Advances in Fracture and Failure Prevention

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Authors: Sukky Jun, Young Min Lee, Sung Youb Kim, Se Young Im
Abstract: Molecular dynamics simulation of nanoindentation on Al(111) surface is presented. The simulation is performed using the Ercolessi-Adams glue potential and the Berendsen thermostat. Boundary conditions of 'pseudo' thin film are imposed in order to focus on the dislocation motion in ultra-thin film. Nucleation and development of defects underneath the indenter tip are visualized, and the gliding patterns of dislocation loops are investigated with particular emphasis on the effect of film thickness. Simulation results show that the early emission of dislocation loop is highly dependent on the film thickness.
Authors: Akiyuki Takahashi, Naoki Soneda, A. Nomoto, G. Yagawa
Abstract: This paper describes dislocation dynamics simulation of grain boundary effects on yield behavior of metals, such as α-Fe bcc metal. Since the stress field arising from the grain boundary has not been well understood yet, the geometrical effect of the grain boundary can be handled in the simulation by the use of rigid boundary condition. The dislocation pileups can be observed near the grain boundary in the result of the DD simulation. And the yield stress in the crystal having the grain boundary becomes larger than that in the crystal having free surface. This result tells us that the Hall-Petch effect can actually describe well the effects of the grain boundary on the yield behavior of metals.
Authors: Akira Shinozaki, Masaki Omiya, Hisahiro Inoue, Kikuo Kishimoto
Abstract: The mechanical properties of polymers are strongly influenced by meso-scale structure such as entanglement, orientation, folded chain, etc. However, the relationship between the meso-scale structure and macro-scale mechanical properties of polymers has not been clarified. In this paper, network models of polymer chains are introduced to simulate the meso-scale interactions. From the FEM analysis of this model, the effects of interactions on macro-scale mechanical properties are investigated.
Authors: M.L.L. Wijerathne, Kenji Oguni, Muneo Hori
Abstract: A new nondestructive method for identifying boundary conditions applied on a 3D linear elastic body is developed based on the load incremental approach, which linearizes the nonlinear governing equation of photoelasticity by considering small increments in applied load. Direct stress identification based on load incremental approach is highly sensitive to measurement errors and involves considerable amount of computations. On the other hand, identification of boundary conditions based on load incremental approach and thereby the state of stress is not only less sensitive to measurement errors but also involves less computation. This boundary conditions identification can be considered as an introduction of equilibrium condition and the property of linear elasticity to overcome the shortcomings of direct stress identification.
Authors: Kai Wang, Xi De Li
Abstract: Quantitative nondestructive testing (QNDT) is required for the in-service inspection of high-cost structures whose failure could lead tragic consequences. The optical methods are widely used for NDT and NDE. However, most of them base on the qualitative detection of the partial fringes induced by the defects. The defect characteristic parameters (DCPs), such as coordinates and types, are easily obtained, but it is difficult to obtain other parameters, e.g. the defect size and embedded depth due to the non-unique relation between the DCPs and the deformation of detected defects. In this paper, the optical method, design optimization and FEM are combined to accomplish QNDT. Three types of defects are inspected and their DCPs values are obtained quantitatively. Moreover, factors that influence detection accuracy of the DCPs are also discussed.
Authors: T. Noguchi, Kenji Amaya, Shigeru Aoki
Authors: Gabriela Maria Atanasiu
Abstract: Damage evaluation of constructions, subjected to earthquakes is an issue focused by many researchers, being a complicated matter. It is based on a multiple stage concept, depending on the level of understanding of the problem hierarchy for a requested safety level, based on structural performances. The structural modeling for simulations of lifetime constructions' behavior to seismic loads takes is a computational multiphase process based on the following stages: a priori modeling for initial design, on line monitoring of structure during lifetime functioning, damage identification and model re-evaluation. Recent results of research in computational earthquake engineering highlights the real need for re-evaluation of dynamical models of constructions, after they have experienced several seismic events. The re-evaluation should be based on their real engineering performance of the structure experience during several earthquakes. The paper deals with the problem of structural model's re-evaluation using some experimental available data. The purpose of re-evaluation is to increase the seismic safety of damaged existing buildings located in seismic high-risk areas. The correction of structural models for damaged constructions is based on a deterministic procedure. The methodology used for structural models' adjustment is exposed below, being validated by a study case done on a frame model of a reinforced 3 stories frame construction.
Authors: Yun Hae Kim, J.D. Kim, V.A. Shuripa, Cheolmun Yim, Tae Gyu Park
Abstract: Decreasing of wind turbine blade weight by using honeycomb sandwich collides with strength lack of the honeycomb facets at the high loaded places of the blade under heavy wind load. For providing tensile and compressive strength profiling of the variable thickness facets was made. By using response surface model based on design space the facets rational thickness distribution was performed by using optimization. The condition of evenly distributed stresses at narrow range of values for reinforced facets was used like state variables for optimum designing. By combining finite element analysis and sequential programming the response of the thickness within the process integration framework on criteria the rationalization of the facets thickness was performed. The facets thickness variations are assigned by polynomial of fifth degree to provide small difference of stresses in the facets for blade. The angles of the glass fiber stacking relatively of the blade axis for mass minimization were selected on the similar stress reinforcement condition for outside and inside facets of the honeycomb sandwich. The structure of the reinforcing was built to coincide the principal stresses and strains of the facets to longitudinal and transversal direction of the blade. Calculation results were obtained for glass fiber -epoxy resin composite material having and shown that decreasing total mass of the blade 19% compare to shape optimization.
Authors: Ki Sung Kim, Kyung Su Kim, Hyoung Jin Park
Abstract: Grillage is common types of structures in marine and land-based structural system. Grillage system that increases the stiffness of plate used by two rectangular stiffeners is a part of deck, side shell and bottom of ships. The worst load point of those structures is dependent on the loads, which are vertical, in-plane or combination of those directions as well as boundary conditions. The worst deflection point is produced when the point load is examined at central intersection. But the worst loading point would not necessarily be at the central point. To find the worst load point, a moving point load is applied to along the vertical and horizontal beams around mid-spans. Direct stiffness method is used as an analysis tool. Structural model tests are also carried out to confirm the theoretical analysis results. To find the optimum arrangement of grid system under a given point load, an optimization technique is applied. In this case, the minimum weight is the objective function and allowable stress, deflection and other dimension limitations are constraints.
Authors: Young Jae Park, Sang Min Lee, H.S. Yim, Jae Boong Choi, Young Jin Kim, E.C. Roh, B.I. Lee
Abstract: In this paper, a knowledge-based information system for the plant operation of steel making company has been proposed. The system, which is named as K-VRS(Knowledge-based Virtual Reality System), provides a connection between ERP plant maintenance module and knowledge-based engineering methodologies, and thus, enables network-based highly effective plant maintenance process. The developed system is expected to play a great role for more efficient and safer plant maintenance.

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