Thermoelastic contact of a retaining ring with a cylinder under the conditions of frictional heat generation

We give the mathematical statement and construct the solution of the static thermoelastic problem of contact interaction of an elastic retaining ring with a circular hollow cylinder inserted in it. The bodies are compressed by a load varying along the axis of the system under the conditions of load-free contact on the surface of the ring or along an arc of the circle. In the case where radial displacements of the contact surface of the retaining ring are approximated by displacements of the surface of a long circular hollow cylinder and the process of stationary frictional heat generation is taken into account, we reduce the posed problem to systems of integral equations whose structure is determined by the type of conditions of thermal contact. We propose a numerical algorithm for the solution of these systems and study the influence of the input parameters of the problem on the distributions of contact pressure and temperature. On the basis of these results, we make a conclusion that the influence of the character of variation of the compressive load along the axis on the distribution of contact pressure is significant in the case where the kinematic conditions of interaction of the bodies are described by the Hertz theory. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36. No. 3. pp. 42–52, May-June, 2000.     

Plane problem for a piecewise-homogeneous anisotropic body with elastic inclusion in the form of a strip

A plane problem of the theory of elasticity for a piecewise-homogeneous anisotropic plane with elastic inclusions in the form of strips is solved by the method of jump functions. Inclusions are simulated by the jumps of the vector of stresses and the derivative of the vector of displacements on the median surfaces. By using complex potentials, we obtain the dependences of the components of the stress tensor and the vector of displacements on the load and unknown jump functions. In view of the conditions of interaction of a thin inclusion with an anisotropic medium, the problem is reduced to a system of singular integral equations for the jump functions. In the general case, this system is solved by the collocation method. For the cases of a slot and a perfectly rigid inclusion, we deduce the dependences of the generalized stress intensity factors on the concentrated forces and edge dislocations. Franko L'viv University, L'viv; Pidstryhach Institute of Applied Problems of Mechanics and Mathematics. Ukranian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 6, pp. 7–16. November–December, 1999.     

Graphite-fibre/carbide-matrix composites—II: Structure and electrical properties

The measurement of electrical properties of ceramic-matrix composites supplies data which can be used directly with information about the structure of the composites. The structures of graphite-fibre/carbide-matrix composites may be varied within large intervals of appropriate parameters, as shown in a previous publication. A corresponding variety of behaviour patterns of such materials in the electrical field had been expected and was actually observed. The matrices of the composites were boron, niobium, and tantalum carbides, and the fibres were Kulon and VMN-4. The electrical conductivity of graphite-fibre/carbide-matrix composites has been determined, including that at cryogenic temperatures. A preliminary series of experiments gives the characteristics of piezo-resistance of the C/NbC composites. The experimental data yield a set of characteristics of the fibre, matrix, and composite structure. The conductivity characteristics of the graphite fibres and carbide matrices obtained in this way correspond to the expected ones. That also includes a type of conductivity behaviour revealed by the temperature dependence of the conductivity. Graphite fibre behaviour is of the metallic type, while boron carbide is a semiconductor-type material. The conductivity of pure matrices differs essentially from that of the matrices obtained as an extrapolation of the conductivity versus fibre volume fraction dependence to zero fibre content. Active diffusion of carbon from the fibre/matrix interface makes the stoichiometry of a carbide better and its conductivity higher. But a distinctive dependence of the piezo-resistance of the C/NbC composites on the fibre volume fraction may lead to an assumption about the possibility of the existence of another mode of influence of the carbon fibres on the conductive properties of carbides. Calculation of the ineffective length of a fibre (from the viewpoint of conductivity) yields an estimate of the conductivity of the interface. It is clearly connected to the structure of the interface.     

Relaxation methods for the investigation of the influence of surfactants on the rate of corrosion

We develop a theory of the application of low-level relaxation methods (basic and pulse potentiostatic methods, basic and pulse galvanostatic methods, and the method of electrode impedance) to the investigation of the influence of surfactants on the rate of corrosion. To evaluate the possibilities of this theory. we consider an example of a corrosion model characterized by the adsorption of surfactants which affects the rates of both cathodic and anodic processes. The cathodic process includes the adsorption of hydrogen atoms and the anodic process includes the adsorption of subions of the metal. We deduce equations for the calculation of the electrode parameters of the model on the basis of the experimental data and show that the complexity of the proposed model is maximum for all relaxation methods, except the method of electrode impedance. Dneprodzerzhinsk State Technical University, Dneprodzerzhinsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 4, pp. 75–80, July–August, 1996.     

