Simulation as a planning technique for a complex machine shop

A deterministic simulation study of a complex machine shop consisting of 69 work centres is presented. The purpose of the simulation study was to develop a planning tool to evaluate effects on overtime, work centre bottlenecks, in-process inventory buildup, delivery delays and other output variables caused by individual part delays of different load mixes, modifications in work centre capacities, installation of more automated machinery, and modification in scheduling rules.

The simulation programme and the machine shop it models are described. It was found that the developed simulation programme can be used as a useful planning tool for evaluating short-term and intermediate-term alternatives.     

混合润滑状态下结合面的法向接触刚度研究

针对润滑条件下机械结合面的接触特性受油膜影响的问题,基于结合面接触刚度由油膜接触刚度和固体表面接触刚度组成的思想,建立混合润滑状态下结合面的法向接触刚度模型。采用三维的Weierstrass-Mandelbrot函数获得具有分形特征的粗糙表面,并基于统计学方法建立干摩擦条件下结合面的法向接触刚度模型,考虑了微凸体的完全弹性变形、弹塑性变形以及完全塑性变形过程。在此基础上,求解了油膜的等效厚度并建立油膜的接触刚度模型。结果表明:结合面的法向接触刚度随法向载荷的增加而增加,且混合润滑状态下结合面的接触刚度大于干摩擦条件下结合面的接触刚度;该模型避免了油膜厚度测量难的问题,为机械结构的润滑状态预测提供了帮助。     

移动式架车机伸缩托头-托架接触的有限元分析

采用基于接触对的非线性接触分析处理接触问题时,其分析结果更接近工程应用实际,但计算成本比较高且存在不收敛的情况。而自由度节点耦合分析不但能降低计算成本,而且能够保证一定精度。为了探究在一定误差范围内选用自由度节点耦合分析来替代基于接触对的非线性接触分析的可行性,以举升重量为15 t的移动式架车机为研究对象,在ANSYS软件中建立伸缩托头-托架的接触模型与节点耦合模型,在举升高度最大且伸缩托头完全伸出的工况下进行有限元分析,考虑接触刚度系数与摩擦因数对有限元分析结果的影响,分析了2种模型各接触区域等效应力的区别。通过比较2种模型的有限元分析结果可知,2种模型各接触区域的等效应力值存在一定的相对误差,且接触区域内2个接触面的相对滑动程度决定了接触分析的精度。对于精度要求不高的机械结构,可以考虑用自由度节点耦合分析来替代基于接触对的非线性接触分析。     

悬臂梁防振包装系统功率流研究

将子结构导纳法和当量导纳技术相结合，采用连续隔振器模型，对通过连续隔振器流入悬臂梁式结构的包装体的功率流进行研究，从功率流的角度提出避免共振破坏，提高防振包装效果的条件和参数选择方法。     

Waiting for another catastrophe

On April 26, 1986 the worst accident in history of the nuclear power industry happened at Chernobyl Nuclear Power Plant (ChNPP) when one of the four reactors exploded causing significant damage to ChNPP buildings and releasing into the atmosphere large amounts of radioactive materials. Immediately after the accident, a temporary shelter was constructed to confine the damaged unit. The Shelter was built hastily, under extreme conditions of radiation, using original structures damaged by the explosion to support new structures. Following the accident, several structural evaluations of the Shelter were carried out and steps taken to strengthen some unstable structures. In 1996, based on available structural data, the European team of experts concluded that the Shelter was in critical condition. An estimated remaining service life of the Shelter in 1996 was 10–13 years under ordinary and none under extreme loads. Collapse of the Shelter could lead to a release of radioactive dust and increase the criticality hazard. To prevent this from happening the Team of experts developed a plan, according to which the Shelter would be stabilized during 1997–2001. In spite of the perceived urgency, no stabilization works have been carried out to date. Recent analysis of results of previous studies and stabilization efforts shows that the existing Shelter may be in danger of collapse. The only remaining safe solution is an expedient construction of a new confinement around the Shelter.     

Dynamic scheduling system utilizing machine learning as a knowledge acquisition tool

Dynamic selection of scheduling rules during real operations has been recognized as a promising approach to the scheduling of the production line. For this strategy to work effectively, sufficient knowledge is required to enable prediction of which rule is the best to use under the current line status. In this paper, a new learning algorithm for acquiring such knowledge is proposed. In this algorithm, a binary decision tree is automatically generated using empirical data obtained by iterative production line simulations, and it decides in real time which rule to be used at decision points during the actual production operations. The configuration of the developed dynamic scheduling system and the learning algorithm are described in detail. Simulation results on its application to the dispatching problem are discussed with regard to its scheduling performance and learning capability.     

Modelling and forecasting contact time as a measure of item informativeness

The value or informativeness of an item in a library collection or database has been measured by its frequency of circulation or access. This paper presents a more discriminating measure, user contact time, and develops a model for its distribution over users and over time. The model is applied to the problem of predicting future informativeness of an item.     

