第三类边界条件下大型圆柱体钢锭加热速度计算

针对大型钢锭在第三类边界条件下的加热过程进行分析,利用加热时温度沿钢锭横截面的分布变化和由温度梯度导致的钢锭瞬时热应力计算方法,建立了加热过程中钢锭径向、横向和切向的瞬时应力模型。在瞬时应力模型的基础上,根据钢锭在某一温度下的屈服强度和加热炉温度值,提出了控制钢锭加热速度的计算式。用此计算式计算加热工艺参数,可以有效控制钢锭在加热过程的温升速度,避免钢锭在加热过程中产生裂纹,该计算方法已在某特殊钢锻造厂得到实际应用,生产实践证明该方法可行。     

Relaxation Properties and Chemical Nature of Polymer Surface Layers as Related to the Strength of Adhesive Joints with Metals

A new approach based on the theory of elasticity is proposed to study relaxation properties of adhesive transition layers. It involves experimental evaluation of the rate dependence of the fracture energy of the bulk polymer and its adhesive joint.

The investigation of the interaction of a polymer surface layer with electroplated copper by XPS using the effect of differential charging (the latter produced by potential shift of the sample by 10V), makes it possible to identify the functional groups of adhesive brought into contact with substrate surface. For ABS copolymers a bond of -O … Cu type was formed.

The mechanism of adhesive contact formation and factors affecting the strength of adhesive joints could be understood better by determining the properties of surface and transition layers.     

MOMENTUM INTEGRAL METHOD FOR FORCED CONVECTION IN THERMAL NONEQUILIBRIUM POWER-LAW FLUID-SATURATED POROUS MEDIA

Forced convection heat transfer for power-law fluid flow in porous media was studied analytically. The analytical solutions were obtained based on the Brinkman-extended Darcy model for fluid flow and the two-equation model for forced convection heat transfer. As a closed-form exact velocity profile is unobtainable for the general power-law index, an approximate velocity profile based on the parabolic model is proposed by subscribing to the momentum boundary layer integral method. Heat transfer analysis is based on the two-equation model by considering local thermal nonequilibrium between fluid and solid phases and constant heat flux boundary conditions. The velocity and temperature distributions obtained based on the parabolic model were verified to be reasonably accurate and improvement is justified compared to the linear model. The expression for the overall Nusselt number was derived based on the proposed parabolic model. The effects of the governing parameters of engineering importance such as Darcy number, power-law index, nondimensional interfacial heat transfer coefficient, and effective thermal conductivity ratio on the convective heat transfer characteristics of non-Newtonian fluids in porous media are analyzed and discussed.     

Deep drawing of tungsten plates for structural divertor applications in future fusion devices

The reference design of a helium cooled divertor for future fusion reactors makes use of hundreds of thousands of finger units consisting of a pressurized structural part called a thimble. Due to the high number of parts needed, the thimble has to be fabricated by mass production techniques like deep drawing. As the thimble is a pressurized part exposed to an internal pressure of 100 bar, the demands for the material are high, which means that it requires the best available tungsten material. Former work has shown that pure tungsten material has the best impact properties and has to be preferred over other commercially available tungsten materials, such as that doped with potassium or strengthened with oxides like lanthanum oxide.Furthermore the inherent weakness of the grain boundaries has to be taken into account, which requires the need for grains that are aligned to the contour of the part (grain boundary alignment).This paper describes the successful deep drawing of a 1 mm tungsten plate in high vacuum at 600 °C. In doing this, a thimble can be machined with grains that follow the contour. Furthermore the characterization of a 1 mm tungsten plate is conducted by tensile tests at room temperature and at 600 °C, as well as by Charpy tests taking into account the anisotropic material behaviour.     

