Progresses in Fracture and Strength of Materials and Structures

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Authors: Yue Gang Luo, Song He Zhang, Xiao Dong Liu, Bang Chun Wen
Abstract: A dynamic model was set up for the two-span rotor–bearing system with coupling faults of crack and rub-impact. Using the continuation-shooting algorithm for periodic solution of nonlinear non-autonomous system, the stability of the system periodic motion was studied by the Floquet theory. The unstable form of the rotor system with coupling faults is Hopf bifurcation when the depth of crack is smaller. The influence to the response of the system increased along with the depth of crack, the unstable form of the rotor system with coupling faults is period-doubling bifurcation. The conclusions provide theoretic basis reference for the failure diagnosis of the rotorbearing system.
Authors: Yu Jiong Gu, Xiao Bo Li, Cheng Bing He
Abstract: The accuracy of parameters in model has important influence on torsion vibration analysis of turbo-generator shafts. In this paper, a method for torsion vibration response calculation based on multistage lumped mass model is introduced. A method for identification and correction on stiffness and damping in torsion vibration monitoring is put forward. Pre-revision on shaft stiffness is realized through analytic calculation of the temperature distribution of turbine-generator shafts. The difference of natural frequencies and response of torsion vibration of shafts are calculated and analyzed after parameter correction, which offers the reference for studying torsion vibration fatigue of shafts.
Authors: Shui Lin Wang, Ying Hui Lu, Yu Yong Jiao, Chun Guang Li
Abstract: There are a large number of cracks, joints and layers with different scales and orientations in the rock masses. With the structural formation in it, the rock mass is unlike the isotropic and homogenous materials in physics and mechanics characteristics, and the failure of the rock mass is controlled by those discontinuities. This paper studies the stability of a jointed rock slope with bedding-planes. Universal Distinct Element Code (UDEC) is used to carry out the numerical analysis. The factor of safety (FOS) and failure mode are obtained by strength reduction technique before and after the steel bolts are installed in the slope. In addition, the forces along the bolts indicate that they reaches the maximum value in the potential slip surface of the slope.
Authors: Bo Lin He, Ying Xia Yu, Li Xing Huo, Yu Feng Zhang
Abstract: The reliability of welded pressure pipe with circumferential surface crack was calculated by using 3-D stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on 3-D elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as bending moment, the inner pressure on the structure reliability were discussed. The calculation results indicate that the bending moment has great effect on the reliability of the welded pipe, and the inner pressure has little effect on the reliability of the welded pipe if the inner pressure is less than 10MPa. If the mean value of the inner pressure changed from 0.5MPa to 30MPa, the failure probability will changes from 10-6 to 10-2. The bending moment also has great effect on the reliability. When the mean value of moment is changed from10000 Nm to 15000 Nm, the failure probability of the welded pipe increases dramatically for the same inner pressure. Irrespective of the changing of moment, the pipe has higher reliability if the inner pressure is less than 6 MPa. The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.
Authors: Xiao Jing Li, Wei Shen Zhu, Wei Min Yang
Abstract: Based on the underground structure scheme of Langyashan hydro-electrical project, lots of elastic-plastic numerical analysis were conducted considering modulus of deformation, layout depth of underground opening, height of main factory premises, coefficient of lateral compressive stress, as the mainly mechanical parameters that influenced the stability analysis of underground openings. The mathematical statistics method was employed to investigate the displacement variation law of key point surrounding house periphery and found the forecast model. Then the forecast model was used to analyze the sensitivity parameters. It was shown that there was a good agreement between theoretic result and monitoring result in situ.
Authors: Jun Ying Lian, Tai Quan Zhou, Yuan Hua, Guo Liang Dai
Abstract: Variability in the physical properties of rock mass is a major source of uncertainty encountered in railway tunnel stability analysis. The conventional safety factor method on stability assessment of railway tunnel within soft and weak rock mass can not represent the variability of rock mass. A formulation to compute the reliability of soft and weak rock mass, in which physical non-linearity is taken into account, is proposed. To consider the intermediate principal stress effect on the rock mass strength, the unified elasto-plastic strength criterion is proposed in the nonlinear finite element analysis. The unified rock mass elasto-plastic material model is implemented in ABAQUS user interface. The reliability analysis is performed in two steps. Firstly, the failure response is obtained by fitting the limit state function of the rock mass using the quadratic polynomial based on the nonlinear finite element analysis of the rock mass. Secondly, the JC method is proposed to obtain the design point and the reliability index of rock mass. As a case for study, the reliability analysis of Jinhuashan railway tunnel within soft and weak rock mass is studied using the proposed method. The two dimensional analysis is performed to consider the excavation stage effect and the unloading effect on the rock mass. Computation result shows that the rock mass is in stability.
