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961.
The stability of elastic columns subjected to axial pressure is studied. An elastic multistepped column with rectangular cross
sections are considered assuming that at the re-entrant corners of the column stable cracks are located. The influence of
a crack on the loss of stability of the column is described by means of local flexibility and the function of compliance coupled
with the stress intensity factor, which is known from the linear elastic fracture mechanics. A column with a single step is
studied in more detail. The influence of crack location and length on the buckling load is assessed numerically.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 87–100, January–February, 2006. 相似文献
962.
赵丽荣 《科技情报开发与经济》2006,16(15):261-263
主要对预应力混凝土板梁裂缝形成的原因进行了详细分析,总结了裂缝发生的常见部位及规律,并进一步提出了裂缝的防治以及维修与加固措施。 相似文献
963.
Fatigue crack propagation tests on annealed and quenched medium-density polyethylene showed the annealed specimens to have much lower resistance to crack initiation and subsequent propagation. Although the same fracture mechanism, in which the brittle crack gradually becomes more ductile, prevailed in both cases, the voided and fibrillated crack tip root craze in the annealed material was much weaker that the nonfibrillated quenched root craze. Microstructural analyses indicate that the annealed material had separate crystallite populations, whereas the quenched material had a more homogeneous morphology. The highest melting fraction of the annealed material was composed of lamellae that were about 270 Å thick, and the quenched lamellae were estimated to be 160 Å thick. The reduced fatigue crack propagation resistance of the annealed material was suggested to be a result of a lower concentration of tie molecules and its reduced damping capability, compared to the quenched material. © 1995 John Wiley & Sons, Inc. 相似文献
964.
Summary A finite crack propagating at constant speed in a functionally graded piezoelectric strip (FGPS) bonded to a homogeneous piezoelectric strip is considered. It is assumed that the electroelastic material properties of the FGPS vary exponentially across the thickness of the strip, and that the bimaterial strip is under combined anti-plane mechanical shear and in-plane electrical loads. The analysis is conducted for the electrically unified crack boundary condition, which includes both the traditional permeable and the impermeable ones. By using the Fourier transform, the problem is reduced to the solution of Fredholm integral equations of the second kind. Numerical results for the stress intensity factor and the crack sliding displacement are presented to show the influences of the crack propagation speed, electric loads, FGPS gradation, crack length, electromechanical coupling coefficient, properties of the bonded homogeneous piezoelectric strip and crack location. 相似文献
965.
中国近代的留学教育是中西文化反差的必然产物,其本质是中国向西方先进文化学习的单向文化交流.在近代中国特殊的历史背景下,留学教育经历了艰难的起步和潮涨潮落的曲折变迁,在其整个发展过程中呈现出明显的阶段性特征.本文在论述中国近代留学教育的演变历程的同时,对这一时期留学教育的发展也进行了反思. 相似文献
966.
967.
Chen Shuxing 《中国科学A辑(英文版)》1998,41(1):39-47
The supersonic flow past a concave double wedge is discussed. Because of the interaction between the outer shock attached
at the head of the wedge and the inner shock issued from the concave corner, there is a rarefaction wave issued from the intersection
of the outer and inner shock. The rarefaction wave is reflected by the outer shock and the wedge infinitely, while the outer
shock is also bent due to interaction. The global existence of the solution is proved under the assumptions that the outer
shock is weak and the difference of two slopes of the double wedge is small. Meanwhile, a rigorous proof of the asymptotic
behavior of the global solution is given. The property is often ap plied to numerical computation.
Project partially supported by the National Natural Science Foundation of China and Doctoral Programme Foundation of IHEC. 相似文献
968.
文章提出一种二维裂隙网络模式,依据标度不变性原理,运用重正化群技术求取了裂隙网络模型连通概率的临界值为0.2928933,对应的单条裂隙导通的临界概率P0c为0.3581209。当单条裂隙的导通概率Pb小于P0c时,网络连通仅是局部的;而当单条裂隙的连通概率Pb大于P0c时,则整个裂隙网络是连通的。同时求取了关联长度指数值和分维。 相似文献
969.
陈华鹏 《宁波大学学报(理工版)》1990,(1)
假定位移场,并将位移势函数展开成一系列的特征函数,代入空间轴对称变形的基本方程,推得界面裂纹的特征值理论。把这一理论应用到单向增强的连续纤维复合材料上,建立了纤维断裂、基体开裂等模型下应力奇异性的特征方程,分析了界面裂纹尖端的应力奇异性。 相似文献
970.
中小学的文学经典名著教学,存在着诸多不足与缺失,有必要引入“行动研究”对教学过程中所遇到的一些问题进行教改试验。通过对中小学文学名著教学所进行的阅读兴趣、效果优化和鉴赏能力的行动研究.不但可以取得一定的教改成效,还可以获得不少有益的启示,有利于推动文学经典名著教学的稳步发展。 相似文献