the stress ratio dependency of the fatigue crack propagation curve can be cleared in a successful manner.The fatigue characteristic stress intensities, Ke and Kv, are proposed to define the transition behaviour in fatigue crack growth curve, from so called region 1 to 2, and from region 2 to 3, respectively. Especially the Kv valua can be specified to be the 0.63Kfc.

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Résumé On a étudié la vitesse de propagation de fissure en fatigue da/dN de deux aciers à haute résistance dans un atmosphère de laboratoire sous des sollicitations couvrant toute la gamme des intensités de contraintes variables K, depuis une valeur voisine de la valeur du seuil Kth jusqu'à celle correspondant à rupture finale.La ténacité à la rupture par fatigue Kfe correspondant à la rupture finale par fatigue a été également déterminée. II s'avère que plus Kfe est faible, plus élevée est da/dN et plus Kth est réduite. Cette correlation est analysée quantitativement en se basant sur la fonction de Weibull à quatre paramètres. On peut ainsi clarifier la manière dont le rapport de contraintes influe les courbes de propagation des fissures de fatigue.On propose de définir pas les facteurs caractéristiques d'intensité de contrainte Ke et Kv les comportements de transition de la courbe de vitesse de propagation de la fissure entre respectivement les régions dénommées 1 et 2, et 2 et 3.En particulier, on peut spécifier que la valeur Kv vaut 0,63 Kfe.

     

Production of Ni-Pd-Si and Ni-Pd-P amorphous wires and their mechanical and corrosion properties

Wire-shaped nickel-based amorphous alloys exhibiting high strength and good ductility combined with a high corrosion resistance were produced for Ni-Pd-Si and Ni-Pd-P alloys by melt spinning in rotating water. The amorphous wires were formed over a relatively wide range from 29 to 82 at % palladium for (Ni-Pd)₈₂Si₁₈ alloys and from 12 to 52 at % palladium for (Ni-Pd)₈₀P₂₀ alloys. The Ni-Pd-Metalloid amorphous wires had a circular cross-section and smooth surface, and their diameters were 80 to 150m. With increasing nickel content, their tensile strength, _f, increased from 1340 to 1710 MPa and the elongation to fracture, _f, decreased slightly from 2.2% to 1.9%. Cold-drawing the wires was an easy technique to reduce their diameter and to increase _f and _f up to an appropriate value of reduction in diameter. In addition, it is also effective in smoothing the wire surface. Their corrosion resistance was assumed to be sufficiently high since their polarization behaviour in 1 N H₂SO₄ solution was similar to palladium metal. Cold-drawing did not enhance corrosion and rather decreased apparently the active dissolution current density of some alloys owing to smoothing of the surface.     

Instability of Quantized Vortices Attached to Oscillating Boundaries in Superfluid 4He

The motion of quantized vortices is studied using a vibrating wire in superfluid ⁴He. A vortex filtering method provides a superfluid practically free of remanent vortices in which the vibration of a wire cannot generate turbulence. Vortex lines are produced by cooling through the superfluid transition and remain forming bridges between a wire and a surrounding wall. Bridged remanent vortices increase the resonance frequency of a vibrating wire: the rate of an increase due to the remanent vortices is constant in a laminar flow regime and steeply increases in a turbulent flow regime with increasing wire velocity. These results suggest that oscillation of the bridged vortices provides a linear contribution to the wire vibration in the laminar flow regime, until instability occurs in the oscillation of the vortices, causing turbulence.      

Enhancement of visible light-induced hydrophilicity on nitrogen and sulfur-codoped TiO2 thin films

We fabricated N, S-codoped, N-doped, S-doped TiO₂ anatase thin films by a radio-frequency (RF) sputtering method and evaluated the photoelectrochemical and photoinduced hydrophilic activities. The N, S-codoped TiO₂ thin film showed obviously higher activities than either the N-doped or S-doped TiO₂ under visible light irradiation. The photoinduced hydrophilic activity of the N, S-codoped TiO₂ was also greater than that of the undoped TiO₂ even under fluorescent light bulb, which contained both visible and UV lights. The high activities of the N, S-codoped TiO₂ could be attributed to the hybridization of the introduced N 2p and S 3p, which was supported by the results of ab initio calculations.     

