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141.
连续CO2激光对红外窗口材料损伤研究 总被引:4,自引:0,他引:4
研究了连续CO2激光对几种红外窗口材料的表面损伤特性,研究表明,损伤机制在于杂质缺陷吸收造成的热冲击应力破坏。深入研究了杂质缺陷密度、焦斑与材料损伤阈值的关系,并建立了一个损伤模型。同时分析了热冲击应力破坏方式。 相似文献
142.
The piecewise-homogeneous material model and the three-dimensional linearized theory of stability with the assumption of small
subcritical strains are used to study the surface buckling of orthotropic and transtropic laminates. A plane problem is formulated,
and characteristic equations are derived. A solution is found for a specific transtropic material with different orientations
of the isotropy axis
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 7, pp. 64–72, July 2006. 相似文献
143.
P. Galinetto M. Marinone D. Grando G. Samoggia F. Caccavale A. Morbiato M. Musolino 《Optics and Lasers in Engineering》2007,45(3):380
In this work we report on micro-Raman analysis on lithium niobate (LN) substrates in order to study the compositional homogeneity of the crystals and to clear up the effects of etching and polishing processes on the surface of wafers and crystals.The fact that the linewidth of some Raman modes scale with the composition of LN crystals, together with the use of a confocal microscope, allowed a three-dimensional determination of the sample stoichiometry and of the crystalline quality. This local tool can supply additional information, which can be complementary to the electro-optic coefficients, carefully measured as well in order to check functional parameters.Raman spectra from buried regions were obtained on as-grown, etched and polished crystals and wafers. The depth profile of the peak energy and the linewidth of the Raman mode at 872 cm−1 indicate that mechanical processing of surfaces causes, in some cases, structural modifications till a depth of 15 μm. 相似文献
144.
A stochastic theory for the cumulative fatigue damage of structural components with random fatigue strength under random loading is proposed on the basis of Stratonovich-Khasminskii theorem. The analytical solutions for the probability densities of the cumulative fatigue damage and fatigue life and for the reliability function are given for steel and reinforced concrete components with constant fatigue strength subject to a narrow band stationary Gaussian stress process with zero mean. The results agree very well with those of digital simulation. It is noted that the theory can be applied, in principle, to both metallic and non-metallic materials, narrow band and wide band stress process, and adapted to a sequence ofn, stationary stress processes or quasi-stationary stress process. The scatter and degradation of fatigue strength and the inspection maintenance can also be incorporated into the theory. 相似文献
145.
146.
The methods for determining the nonaxisymmetric thermoelastoplastic stress-strain state of layered orthotropic shells of revolution are developed. It is assumed that the layered package deforms without mutual slippage or separation of layers. The problem is solved using the geometrically nonlinear theory of shells based on the Kirchhoff-Love hypotheses. In the isotropic layers, plastic deformations may appear, whereas the orthotropic layers deform in the elastic region. It is assumed that the mechanical properties of the materials are temperature-dependent. The thermoplasticity equations are presented in a form corresponding to the method of additional deformations. The order of the system of partial differential equations obtained is reduced with the help of trigonometric series in the circumferential coordinate. The resulting systems of ordinary differential equations are solved by the Godunov technique of discrete orthogonalization. The nonaxisymmetric thermoelastoplastic stress-strain states of layered shells of revolution are considered as examples. 相似文献
147.
详细分析了不同形状断裂试件及小范围屈服模型裂纹端部的损伤演化,提出了韧性断裂的宏观起裂相当于裂尖前方一特征位置处的损伤达到一临界值。利用此模型获得了与实验相一致的宏观断裂韧性及与约束无关的理论断裂韧性。 相似文献
148.
149.
The boundaries between the three phases of the Domany-Kinzel probabilistic cellular automaton are determined with high accuracy via the gradient method. The difficulties the extrapolation to the thermodynamic limit are circumvented and the critical exponents are also presented. 相似文献
150.
Theoretical model for deformability of brittle rock-like materials in the presence of an oriented damage of their internal structure is formulated and verified experimentally. This model is based on the assumption that non-linearity of the stress–strain curves of these materials is a result of irreversible process of oriented damage growth. It was also assumed that a material response, represented by the strain tensor, is a function of two tensorial variables: the stress tensor and the damage effect tensor that is responsible for the current state of the internal structure of the material. The explicit form of the respective non-linear stress–strain relations that account for the appropriate damage evolution equation was obtained by employing the theory of tensor function representations and by using the results of own experiments on damage growth. Such an oriented damage that grows in the material, described by the second order symmetric damage effect tensor, results in gradual development of the material anisotropy. The validity of the constitutive equations proposed was verified by using the available experimental results for concrete subjected to the plane state of stress. The relevant experimental data for sandstone and concrete subjected to tri-axial state of stress were also used. 相似文献