Biaxiale Ermüdung reibrührgeschweißter Strukturelemente

Biaxial fatigue of friction stir welded stiffened panels Within the framework of the European WelAir project, cruciform specimens made from stiffening FSW overlap joints were fatigued in the DLR biaxial test rig. To resemble the loading situation of pressurized fuselage structures, proportional loading without any phase shift, but with different load ratios λ between the loading components in both directions was applied.Natural crack initiation and subsequent crack growth were governed by the stiffness gradient caused by introducing the stringer. Cracks initiated and propagated at run‐in and run‐out locations in a direction perpendicular to the weld seam. The shortest fatigue life was observed for uniaxial loading in welding direction (λ = 0). An additional stress component perpendicular to the joint line (λ > 0) resulted in a higher number of cycles to failure. Similar to single stringer panels, increasing the load ratio also increased the number of cycles to failure for FSW clip‐stringer structural members, but additionally gives a different location of the fatal crack.     

The flame retardant mechanism of polyolefins modified with chalk and silicone elastomer

This paper presents the current understanding of the flame retardant mechanism of Casico?. The study includes the flame retardant effect of each individual component: ethylene–acrylate copolymer, chalk and silicone elastomer, as well as the formation of an intumescent structure during heating. The flame retardant properties were investigated by cone calorimetry and oxygen index tests. To obtain insight into the flame retardant mechanism, heat treatment under different conditions has also been performed. The results indicate that the flame retardant mechanism of Casico is complex and is related to a number of reactions, e.g. ester pyrolysis of acrylate groups, formation of carbon dioxide by reaction between carboxylic acid and chalk, ionomer formation and formation of an intumescent structure stabilized by a protecting char. Special emphasis is given to the formation of the intumescent structure and its molecular structure as evaluated from ¹³C MAS‐NMR and ²⁹Si MAS‐NMR, ESCA and XRD analysis. After treatment at 500°C the intumescent structure consists mainly of silicon oxides and calcium carbonate and after treatment at 1000°C the intumescent structure consists of calcium silicate, calcium oxide and calcium hydroxide. Copyright © 2003 John Wiley & Sons, Ltd.     

Associative properties of perfluorooctyl end‐functionalized polystyrene–poly(ethylene oxide) diblock copolymers

The synthesis of 2,2,3,3‐tetrahydro‐perfluoroundecanoyl end‐functionalized polystyrene–poly(ethylene oxide) block (PS‐block‐PEO‐R_F) copolymers and their matching PS‐block‐PEO diblock copolymers was carried out by sequential anionic polymerization. Viscometry and ¹⁹F NMR studies show that the PS‐block‐PEO copolymers, in contrast to their matching PS‐block‐PEO‐R_F copolymers, exhibit a micellar rather than the associative behavior seen for the latter. However, the presence of an excess of fluorinated acid, used for end‐functionalization, produces a reduction of the associative behavior above the overlap concentration, with the fluorinated acid acting like a surfactant. A competition may also occur between PS—and R_F—mediated micellization. Copyright © 2004 Society of Chemical Industry     

Methacryloxyethyl phosphate‐grafted expanded polytetrafluoroethylene membranes for biomedical applications

Expanded polytetrafluoroethylene (ePTFE) membranes were modified by graft copolymerization with methacryloxyethyl phosphate (MOEP) in methanol and 2‐butanone (methyl ethyl ketone (MEK)) at ambient temperature using gamma irradiation. The effect of dose rate (0.46 and 4.6 kGy h^?1), monomer concentration (1–40 %) and solvent were studied and the modified membranes were characterized by weight increase, X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XPS was used to determine the % degree of surface coverage using the C? F (ePTFE membrane) and the C? C (MOEP graft copolymer) peaks. Grafting yield, as well as surface coverage, were found to increase with increasing monomer concentration and were significantly higher for samples grafted in MEK than in methanol solution. SEM images showed distinctly different surface morphologies for the membranes grafted in methanol (smooth) and MEK (globular), hence indicating phase separation of the homopolymer in MEK. We propose that in our system, the non‐solvent properties of MEK for the homopolymer play a more important role than solvent chain transfer reactions in determining grafting outcomes. Copyright © 2005 Society of Chemical Industry     

Possibilities and extension of XRD material response analysis in failure research for the advanced evaluation of the damage level of Hertzian loaded components

Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology.     

关于Ada95变体部分等语法的修正意见

本文指出了Ａｄａ９５ 参考手册中记录变体部分、记录聚集、分情形语句与异常处理段等语法描述中存在的问题，并分别给出了它们的修正方案。     

A BOUNDARY INTEGRAL EQUATION AND ITS NUMERICAL SOLUTION OF POTENTIAL FLOW AROUND SURFACE-IRREGULA-RITIES

In this paper,using complex functional theory,the authors turn the potentialflow around the surface irregularities in a pressure conduit and semi-infinite platforms intoDirichlet problem.Based on Schwarz formula and by the application of Plemelj's formula,theauthors change the problem into the integration of a Cauchy boundary integral equation in theflow plane through the substitution of variables.Using numerical integration,the authors obtainthe velocity distribution and pressure coefficient along surface irregularities and platforms.Thephysical concept of this method is clear,the convergent speed is rapid and the computative effi-ciency is high.The calculated values agree well with the measured results.It is an effective andsimple method in solving potential flow.     

Optical phase conjugation of multiwavelength signals in adispersion-shifted fiber

Optical phase conjugation (OPC) of multiwavelength signals in a dispersion-shifted fiber (DSF), which can be used for dispersion compensation in the wavelength division multiplexing communication system, is theoretically studied. The multiwavelength phase-conjugate signals are generated by four-wave mixing (FWM) in the dispersion-shifted fiber. There are the pulse-shape distortion and the induced frequency chirping in the phase-conjugate signals owing to pump depletion and the cross-phase modulation among the signals and phase-conjugate signals, respectively. The FWM among the pump wave, signals, and phase-conjugate signals causes unequal conversion efficiencies for the multiwavelength signals and enhances the induced frequency chirping in the phase-conjugate signals. The induced frequency chirping may deteriorate the restoration of the pulse shape. Both the pulse-shape distortion and induced frequency chirping increase with the signal and pump powers. The formula for the induced frequency chirping that is only caused by the signals through cross-phase modulation is derived. The requirement of the signal power in the dispersion-shifted fiber for the restoration of the pulse shape by the optical phase conjugation is estimated and numerically verified     

Quantitative NMR spectroscopy by matrix pencil methods

The matrix pencil (MP) method, based on the singular value decomposition (SVD), is applied to quantitative NMR spectroscopy. Its relationship to other SVD-based methods is also presented. Simulations and applications are given to demonstrate the capability of superior performance.©1993 John Wiley & Sons Inc