Effect of plastic deformations on the growth of a periodic system of cracks in stringer panels

Development of a crack in an isotropic panel reinforced with supporting strengthening ribs is studied taking into account plastic deformations. An infinitely thin panel made of an elastic and ideally plastic material with a periodic system of linear cracks is considered. The problem of initial development of plastic deformations at the tips of cracks is solved by reducing it to the linear conjunction boundary problem. Using a criterion for critical opening of a crack, the dependence of the residual strength of a panel is determined. Relations enabling studies of the crack growth at the precritical development stage are derived.     

Frictional heating of a half-space with cracks. I. Single or periodic system of subsurface cracks

The paper deals with the two-dimensional problem of frictional heating for an elastic half-space containing one or a system of periodic subsurface cracks. The generation of frictional heating in the region of contact is estimated by the use of sliding speed, frictional coefficient and contact pressure. The problem is reduced to a pair of singular integral equations which are solved numerically. The influence of the location of cracks on the stress intensity factor is investigated.     

Limit pressure of a cylindrical shell with a two-dimensional array of nozzles with associated axial cracks

The limit pressure of a cylindrical shell with a two-dimensional array of penetrating nozzles and associated defects covering the whole shell has been calculated and compared with the limit pressure of the plain cylindrical shell. A lower-bound method was used. The conventional ligament efficiency method of calculating the limit pressure is too conservative. It is necessary to claim some strength from the nozzles. Hence a more elaborate method has been used here. If there are axial cracks in the main vessel tangential to some nozzles, the limit pressure is reduced to a value which is between the ligament efficiency and the value for a single crack in a plain cylinder. The actual reduction has been calculated for a range of crack lengths for a typical geometry.     

Constrained zones in a periodic array of collinear equal cracks

Thin plates made of Perspex and containing an array of collinear equal cracks were subjected to a combined mode of loading consisting of biaxial tension and shear at infinity. The thickness variation of the plates was depicted by the reflected shadow method developed by the author. According to this method a coherent monochromatic light beam was diffracted along the thickness when the plate was traversed and partly reflected on the rear face. The reflected part, which was again refracted through the thickness and afterwards emerged from the plate, was retarded according to Neumann's law. The retarded light rays created deviating wave-fronts which followed the Eikonal equation of geometric optics. If these rays were received on a ground-glass screen, they created a bright envelope, a caustic, which was related to the constrained zones surrounding the crack tips of the plate. In this paper the case of an array of collinear equal internal cracks was studied and especially the influence of neighbouring cracks on the shape and size of the caustic of each crack. The dimensions of the envelope are directly related to the stress-intensity factor corresponding to each crack tip which can be derived from the dimensions of the caustic. Experimental evidence with cracked Perspex plates corroborated the theory.     

Elastoplastic fracture of a perforated stringer plate

The development of a crack in an isotropic perforated stringer plate, weakened by a periodic system of straight-linear cracks originating from the contours of holes, is considered. The plate material is considered elastoplastic. The relation to the residual plate strength is found using the deformation fracture criterion.     

Ultimate state of a plate with a regular system of stringers and cracks issuing from a circular hole

A fracture mechanics problem on crack development in a stiffened plate with a round hole is considered. A crack model with domains in which crack borders interact is used. This interaction in the end domain is simulated by introducing bonds (cohesive forces) between the crack borders. A boundary problem on the equilibrium of cracks issuing from the surface around the circular hole and exposed to external tensile loads is reduced to a nonlinear singular integral equation. From solving this equation, stresses in bonds are found. The condition of crack development is formulated taking into account a criterion of ultimate opening of interparticle bonds of material.     

Mode I interaction of a periodic array of parallel cracks in a functionally graded nonhomogeneous plane

The mode I interaction of a periodic array of parallel cracks which are uniformly spaced apart in a functionally graded material is investigated. The two-dimensional theory of nonhomogeneous elasticity is employed as the basic framework for this study. The material nonhomogeneity is represented in terms of the spatial variation of the shear modulus in the exponential form along the direction of cracks, while Poisson’s ratio is assumed to be constant. Formulation of the proposed mixed boundary value problem is reduced to solving a hypersingular integral equation with the crack surface displacement as a new unknown function. As a result, the variations of stress intensity factors are illustrated as a function of possible range of periodic crack spacing in conjunction with the different values of the material nonhomogeneity parameter. Furthermore, crack opening displaccements are presented for various geometric and material combinations.     

