圆杆弹性和弹—塑性扭转公式的探讨

对圆杆在线弹性阶段，弹－塑性阶段和全塑性阶段的扭转剪应力的计算公式作了分析，并推导了在材料的应力－应变关系（τ－γ关系）不服从虎克定律时，扭转真实剪应力的计算公式。文中对扭转强度计算公式的来源，物理含义及其都作了详细的说明。这对执行和理解国家ＧＢ１０１２８－８８《金属室温扭转试验方法》是有益的，而且对高校中材料力学的教学具有一定的参考价值。     

A theoretical and photoelastic contact stress analysis relevant to orthopaedic knee prostheses

This study is based on a theoretical and photoelastic static contact stress analysis, relevant to the design of the plastic tibial plateau in an orthopaedic knee prosthesis. It involves the review of existing theoretical analyses concerned with the contact mechanics of layered elastic systems and, where possible, the validation of any relevant findings using two dimensional photoelasticity. Significant findings include the identification of a general minimum recommendable design thickness for the plastic tibial plateau, the endorsement of using the Hertzian contact theory to predict contact stress levels in the tibial plateau of certain knee implants and the slight improvement in contact conditions in the plastic when the plateau is perfectly bonded to its supporting metal tray.     

Calculation of fatigue limits of case-hardened specimens with consideration of mean stresses and residual stresses

 The strength of case-hardened parts under cyclic loading can be determined in an experimental manner, but this can produce a large amount of costs due to the expenditure of material and testing time. Therefore, a calculation method is developed, that strongly reduces the number of experiments. The presented model is based on Weibull's weakest-link concept and allows to compute the survival probability of a case-hardened part which is loaded close to the fatigue limit. The essential quantities in this model are the distribution of Vicker's hardness of the material, the exponents of the Weibull distribution of the volume and the surface, the residual stress state, the surface roughness and the surface oxidation depth. By integrating the survival probabilities of the surface and the volume, the survival probability of the entire specimen or part can be calculated, which allows to compute the fatigue limit. The necessary parameters have to be determined from reference specimens. The model is successfully examined by comparing experimental and calculated results of smooth and notched case-hardened specimens under alternating torsion, rotating bending, repeated tension and tension-compression. Received 20 August 2001 / Accepted 11 November 2001     

MODELING LIQUID MASS TRANSFER IN HIGEE SEPARATION PROCESS

Correspondence concerning this paper should be addressed to Professor Richard S.H. Mah. Hsien-Hsin Tung is now affiliated with Department of Chemical Engineering, California Institute of Technology

Penetration theory is used to describe the liquid mass transfer in Higee separation process. Within a possible range of effective areas, it is shown that the predicted mass transfer coefficients are in reasonable agreement with the estimated mass transfer coefficients. The estimated coefficients were calculated from the experimental data and the possible effective areas. Hence it is concluded the penetration theory is generally applicable to describe liquid mass transfer in Higee separation process. The comparison also suggests that liquid mixing at the junctions of packing materials may be more complete in Higee process than in traditional process.     

超薄氧化层中的中性陷阱对隧穿电流的影响和应变诱导漏电流

用数值分析的方法讨论了中性陷阱对超薄场效应晶体管(MOSFET )隧穿电流的影响.中性陷阱引起势垒的变化在二氧化硅的导带中形成一个方形的势阱.对于不同的势垒变化,计算了电子隧穿氧化层厚度为4nm的超薄金属氧化物半导体结构的电流.结果表明,中性陷阱对隧穿电流的影响不能被忽略,中性陷阱的存在使隧穿电流增加,并且通过这个简单的模型能够理解应变诱导漏电流的产生机制.     

秦山核电厂气载放射性释放的环境影响

本文评价了秦山核电厂气载放射性流出物对环境的影响。应用现场及风洞大气扩释实验结果和厂址周围的人口与食谱调查资料,估算了秦山核电厂在正常运行和事故条件下释放的气载放射性流出物对公众产生的个人有效剂量当量和集体有效剂量当量。计算结果表明,正常运行时厂址边界(0.5km)处的最大个人有效剂量当量为2.7×10~(-2)mSv/a,该剂量的大部分来自~(137)Cs 的食入(主要由地表湿沉积引起);80km 范围内的集体有效剂量当量为1.1人·Sv/a,归一化集体有效剂量当量为3.7人·Sv/GW(e)·a。文中还给出了事故情况下剂量估算结果。     

Non-destructive evaluation of residual stresses in thin films via x-ray diffraction topography methods

Quantitative x-ray diffraction topography techniques have been used to measure the residual strain magnitude and uniformity of deposition for Mo and W sputtered films on Si(100) substrates. High sensitivity rocking curve measurements were able to determine differential strains for films as thin as 2.5 nm; while Bragg angle contour mapping had similar sensitivity and was also able to assess coating uniformity and stress distribution over areas covering a whole wafer. Measurements of strain versus film thickness over a range of 2.5 nm to 80 nm showed that a critical thickness exists for maximum residual strain. Growth beyond this range produces stress relaxation. This non-destructive type of analysis could be employed on a wide range of film-substrate combinations.     

羰基铁类随机混合吸波材料等效电磁参数的计算

本文为计及多重散射偶极子间的相互作用，引入参量εｈ和μｈ，导得一组公式。它不仅能计算铁氧体类也能计算羰基铁类的随机混合吸波材料的等效电磁参数，均与实验结果吻合良好。