Modelling of internal architecture of kinesin nanomotor as a machine language

Kinesin is a protein-based natural nanomotor that transports molecular cargoes within cells by walking along microtubules. Kinesin nanomotor is considered as a bio-nanoagent which is able to sense the cell through its sensors (i.e. its heads and tail), make the decision internally and perform actions on the cell through its actuator (i.e. its motor domain). The study maps the agent-based architectural model of internal decision-making process of kinesin nanomotor to a machine language using an automata algorithm. The applied automata algorithm receives the internal agent-based architectural model of kinesin nanomotor as a deterministic finite automaton (DFA) model and generates a regular machine language. The generated regular machine language was acceptable by the architectural DFA model of the nanomotor and also in good agreement with its natural behaviour. The internal agent-based architectural model of kinesin nanomotor indicates the degree of autonomy and intelligence of the nanomotor interactions with its cell. Thus, our developed regular machine language can model the degree of autonomy and intelligence of kinesin nanomotor interactions with its cell as a language. Modelling of internal architectures of autonomous and intelligent bio-nanosystems as machine languages can lay the foundation towards the concept of bio-nanoswarms and next phases of the bio-nanorobotic systems development.     

Elasticity Solution of a Cantilever Functionally Graded Beam

This paper considers the plane stress problem of a cantilever functionally graded beam subjected to linearly distributed load. The material properties of the functionally graded beam are assumed to vary continuously through the thickness, according to a power-law distribution of the volume fraction of the constituents. First, the partial differential equation, which is satisfied by the stress functions for the axisymmetric deformation problem is derived. Then, stress functions are obtained by proper manipulation. A numerical example is finally presented to show the effect of material inhomogeneity on the elastic field in a functionally graded cantilever beam.     

巨磁致伸缩薄膜-衬底悬臂梁系统的力学特性

利用四参量能量极小化方法求解了任意薄膜／衬底厚度比悬臂梁系统的弯曲问题．在此基础上重点分析了磁膜应力和应变与构成悬臂梁的两种材料的几何参数和物理参数的关系,给出了这些参数对磁膜-衬底悬臂梁系统中平面弯曲特性的影响．计算结果表明,中平面在一般情况下是各向异性的,且随着磁膜厚度的增加中平面迅速下降;磁膜应力随着膜厚增加而减小,应变随膜厚增加而增加;材料泊松比对垂直于磁化方向的应力和应变以及中平面的影响很大,但是,泊松比对磁化方向的应力、应变和中平面的影响很小,可以忽略不计．     

Changes in contact angles as a function of time on some pre-oxidized biomaterials

Interfaces between biomaterials, tissue and body fluids such as blood play a key role in determining the nature of the interaction between biomaterials and the living organism. The wettability of these biomaterials in relationship to their microenvironment is an important factor to consider when characterizing surface behaviour. The measure of the contact angle between a fluid and material surface can be used to define wettability for that particular microenvironment.In this study, pure Ti, Ti6AI4V alloy, austenitic and martensitic Ni-Ti alloys, pure Ni, AISI Type 316L stainless steel, Co-Cr alloy, and -alumina were investigated. All metallic materials were mechanically polished and oxidized at 300 °C for 30 min in pure oxygen. Oxide films formed on the surfaces of these materials were examined under the electron microscope and their crystalline structures were identified by the electron diffraction method. The initial contact angle (_o) and its changes (/t) as a function of time in 1% NaCl solution drop were measured.The results of this study indicated that (i) Ti and its alloys were covered with mainly TiO₂ (tetragonal structure), (ii) NiO (cubic structure) was found on pure Ni, (iii) the spinel type oxide (cubic structure) was formed on both 316L stainless steel and Co-Cr alloy, (iv) TiO₂ (except for oxides formed on Ti6AI4V alloy) showed a rapid spreading characteristic in 1% NaCl solution; while (v) a relatively slow spreading behaviour was observed on the cubic structure oxides.     

Fretting fatigue limit as a short crack problem at the edge of contact

This paper proposes a local stress concept to evaluate the fretting fatigue limit for contact edge cracks. A unique S–N curve based on the local stress could be obtained for a contact edge crack irrespective of mechanical factors such as contact pressure, relative slip, contact length, specimen size and loading type. The analytical background for the local stress concept was studied using FEM analysis. It was shown that the local stress uniquely determined the ΔK change due to crack growth as well as the stress distribution near the contact edge. The condition that determined the fretting fatigue limit was predicted by combining the ΔK change due to crack growth and the ΔK_th for a short crack. The formation of a non‐propagating crack at the fatigue limit was predicted by the model and it was experimentally confirmed by a long‐life fretting fatigue test.     

Explosive treatment as a means of redistribution of residual stresses in machine parts

The level and character of residual stress redistribution in cylindrical and flat specimens subjected to shock wave treatment were experimentally investigated. The stresses were measured using methods of destructive and nondestructive testing. It was shown that explosive treatment is an effective means of residual stress redistribution in machine parts regardless of their design features.Translated from Problemy Prochnosti, No. 11, pp. 50–54, November, 1994.     

Towards a catastrophe theory for the mechanics of plasticity and fracture

The catastrophe theory has established that the conservative systems have only a few ways to lose their stability. We sketch a similar classification for a class of dissipative systems. Although our scope is limited to the case of two dissipative variables, we find six elementary catastrophes. We present examples from discrete plasticity, crack and friction mechanics.     

Evaluation of the Critical Following Force for a Cantilever Rod

The authors use the methods of initial parameters in the matrix form to study the stability of rods under the action of the following forces. They consider rods with various fastening of the ends. The obtained theoretical results have been verified by an experiment. It is shown that the difference between the theoretical and experimental values of the critical following forces does not exceed 5%.