Impact response of an interface crack in a hybrid piezoelectric laminate

Summary  In a hybrid laminate containing an interfacial crack between piezoelectric and orthotropic layers, the dynamic field intensity factors and energy release rates are obtained for electro-mechanical impact loading. The analysis is performed within the framework of linear piezoelectricity. By using integral transform techniques, the problem is reduced to the solution of a Fredholm integral equation of the second kind, which is obtained from one pair of dual integral equations. Numerical results for the dynamic stress intensity factor show the influence of the geometry and electric field. Received 29 June 2001; accepted for publication 3 December 2001     

抗冲聚丙烯微结构的研究

利用¹³C NMR对抗冲聚丙烯的微结构进行了研究.结果表明,由于抗冲聚丙烯聚合工艺的差别,4个抗冲聚丙烯样品中的乙烯链段的序列分布也不同.根据抗冲聚丙烯的¹³C NMR谱,计算出了丙烯段的次甲基和甲基的峰强度,由此建立了表征抗冲聚丙烯共聚物中丙烯链段的立构规整度的方法.     

Weierstrass points and their impact in the study of algebraic curves: a historical account from the “Lückensatz” to the 1970s

In this note we give a historical account of the origin and the development of the concept of Weierstrass point. We also explain how Weierstrass points have contributed to the study of compact Riemann surfaces and algebraic curves in the century from Weierstrass’ statement of the gap theorem to the 1970s. In particular, we focus on the seminal work of Hürwitz that raised questions which are at the center of contemporary research on this topic.      

Energy distribution of reflected ions at normal incidence on the target surface

Summary The energy distribution of reflected ions at normal incidence of the primary beam on the target surface is obtained as a result of approximate solution of the Boltzmann equation by the method of discrete streams. This method gives the opportunity to avoid the problem of negative distribution function, arising in the generally applied method of spherical harmonics, and to present the final result in analytical form. The analysis is performed for a power scattering cross-section and the theoretical energy distribution demonstrates one maximum when the ion mass is equal to the mass of a target atom, and two maxima when the ion mass is much less than the mass of a target atom.     

Grazing bifurcations in an elastic structure excited by harmonic impactor motions

In this article, non-smooth dynamics of an elastic structure excited by a harmonic impactor motion is studied through a combination of experimental, numerical, and analytical efforts. The test apparatus consists of a stainless steel cantilever structure with a tip mass that is impacted by a shaker. Soft impact between the impactor and the structure is considered, and bifurcations with respect to quasi-static variation of the shaker excitation frequency are examined. In the experiments, qualitative changes that can be associated with grazing and corner-collision bifurcations are observed. Aperiodic motions are also observed in the vicinity of the non-smooth bifurcation points. Assuming the system response to be dominated by the structure’s fundamental mode, a non-autonomous, single degree-of-freedom model is developed and used for local analysis and numerical simulations. The predicted grazing and corner-collision bifurcations are in agreement with the experimental results. To study the local bifurcation behavior at the corner-collision point and explore the mechanism responsible for the aperiodic motions, a derivation is carried out to construct local Poincaré maps of periodic orbits at a corner-collision point such as the one observed in the soft-impact oscillator.     

CFRP索斜拉桥的结构动态测试研究与分析

为获知CFRP索斜拉桥的动力特性,推动CFRP索斜拉桥在我国的发展并积累经验,对国内首座CFRP索斜拉桥分别进行了基于环境激励和锤击激励的结构动态特性测试研究,对不同测试方案的试验结果进行了对比分析,结果表明脉动测试与锤击激励测试结果在对应的频率值误差小、振型相似;环境激励测试法从测试的可行性、方便性及测试所得频率成分的组成上较锤击激励测试法更为丰富.     

Flat ended projectile penetrating ultra-high strength concrete plate target

Reactive powder concrete (RPC), a composite that has been developed in recent years, is a special mixture that is cured to have a higher compressive strength than that of concrete (about 200 MPa). Adding a few steel fibers can markedly increase its mechanical properties, such as tensile and bending strength, impact resistance and toughness. Hence, RPC is highly promising for use in the containment structures of nuclear power plants and in the protection of military facilities. This study evaluates the resistance of ultra-high strength concrete targets by high-velocity impact experiments. Test variables include the impact velocity and the amount of steel fibers added. The experimental results reveal that RPC plates, because of their higher compressive strength, are more fragile than normal concrete (NC) plates. However, adding a small amount of steel fibers significantly improved the impact resistance of the target plates. Moreover, a numerical simulation based on the nonlinear finite element code LS-DYNA was performed. The results of the numerical simulation have a good agreement with the experimental data and can be used for further research.     

关于分形和炸药撞击感度的一点记注

通过对现有炸药冲击感度的标度方法进行了分析和讨论。从落锤试验分幅照相结果,初步建议用分形维数作为炸药冲击感度的标度,识为是有这种可能性。并讨论了这种方法的优点。     

浆体管道输送水击压力波波速的探讨

在考虑自由气体存在的影响下,推导出浆体水击压力波波速的计算公式.分析表明很少量的气体存在会使波速明显降低. 气体体积浓度较大时波速随浆体浓度的增大而减小,重质物料的减小趋势较为明显;气体体积浓度较小时轻质物料波速随浓度的增加而增加.相同条件下非均质流波速比伪均质流波速大,两者差异主要受浆体中固体物料的密度和浆体体积浓度影响. 考虑气体影响作用的浆击波速计算值与实测结果更吻合.