Probabilistic models and statistical methods for the analysis of vibrational signals in the problems of diagnostics of machines and structures

We consider probabilistic models of vibrations of machines in the form of periodically correlated random processes and almost periodically correlated random processes. The problem of selection of diagnostic symptoms from the entire set of the experimental data is formulated on the basis of the developed methods for the analysis of the probabilistic characteristics of periodically correlated random processes and almost periodically correlatted random processes. Within the framework of the spectral correlation theory of the indicated classes of nonstationary random processes, we check the validity of the general approaches to the investigation of stochastically amplitude- and phase-modulated signals. We propose new methods for the assessment of the probabilistic characteristics of periodically correlated random processes and their generalizations. The problem of finding hidden periodicities in vibrational signals is solved in a new statement. On the basis of the developed methods, we designed a computerized information-measuring system for the vibrodiagnostics of machines and structures. The possibility of inspection of the technical state of a bearing unit of an electric motor is illustrated on the basis of the analysis of its vibrations. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 5, pp. 61–74, September-October, 1997.     

Special Features in the Realization of Film Boiling on Wire Heaters. Distilled Water

The existence of a region of self-oscillatory instability of heat transfer is revealed under conditions of film boiling of water subcooled to the saturation temperature. In the case of short heaters, whose length is commensurable with the Taylor instability wavelength, the process is regular. For heaters of the same length, the form of oscillations and their characteristics are fully reproducible. An increase in the heater length results in the emergence of spatially distributed oscillations. It is found that an increase in subcooling on the interface between the modes of boiling is accompanied by the formation of a structure consisting of a system of single domains of continuously decreasing size. The formation of this structure causes a significant change in the temperature distribution in the zone adjoining that of nucleate boiling, which considerably reduces the film stability. A single domain of the film mode of boiling was stable at any temperature of the liquid. The singularities of realization of minimal-size domains of the film mode of boiling under conditions of stabilization of the integral mean temperature of the heater are investigated. It is found that the minimal zone of the film mode of boiling is a system of three elementary domains.     

The initial section of a plane nonisothermal jet developing under asymmetric conditions with and without combustion

A solution of the problem obtained with the method of integral relations is given here. It is obtained in the form of simple algebraic formulas for the boundaries of the mixing zones on both sides of the jet, the position of the flame front, and the axis of the jet at the end of the initial section. It is found that asymmetry of the boundary conditions has a substantial effect on the characteristics of the jet: the position of the axis of the jet at the end of the initial section can change its sign, depending on the temperature ratio at the boundaries of the jet and for given ratios of the velocity at the boundaries of the jet to the velocity of the jet outflow, the length of the initial section can change several fold.Moscow State Aviation Institute, Moscow, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 372–379, May–June, 1995.     

OPTIMAL DESIGN FOR NON-STEADY-STATE METAL FORMING PROCESSES—II. APPLICATION OF SHAPE OPTIMIZATION IN FORGING

This paper is the second part of a two-part article about shape optimization of metal forming processes. This part is focused on numerical applications of the optimization method which has been described in the first paper. The main feature of this work is the analytical calculations of the derivatives of the objective function for a non-linear, non-steady-state problem with large deformations. The calculations are based on the differentiation of the discrete objective function and on the differentiation of the discrete equations of the forging problem. Our aim here is to show the feasibility and the efficiency of such a method with numerical examples. We recall the formulation and the resolution of the direct problem of hot axisymmetrical forging. Then, a first type of shape optimization problem is considered: the optimization of the shape of the initial part for a one-step forging operation. Two academic problems allow for checking the accuracy of the analytical derivatives, and for studying the convergence rate of the optimization procedure. Both constrained and unconstrained problems are considered. Afterwards, a second type of inverse problem of design is considered: the shape optimization of the preforming tool, for a two-step forging process. A satisfactory shape is obtained after few iterations of the optimization procedure.     

On the effective constitutive properties of a thin adhesive layer loaded in peel

An experimental method to determine the complete stress-elongation relation for a structural adhesive loaded in peel is presented. Experiments are performed on the double cantilever beam specimen, which facilitates a more stable experimental set-up as compared with conventional methods like the butt-joint test. The method is based on the concept of equilibrium of the energetic forces acting on the specimen. Two sources of energetic forces are identified: the start of the adhesive layer and the positions of the two acting loads. By use of the concept of equilibrium of energetic forces, it is possible to measure the energy release rate of the adhesive layer instantaneously during an experiment. The complete stress-elongation relation is found to be the derivative of the energy release rate with respect to the elongation of the adhesive layer at its start. By this procedure, an effective property of the adhesive layer is measured. That is, the fields are assumed to be constant through the thickness of the layer and only vary along the layer. To investigate the validity of this approach, experiments are performed on five different groups of specimens with different dimensions. This leads to large variations in the length of the damage zone at the start of the adhesive layer. Four of the experimental groups are used to determine the stress-elongation relation. This is found to be independent of the geometry. For the remaining experimental group, the adherends deform plastically and simulations are performed with the stress-elongation relation determined from the four elastic groups. It is found that the relation cannot be used to accurately predict the behaviour of the experiments where the adherends deform plastically. This indicates that the stress-elongation relation has limited applicability.     