Vibration analysis of multi-supported curved panel using the periodic structure approach

This papers deals with the radial vibration of a row of cylindrical panels of finite length using the concept of wave propagation in periodic structures. For this study, the structure is considered as an assemblage of a number of identical cylindrically curved panels each of which will be referred to as a periodic element. For a given geometry dispersion curves of the propagation constant versus (non-dimensional) natural frequency have been drawn corresponding to the circumferential wave propagation. New conclusions that have emerged from this study are as follows. It is shown that by a proper choice of the periodic element the bounding frequencies and the corresponding modes in all the propagation bands can be determined. These have been shown to correspond to a single curved panel with all its edges simply supported. It is noted that there are no attenuation gaps in the entire frequency spectrum beyond the lowest bounding frequency. This is a unique feature of circumferential wave propagation around circular cylindrical shells and panels, as opposed to the wave propagation of periodically supported beams and rectangular panels without curvature. The natural frequency corresponding to every circumferential mode of the complete shell has been identified on the propagation constant curve. It has been observed that the natural frequencies of a cylindrically curved panel of a given curvature and length but of different circumferential arc length (corresponding to different angles subtended at the centre of any circular cross-section) may also be identified on the same propagation constant curve. Finally, it is shown that the same propagation constant curve may also be used to determine all the natural frequencies of a finite row of curved panels with the extreme edges simply supported. Wherever possible the numerical results have been compared with those obtained independently from finite element analysis and/or results available in the literature. Flutter analysis of multi-span curved panels using a wave approach is the ultimate objective of this work.     

基于现场总线的发电机状态监测仪

随着水轮发电机组单机容量的增大，其安全、经济运行显得尤为重要，而常规的监测系统不能满足现代化水电厂实行状态检测、预知维护的需要。本文在介绍了CAN总线特点以后，主要讨论了一种基于现场总线的发电机状态监测仪的设计方案，给出了系统结构框图和关键硬件的设计。最后简要介绍了系统软件设计。     

带裂纹压力管道安全评定的应力强度因子曲线

根据压力管道安全评定的工程需要,给出了管道周期环向裂纹应力强度因子通用曲线.通过管道裂纹角和周期裂纹数,就可在曲线上查得正则化应力强度因子.类似的曲线可以根据管道的特点给出多条,便于工程应用.     

Interaction of a periodic system of foreign elastic inclusions whose surface is uniformly covered with a homogeneous cylindrical film and two systems of straight line cracks with end zones

Elastic media (a plane) weakened with a periodic system of round holes filled with plugs made of homogenous elastic material with the surface was covered by a homogenous cylindrical film. The plane is weakened by two periodic systems of straight line cracks with connections between edges at the tip regions. General concepts describing a type of problem with a periodic distribution of stresses outside round holes and cracks for lateral shear are proposed. The solution to the problem is reduced to solution of two nonlinear singular integral equations. The solution of these two equations define forces in relation to the tip regions. The condition for the propagation of a crack is formed considering criteria for the limiting shear of bonds inside the material.     

一种触摸屏监控的分布式控制系统的实现

介绍了一种触摸屏监控的PLC网络系统,阐述了系统的组成及原理。     

Performance evaluation of a water-to-water heat pump with a floor panel heating system

The performance of heat pump is severely degraded as the temperature of the heat source is decreased. For air source heat pumps, this results in a serious mismatch of heat pump output and space heating demand. Although the outdoor temperature is below 0°C, the use of a water-to-water heat pump with a floor panel heating system can operate for extended periods of time without frost-defrost cycling and therefore at a high seasonal efficiency. This paper focuses on the performance of a water-to-water heat pump that uses well water as a heat source and a floor panel heating system as a sink.     