Authors: Yang Pei, Bi Feng Song, Qing Han
Abstract: In fault tree analysis, the system failure probability and the component importance measures cannot totally include the contribution of all the component existing states to system reliability. It is for this reason that an ‘equivalent’ failure probability concept is proposed. First, the system existing states are analyzed by probability decomposition method. Then Markov chain method and the expectation theory are used to calculate the expected working number resulting in system failure. And the system equivalent failure probability is finally attained. Analysis shows that: (1) equivalent failure probability not only includes the contribution of critical states of component to system reliability, but also the non-critical states of component are considered; and (2) it may provide a thorough assessment of system reliability and is useful for reliability design.
Authors: L. Wang, A. Xiao, K.M.B. Jansen, M. Bartek, T. Zoumpoulidis, L.J. Ernst, G.Q. Zhang
Abstract: Substrate transfer technology for SOI and non-SOI single-crystalline silicon wafers was demonstrated allowing for high-performance low-power RF applications. 3D deformable electronics could be realized by vertically thinning and laterally partitioning of the silicon substrate on sub-millimeter scale. By varying the partition dimensions and the geometry of connecting bridges, the level of acceptable deformations can be controlled. The targeted applications of this technology are wireless ID tags and sensor networks. The mechanical properties such as crack, interfacial delamination are critical to reach the flexible substrate. In this contribution, results of our work on mechanical reliability issues of poly- and single crystalline silicon on ultra-thin polyimide substrates are presented. To improve reliability, square and hexagonal segmentation with different size is applied to the silicon layer before it is transferred onto an ultra-thin polyimide substrate using wafer-to-wafer substrate transfer technique based on a temporary glass carrier. Generation of cracks within the silicon and dielectric layers is then studied under controlled bending and tensile loads. The formation of cracks is studied experimentally using specially for this purpose designed bending and tensile tools. Ultra-thin interfacial delamination are also focused in this work by experimental and FE simulation method. A new test setup is designed for mixed mode bending testing which has capacity to observation specimen and recording the crack length and crack opening by microscope. The critical energy release depended on mixed angle can be reach by combination experimental data with FEM simulation.
Authors: Da Fei Han
Abstract: he transition fillet regions linking the bell crank and the crank-arm and linking the crankarm and the bearing journal are the regions where the strength is the weakest in crankshaft. Based on a crank-shaft model, the effect of the geometric parameters on maximal principal stress at the two transition fillet regions was analyzed using FEM and software ANSYS8.0. It was concluded that the maximal principal stress at the two transition fillet regions is related not only to the transition fillet radius but also to the bell crank length and the crank-arm width.
Authors: An Nan Jiang
Abstract: Shuibuya hydroelectric project is the most upstream power station in the Qingjiang cascade development of China. The power plant is designed as underground powerhouse, from seventh to eighth construction step, how to ensure the stability of surrounding rock mass of generator socket and controlling the displacement of lower side wall where the soft stratum located in is a key problem. To solve the problem, the three dimensional numerical model of the underground powerhouse was established based on the results of geological investigation. Then, the detailed construction processes, including the replacement of soft rock, excavation as well as support, were numerically simulated. In order to improve the simulation accuracy, the rock mechanics parameters were back analyzed based on in-situ monitor data before sixth construction step, then using Mohr-Coulomb criterion, the paper simulated and analyzed the damage zones of surrounding rock and displacement of lower side wall corresponding to different schemes. The best scheme was recommended by synthetically considering the stability indexes of each scheme. The study had a scientific meaning to guide Shuibuya project construction. Introduction When the underground cavern is excavated, the initial ground stress is released

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