Calculation of the number of cracks and their dimensional distribution in pulsed ductile fracture of a ring

The basic parameters of the shear fracture process of cylindrical shells under intense pulsed (particularly explosive) loads were evaluated on the basis of the proposal of a critical intensity of deformations based on the amount of the work of plastic deformation. The position of the front of fracture, the radius of fracture, the number of cracks in the ring and the number of divisions on the axis of the cylinder, and the size distribution of the number of cracks with and without taking into consideration their mutual intersection and also of the number of fragments of the cylindrical shell by weight were determined. As a first approximation the yield strength, the reduction in area, and the impact strength were used as the parameters characterizing the shell material. A comparison is given of the calculated data and the experimental for the number of through cracks in the ring and the weight distribution of the number of fragments of cylindrical shells.Translated from Problemy Prochnosti, No. 9, pp. 73–79, September, 1989.     

Case Study on Failure of Ball Bearing of an Aeroengine

Heavy damage was reported on the outer race and rolling elements of a ball bearing belonging to jet engine of a military aircraft. Flaking type of damage was noticed only at one particular location on the outer race of the bearing and on almost all the balls of the bearing. The inner race and the cage of the bearing were free from any damage. The chemistry, hardness, and microstructure of the bearing components met the specification requirements. In the actual engine assembly, the bearing was mounted on shaft of bevel gear. Careful examination of the inner diameter (ID) of the inner ring of the bearing revealed nonuniform contact marks. The contact marks were observed in the form of discoloration of the ID surface. The nonuniform contact was attributed to eccentricity caused by improper mounting of the bearing onto the shaft of the bevel gear. This resulted in preferential loading, causing flaking at one particular location on the raceway of the outer ring and damage to the balls of the bearing. Hence, it was concluded that the ball bearing had failed because of assembly error after the last repair of the engine.     

The inclusion of the effect of the evaporation coefficient on the rate of variation of droplet radius

The paper deals with the investigation of the effect of the evaporation (condensation) coefficient of droplet substance on the rate of unsteady variation of the radius of a spherical aerosol droplet in the cases of direct and indirect inclusion of this coefficient. It is found in both cases that the effect of evaporation coefficient is most significant at the initial instant of unsteady-state process of evaporation and of condensation growth of the droplet. At this instant, the size of spherical droplet has hardly any impact on the rate of variation of its radius. As the unsteady-state process continues, the effect of the evaporation coefficient on the rate of variation of the droplet radius depends significantly on the droplet size. The larger the droplet under consideration, the lower the effect of the evaporation coefficient on the rate of variation of its radius. The rates of variation, calculated for the same values of the evaporation coefficient but for different ways of inclusion of this coefficient, differ less for larger aerosol droplets. These methods of inclusion of the evaporation coefficient are considered for the process of slow evaporation of a droplet.     

阻尼器对卫星太阳翼锁定冲击力矩影响的研究

本文在卫星太阳翼系统建模的基础上,利用多体动力学分析软件MSC.ADAMS对太阳翼展开过程进行了动力学仿真分析,通过展开过程中对帆板之间的冲击力矩变化进行考察,分析了阻尼器在不同位置的情况下,锁定过程中的锁定冲击力矩的变化,评估阻尼器的抑振效果,从而确定阻尼器安装的最佳位置。     

Conductive properties of foam materials with open or closed cells

The work is devoted to computer simulations of the effective conductive properties of open and closed-cell foam materials. The conductivity of the solid phase of the foam is assumed to be much larger than the one of the filler. For the calculation of the effective conductivity, a complex cell element of the foam that consists of a typical cell and its nearest neighbors is introduced. This element is embedded in the medium with the conductivity of the solid phase. For the calculation of the field and field flux in the complex cell, 3D-integral equations for the fields in heterogenous media are used. The effective conductivity is the coefficient that relates the average field and the field flux in the central part of the complex cell. The method is applied to the calculation of the effective conductivity of open cell foams with various shapes of ligaments. Transition from open to closed-cell foams is considered. Predictions of the method are compared with the experimental data available in the literature.     

