Viscoplastic dynamics of isotropic plates of variable thickness under explosive loading

A problem of viscoplastic dynamic bending of isotropic plates of variable thickness is formulated. A method for integrating the initial-boundary problem is developed. Numerical results are compared with a known analytical solution obtained within a rigid-plastic model; good agreement is demonstrated. The efficiency of the method developed is verified by numerical computations. It is shown that the final flexure of plates can be reduced severalfold by applying rational design. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 123–134, March–April, 2007.     

合肥光源慢加速过程中高频系统的调节

 合肥光源是一台专用同步辐射光源，它在低能注入积累束流，然后同步地把束流加速到高能并在储存环中稳定运行。在加速过程中，粒子的同步辐射能量损失迅速增加，束流负载效应发生变化，需要相应地调节高频系统参数保持束流稳定。讨论了合肥光源加速过程中高频系统可能的两种高频系统调节方式以及高能情况下高频系统的最佳运行状态。     

Effect of temperature on the fracture modes of BHW-35 steel under mode-II loading

Finite element method (FEM) has been used to analyze the stress and strain fields and the stress tri-axial levels around the tip of the crack under mode- II loading. The results show that: under mode- II loading, the direction of the maximum tensile stress and that of the maximum tri-axial levels (R _o ) exist at an angle of –75. 3° from the original crack plane; the maximum shear stress andR _o = 0 exist along the original crack plane.Mode- II loading experiment using BHW-35 steel at different temperatures show that there are two kinds of fracture mode, opening mode (or tensile mode) and sliding mode (or shear mode). A decrease in temperature causes the fracture mode to change from shear mode to tensile mode. For BHW-35 steel, this critical temperature is about –90 C. Actually, under any kind of loading mode (mode I . mode II , mode III or mixed mode), there always exist several kinds of potenital fracture modes (for example, opening mode, sliding mode, tearing mode or mixed mode). The effect of temperature under mode- II loading is actually related to the change of the elastic-plastic properties of the material.     

Dislocation Plasticity Effects on Interfacial Fracture

Analyses are reviewed where plastic flow in the vicinity of an interfacial crack is represented in terms of the nucleation and glide of discrete dislocations. Attention is confined to cracks along a metal-ceramic interface, with the ceramic idealized as being rigid. Both monotonic and fatigue loading are considered. The main focus is on the stress and deformation fields near the crack tip predicted by discrete dislocation plasticity, in comparison with those obtained from conventional continuum plasticity theory. The role that discrete dislocation plasticity can play in interpreting interface fracture properties in the presence of plastic flow is discussed.     

Calculation of the Ultimate State of Reinforced Plastics and Unoriented Polymers in Asymmetric High-Cycle Tension–Compression

The fatigue failure of reinforced plastics and unoriented polymers under a joint action of static and high-cycle loadings is considered. The fatigue failure strength is estimated from stress range diagrams with a static tensile component. The models of ultimate state are constructed based on the hypothesis of existence of a unified ultimate diagram invariant with respect to the number of cycles to failure. The unified diagram is given by a transcendental power function whose exponent characterizes the sensitivity of the material to the stress-cycle asymmetry. The models of ultimate state make it possible to span practically all forms of ultimate diagrams of composite and polymer materials, including concave, rectilinear, S-shaped, and convex ones.     

A unified multiaxial fatigue damage parameter

According to the critical plane principle, a unified multiaxial fatigue damage parameter is presented based on the varying behaviour of the strains of the critical plane. Both the parameters of the maximum shear strain amplitude and normal strain excursion between adjacent turning points of the maximum shear strain on the critical plane are considered in the multiaxial fatigue damage parameter presented. An equivalent strain amplitude is made with both parameters of the maximum shear strain amplitude and normal strain excursion by means of von Mises criterion. Thus a new multiaxial fatigue damage parameter proposed in this paper may be used under either proportional or nonproportional loading, and may also be reduced to a uniaxial form. It is used to predict multiaxial fatigue life and good agreement is demonstrated by experimental data. The project is supported by the National Doctoral Foundation of China and National Natural Science Foundation of China.     

Forced Vibration of Three-Layered Spherical and Ellipsoidal Shells under Axisymmetric Loads

A variant of vibration theory for three-layered shells of revolution under axisymmetric loads is elaborated by applying independent kinematic and static hypotheses to each layer, with account of transverse normal and shear strains in the core. Based on the Reissner variational principle for dynamic processes, equations of nonlinear vibrations and natural boundary conditions are obtained. The numerical method proposed for solving initial boundary-value problems is based on the use of integrodifferential approach for constructing finite-difference schemes with respect to spatial and time coordinates. Numerical solutions are obtained for dynamic deformations of open three-layered spherical and ellipsoidal shells, over a wide range of geometric and physical parameters of the core, for different types of boundary conditions. A comparative analysis is given for the results of investigating the dynamic behavior of three-layered shells of revolution by the equations proposed and the shell equations of Timoshenko and Kirhhoff-Love type, with the use of unified hypotheses across the heterogeneous structure of shells.     

A goal-driven prototype column generation strategy for the multiple container loading cost minimization problem

In the multiple container loading cost minimization problem (MCLCMP), rectangular boxes of various dimensions are loaded into rectangular containers of various sizes so as to minimize the total shipping cost. The MCLCMP can be naturally modeled as a set cover problem. We generalize the set cover formulation by introducing a new parameter to model the gross volume utilization of containers in a solution. The state-of-the-art algorithm tackles the MCLCMP using the prototype column generation (PCG) technique. PCG is an effective technique for speeding up the column generation technique for extremely hard optimization problems where their corresponding pricing subproblems are NP-hard. We propose a new approach to the MCLCMP that combines the PCG technique with a goal-driven search. Our goal-driven prototype column generation (GD-PCG) algorithm improves the original PCG approach in three respects. Computational experiments suggest that all three enhancements are effective. Our GD-PCG algorithm produces significantly better solutions for the 350 existing benchmark instances than all other approaches in the literature using less computation time. We also generate two new set instances based on industrial data and the classical single container loading instances.     

On certain bounds for the in-plane translational stiffness of a disc inclusion at a bi-material elastic interface

This paper presents a set of bounds that can be used to estimate the in-plane translational stiffness of a rigid circular disc inclusion that is embedded at the interface between two dissimilar elastic half-space regions.     

General results for complete contacts subject to oscillatory shear

In this paper, we consider the general interfacial characteristics of a square elastic block, pressed onto an elastically similar half-plane by a constant normal force, and subjected to oscillatory shear. It is found that there is a critical coefficient of friction, 0.543, above which the contact is permanently stuck along its entire length for a shearing force below about 55% of that needed to cause sliding. For shearing forces above this, the contact interface will either shakedown to a fully adhered state (depending on the degree of reversal of the shear loading) or will exhibit cyclic slip at an interior point. If the coefficient of friction is below 0.543, the application of normal load alone will produce equal and opposite slip zones attached to the contact edges. The subsequent imposition of a shear force causes the leading edge slip zone to increase in length while the presence of residual slipping tractions at the trailing edge causes the trailing edge to lift off. Under oscillatory loading, the contact edges cycle between slip and separation over a minute region while an interior point may exhibit cyclic slip if the loading history is sufficiently demanding. The results found are of practical relevance to the study of fretting fatigue of complete contacts, such as some types of spline joint.