Key Engineering Materials Vols. 297-300

Abstract: Based on the heterogeneous and porous characteristics of rock materials, a flow-stressdamage (FSD) model, implemented with the Rock Failure Process Analysis code (RFPA2D), is used to investigate the behavior of fluid flow and damage evolution, and their coupling action in rock sample that are subjected to both hydraulic and uniaxial compressive loading. A highly heterogeneous sample, containing grains, grain boundaries and weak zones, is employed in the numerical simulation. The simulation results provide a deep insight in the physical essence of the evolutionary nature of fracture phenomena as well as the fluid flow in heterogeneous materials, especially when they are highly stressed. The simulation result suggests that the nature of fluid flow and strength character in rocks strongly depends upon the heterogeneity of the rocks.

Abstract: Surrounding rocks of deep underground engineering are generally cracked, between which and support exists combined effect that can be reflected by the mechanical characteristics of cracked rock mass under lateral Constraints. In this paper, the strength and deformation characteristics of the cracked rock mass under lateral Constraints are investigated with methods of physical and numerical experiments. The results show that the rock mass behaves as equivalent continuum and tends to stable after deforming and re-fracturing, and has stress hardening behavior. These characteristics are obviously different from that of shearing slippage of rock samples at the residual stage of triaxial experiment.

Abstract: A series of numerical simulations were performed to investigate the effects of geometric and mechanical heterogeneity of pre-existing faults of rocks on their failure and induced earthquake precursors. The numerical results revealed that rock failures with the different heterogeneity produce the different earthquake precursors, which are in a good agreement with those of observations in nature.

Abstract: Reinforced concrete structures are generally designed to allow cracking under service loading. Accurate modeling of crack formation and propagation at lower load levels is therefore important. In this paper, a Material Failure Process Analysis code (MFPA2D) is used to model the crack initiation and propagation in reinforced concrete bridge pier subjected to eccentric loading. In our numerical model, the reinforced concrete is assumed to be a three-phase composite composed of concrete, reinforcement and interfaces between them. Numerically obtained results of cracking loads and global load-displacement response agree well with experimentally measured values. It has been found that the fracture of the concrete observed at the macroscopic level is predominated by tensile damage at the mesoscopic level.

Abstract: Rock masses usually contain intermittent joints. The existence of joints not only significantly affects the static properties of rock masses, but also their dynamic response and stability under blast waves. The present study focuses on investigating the fundamental fracture characteristics of intermittent jointed rock masses subjected to blast loading. A series of blasting tests were conducted on organic glass samples. The results are analyzed in order to obtain the characteristics of initiation, propagation and coalescence of wing cracks in rock bridges. The study indicates that the fracture behavior of intermittent jointed rock masses may be significantly affected by the preliminary static stress fields, the density and filling states of rock joints, the incident angles of blast waves relative to the joints, and the amplitudes of incident waves. From visual observation, three initiation modes and four coalescence modes of wing cracks are suggested. Finally, a comparison has been made between the fracture characteristics of intermittent jointed rock masses under single static stress field and that of under blast loading.

Abstract: Cement structures such as bridges and dams often come into being distortion or exhibit excessive thermal stresses due to the sun radiation or freeze-thaw cycle. Therefore, temperature especially inner temperature difference or deformation of structures must be controlled or regulated sometimes in order to reduce thermal stresses or excessive deformation and to extend the life-span of structures. In this paper, the electro-thermal effects of smart cement are used to adjust temperature difference or deformation of concrete beams without the need of peripheral non-structural materials. Concrete beams for temperature and deformation adjustment were fabricated, and some experimental results as well as the related conclusions about temperature difference and deformation were produced. Based on these results, experiments of temperature difference or deflection adjustment are further conducted successfully. The research results in this paper are the bases of temperature and deformation adjustment for mass concrete structures. A new path will be broken to adjust temperature or deformation easily for some structures.

Abstract: An expert system in fatigue and fracture analysis based on Web is developed in this paper. The system consists of six functional parts: a general inference engine, some knowledge bases, a context, an interpretation engine, a bases administration system and the interface (includes browser, Web-server, etc.). It can simulate a human expert to make analysis and design scheme for some typical structural components: pressure vessels, huge rotation constructions, welded structures, etc. It is an open system which may be broadened and perfected to cover a wider range of application through the modification and enlargement of the knowledge and data bases on Web.

Abstract: Features of the materials database system for plant facilities management are discussed here. Korea Electric Power Research Institute (KEPRI) has developed web-based materials database system for power plant engineers with an aim to give them the integrated materials information which is needed in solving material-related problems frequently occurred in plant maintenance activities. The materials database system contains more than twenty thousands material standard data of eight countries including chemical composition, mechanical properties, and their applications in the power plant facilities. Using the system, users can find useful information of equivalent material standards and physical or chemical environments where the material is applied. Integration of material data with facility data is expected to give more valuable information to plant engineers in solving their material related problems. The database system also adopted state-of-arts extensible markup language (XML) technology and was designed to share its data easily with other information systems such as plant engineering expert system, materials management system, enterprise resource planning (ERP) system and so on.

Abstract: Recently, regulatory bodies quite often encourage to adopt risk-based inspection (RBI) and management programs because they can enhance safety simultaneously with deregulation in Korea. RBI is an integrated methodology that factors risk into inspection and maintenance decision making. This paper describes an example of how to use known risk assessment codes (API 580, API 581 BRD) to address such safety analysis requirements for risk management in the refining industry. Specifically, this paper reports the methodology and the results of application to the refinery units using the KGS-RBITM program, developed by the Korea Gas Safety Corporation in reference of API Codes and ASME PC (Post Construction) with a suitable consideration of Korean situation. The results of the risk and reliability assessment using KGS-RBITM program are useful in determining whether the detected defects are tolerable or required to be repaired. The subsequent decisions are to manage the future inspection, repair and maintenance planning in the risk reduction control.

Abstract: Nuclear power company plant maintenance has been conservative since it was born. Before we adopted DREAMS system, most of PM documents were handled with paperwork and we spent much time to perform plant maintenance. Last year KHNP constructed and implemented the computerized PM system, which was part of SAP system named DREAMS, and it made KHNP cut down expenses, save time, decrease trouble and optimize work intervals. To make PM system much better, we are trying to import equipment reliability process and we have a plan to initiate it within a year. Therefore the purpose of this paper is not only introducing an advanced methodology of plant maintenance, but showing the optimized PM system (equipment reliability process), considering safety and cost-effectiveness simultaneously.