Path-independent line integrals for steady-state,two-dimensional thermoelasticity

Three path-independent line integrals J' _k, M', and L' ₃ are derived for steady-state, two-dimensional thermoelasticity. These integrals are similar to the J _k, M, and L ₃ presented by Knowles and Sternberg [1], but include additional terms of either free expansion displacement vector u _k ^* or temperature and its conjugate harmonic function in their formulation. These new line integrals enable us to avoid the undesirable area integration [3–8] when calculating the strain energy release rate for crack problems. Application of J/ _k, M', and L' ₃ is demonstrated through a sample problem of a constant heat flux disturbed by a finite crack in an infinite plate.

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Résumé On établit les intégrales linéaires J _k, M' et L' ₃ indépendantes du parcours applicables aux problèmes de thermo-élasticité en état stable et suivant deux dimensions. Ces intégrales sont similaires aux intégrales de conservation J _k, M et L ₃ introduites par Knowles et Sternberg, mais comportent des termes supplémentaires prenant en compte dans la formulation le vecteur de déplacement u _k ^* en dilatation libre ou la température et sa fonction complexe .Ces nouvelles intégrales linéaires permettent aux auteurs d'éviter une intégration sur des zones inutiles lors du calcul, dans des problèmes de fissuration, de la vitesse de relaxation de l'énergie de déformation.On démontre l'applicabilité de J' _k, M' et L' ₃ dans un exemple de problème de flux de chaleur constant soumis à une perturbation par une fissure finie dans une plaque infinie.

     

配电网信息物理系统恶性数据链检测与识别

由于恶性数据链干扰配电网的信息输出和转发控制能力,因此需检测配电网信息物理系统中的恶性数据链。根据恶性数据时间序列节点融合恶性数据链能量特征,并构建其高维映射结构,通过高维映射结构拟合恶性数据,获取恶性数据链。采用谱特征提取方法建立恶性数据链谱特征量模型,实现配电网信息物理系统恶性数据链的分类检测。仿真结果表明,采用该方法进行配电网信息物理系统恶性数据链检测的自适应性较好,分辨能力较强,在配电网信息物理系统恶性数据链检测识别中具有很好的应用价值。     

Observation of phosphorus segregation onto the free surface of an amorphous Fe44Ni36P14B6 alloy

Phosphorus segregation to the free surface of an amorphous Fe₄₄Ni₃₆P₁₄B₆ alloy during annealing in the temperature range 180 to 300° C has been studied by Auger electron spectroscopy. The phosphorus concentration increased with annealing temperature with an abrupt change appearing at about 250° C. At 276° C the phosphorus Peak Height Ratio on the surface was three times as high as that of a sputtered surface. A step-heating scheme has been employed to observe the surface segregation of phosphorus in the temperature range 25 to 290° C. On heating, the segregation behaviour can be correlated with a degradation in toughness properties. It is concluded that the segregation of phosphorus onto the free surface of this amorphous alloy is an indication of some local atomic migration processes, for example clustering, occurring inside the bulk.     

Effect of microscopic parameters on EBSD spatial resolution

In this study, a quantitative approach is proposed to understand the effect of the accelerating voltage and the probe current on the physical resolution of EBSD. The accelerating voltage was varied from 5 to 30kV and probe currents of 1, 10, and 40nA were selected. The lateral, longitudinal, and depth resolutions at 10kV and 1nA were 34.5, 44.7, and 46nm for copper, respectively. When the accelerating voltage was in the range of 5-20kV, the ratio of the longitudinal to the lateral resolution was below the theoretical ratio of 2.9. Considering the channeling effect, the best physical depth resolution of 38nm was achieved at 5kV and 10nA. The physical depth resolution in an EBSD measurement is much larger due to the channel effect than that obtained without considering this effect.     

Investigation of the friction effect at pin joints for the five-point double-toggle clamping mechanisms of injection molding machines

In this study, an analytical formulation for the necessary thrust of the crosshead of the five-point double-toggle clamping mechanism during real-mold clamping operation is proposed in order to investigate the effect of the friction at pin joints. The friction is considered to be a Coulomb friction. The inertia effects are not considered.Numerical examples are studied for different values of coefficient of friction to investigate the effects of friction at pin joints. In order to estimate the kinetic friction coefficient at pin joints, the motor torques required for real-mold clamping obtained by the present study are adjusted by using different values of coefficient of friction and mechanical efficiency to fit the experimental data.     

