Elastic T-stress solutions for semi-elliptical surface cracks in finite thickness plates

Three-dimensional finite element analyses have been conducted to calculate the elastic T-stress for semi-elliptical surface cracks in finite thickness plates. Far-field tension and bending loads were considered. The analysis procedures and results were verified using both exact solutions and approximate solutions. The T-stress solutions are presented along the crack front for cracks with a/t values of 0.2, 0.4, 0.6 or 0.8 and a/c values of 0.2, 0.4, 0.6 or 1.0. Based on the present finite element calculations for T-stress, empirical equations for the T-stress at three locations: the deepest, the surface and the middle points of the crack front under tension or bending are presented. The numerical results are approximated by empirical formulae fitted with an accuracy of 1% or better. They are valid for 0.2?a/c?1 and 0?a/t?0.8. These T-stress results together with the corresponding K or J values for surface cracks are suitable for the analysis of constraint effects for surface cracked components.     

Low surface energy films based on partially fluorinated isocyanates: the effects of curing temperature

Self-stratification strategy can be used to prepare films in which both bulk and surface properties can be optimized. By using this approach, only a very small quantity of fluorinated species is needed to generate a surface with low surface energy. When cross-linking is involved during film formation, we are dealing with a competition behavior between the diffusion of fluorinated species and the formation of cross-linked network. In this study low surface energy polymeric films were prepared on the basis of partially fluorinated polyisocyanates, in combination with hydroxyl-end-capped three-armed solventless liquid oligoesters and modified hyperbranched polyesters. At a fluorine concentration of only 0.5 wt.%, contact angles of water and hexadecane can reach 120° and 80°, respectively. A surface energy as low as 10–15 mN/m can be obtained upon the addition of less than 1 wt.% of fluorine in the films. It was shown, from real time ATR-FTIR and contact angle measurements, that the curing temperatures demonstrated significant effects on the cross-linking rate as well as on the wettability of the films.     

INTERFACE/INTERPHASE ENGINEERING OF POLYMERS FOR ADHESION ENHANCEMENT: PART II. THEORETICAL AND TECHNOLOGICAL ASPECTS OF SURFACE-ENGINEERED INTERPHASE-INTERFACE SYSTEMS FOR ADHESION ENHANCEMENT

Part I of this paper reviewed the theoretical principles of the macromolecular design of polymer interface/interphase systems for obtaining maximum adhesion and fracture performance of adhesively bonded assemblies. In Part II a novel, relatively simple and industry-feasible technology for surface-grafting connector molecules is demonstrated and discussed in detail and supported by a range of experimental examples. It is shown, in agreement with contemporary theory, that the use of chemically attached graft chemicals of controlled spatial geometry and chemical functionality enables a significant increase in the strength and fracture energy of the interphase, to the point of cohesive fracture of the substrate, or that of an adjacent medium such as adhesive, elastomer, or other material. This occurs even after prolonged exposure of investigated systems to adverse environments such as hot water.     

在p+GaAs体单晶材料上进行的NEA活化实验

NEA活化实验是利用体单晶材料进行的,未经任何外延或真空解理手续。为确立活化工艺,特别是表面清洁处理规范,作了相应AES分析。借助于测量样品附近高纯Al的熔点以校准及控制样品表面的温度。在不太好的本底真空(2×10^-7—6×10^-7Pa)条件下,活化好的GaAs样品之白光光电灵敏度可达1000μA/lm以上。     

Experimental investigation of natural convection from a horizontal ice surface melting in pure water

A study on natural convection from a horizontal ice surface melting in pure water was conducted experimentally for the ambient water temperature from 2▿C to 10°C. Natural convection flow around upward-or downward-facing horizontal ice plate was divided into three regions according to the temperature variation of ambient water. The flow patterns of three regions were no flow, two-dimensional steady laminar flow and unsteady flow. Mean Nusselt number for the upward-facing surface had its maximum value at about 3°C of ambient water temperature. However, in the case of the downward-facing surface it increased as the ambient water temperature increased.     

近程地对地战术导弹的作用与问题

海湾战争中,“爱国者”导弹成功地拦截了“飞毛腿”导弹,给近程地对地战术导弹的作用、发展与装备方向提出了值得思考的问题。本文着重讨论在局部战争中,近程地对地战术导弹的作用、使用场合及其技术发展方向。     

The catalytic activity and surface characterization of Ln2B2O7 (Ln=Sm, Eu, Gd and Tb; B=Ti or Zr) with pyrochlore structure as novel CH4 combustion catalyst

Ln₂B₂O₇ (Ln=Sm, Eu, Gd and Tb; B=Zr or Ti) with pyrochlore structure was prepared by sol–gel method for the high-temperature catalytic combustion. The crystal structure of Ln₂B₂O₇ was identified by XRD and their surface area was about 4 m²/g after calcinations at 1200 °C. Catalytic activity of methane combustion was observed for Ln₂Zr₂O₇ series and the best catalyst was Sm₂Zr₂O₇. Its relative reaction rate per unit surface area at 600 °C was 2 cm³/m² min, which was twice higher than that of Mn-substituted Sr hexaaluminate. From surface analysis by XPS, the low binding energy of each Ln element of Ln₂Zr₂O₇ compared to that of Ln₂Ti₂O₇, gave the catalytic activity of methane combustion.     

The growth of roughness during electrodeposition

Measurements of the growth rate of roughness on a cathode surface can be used to study the physics of cathodic processes. But these growth rates are cell wide variables and they ordinarily depend on what is taking place at the anode as well as at the cathode. Our aim is to derive a simple condition under which the anode makes no contribution to the interpretation of growth rate measurements at the cathode.Our condition stems from the contribution of ion diffusion to the growth rate and it is satisfied for all non-small values of the wave number of a growing disturbance. This, together with the fact that surface tension is the only stabilizing factor and the fact that the surface tension coefficient multiplying the wave number is small, means that the anode ought not to be important for the fastest growing wave numbers.Once the effect of the anode is eliminated, the growth rate at the cathode can be expressed in a formula so simple that pencil and paper calculations are possible and this makes important questions in cell design easy to answer, e.g., is the growth rate diffusion controlled?     

Very low surface recombination velocities on p-type silicon wafers passivated with a dielectric with fixed negative charge

Surface recombination velocities as low as 10 cm/s have been obtained by treated atomic layer deposition (ALD) of Al₂O₃ layers on p-type CZ silicon wafers. Low surface recombination is achieved by means of field induced surface passivation due to a high density of negative charges stored at the interface. In comparison to a diffused back surface field, an external field source allows for higher band bending, that is, a better performance. While this process yields state of the art results, it is not suited for large-scale production. Preliminary results on an industrially viable, alternative process based on a pseudo-binary system containing Al₂O₃ are presented, too. With this process, surface recombination velocities of 500–1000 cm/s have been attained on mc-Si wafers.