A circuit model for nonlinear simulation of radio-frequency filters using bulk acoustic wave resonators

This paper describes a circuit model for the analysis of nonlinearity in the filters based on radiofrequency (RF) bulk acoustic wave (BAW) resonators. The nonlinear output is expressed by a current source connected parallel to the linear resonator. Amplitude of the nonlinear current source is programmed proportional to the product of linear currents flowing in the resonator. Thus, the nonlinear analysis is performed by the common linear analysis, even for complex device structures. The analysis is applied to a ladder-type RF BAW filter, and frequency dependence of the nonlinear output is discussed. Furthermore, this analysis is verified through comparison with experiments.     

Local Controlled Release of Polyphenol Conjugated with Gelatin Facilitates Bone Formation

Catechins are extensively used in health care treatments. Nevertheless, there is scarce information about the feasibility of local administration with polyphenols for bone regeneration therapy, possibly due to lack of effective delivery systems. Here we demonstrated that the epigallocatechin-3-gallate-conjugated gelatin (EGCG/Gel) prepared by an aqueous chemical synthesis using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-morpholinium chloride (DMT-MM) gradually disintegrated with time and facilitated bone formation in a critical size defect of a mouse calvaria. Conjugation of EGCG with the Gel generated cross-linking between the two molecules, thereby leading to a retardation of the degradation of the EGCG/Gel and to a delayed release of EGCG. The prepared EGCG/Gels represented significant osteogenic capability compared with that of the uncross-linked Gel and the cross-linked Gel with uncombined-EGCG. In vitro experiments disclosed that the EGCG/Gel induced osteoblastogenesis of a mouse mesenchymal stem cell line (D1 cells) within 14 days. Using fluorescently-labeled EGCG/Gel, we found that the fraction of EGCG/Gel adsorbed onto the cell membrane of the D1 cells possibly via a Gel-cell interaction. The interaction might confer the long-term effects of EGCG on the cells, resulting in a potent osteogenic capability of the EGCG/Gel in vivo. These results should provide insight into local controlled release of polyphenols for bone therapy.     

Sodium-doped carbon nitride nanotubes for efficient visible light-driven hydrogen production

Nano Research - Sodium-doped carbon nitride nanotubes (Na x -CNNTs) were prepared by a green and simple two-step method and applied in photocatalytic water splitting for the first time....     

Influence of aluminum precursors on structure and acidic properties of hollow silica–alumina composite spheres,and their activity for hydrolytic dehydrogenation of ammonia borane

In this study, we investigated the influence of aluminum precursors on structure and acidic properties of hollow silica–alumina composite spheres, as well as their activity for hydrolytic dehydrogenation of ammonia borane. Hollow silica–alumina composite spheres were prepared via the sol–gel method using polystyrene particles as templates. Activities of the hollow spheres prepared using various aluminum precursors for hydrolytic dehydrogenation of ammonia borane were compared. The molar ratios of evolved hydrogen to ammonia borane introduced were 1.0, 2.8, 1.5, and 3.0 in the presence of the hollow spheres prepared using aluminum ethoxide, aluminum isopropoxide, aluminum tributoxide, and aluminum-tri-sec-butoxide, respectively. Hollow spheres prepared using aluminum precursors with branched alkyl groups exhibit more hydrogen evolution than those prepared using aluminum precursors with normal alkyl groups. From the result of solid-state ²⁷Al nuclear magnetic resonance spectra and temperature-programmed desorption of ammonia, 4-coordinated aluminum species are related to Brønsted acid sites, and highly dispersed aluminum species increase the number of Brønsted acid sites.     

Intention-Sensing Recipe Guidance via User Accessing to Objects

Sensing the intention of a user’s forthcoming action is a necessary function for systems that assist human physical activity. In this article, a strategy for recipe guidance systems that can predict the forthcoming intended subtask in a cooking task is investigated. The focus is on user accessing objects, that is, touching and releasing objects. Touching can indicate the start of the forthcoming subtask and releasing can indicate the end of the task. The main difficulty lies in the fact that humans may move objects because they are in the way and use cooking tools that are unanticipated by an assistive system. In such cases, the accessed object should not indicate the forthcoming subtask. A method is proposed to track the progress of a task based on the object access history. This enables to eliminate object accesses that are out of context. Simultaneously, the method predicts the forthcoming subtask based on a combination of progress and materials rather than tools and materials. Then, a guidance system that runs as a web service is developed. In experiments, real cooking activities navigated by this system are observed. The Wizard of OZ method is utilized to simulate a system that detects object accesses. The experimental results show that 73.6% accuracy is achieved in the selection of the displayed information. This result supports the use of “access to objects” realize effective intention-sensing systems.