等熵轻质活塞风洞中活塞行程、速度和压力的变化

等熵轻质活塞风洞是一种工作时间很短的风洞，来自高压空器中的气体推动活塞使气体等熵压缩，并在恒定的匹配压力下进入实验段，这对于瞬时热传导技术是合适的，已用于燃气透平叶片的冷却问题的实验研究中，本文对等熵轻质活塞风洞中的一些气动问题做了研究，分析出在不考虑活塞质量时活塞行程、速度与压力的关系式，并进行了实例分析。     

基于传质现象的高速铁路隧道入口压缩波数值分析

基于一维可压缩非定常不等熵流动理论,认为隧道内空气流通截面是流动时间和流动距离的二元函数,考虑了空气与隧道壁和列车壁之间的摩擦和传热效应,采用广义黎曼特征线法,对高速列车进入存在传质现象的等截面缓冲罩隧道引起的入口压缩波进行了数值计算。另外进行了不同缓冲罩参数的计算,并且对计算结果进行了定性与定量分析,结果说明了相关的空气动力学效应。     

单向应力状态下钢材高温分析的损伤模型

本文结合结构钢材火灾高温分析的特点，通过对Ｌｅｍａｉｔｒｅ关于常温下金属材料延性损伤模型和修改，提出一种适用应力状态下钢材高温分析的损伤模型，为进行钢框架在火灾高温作用下及火灾冷却后的２和损伤分析提供可能性。     

Prediction models of fatigue crack closure and growth under random loading

The effects of plastic zones both in front of and behind crack tip on crack closure have been analysed. The total residual deformations of crack surfaces involve two parts, that is, the amount of plastic blunting of crack tip and the residual deformation in the wake of the tip. This paper presents a fatigue crack closure model in which the influences of compressive load on closure stress are discussed. The model is applied to random loading conditions by the assumption of limited memory properties. The fatigue lives are predicted using the proposed crack growth model for CCT plane stress specimen cut from 2219-T851 aluminum alloy under flight spectrum loadings, and the prediction values agree with the test results.The project was supported by the natural science foundation of China.     

Secondary buckling of an elastic column with spring-supports at clamped ends

Summary The postbuckling behavior of an elastic column with spring supports of equal stiffness of extensional type at both clamped ends is studied. Attention is focused on those of spring stiffnesses near the critical value at which, under axial load, the column becomes critical with respect to two buckling modes simultaneously. By using the Liapunov-Schmidt-Koiter approach, we show that there are precisely two secondary bifurcation points on each primary postbuckling state for the spring stiffness greater than the critical value. The bifurcation takes place at one of the two least buckling loads. The corresponding secondary postbuckling states connect all the secondary bifurcation points in a loop. For the spring stiffness less than the critical value, no secondary bifurcation occurs. Asymptotic expansions of the primary and secondary postbuckling states are constructed. The stability analysis indicates that the primary postbuckling state for the spring stiffness greater than the critical value is bifurcating from the first buckling load and becomes unstable from a stable state via the secondary bifurcation, i.e., secondary buckling occurs. Received 22 April 1997; accepted for publication 22 December 1997     

Uniaxial extension and shear in combination with cyclic straining as a promising method for studying the viscoelasticity of polymers over a wide range of stresses and strains atT > T g

Simple relations are found between the fracture strains, the long-term durability and the initial values of parameters characterizing polymer rheology at deformation rates and stresses approaching zero. Fracture regimes are determined by two groups of parameters. One includes critical values of stresses. They are invariant with repect to temperature and molecular weight of the polymers; the values of critical stresses for different polymer compositions differ by a factor of 10 to 20. The second group of critical parameters includes the rates of deformation determined by the initial viscosity. The latter may vary by many orders of magnitude. There exists a universal critical value determining polymer fracture independent of linear macromolecule composition, its molecular weight, the temperature and the way of attaining a given state. This value is the recoverable strain and is equal to 0.5 according to Hencky. There exists a relation between the maximum value of recoverable strain in the transition region from the rubbery to the leathery state and the extensibility of macromolecules for polymers with various molecular weights. Quenching of the polymer near the maximum recoverable strain makes it possible to obtain high strength samples. Overspurt regimes for polymer flow have also been studied. It has been shown that this causes polymer static electrification. Simple and unique dependences of the charge density on temperature and polymer molecular weight have been established.Presented at the 28th IUPAC International Symposium on Macromolecules, June 1982, Amherst, Mass. (USA)Dedicated to Prof. Dr. Josef Schurz on the occassion of his 60th birthday     