Multilevel solution for thermal elastohydrodynamic lubrication of rolling/sliding circular contacts

A fast multigrid approach is presented for the analysis of thermal elastohydrodynamic lubrication (EHL) under rolling/sliding circular contacts at high loads and high slip ratios with low computing time on a personal computer. This fast solver combines directiteration, multigrid, Newton-Raphson, Gauss-Seidel iteration, and multilevel multi-integration methods into one working environment that can reduce the computational complexity from O(n³ to O(nlnn) for the thermal EHL problem under rolling/sliding circular contacts. Since the couped Reynolds and energy equations are simultaneously solved by the Newton-Raphson scheme, the iteration for the convergence solution is less than those of the classical approach. Results show that thermal effects on the pressure profile and film thickness are significant for a wide range of loads, speeds and slip ratios. The maximum midfilm and surface temperature rise in the Hertzian contact region increases with increasing slip ratio, dimensionless speed, and load. The minimum film thickness decreases with increasing load and slip ratio, and decreasing dimensionless speed.     

Control of a permanent magnet synchronous motor with a fuzzy sliding-mode controller

This paper is concerned with the topics in the speed control of a permanent magnet synchronous motor (PMSM). First, the vector control scheme in the synchronously rotating reference frame is used to formulate the PMSM model as the system plant. Then, the modern control theory using a sliding mode with fuzzy controller is presented to design the corresponding closed-loop system and Matlab/Simulink software is used for computer simulation. The original PMSM is stable, sluggish with large overshoot deficiency. It can be shown that the proposed fuzzy sliding-mode controller not only can delete the overshoot problem and achieve very good tracking performance without zero steady-state errors, but can also obtain good robustness to system parameter uncertainty. This proposed fuzzy-sliding mode controller for PMSM can be applied to the positioning control of the robot arms to suppress unnecessary vibrations. For assembly lines, this proposed controller can be used to obtain fast tracking ability, less steady-state errors, and robustness for different velocity movements.     

Fabrication of 3D Metal Microstructures Using a Hybrid Process of Micro-EDM and Laser Assembly

A fabrication technique for 3D metal microstructures using hybrid process integrated micromachining and welding on a workstation is described in the paper. The system uses a micro-EDM (micro electro-discharge machining) process to fabricate microparts, and Nd-YAG laser welding to microassemble these microparts precisely. A diverse pattern of 3D metal microstructures or micromoulds can be attained via further machining procedures controlled by a CAD/CAM path after assembling. Since the product is completed in one integrated manufacturing process, some particular problems resulting from their small dimensions can be overcome, e.g. their high failure sensitivity, and the required micro-precision in the microassembly process. Using these procedures, diverse patterns, and high aspect ratios and high joint strength microstructures can be created precisely. To illustrate the microassembly strategies and procedures, a diverse pin–plate metal microstructure has been used and discussed in the study. It requires that the perpendicular tolerance between pin and plate, and the parallel tolerance between pins are good, and the twisting strength at the joint is strong. A diverse feature on the top of the pin was then further machined as a square, or hollow construction having an equiangular partition.     

Debugging Finite Element Programs Input Data with Machine Learning

Abstract: Debugging of the input data of a structural analysis program is a troublesome task which is heavily dependent on empirical knowledge. The paper describes an effort that applies machine learning to build an expert system for debugging faults in structural analysis program input data. ID3 decision tree induction algorithm is employed to build the automatic learning mechanism. This method Oflkrs an attractive potential for knowledge acquisition in the civil engineering domain in which expertise plays a dominant role. This paper is novel in at least three aspects: (1) machine learning is employed to build expert systems automatically; (2) a novel impurity function is proposed for splitting the decision tree; (3) a formulated comparison is proposed for evaluating learning results.     

Home ownership policy in Singapore: An assessment

Since independence in 1965, housing conditions in the city‐state of Singapore, with a population of 2.6 million in 1988, have improved considerably. Much of the credit for this must be attributed to the government's policy of building homes for the lower income groups. One objective of the housing policy is 100 per cent home ownership for public housing. In pursuing this policy the political and social aspects are often emphasised. This paper attempts an economic evaluation of the 100 per cent home ownership target. It examines the demand and supply side policies that are employed to achieve the target. In analysing the economic implications of the policy, it is observed that such a policy distorts household expenditure, leads to overconsumption of housing and results in a thinner rental market and constrains tenure choice. These economic losses need to be recognised even while accepting the political and social importance of the policy.