Process of self-organization in metal

Conclusions 1. As a result of special features of the physical and chemical structure the dissipative structure in the solid forms only in a thin subsurface layer of the metal during friction and represents dynamic nonequilibrium interaction of the diffusion flow of climbing dislocation with counterflows of vacancies. This results in inhalation of the dislocations which formed during deformation of the layer (selective transfer).2. In addition to special conditions (selective dissolution), formation of the dissipative structure in the surface layer is supported by the proximity of the surface creating suitable conditions for saturating the layer with the vacancies and for formation of a dislocation sink. The fact that these conditions do not exist in the volume indicates that the dissipation systems are insufficient for organizing the dissipative structure in the volume of the solid.3. If the phase transition in dislocation movement is not completed by the evolution of the structures as in, for example, the system of boundary friction (close system), the development of dissipative subsystems nevertheless may continue (synergetics of the zero order) together with an increase of the degree of chaos.4. Structural adaptability in the closed system of the solid (synergetics of the zero order), generated from the outside or formed naturally during evolution of the structures, may be used to reduce the entropy rate.A. A. Blagonravov Engineering Institute, Russian Academy of Sciences, Moscow. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 2, pp. 19–27, March–April, 1993.     

除尘器壳体双肢组合截面立柱轴压稳定性研究

除尘器壳体围护结构中的立柱因需要支承顶部较宽截面的箱形梁以及承担较大的轴力而设计成双肢H型钢组合截面。利用非线性有限元方法,研究此双肢组合截面柱在考虑初始缺陷情况下承受轴向压力时的稳定性。研究表明,立柱轧制、墙板与立柱焊接产生的残余应力会小幅降低立柱稳定承载力。立柱的失稳形式为柱顶跨段内前翼缘与前腹板组成T形截面整体弯扭失稳与腹板局部失稳同时发生的相关失稳。墙板与两肢间连接墙板作为蒙皮板,为立柱承担部分荷载并约束其侧向变形。连接墙板越靠近前翼缘,立柱的稳定性越好。连接墙板宽度、墙板宽度、墙板角钢加劲肋刚度和节点连接板厚度等因素对立柱稳定性影响较小。仅邻近立柱的墙板和连接墙板增厚可对立柱稳定性有增强作用,远离立柱的墙板壁厚影响较小。立柱稳定系数与H型钢柱翼缘宽厚比的关系不是单调的;立柱绕弱轴弯曲长细比、腹板高厚比的增大会降低立柱稳定性。基于大量非线性有限元计算结果,提出了除尘器壳体中双肢组合截面轴心受压柱稳定承载力的计算建议。     

面向壁厚均匀的液压成形三通管的坯料设计方法与参数优化

目的 研究连续变厚度管液压成形过程中三通管的壁厚均匀性问题。方法 首先,利用有限元软件分析得到了等厚管液压成形三通管过程中的成形规律,根据其成形规律,反向设计了用于液压成形三通管的连续变厚度管坯;其次,采用正交试验方法,研究了连续变厚度管厚区壁厚、过渡区长度对液压成形三通管成形质量的影响;最后,采用多岛遗传算法,对连续变厚度管的结构参数进行了优化验证,提高了液压成形三通管的成形质量。结果 在等厚管液压成形三通管成形过程中,支管顶部壁厚值持续减小、轴向过渡圆角及直管底部中间位置处壁厚值持续增大;环向过渡圆角处等效应力最大,其他位置连续变化;轴向压应力使得三通管壁厚增大,拉应力使得壁厚减小;正交试验结果表明,当连续变厚度管厚区厚度、环向过渡区长度达到某一值时将出现较好的壁厚均匀性;在4种过渡区曲线线型中,直线型的壁厚均匀性最好;通过多目标优化得到最佳连续变厚度管结构参数,并通过有限元仿真进行验证,相对误差均在2 %以内,使用优化后的连续变厚度管液压成形三通管相对于等厚管,壁厚均匀值减小了0.423 mm。结论 可以采用厚度补偿或减薄的方式来提高成形三通管的壁厚均匀性;连续变厚度管坯相比于等厚管,显著提高了液压成形三通管的壁厚均匀性。     

某多用途货车传动系扭振试验分析与优化

某多用途货车加速行驶时,在发动机转速1200 r/min～1500 r/min范围内,传动系出现明显振动,影响整车NVH品质.针对此问题在传动系关键节点处加装传感器,对车辆6个前进挡在加速工况下进行扭振测试,由数据处理获得传动系各部位的角加速度振幅随发动机转速变化的关系.分析获得各部位振动的主要阶次,确定发动机2阶激励...