Modelling the transverse viscoelasticity of green wood using a combination of two parabolic elementsModélisation de la viscoélasticité transverse du bois vert à l'aide d'une combinaison de deux éléments paraboliques

The rigidity in radial compression at different levels of temperature and strain rate have been measured on green Boco, with a drastic softening around $\text{60}{}^{\mathrm{<mspace\; sp="0.2"\; width="2px"\; linebreak="nobreak"\; is="true"></mspace><mtext>°</mtext>}}$C attributed to the glassy transition of lignin. The representation of experimental results in an approximated complex diagram revealed a secondary viscoelastic process occurring at lower temperature. A multiparabolic model was used for the analysis. For convenience, each parabolic element was replaced by a generalised Maxwell model with a modified-Gaussian relaxation spectrum. This model fitted correctly the observed behaviour of wood in the time range of 0.05 to 50 sec and temperature between 10 to $\text{90}{}^{\mathrm{<mspace\; sp="0.2"\; width="2px"\; linebreak="nobreak"\; is="true"></mspace><mtext>°</mtext>}}$C. To cite this article: S. Bardet, J. Gril, C. R. Mecanique 330 (2002) 549–556.     

Experimental investigation of the stability of reinforced cylindrical shells subject to axial compression

The paper presents the results from experimental study of the influence of reinforcement (rectangular plates) on the buckling loads and stresses of two sets of cylindrical shells subject to axial compression __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 5, pp. 117–119, May 2006.     

Continuous, large strain, tension/compression testing of sheet material

Modeling sheet metal forming operations requires understanding of the plastic behavior of sheet alloys along non-proportional strain paths. Measurement of hardening under reversed uniaxial loading is of particular interest because of its simplicity of interpretation and its application to material elements drawn over a die radius. However, the compressive strain range attainable with conventional tests of this type is severely limited by buckling. A new method has been developed and optimized employing a simple device, a special specimen geometry, and corrections for friction and off-axis loading. Continuous strain reversal tests have been carried out to compressive strains greater than 0.20 following the guidelines provided for optimizing the test. The breadth of application of the technique has been demonstrated by preliminary tests to reveal the nature of the Bauschinger effect, room-temperature creep, and anelasticity after strain reversals in commercial sheet alloys.     

On Two-Scale Model of Fracture Mesomechanics of Composites with Cracks under Compression

A two-level fracture model of composites with cracks under compression is proposed. Fiber-reinforced laminated panels with a hole are considered. The panels are compressed along the fibers so that two cracks propagate from the hole boundary at a right angle to the loading direction. The fracture mechanism is analyzed at two levels. The first level is the compression-induced stress concentration at the tip of a finite-thickness crack filled with a fractured material. At this level, the theory of elasticity of linear orthotropic body is used. The second level is compression fracture at the crack tip. The analysis performed at this level involves the three-dimensional linearized theory of stability of solids, considering microcracks in the interface between the fractured and intact materials, and the exact solution describing the compression-induced instability of the cracked interface. The second level is where results obtained by the author are used. Thus, the approach proposed employs the theory of elasticity of linear orthotropic body and the three-dimensional linearized theory of stability of solids to analyze a specific mechanism of fracture__________Published in Prikladnaya Mekhanika, Vol. 41, No. 5, pp. 141–144, May 2005Reported at ICF-11 (Turin, Italy, March 20–25, 2005). The ICF-11 proceedings have been published on CD-ROM. The author ‘s other reports presented at ICF-6 (1984) to ICF-10 (2001) are listed in Appendix.