The orientation relationships and interfaces between δ-AuSn and Au

The orientation relationships and interfaces of δ-AuSn with the Au (001), (110) and (111) surfaces have been studied with transmission electron microscopy. Au was evaporated onto the NaCl (001), (011) and (111) surfaces to form epitaxial Au thin films and Sn was evaporated onto the Au films to form δ-AuSn. Two types of orientation relationships have been found: (1) _δ//(001)_Au, (0001)_δ//(110)_Au, and _δ//_Au, which was found on the _δ/(001)_Au interface and the _δ/_Au interfaces; and (2) _δ//_Au, (0001)_δ//(110)_Au, and _δ//_Au, which was found on the _δ/_Au interface. The interfaces are analyzed by the structures of the surfaces and the orientation relationships. The nucleation of δ-AuSn on these interfaces is also discussed.     

Analysis of a transiently propagating crack in functionally graded materials under mode I and II

Crack tip stress and displacement fields for a transiently propagating crack along gradient in functionally graded materials (FGMs) with a linear variation of shear modulus are developed. The higher order terms of the transient stress and displacement fields at crack tip were obtained by transforming the general partial differential equations of the dynamic equilibrium into Laplace’s equations whose solutions have harmonic functions. Thus, the fields can be expressed very simply. Using these stress components, isochromatics and the first invariant at crack tip are generated.The results show that the isochromatics (constant maximum shear stress) for mode I crack tilt backward around the crack tip with an increase of crack tip acceleration , and tilt forward around the crack tip with an increase of rate of change of dynamic mode I stress intensity factor . The isochromatics for mixed mode crack move to upper direction with an increases of and , and lower direction with an increase of . Contours of the first stress invariant for mode I crack enlarge around the crack tip with an increase of , and decrease around the crack tip with an increase of . As decreases at crack initiation, the predicted kinking angles increase. As increases, the predicted kinking angles also increase.     

Role of microstructures on the growth of long fatigue cracks

An analysis is presented to understand the role of microstructures on the two crack growth driving force parameters, and , without invoking the extrinsic crack closure concepts. Microstructural variables considered are: grain size, precipitates and stacking fault energy. It is shown that is strongly affected by the scale of the microstructure, such as grain size or precipitate spacing. For each case, the mode of slip deformation and environment affects the fatigue resistance as represented by . However, the microstructures seem to have a smaller effect on . Also, the enhanced planarity of slip from the reduction in stacking fault energy has a pronounced effect on when compared with the materials deforming under homogeneous slip.     

Very low temperature thermal conductivity of Kevlar 49

We measured the thermal conductivity of a Kevlar 49 in the temperature range. The data were fitted with a power-law: . Kevlar 49 is a candidate material for the supports of CUORE experiment.     

Stability analyses of the beam tube cooling system in the KATRIN source cryostat

The Karlsruhe Tritium Neutrino Experiment (KATRIN) will measure the mass of the electron antineutrino with a sensitivity of , based on the precise measurement of the T₂β spectrum in a region close to the endpoint. This requires a T₂ source, which can provide 10¹¹β decay electrons per second. The KATRIN source cryostat consists in its centre of a 10 m long beam tube of 90 mm inner diameter, operated at 30 K. Molecular T₂ is injected in the beam tube through a central injection chamber and pumped at either tube end. The T₂ density profile must have a stability of 10^-3 in order to limit the systematic errors, yielding stringent requirements on the beam tube temperature homogeneity and stability of . This shall be achieved with a design, where the thermal radiation from the vacuum pumps is almost entirely absorbed by LN₂ and He heat exchangers on the pump ports. The beam tube itself is cooled with two-phase tubes that are part of a Ne thermosiphon. After describing the thermal environment of the beam tube, the design parameters and the operational limits of the thermosiphon will be discussed. This is followed by a detailed analysis of its dynamic behaviour, based on experimental data taken in the primary He cooling system. A “tailor-made” Ne condenser design is presented, enabling the suppression of the primary He temperature variations by two orders of magnitude, from c. to below .     

Ion-molecule reactions in mixtures of methane with carbon tetrafluoride

Ion-molecule reactions have been measured for methane-carbon tetrafluoride mixtures of different composition using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment). Primary ions , , F⁺, CF⁺ and were produced by electrons with energy of 300 eV. Secondary ions , , , , and were observed as the result of ion-molecule reactions. Relative current intensities for primary and secondary ions are presented as a function of both total mixture pressure and concentration of methane in the mixture. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. Total mixture pressure was changed from 0.7 to 33.3 Pa. Schemes of ion-molecule reactions were proposed.     

Physical meaning of ΔKRP and fatigue crack propagation in the residual stress distribution field

Previous papers have shown ΔK_RP to be a useful parameter describing fatigue crack propagation behavior, where ΔK_RP is an effective stress intensity factor range corresponding to the excess RPG load (re-tensile plastic zone's generated load) in which the retensile plastic zone appears under the loading process. In this paper, the relationship between ΔK_RP and the zone size () (which is smaller between the tensile plastic zone at maximum load and the compressive plastic zone at minimum load) was investigated using a crack opening/closing simulation model so as to consider a physical meaning of ΔK_RP. As a result, it becomes clear that ΔK_RP dominates the zone size where fatigue damage mostly occurs. This result supports the following crack propagation equation

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