EFFECTS OF DISLOCATION CONFIGURATION, CRACK BLUNTING AND FREE SURFACES ON THE TRIGGERING LOAD OF DISLOCATION SOURCES

The effects of dislocation configuration,crack blunting and free surfaces on the triggering load of dislocation sources in the vicinity of a crack or a wedge tip subjected to a tensile load in the far field are investigated.An appropriate triggering criterion for dislocation sources is proposed by considering the configurational forces acting on each dislocation.The triggering behaviors of dislocation sources near the tips of a crack and a wedge are compared.It is also found that the blunting of crack tip and the presence of free surfaces near the crack or the wedge have considerable influences on the triggering load of dislocation sources.This study might be of significance to gaining a deeper understanding of the brittle-to-ductile transition of materials.     

Numerical and experimental study of turbulent impinging twin-jet flow

The two dimensional impinging circular twin-jet flow with no-cross flow is studied numerically and experimentally. The theoretical predications are carried out through numerical procedure based on finite volume method to solve the governing mass, momentum, turbulent kinetic energy and turbulent kinetic energy dissipation rate. The parameters studied were jet Reynolds number (9.5 × 10⁴  Re  22.4 × 10⁴), nozzle to plate spacing (3  h/d  12), nozzle to nozzle centerline spacing (l/d = 3, 5 and 8) and jet angle (0°  θ  20°). It is concluded that the stagnation primary point moves away in the radial main flow direction by increasing the jet angle. This shift becomes stronger by increasing the nozzle to nozzle centerline spacing (l/d). A secondary stagnation point is set up between two jets. The value of pressure at this point decreases by decreasing Reynolds number and/or increasing the jet angle.

The sub atmospheric region occurs on the impingement plate. It increases strongly by increasing Reynolds number and decreases as the jet angle and/or a nozzle to plate spacing increases. The spreading of jet decreases by increasing nozzle to plate spacing. The intensity of re-circulation zone between two jets decreases by increasing of h/d and jet angle. The increase of turbulence kinetic energy occurs within high gradient velocity.     

用矩量法解阻尼介质中简支方板的塑性动力响应问题

本文用矩量法解薄板塑性动力响应问题，分析阻尼介质对简支方板塑性动力响应的影响，对计算结果进行了讨论．     

Analysis of penetration of axisymmetric projectiles into semi-infinite targets

The process of penetration of a projectile into a semi-infinitetarget is studied in this paper. Using certain assumptions, the propagation of plastic wave in the target is analyzed and the pressure on the surface of penetrator is given. The results calculated from the formulas of this paper agree well with experimental data and numerical results.     

Mechanism of Fatigue-Crack Growth under Compressive External Stresses

A specimen with a crack shaped like a thin long defect with parallel edges and a rounded tip of finite radius is considered. When the specimen is subjected to compressive cyclic loads, the stresses in zones adjacent to the crack tip vary according to a sign-variable cycle because of plastic strains occurring at the crack tip. This can cause fatigue-crack growth. Results of numerical simulations and experimental data support the possibility of fatigue-crack growth in the field of compressive external stresses. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 108–115, November–December, 2005.     

Microconvection in a Binary System

On the basis of an essentially subsonic-flow approximation, the effect of small density variations of the medium on the development of natural convection in a slightly nonisothermal binary mixture at very small Rayleigh numbers and a constant mean thermodynamic pressure (microconvection) is studied analytically and numerically. Microconvective flows are characterized by a nonsolenoidal velocity field. As compared with microconvection in pure fluid, the presence of an admixture and the thermodiffusion effect result in a number of new interesting opportunities. Attention is mainly focused on essentially unsteady processes (transition processes after two different media are brought into contact and convection in rapidly varying temperature fields), in which the medium volume expansion is very significant. The conditions of onset of monotonic modes of the Rayleigh-Bénard and Bénard-Marangoni long-wave instabilities are also considered.     

Stress-strain analysis of a composite truncated conical shell

The stress-strain state of a nonshallow truncated conical shell made of a composite material and subjected to axial forces at the ends is studied. A variational difference method is used. Calculations are carried out for an orthotropic shell with low shear stiffness __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 7, pp. 66–72, July 2007.     

底层大空间高层结构自由振动的实用计算方法

本文以连杆节间为界，按弹性支座上和Ｔｉｍｏｓｈｅｎｋｏ悬臂梁建立力墙部分的振动方程，按一般框架建立框架部分的振动方程，根据力，变形协调条件，形成底层大空间高层建筑结构的自由振动，并据此计算其自由振动。     

Stress concentration around a spheroidal crack caused by a harmonic wave incident at an arbitrary angle

A method is proposed to study the stress concentration around a shallow spheroidal crack in an infinite elastic body. The stress concentration is due to the diffraction of a low-frequency plane longitudinal wave by the crack. The direction of wave propagation is established in which the combined concentration of mode I and mode II stresses is maximum __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 1, pp. 70–77, January 2006.     

A criterion for the onset of growth of two shear cracks in an elastic body under plane-strain conditions

The Wiener-Hopf method is used to find a solution to a symmetric problem that gives a criterion for the onset of growth of long shear cracks emanating from a corner point on the boundary of a hole and filled with a plastic material __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 4, pp. 83–90, April 2006.