An estimate of maximum ground surface motion for non zero surface velocityEstimation du mouvement sismique maximal à la surface du sol pour une celerite d'ondes non nulle en surface

The increasing need for probability seismic hazard assessment (PSHA) of critical facilities sometimes leads to unrealistic earthquake scenarios with very high induced ground motions. From a physical standpoint these high motions cannot exist because of the limiting resistance capacity of the soil strata through which the seismic waves travel. A simple analytical model is proposed to bound the maximum ground surface acceleration that any soil deposit can transfer. This model is an extension to non zero ground surface velocity of a previously presented model. To cite this article: A. Pecker, C. R. Mecanique 332 (2004).     

Fatigue strength of metallic and composite materials under repeated high-cycle bending

The problem of fatigue strength analysis of metallic and composite materials subjected to combined static and cyclic bending is resolved. The analysis is based on limit-state models, which allow describing limiting-stress curves of all known shapes, including convex, rectilinear, S-shaped, and concave. The fatigue strength of the following materials is evaluated: carbon and alloyed steels, aluminum alloys, unidirectional organic plastics, laminated plastics, and glassfiber-reinforced plastics. The calculated and experimental data are in satisfactory agreement __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 5, pp. 26–36, May 2006.     

基于Hindmarsh-Rose神经元模型的模式分割

联想记忆和模式分割是大脑的重要功能,大脑海马区是这一功能的重要物质基础。Hindmarsh-Rose神经元模型能够较好地模拟大脑海马区神经元的特性。本文以Hindmarsh-Rose神经元为节点,按Hopfield规则构造网络,同时,考虑到大脑中神经元连接的生理学实际情况,通过数值模拟,实现了在弱、中、强三种连接强度情况下的模式分割以及在随机概率连接情况下的模式分割,通过分析比较,提出了进一步改进的方向。     

An estimate of maximum ground surface motionEstimation du mouvement sismique maximal à la surface du sol

The increasing need for probability seismic hazard assessment (PSHA) of critical facilities sometimes leads to unrealistic earthquake scenarios with very high induced ground motions. From a physical standpoint these high motions cannot exist because of the limiting resistance capacity of the soil strata through which the seismic waves travel. A simple analytical model is proposed to estimate a bound to the maximum ground surface acceleration that any soil deposit can transfer. To cite this article: A. Pecker, C. R. Mecanique 331 (2003).     

Fluctuation strength of modulated sound radiated from rectangular plates with mixed boundary conditions

A generalized differential quadrature method is developed for solving the sound radiated from the forced vibrating rectangular plates with mixed boundary conditions in this paper. The fluctuation strength of the radiated sound, which is modulated by another sound near the plates, is studied. The effects of the modulation frequency and the modulation degree on fluctuation strength are revealed. The effects of the radiated sound frequency and the structural modal density are also studied and compared. The numerical results are presented to show the characteristics of the fluctuation strength of the modulated sound radiated from rectangular plates with mixed boundary conditions.     

Net shape manufacturing and the performance of polymer composites under dynamic loads

An experimental investigation was conducted to determine the influence of postmold trimming and resultant edge quality on the performance of fiber-reinforced plastics (FRP) under dynamic loads. Graphite/epoxy and graphite/bismaleimide laminates were machined using three state-of-the-art industrial techniques and subjected to three-point bend impact to failure. The load load-line displacement records were used to obtain the load, bend deflection and energy absorbed to fracture. High-speed photography was also employed to identify the initiation and progression of failure and record the time dependent fracture process. From a comparison of edge quality and subsequent material performance for both polymeric composites, it was found that the impact response of FRPs is highly process dependent. In general, the load and energy absorbed to fracture decreases with increasing surface roughness. Reductions in the load and energy to the onset of fracture with degrading surface quality were as high as 20 percent. The dynamic response was also found to be dependent on the constituents, stacking sequence and impact velocity.     

超高真空下过渡金属Nb与Nb、Ta、Ti、W相互间粘附特性的试验研究

本文在超高真空(10~(-7)Pa)条件下量测了Nb-Nb(110)、Nb-Ta(110)、Nb-W(110)及Nb-Ti4个粘附对的粘附力,并从接触表面形貌的角度求得了真实接触面积,进而得到了各粘附对间的粘附强度,结果与采用简单紧束缚自洽矩方法计算所得理论结果一致。研究表明,超高真空下过渡金属间存在一种相互作用——由两金属间共用电子引起的化学键,而且主要由其外层d电子态密度所决定。过渡金属Nb与Nb、Ta、W、Ti之间粘附强度的实测值介于每对原子0.2～2.0eV之间。当样品受热升温后,由于C、N、B、S等少量非金属杂质的表面偏析致使粘附强度明显降低。     

加筋粉煤灰的静动强度指标试验与研究

从加筋机理入手，本文建立了加筋土强度的等效侧向约束力模型。分析了加筋粉煤灰静、动强度的拉力破坏和粘着破坏两种情况下的强度指标。理论分析得到了试验结果的验证。     

谱荷载下剩余强度衰减的混凝土疲劳寿命可靠性分析

在Ｓ－Ｎ曲线的基础上，建立了一个描述混凝土剩余强度衰减的模型，并利用该模型对在谱荷载作用下混凝土试件的疲劳寿命及其可靠性进行了分析，得到疲劳寿命基于三参数Ｗｅｉｂｕｌｌ分布的分布函数．通过试验验证了该方法得出的结果是可靠的，且计算简便，便于在工程中应用．     

Comparison of tensile and bulge tests for thin-film silicon nitride

The mechanical properties of thin-film, low-pressure chemical vapor deposited silicon nitride were measured in uniaxial tension and by a bulge test method suitable for wafer-level testing. This research compares the two approaches and presents additional data on silicon nitride. The common property from the two test methods is the Young's modulus. Tensile tests performed at the Johns Hopkins University provided a value of 257±5 GPa. Bulge tests conducted by Exponent, Inc., an engineering and scientific consulting firm, yielded a value of 258±1 GPa. It is concluded that this bulge test is a valid wafer-level test method. These tensile results, when added to earlier results, yield the following properties for low-stress silicon nitride: Young's modulus =255±5 GPa, Poisson ratio=0.23±0.02, and fracture strength=5.87±0.62 GPa.