On reconstruction of cracks with interacting edges

A method for the reconstruction of the configuration of cracks is suggested based on finding heat sources that model the interaction between cracks edges (such as friction and collapse) in solids exposed to external ultrasound. The input information for reconstruction is a stationary temperature field on a solid boundary. The functional of nonreciprocity was constructed; the study of this functional made it possible to convert the problem of determining a cracks parameters into a few transcendental equations; explicit formulas were obtained for small cracks. The results of computational experiments on reconstruction of the parameters of a straight crack are considered.Translated from Defektoskopiya, Vol. 40, No. 10, 2004, pp. 62–69.Original Russian Text Copyright © 2004 by Vatulyan, Solovev.     

Free vibrations of thin periodic plates interacting with an elastic periodic foundation

A dynamic behaviour of thin periodic plates interacting with an elastic periodic foundation is analysed. The main aim is to investigate free vibrations and calculate frequencies for these plates. The presented modelling approach to the linear-elastic plates, having periodic structure in planes parallel to the midplane, is adopted from the tolerance averaging method developed by Woźniak and Wierzbicki (Averaging techniques in thermomechanics of Composite Solids, Wydawnictwo Politechniki Cz stochowskiej, Cz stochowa, 2000) for periodic composites. The obtained plate model describes the effect of the periodicity cell size on the overall plate behaviour. In this paper this effect is analysed in the free vibrations problem. Two special cases are taken into account: a square plate with a periodic thickness interacting with a homogeneous foundation and a square plate with a constant thickness interacting with a periodic foundation. A certain justification of the model is also presented.     

某故障轴承钢球裂纹分析

对故障轴承钢球开裂后的断口进行宏观和微观观察,并对裂纹断口纵剖面以及沿直径方向的剖面进行了金相检查和微观组织分析。通过对比同类产品,综合分析了钢球开裂的性质和发生开裂的原因。     

Reliability analysis of a compression section of a gas pipeline with the presence of longitudinal cracks

An algorithm is developed to find the expectation of the length of a longitudinal crack for a defective pipe at which the normative safe reliability level for a gas pipeline is maintained. The solution is obtained for the condition that crack resistance of pipe steel, compression force, gas pressure, coefficient of linear expansion, modulus of elongation, temperature difference of pipe walls, pipe diameter, and thickness are normally distributed.     

Nonlinear finite element analysis of a laminated cylindrical shell with transverse matrix cracks

A clamped laminated cylindrical shell is presented to investigate nonlinear structural behavior involving geometrically nonlinear deformation. In the investigation, transverse matrix cracks are considered in the stiffness of the laminated cylindrical shell. Stiffness degradation is examined for several laminated angles and transverse crack density. Micro-mechanics theory on the composite material was used to derive the degraded stiffness of the laminated cylindrical shell due to the crack density. Iterative numerical scheme was developed to calculate the degraded composite stiffness which is a complicated relation with the crack density. A nonlinear finite element program was developed using 3-D degenerated shell element and the fist order shear deformation theory to consider the large deformation of the clamped laminated cylindrical shell. The updated Lagrangian method is used for nonlinear finite element analysis. Nonlinear structural responses of the laminated cylindrical shell were examined for various stacking sequences and crack density under transversely loaded pressure. Also, the effect of crack opening/closed was considered in the examination. Through this study, it is realized that the transverse matrix crack causes moderate stiffness reduction and affects the responses of the composite shell.     

直齿行星排止推垫圈润滑状态的仿真分析

在车辆的传动装置中,直齿行星排的行星齿轮止推垫圈磨损现象严重.基于润滑理论建立了直齿行星排行星齿轮止推垫圈的油膜润滑方程,并考虑了表面粗糙度与端面倾角对润滑状态的影响.给出了油膜压力分布、承载力的计算模型,并结合实际情况运用有限差分法与数值迭代法进行了仿真分析.通过分析具体工况条件下直齿行星齿轮轴向推力与止推垫圈承载力的平衡关系,确定出止推垫圈的润滑状态.为进一步研究直齿行星排止推垫圈的摩擦磨损提供了分析方法.     

金属构件裂纹的修补参数研究

金属结构的裂纹可以用加补强板的方法修补，但有限元程序计算表明：选择补强板的参数应按照最大限度降低裂纹尖端应力的原则。笔者用实例说明修补裂纹只能延缓裂纹的扩展速度而不能根除裂纹的存在。