A combined analytical‐experimental investigation of friction in cylinder liner inserts under mixed and boundary regimes of lubrication

It is necessary to develop an analytical solution in order to combine predictions with measured tribological parameters and fundamentally understand the mechanism of lubrication in a typical region of engine cycle, using tribometric studies. This paper deals with the development of such a representative approach. An analytical, rather than a numerical approach is expounded, as it is shown to suffice for the purpose of precise time‐efficient predictions, which conform well to the measurements. The effect of surface topography, material and operating conditions are ascertained for the representative case of top compression ring—cylinder liner contact at the top dead centre reversal in transition from the compression to power stroke. Stainless steel uncoated surface used as press fit cylinder liners for niche original equipment manufacturer applications are compared with those furnished with a Nickel‐Silicon Carbide wear‐resistant coating of choice in high performance motorsport. © 2017 The Authors Lubrication Science Published by John Wiley & Sons Ltd.     

A study on flame structure and extinction in downstream interaction between lean premixed CH4-air and (50% H2 + 50% CO) syngas-air flames

Downstream interactions between lean premixed flames with mutually different fuels of (50% H₂ + 50% CO) and CH₄ are numerically investigated particularly on and near lean extinction limits in order to provide fundamental database for the design of cofiring burners with hydrocarbon and syngas under a retrofit concept. In the current study the anomalous combination of lean premixed flames is provided such that even a weaker CH₄-air flame temperature is higher than a stronger syngas-air flame temperature, and, based on a deficient reactant concept, the effective Lewis numbers Le_eff ≈ 1 for lean premixed (50% H₂ + 50% CO)-air mixture and Le_D < 1 for CH₄-air mixture. It is found that the interaction characteristics between lean premixed (50% H₂ + 50% CO)-air and CH₄-air flames are quite different from those between the same hydrocarbon flames. The lean extinction boundaries are of slanted shape, thereby indicating strong interactions. The upper extinction boundaries have negative flame speeds while the lower extinction boundaries have both negative and positive flame speeds. The results also show that the flame interaction characteristics do not follow the general tendency of Lewis number, which has been well described in interactions between the same hydrocarbon flames, but have the strong dependency of direct interaction factors such as flame temperature, the distance between two flames, and radical-sharing. Importance of chain carrier radicals such as H is also addressed in the downstream interactions between lean premixed (50% H₂ + 50% CO)-air and CH₄-air flames.     

Formation mechanisms of high quality diffusion bonded martensitic stainless steel joints

Abstract

Diffusion bonding of martensitic stainless steel was conducted at different times. Based on the interface characteristic and shear strength, bonding mechanisms were discussed. Results showed that the bonding quality was controlled by void shrinkage and interface grain boundary migration. Large voids with scraggly edges changed to small voids with smooth edges, leading to an increase in interface bonding ratio. Two cases of interface grain boundary migration were revealed: interface grain boundary migration at the triple junction induced by the reduction in grain boundary energy and strain induced interface grain boundary migration resulted from the stored energy. Owing to the void shrinkage and interface grain boundary migration, the shear strength of the joint matched that of the base material.     

Free convection to power‐law fluids from a vertical cone of variable surface temperature

Steady free convection laminar boundary‐layer flow about a heated vertical cone immersed in a quiescent power‐law fluid is investigated. Surface temperature is assumed to have a power‐law variation with the distance. Similarity solutions are obtained numerically for the boundary‐layer velocity and temperature profiles. Magnitudes of the velocity and temperature profiles are found to decrease with increasing values of the flow behaviour index and the surface temperature exponent. The effects of flow behaviour index and the generalized Prandtl number on the surface shear stress and heat flux are determined. Copyright © 2001 John Wiley & Sons, Ltd.     

油水界面仪的研制及其应用

以7．4×108Bq(137)Cs为辐射源，研制了一台用于检测贮油罐中的油水分界面的油水界面仪，从而实现自动切水，消除了由于人工切水所产生的跑油和由此而引起的着火爆炸事故的发生。     

Transmitting boundary and radiation conditions at infinity

Relationship between the radiation conditions at infinity and the transmitting boundary for numerical simulation of the near-field wave motion has been studied in this paper. The conclusion is that the transmitting boundary is approximately equivalent to the radiation conditions at infinity for a large class of infinite media. And the errors of the approximation are of the same order of magnitude as those of the finite elements or finite differences in numerical simulation of wave motion. This result provides a sound theoretical basis for the transmitting boundary used in the numerical simulation of the near-field wave motion and gives a complete explanation for the major experiences accumulated in applications of the transmitting boundary to the numerical simulation.