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41.
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The extreme lightweight potential of modern composites for the application in highly strained and thick walled components
can only be sucessfully utilized with the help of adapted design procedures. Therefore, the stress and strain analysis of
fibre reinforced components has experienced a tremendous improvement in recent years. The derived mechanical methods and the
existing computing facilities are now capable of calculating complex and three-dimensional states of stress for single layers
within laminated structures. The adequate development of appropriate failure criteria for the evaluation of such stress states
has unfortunately not been promoted in the desired manner. In 1980, Hashin proposed a new generation of physically based failure
analysis which could only be realized by a considerably increased numerical effort. Recently, Puck made a new attempt based
on Hashin's concept using fundamental elements of the failure criterion by Mohr and Coulomb. Applying this model, the three-dimensional
state of stress is evaluated in a realistic manner. It is assumed that besides the occurence of fibre failure only tensile
stresses and shear stresses in loading planes tangential to the fibre direction induce the inter-fibre failure of the unidirectionally
reinforced composite, whereas compressive stresses in these planes obstruct failure. 相似文献
43.
Summary Poly-p-trimethylsilylphenylmethacrylate(75)-co-glycidylmethacrylate (25) containing aromatic bisazides exhibits uv sensitivity as a negative type photoresist. Sensitometric data have been evaluated. The pressure-dependant reactivity under the conditions of oxygen reactive ion etching was determined. 相似文献
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Lothar Gröschel Rami Haidar Andreas Beyer Karl-Heinz Reichert Reinhard Schomäcker 《Catalysis Letters》2004,95(1-2):67-75
Palladium particles can be prepared in sizes of a few nanometers from Pd(OAc)2in the presence of a block copolymer in aromatic unpolar solvents with suitable reducing agents like NaBH4 or LiAlH4. After mixing the organic metal solution with a polyacrylic acid (PAA) dispersion of defined concentration and following a crosslinking process with an epoxide, reactive membranes with a well-defined pore diameter were obtained. The catalytic activity of the prepared palladium particles incorporated in the crosslinked PAA network has been proven by the gas phase hydrogenation of propyne in a special membrane reactor. 相似文献
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Gemini Surfactants Foam Formation Ability and Foam Stability Depends on Spacer Length 总被引:1,自引:0,他引:1
A series of cationic gemini surfactants containing different spacer length were synthesized and analyzed structurally. It was shown that the surface tension (σ) and critical micelle concentration (CMC), which had a maximum for the n-C4H8 spacer depended on the spacer length. The foaming ability and foam stability are high for the gemini surfactants with short spacers (C2H4 to n-C4H8), while longer spacers lead to a distinct decrease of these foam parameters. Foaming properties are discussed in terms of configuration and conformation of a surfactant molecule and in relation to micellization state kinetic. 相似文献
50.
Jan Herrmann Jürgen KoreckMatthias Maess Lothar Gaul 《Mechanical Systems and Signal Processing》2011,25(3):981-990
The integration of a model for longitudinal hydroacoustic fluid damping in thin hydraulic pipes in 3D finite element models is presented in this paper. In order to perform quantitative prediction of the vibroacoustic behavior and resulting noise levels of such fluid-structure coupled system due to hydraulic excitation, an accurate frequency-dependent fluid damping model including friction effects near the pipe wall is required. This step is achieved by matching complex wave numbers from analytical derivation into a parameterized damped wave equation and consecutive translation into finite element modeling.Since the friction effect close to the pipe wall changes locally with the inner pipe radius, the fluid damping model is applied segment-wise in order to model the influence of cross-sectional discontinuity, such as orifices, on the oscillating pressure pulsations. A component synthesis approach, which uses pipe segments as substructures, allows a simple model generation and fast computation times.The numerical harmonic results are compared to experimental frequency response functions, which are performed on a hydraulic test bench driven by a dynamic pressure source in the kHz-range. 相似文献