Probabilistic analysis of linear elastic cracked structures with uncertain damage

This paper presents a simple and reliable method for the probabilistic characterization of the linear elastic response of cracked structures with uncertain damage. In particular, truss and frame structures with edge cracks of uncertain depth and location are considered. The method of analysis originates from an approach recently appeared in the literature, which is generalized to treat structures with cracks affected by uncertainty. According to this approach, the uncertainties are transformed into superimposed deformations depending on the distribution of internal forces and an iterative procedure is established to solve the resultant equations. The procedure is optimally tuned based on the convergence analysis. Several numerical tests evidence excellent accuracy and convergence qualities also in the case of multicracked structures with large fluctuation of damage.     

隔膜泵隔膜破裂自动报警系统的设计与实现

为往复式隔膜泵开发了一套分布式隔膜破裂自动报警系统,该系统用下位机检测隔膜腔隔膜是否破裂,用上位机显示隔膜泵运行时隔膜工作状态的平面图、隔膜破裂的具体位置,并具有各种管理功能。系统运行可靠,造价低,功能强,提高了生产效率。     

废塑料油化技术及其裂解催化剂的研究进展

分析了国内外废塑料油化技术及其裂解催化剂的研究进展,并指出未来废塑料油化技术的发展方向。     

Vibration analysis of non-uniform beams having multiple edge cracks along the beam's height

Bending vibration of non-uniform rectangular beams with multiple edge cracks along the beam's height is investigated. These cracks are called height-edge cracks in this paper. The energy based method is used for defining the vibration of height-edge cracked beams. The opening form of the height-edge crack is determined when the external moment is assumed to be applied for stretching the beam's width. Strain energy increase is obtained by calculating the strain change at the stretched surface by taking into account the effect of angular displacement of the beam due to the bending. The Rayleigh-Ritz approximation method is used in the analysis. The cases of multiple cracks are analysed in the method by using the approach based on the definition of strain disturbance variation along the beam. Examples are presented on a fixed-fixed beam and several cantilever beams having different taper factors. When the results are compared with the results of a commercial finite element program, good agreement is obtained. The effects of taper factors, boundaries and positions of cracks on the natural frequency ratios are presented in graphics.     

Repair of a cracked Timoshenko beam subjected to a moving mass using piezoelectric patches

This paper presents an analytical method for the application of piezoelectric patches for the repair of cracked beams subjected to a moving mass. The beam equations of motion are obtained based on the Timoshenko beam theory by including the dynamic effect of a moving mass traveling along a vibrating path. The criterion used for the repair is altering the first natural frequency of the cracked beam towards that of the healthy beam using a piezoelectric patch. Conceptually, an external voltage is applied to actuate a piezoelectric patch bonded on the beam. This affects the closure of the crack so that the singularity induced by the crack tip will be decreased. The equations of motion are discretized by using the assumed modes method. The cracked beam is modeled as number of segments connected by two massless springs at the crack locations (one, extensional and the other, rotational). The relationships between any two spans can be obtained by considering the compatibility requirements on the crack section and on the ends of the piezoelectric patch. Using the analytical transfer matrix method, eigensolutions of the system can be calculated explicitly. Finally, numerical simulations are performed with respect to different conditions such as the moving load velocity. It is seen that when the piezoelectric patch is used, the maximum deflection of the cracked beam approaches maximum deflection of the healthy beam.     

松动-裂纹耦合故障转子系统的非线性响应

基于现代非线性动力学和转子动力学理论,采用Newmark-β法和Poincaré映射对裂纹和一端支座松动耦合故障转子系统进行了数值模拟研究,给出了系统响应随转速比、松动质量和裂纹深度变化的分岔图,分析了一些主要参数变化的影响以及典型的Poincaré截面图。研究发现,系统存在拟周期环面破裂、阵发性分岔和多倍T周期运动失稳进入混沌三条混沌道路。这些结论为旋转机械的故障诊断提供了理论基础和参考。     

Circumferentially notched pipe with an external surface crack under complex loading

The influence of a circular-arc circumferential notch in a pipe is analyzed. Firstly, the stress concentration factor (SCF) is determined. Then, an elliptical-arc external surface crack is assumed to exist at the notch root, and the stress-intensity factor (SIF) along the surface crack front is computed for four values of the dimensionless notch radius and for several opening stress distributions on the crack faces. The effect of stress concentration on the SIF values is discussed for both thick- and thin-walled pipes.     

基于幅值与相角小波映射的裂纹转子故障诊断

建立了基于简单铰链裂纹模型和局部柔度理论的裂纹转子动力学模型,得到了裂纹转子与无裂纹转子的数值仿真解及其傅里叶变换的相角;利用连续小波变换研究了裂纹转子与无裂纹转子的幅值与相角小波映射特性,提出了利用幅值与相角小波映射识别裂纹的新方法。数值仿真研究了尺度因子对幅值与相角小波映射准确性和有效性的影响,给出了建议的尺度因子。试验研究验证了该方法在工程实际中的有效性和实用性。     

Forced responses of cracked cantilever beams subjected to a concentrated moving load

An analytical method is developed to present the dynamic response of a cracked cantilever beam subject to a concentrated moving load. The cracked beam system is modeled as a two-span beam and each span of the continuous beam is assumed to obey Euler–Bernoulli beam theory. The crack is modeled as a rotational spring with sectional flexibility. Considering the compatibility requirements on the crack, the relationships between these two spans can be obtained. By using the analytical transfer matrix method, eigensolutions of this cracked system are obtained explicitly. The forced responses can be obtained by the modal expansion theory using the determined eigenfunctions. Some numerical results are shown to present the crack effects (crack extent, location of the crack) and are studied for different speeds of the moving load.     

Measurement of mode I and mode II rock dynamic fracture toughness with cracked straight through flattened Brazilian disc impacted by split Hopkinson pressure bar

In order to find an effective and convincing method to measure rock dynamic fracture toughness for mode I and mode II, cracked straight through flattened Brazilian disc specimens of marble, which were geometrically similar for three size, were diametrically impacted by split Hopkinson pressure bar on the flat end of the specimen with three load angle respectively. History of stress intensity factors (K_I(t) for opening mode I, and K_II(t) for sliding mode II), mode mixture ratio (K_I(t)/K_II(t)), as well as mode I and mode II dynamic fracture toughness at crack initiation (K_Id and K_IId) were determined with the experimental–numerical method. It is found that there is a unique size effect for dynamic fracture test with the specimens, the mode mixture ratio is not solely determined by load angle (the angle between load direction and crack line) as in the static loading; the pure mode II load angle is 19° for the ?50 mm specimen, however it is 10° for the ?130 mm and ?200 mm specimens; the mode II load angle decreases with increment of specimen size. Realization of pure mode II is justified by the mode mixture ratio approaching zero, it can be realized under certain load angle and loading rate for the specimen of specified size. K_IId is generally greater than K_Id. Both K_Id and K_IId increase with increment of specimen size, and this trend for K_IId is more remarkable than that for K_Id.