Theoretical analysis of shunting effect in resistance spot welding (RSW) of AA2219

Shunting effect is the loss of electrical current via the secondary circuit provided due to existence of previous nugget in a series of welding spots. This phenomenon is important for products containing intermittent spots. In this study, a theoretical model is developed for shunting effect in resistance spot welding for aluminum alloy 2219. Welding distance together with welding current and time is included in the model to analyze the shunting effect on final nugget quality. Thermal and electrical interactions are considered in the model as well as geometrical aspects of the process. Temperature dependence of material properties, integration through the whole volume of the nugget and heat-affected zone, and assuming a simple cooling mechanism are the most important modifications designated in the proposed theoretical model. Predicted results of nugget diameter are compatible with experimental and finite element analysis results.     

高熵合金在钎焊和表面工程领域的应用研究进展

随着合金制造水平的提高及性能要求的复杂化,高熵合金逐渐引起极大的关注.目前在材料加工领域内的研究主要集中于钎焊和表面工程两大方向.在钎焊领域,高熵合金可以作为钎焊填充材料应用于高温和低温钎焊,本文归纳了合金高熵化的相关经验参数,阐述了第一性原理计算和相图计算等模拟计算手段在高熵合金填充材料设计领域内的应用;详细介绍了高熵合金钎料在镍基高温合金、陶瓷-金属异种材料、低温封装等连接领域的最新研究进展.同时,分析了工艺参数对高熵合金钎料钎焊接头组织与性能的影响.在表面工程领域,论述了高熵合金薄膜/涂层的应用方向与制备手段,总结了在高温防护涂层、硬质保护层以及其他应用领域的研究进展.同时归纳了高熵合金在钎焊和表面工程领域研究和应用中存在的问题,而未来将在降低钎料熔点、提高焊缝高温力学性能以及发展共晶高熵合金钎料/涂层等领域进一步提高研究水平.     

Emulsifying Properties of Food Proteins: Bovine Mi cellar Casein

The capacity of micellar casein isolated from bovine milk to stabilize oil in water (0:w) emulsions was studied. Emulsion surface area per unit mass of protein, i.e., emulsifying activity (EA), was highest at a protein concentration of 1% and o:w ratio of 1:9. The surface concentration of micellar casein was related to the o:w ratio being highest at an o:w of 4:6. Interfacial surface area decreased at pH 6.7 reflecting micellar stability and improved with increasing pH apparently because of destabilization of the casein micelle. Emulsion stability was high when the EA was high. The apparent viscosity of the emulsions was inversely related to EA.     

Determination of Principal Axes ot Truss Towers

The paper is concerned with the determination of the principal axes of geometrically non linear truss towers by a microcomputer. A knowledge of the principal axes may be used at the planning and design stage to advantageously orient the tower with respect to the dominant wind direction. The principal axes may also be used for the assessment of the truss tower's sensitivity to wind direction. A scale for the evaluation of this sensitivity is proposed in the paper. The sensitivity of a structure to lateral load direction depends on the structure's geometry and topology. An example is presented that shows how sensitivity of a space truss can the affected by the by the modifications of its geometry and topology.     

Comparative tests of plasma-surfaced nickel layers with chromium and titanium carbides

This article presents the results of structural tests of composite coatings on a NiSi₂B alloy matrix containing carbides of Ti and Cr, which have been plasma surfaced from a powder mixture onto a low-alloyed steel substrate. The content and distribution of the strengthening phase in the matrix have been determined. It has been shown that the different nature of the interaction between Ti and Cr carbides and the liquid Ni alloy significantly affects the formation of composite surfacing layers as well as the distribution and content of strengthening phase particles in the matrix.     

ON THE OPTIMALITY OF DISKS OF UNIFORM CREEP STRENGTH AGAINST BRITTLE RUPTURE

Axisymmetric rotating disks of uniform brittle rupture under creep conditions are considered. The similarity of deviators, according to the flow theory, and the time hardening hypothesis combined with the Kachanov-Sdobyrev brittle rupture rule are used as the governing equations for the unsteady creep problem. The concept of a fully damaged design method is applied, when the appropriate iteration of the thickness (the decision variable) is introduced such that the local condition of the Kachanov type ( ↓x_i t_r) = 0 (the objective) to be satisfied for each x_i under the constant volume condition (the constraint). In general, the disk of uniform creep strength, with geometry changes neglected, is found either as optimal or non-optimal with respect to the lifetime. In case of non-stationary loading (due to prestressing), and the geometric constraints allowed for, an additional small improvement of the lifetime is obtained when shape corrections are imposed upon the disk of uniform creep rupture strength     

INFLUENCE OF CONSTRUCTION OF POWER LOSSES IN A SUPERCONDUCTING A.C. GENERATOR SCREENING SYSTEM

ABSTRACT

Results of calculations of a power losses in a superconducting a.c. generator screening system during asymmetrical load are given. The main variants of screening system are considered. The influence of the screening system parameters on the power losses in particular shells of the rotor is discussed     

CONTENT OF BASIC COMPONENTS AND VOLATILE OILS IN GREEN DILL AS DEPENDING ON THE HEIGHT AND USABLE PARTS OF PLANTS

The aim of the present study was to establish the content of basic chemical components (dry matter, ash, reducing sugars, total sugars, starch, dietary fiber, total nitrogen, protein nitrogen, ascorbic acid, titratable acidity) and volatile oils in dill plants. The investigated material consisted of the following parts of dill plants: leaf blade, petiole, whole leaf, stem and whole plants harvested at the plant height of 20, 30, 40, 50 and 60 cm. Differences in the level of the analyzed components depending on the part of dill plants to a great degree exceeded these depending on the plant height. The highest content of all components was ascertained in the leaf blade. The smallest contents of dry matter, ash, starch, dietary fiber, total nitrogen and protein nitrogen, total acids and L‐ascorbic acid were found in the stem, and of sugars and volatile oils in the petiole. With the growth of plants, all analyses showed decreasing tendencies in the content of ash, total nitrogen and protein nitrogen, variation in the level of dry matter, sugars, starch and L‐ascorbic acid, and an increasing tendency in the content of dietary fiber, total acids and volatile oils, with the exception of stems, where the level of volatile oils was stable.