Papers by Keyword: Discontinuity

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Authors: Qiong Yuan, Da Long Ding, Guang Ming Dai, Guo Hui Hong
Abstract: The design of discontinuity facilities is a critical factor in the success of many simulation efforts. This paper discusses the problems caused by detecting a discontinuity in terms of a change of sign in the value of a discontinuity function and describes an alternative which uses a change of the state marker value to suit the simulation of discontinuous systems in engineering applications. Subroutines which implement the method have been successfully built into integration package for stiff system with discontinuities.
Authors: Bao Yun Zhao, Ke Shan Zhu
Abstract: Since rock masses are not a true continuous, homogeneous, isotropic and linear-elastic (CHILE) continuum, the loading and unloading behaviors differ greatly from each other. Professor Ha Qiulin and his co-workers have demonstrated that strength and deformational characteristics, initial rock stresses, scale effects, creep, deformation and fracture patterns are quite different and stress path dependence is particularly emphasized. As engineering unloading of the rock mass is essentially of a dynamic nature by excavation, we will first discuss the excavation process and related stabilization techniques. For the complex stress and deformation conditions around the excavated boundaries, it seems rational to define an excavation disturbed zone (EDZ) as in the last decades. In tunnel excavation, temperature and ventilation effects should be also taken into account. Space-and-time dependence on tunnel behaviors is important. Finally, further research topics are discussed.
Authors: Cecilia Surace, Massimiliano Mattone, Marco Gherlone
Abstract: The present paper describes an experimental validation of a new structural damage detection method based on the Polynomial Annihilation Edge Detection (PAED) technique. It is well known that concentrated damage such as a crack, causes a discontinuity in the rotations and consequently in the first derivatives of the mode shapes. On this basis, the PAED, a numerical method for detecting discontinuities in smooth piecewise functions and their derivatives, can be applied to the problem of damage detection and localisation in beam-like structures for which only post-damage mode shapes are available. As described in this paper, in order to verify this approach experimentally (a numerical assessment having already been documented in previous papers), vibration tests on a cantilever steel beam with a saw-cut have been performed and the Operational Deflection Shapes (ODS) determined. As the approach requires a reasonably high spatial resolution of the ODS, a scanning laser vibrometer, capable of acquiring data rapidly at a very large number of observation points, was used.
Authors: Zeinab Aliabadian, Mansour Sharafisafa
Abstract: Rock masses consist of intact rock and discontinuities such as faults, joints and bedding planes. The presence of such discontinuities in rock masses dominates the response of jointed rock masses to static and dynamic loading. These structural weak planes seriously hinder and affect the propagation of stress waves in rock mass. The joints parameters such as persistence, orientation, distribution patterns, spacing and filling material have a significant effect on the response of rock masses against wave propagation. In most studies of blast induced wave propagation in jointed rock mass, it is assumed that joints are continuous. In many situations the rock mass consists of non-continuous joints and rock bridges. Rock bridges and discontinuous joints have a different effect on wave and fracture propagation in a blasting operation. With regard to complexities associated with rock blasting in particular in jointed media, numerical tools are viable alternatives for rock blasting analysis. In this study the DEM methods was employed to investigate the effects of rock bridges on the wave propagation process. A plain strain 2D scenario was assumed and a single blasthole explosion was simulated. Three models with different jointing orientation patterns including jointing pattern parallel to free face, perpendicular to free face and orientated at 45 degree with respect to free face were analyzed numerically to investigate rock mass fracturing while blast wave propagation. The discontinuous joints were considered to be filled with weak materials (open joints) and rock bridges are composed of intact rock. In order to allow material plastic failure, a Mohr-Coulomb material model was used. The analysis results show that the stress concentration at the rock bridge location leads to excessive fracturing. This effect is more visible at the free face where the stress wave reflection occurs. Moreover, the obtained results show that the pattern and orientation of non-continuous joint system has a pronounced effect on rock fragmentation.
Authors: Qiong Yuan
Abstract: In many techneques for handling discontinuities, the presence of a discontinuity is detected by a change of sign in the value of a discontinuity function. This paper discusses the problems caused by this sign rule of detecting discontinuities for some engineering applications, and describes an alternative which uses a change of the state marker value .The modified program with Runge-Kutta-Merson and Gear integration subroutines have been successfully applied to the simulation for mechanical, electrical and other dynamic systems with discontinuities for which the original program is inefficient.
