工程力学

封面介绍：Launcher structures usually use thin-walled structures，such as cylindrical shells，as primary components. These thin-walled cylinders are prone to be limited in their load carrying capability by buckling and are highly sensitive to geometric imperfections. A knock-down factor is commonly used to take into account the obvious decline of the buckling load in a cylindrical shell caused by the inevitable imperfections. The cover image shows the load vs. end-shortening curve and the deformation of a stiffened cylinder under the axial compression. The former knock-down factors rely on a lower-bound curve taken from experimental data. Recent research has indicated that the old knock-down factors are inclined to produce very conservative estimations for the buckling load of imperfect shells，due to the limitations of the computational power and the experimental skills available five decades ago. The new knock-down factor was derived from a combination of the knock- down factor k1 obtained by considering the geometric imperfection and a knock-down factor k2 achieved by taking into account other imperfections. The results presented demonstrate that for axially loaded stiffened cylinders the new combined knock-down factor leads to a safe and less conservative design compared to the respective design. This allows for a significant reduction in structural weight and design costs（see the article by CHEN Haosen et al. on page 769）.

Dynamic conducting crack propagation in piezoelectric materials: Mode-II problem

CHEN Haosen，WEI Weiyi，LIU Jinxi，et al.

This paper studies the dynamic conducting crack propagation in piezoelectric solids under suddenly in-plane shear loading. Based on the integral transform methods and the Wiener-Hopf technique，the resulting mixed boundary value problem is solved. The analytical solutions of the dynamic stress intensity factor and dynamic electric displacement intensity factor for the Mode II case are derived. Furthermore，the numerical results are presented to illustrate the characteristics of the dynamic crack propagation. It is shown that the universal functions for the dynamic stress and electric displacement intensity factors vanish if the crack propagation speed equals the generalized Rayleigh speed. The results indicate that the defined electro-mechanical coupling coefficient is of great importance to the universal functions and stress intensity factor history.

dynamic crack propagation； piezoelectric materials； dynamic intensity factors； in-plane shear loading； conducting crack

来源出版物：SCIENCE CHINA Technological Sciences，2015，58（5）: 769-774联系邮箱：LIU Jinxi，liujx02@hotmail.com