Key Engineering Materials Vols. 306-308

Abstract: To predict the accurate behavior of bolted joints, detailed 3-D modeling is needed that considers the contact friction, preload, and nonlinear behavior of joints. However, a detailed model with gap elements cannot ensure convergence due to the complicated shape, plus it is inappropriate for a dynamic analysis. Accordingly, this paper suggests three kinds of model for structures with bolted joints: (1) detailed model, (2) practical model, and (3) simple model, which can be selected based on the purpose of the analysis. Through a static experiment using a strain gauge, the accuracy of the detailed model was verified, and the results of a modal test compared with the results of the simple model to confirm its effectiveness in a dynamic analysis. In the case of a static analysis using the simple model, the analysis results almost corresponded with those of the detailed model for a part 2.5d away from the center of the bolt. Among the proposed models, the simple model has the least degree of freedom and requires 59% less memory than the detailed model.

Abstract: A long cylinder composed of periodic structures along the axis can not be treated as a general plane strain(GPS) state, because within a repeated module, the geometry and loading condition may not be uniform along the axial direction. For this kind of situation, a ‘ more general kind of GPS ’ finite element is needed that uses a set of ‘ planar constraints ’, hereinafter called a ‘ pseudo general plane strain(PGPS) finite element ’. Otherwise, a high number of constraints need to be used, which is a tedious job and often gives rise to an input error. Plus, this can also cause a numerically ill conditioned stiffness matrix that results in a trivial or diverged solution. Accordingly, this study proposes several PGPS finite elements that use a set of planar constraints to solve long periodic cylinder problems, as well as conventional long cylinder and plane strain problems.

Abstract: MG (multigrid) method is one of the most promising solvers for large scale problems. Hexahedral mesh generation and its adaptation are not enough to use for practical applications, because its mesh generation is very difficult and still labor intensive work by hand. We have developed hexahedral local refinement technique controlled by posterior error estimation. We have proposed a MG technique for unstructured hexahedral meshes with local mesh refinement. In this paper, the proposed technique is evaluated to check its performance and severe analyses of bending cantilevers. Performance of MG for unstructured hexahedral meshes is compared with that of the PCG (preconditioned conjugate gradient) through several benchmark examples of 3-D static elastic analysis. Proposed MG is faster than PCG for all problems as number of freedoms increases. Finally limitation of the proposed technique is presented.

Abstract: We have proposed a cell based parallel computing system using a cellular automaton model. The proposed system is designed by object-oriented technique to realize extensibility for parallel cellular automaton model. Because the system needs only information of model as cells which are represented by pixel and voxel mesh, model generation is very easy from any data formats. We implement several applications, which are 1-D life game, 2-D life game, 2-D diffusion, 2-D parallel diffusion, 2-D wave propagation, 3-D wave propagation and 3-D parallel wave propagation on the system. Status of cells is updated by adjacent status of cells. In other worth, behavior of system is completely specified in terms of a local relation. Cells can hold many properties to represent its status. Cellular automata system can calculate physical phenomena and discrete problem like a life game simultaneously. We present some results of a physical analysis and discrete analysis, and discuss effectiveness and parallel efficiency of proposed system.

Abstract: The mathematical model to predict the temperature history for wood column is needed in order to determine its fire resistance when exposed to fire. In this paper, an intelligent methodology called Finite Element Method (FEM) of performing analysis for the square and circular wood columns by virtually or artificially developing a temperature history mathematical model. Numerical simulation model has been developed for the wood column by using two-dimensional mathematical model. The two-dimensional mathematical model was developed by using Galerkin’s Weighted Residual technique. This model focuses on the regional material of the wood column for describing its thermal behavior. When the temperature history in a column and relevant materials properties are known, the strength of the column can be calculated at any time during fire. Therefore, the development of the temperature history mathematical model is a must before any further study to be carried out for the wood columns. The flow of convection will result in minimal increase in the rate of heat energy reaching the column core. The analysis shows that the temperature of the column increases with respect to the duration of exposure to fire.

Abstract: Mathematical models of Part A [1] are used to calculate the temperatures, deformations and fire resistance of rectangular, hexagonal, octagonal and I-cross section columns for the purpose of Part B. In this paper the comparison among the configurations of the column has been carried out to predict the temperature history for the column elements for preventing the spread of fire and prolonging the structural time collapse. The columns are varied in section size, among them are the rectangular, hexagonal, octagonal and I-cross section column of Keruing timber. The developed mathematical models defined the failure point as the point which the column can no longer support the applied load. From the comparison, the I-cross section column is the worst configuration than the other configuration.

Abstract: Smoothed Particle Hydrodynamics (SPH) is a relatively new technique for simulating the dynamic response of solids, especially for high velocity impact and fracture problem. However, closer examination of SPH reveals some severe problems. The major difficulties are: (1) tensile instability; (2) zero-energy mode; (3) boundary deficiency; (4) less accuracy. One solution to these major difficulties with SPH is to improve the consistency of the kernel function. Based on the Reproducing Kernel Particle Method (RKPM), the concept of the proposed simplified linear consistency is introduced. The most attractive feature of the simplified linear consistency is the ease and cheapness of doing 3D calculation. One contribution of this paper is to show clearly the accuracy of solution gradually improved by increasing the order of the consistency. Simple 3D impacting models are established with different geometries and higher accurate results are obtained by using higher consistency kernel functions. Other features as numerical convergence, computational efficiency, etc. and some considerations of the simplified linear consistency kernel function are also discussed.

Abstract: Nano-indentation test is used widely to determine the fracture toughness of brittle materials and to provide information on important material properties such as the Young’s modulus and hardness. In this study, using nano-indentation testing, atomic force microscope (AFM), and finite element method (FEM), we performed the indentation fracture toughness and fracture strength measurement for a (100) single crystalline silicon at different load states. In addition, the loads of the phase transformation events during unloading were estimated by the load-depth curves. The phase transformation load and micro-crack propagation events at pop-out during the unloading process depended on the maximum applied indentation load.