Authors: Sittisak Charunetratsamee, Bovornchok Poopat, Chalermkiat Jirarungsatean
Abstract: Acoustic emission testing can be used to detect the energy emitted from material fracture and the advantage of this method is the real time monitoring, however the weld metal discontinuities are normally inspected by using conventional NDT methods such as Penetrant Testing (PT), Magnetic particle Testing (MT), Ultrasonic Testing (UT) and Radiographic Testing (RT) after the completion of welding. The weld defect must be repaired, which involves the cost and consumes a lot of time as well as reduce the reliability of manufactures. This paper presents the application of acoustic emission (AE) technique for monitoring and detecting the discontinuities during welding. In this study, gas tungsten arc welding (GTAW) was selected as test process. Carbon steel plate and autogenous welding technique were used to simulate the hot crack. The data acquisition (DAQ) and AE sensor were used to capture the acoustic signal generated during welding. The AE signals were amplified and filtered by using preamplifier. Then, signals were modified by wavelet transforms (WT) technique and classified by Fast Fourier Transform (FFT) technique. The results showed the possibility to use AE technique for monitoring and detecting the low signal amplitude generated from crack by using frequency domain. The advantage of this research is to propose the technique for monitoring the weld metal discontinuities during welding.
Authors: B.M. Olaleye, O.O. Onyemaobi, J.M. Akande
Abstract: In this work, the permeability characteristics of Nigerian coal seams were determined and these properties were used to investigation the applicability of water infusion in the coal seams to solve coal-mining problems. The experimental work was conducted with Triaxial Compression Machine adapted for the permeability test comprising of Hoek cell, a self- developed water piston, pressure gauge and an overhead water tank. The results of the investigation showed that the permeability measurements of the coals were consistent at the different sites and locations of the coalmines. It also revealed that the difference in coal seam permeability was relatively small in Nigeria.
Authors: Bao Yun Zhao, Dong Yan Liu, Ke Shan Zhu
Abstract: Conventional rock mechanics parameters are not derived directly from loading rock specimens in laboratory or in situ. Instead, they are determined by many different rock classification codes and criteria in different countries, and some of them such as RMR and Q systems are widely used in many countries. None of these codes and classification systems has considered the important factor of unloading of real excavated rock masses for engineering purposes until Professor Ha Qiulin proposed his new concept of unloading rock mechanics some two decades ago. Since rock masses are not a true CHILE continuum, the loading and unloading behaviors differ greatly from each other. Ha and his co-workers such as Li Jianlin have demonstrated that strength and deformational characteristics, initial rock stresses, scale effects, creep, deformation and fracture patterns are quite different and stress path dependence is particularly emphasized. All these findings have practical significance and a brief introduction and some discussions will be presented in this paper.
Authors: Hui Xu, Feng Wang, Di Zhang
Abstract: A special method based on the extended finite element method is developed for the simulation of dynamic crack growth. It shows great advantages in the simulations of moving crack and mixed mode crack. The extended finite element method for two-dimensional crack is described in this paper. The crack form of the extended finite element in the homogeneous medium is studied in detail, and the internal detail in crack tip element and crack penetration element is analyzed. At last, the displacement mode is generated.
Authors: Chuan Sheng Chen, Shi Zhi Wen
Abstract: The mechanical properties of discontinuity are different from those of a whole rock. And the shear strength of discontinuity is closely related to its morphological characteristics. The study of the mechanism of failure of jointed rock mass under shear stress is to reveal its mechanical behavior and its mechanism of failure. This paper presents a fundamental research in the mechanical properties of the regular jugged discontinuity under various normal stresses in the shear test. And it describes the mechanical properties of the regular jugged discontinuity under shear stress and their principal regularities. The strength and roughness of discontinuity under shear stress are investigated by the analysis of the data obtained. And this paper study the calculation of shear stiffness of discontinuity and proposed an empirical formula between the slope ratio and roughness coefficient of discontinuity. Also the changing regularity of the parameters of the shear strength of discontinuity under shear stress is investigated, and an empirical formula is developed to evaluate the shear strength of discontinuity in this paper.
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