Limit analysis of flow through conical converging dies

A variety of mathematical models may be used to analyse plastic deformation during a metal-forming process. One of these methods—limit analysis—places the estimate of required power between an upper bound and a lower bound. The upper and lower bound analyses are designed so that the actual power or forming stress requirement is less than that predicted by the upper bound and greater than that predicted by the lower bound. Finding a lower upper bound and a higher lower bound reduces the uncertainty of the actual power requirement. Upper and lower bounds will permit the determination of such quantities as required forces, limitations on the process, optimal die design, flow patterns, and prediction and prevention of defects.Fundamental to the development of both upper bound and lower bound solutions is the division of the body into zones. For each of the zones there is written either a velocity field (upper bound) or a stress field (lower bound). A better choice of zones and fields brings the calculated values closer to actual values.In the present work, both upper and lower bound solutions are presented for axisymmetric flow through conical converging dies. For the upper bound triangular velocity fields have been solved and compared to previously published work on spherical velocity fields. It is found that each type provides a lower solution over a part of the range of process variables. A previously published lower bound solution for axisymmetric flow is refined.     

Drawing and extrusion of superplastic metals through cone-shaped dies

Closed-form solutions are obtained for the stress and die pressure distributions, time and flow rates for drawing and extruding superplastic cylinders through a cone-shaped die with Coulomb friction. Numerical examples are presented graphically and the possible existence of a maximum limit for area reduction in the drawing process is pointed out and discussed.     

学科会聚、交叉与科研平台建设

本文首先以活动着的知识创造、传递、融合与应用组织系统,这一实践形态的学科含义,区别于知识形态的学科界定,得出实践形态的学科活动最重要的就是学科会聚和交叉的结论,接着阐释了会聚交叉情况下的三种学科发展模式、相应的科研平台,最后对协作组织科研平台、科研群体管理机制平台、实践导向平台建设作了论述。     

The nature of static friction

The factors concerned in friction are discussed, together with a review of the limitations of the various approaches heretofore used. A more satisfactory view of the basic cause of static friction is developed in relation to modern experimental knowledge by considering the pertinent factors in systems having ideal surfaces, then relating this discussion to conditions in the best obtainable practical situation.     

Effect of wall permittivity on electroviscous flow through a contraction

The electroviscous flow at low Reynolds number through a two-dimensional slit contraction with electric double-layer overlap is investigated numerically for cases where the permittivity of the wall material is significant in comparison with the permittivity of the liquid. The liquid-solid interface is assumed to have uniform surface-charge density. It is demonstrated that a finite wall permittivity has a marked effect on the distribution of ions in and around the contraction, with a significant build-up of counter-ions observed at the back-step. The development length of the flow increases substantially as the wall permittivity becomes significant, meaning that the electric double-layers require a longer distance to develop within the contraction. Consequently, there is a corresponding decrease in the hydrodynamic and electro-potential resistance caused by the contraction. The effect of wall-region width on the flow characteristics is also quantified, demonstrating that the development length increases with increasing wall-region width for widths up to 5 channel widths.     

The accelerated flow method for rapid reactions

A manual syringe drive has been found to fulfil the requirements for a high driving force and a small disturbance to the electro-optical system. A syringe bore has been selected with due regard for the force-speed characteristic of the hand and flow velocities of 25 m./sec. have been obtained in this manner. A direct comparison of a manual and an electric drive has been made and it has been found that the mechanical and electrical effects of the latter upon the photoelectric system greatly reduce the possible range of the electric drive method.