Papers by Author: Masanori Kikuchi

Abstract: In this paper, fatigue crack growth simulation of interacting subsurface cracks using the s-version finite element method (SFEM) is presented. In order to evaluate the accuracy and reliability of the proximity rules published by the ASME, during the fatigue crack growth simulations, the subsurface cracks are approximated to either a single elliptical crack or semi-elliptical surface crack in accordance with the proximity rules. Then, the proximity rules are slightly modified for improving the accuracy and reliability. The results of crack depth evolution calculated by the SFEM with the use of the new proximity rules suggest that the approximation to deep cracks drastically improves the accuracy of the fatigue crack growth evaluation. Thus, the approximation to deep cracks must be a promising approach for having better evaluation of fatigue crack growth of subsurface cracks.

Abstract: Ductile fracture of 2024-T3 aluminum alloy has been investigated under tensile and shear loading conditions. In order to predict rupture, a void–based meso–damage constitutive relationship which can deal with both tensile and shear problems is developed and implemented in commercial software ABAQUS. The tensile and shear fracture behaviors including the load–displacement response and crack propagation path, of 2024–T3 aluminum alloy are analyzed using the proposed approach and compared with experimental data. It is shown that the proposed approach can be used to predict the failure of ductile materials under complex loading conditions.

Abstract: The aim of this paper is to present the simulation technique and experimental work for surface crack in a structure. For the sake of test apparatuss feasibility, a semielliptical surface crack in a structure was converted into small specimen size. The specimens represented semielliptical surface crack problem in real application of engineering structure. The specimens with semielliptical surface crack were tested by experiment and simulation. The S-version Finite Element Model (S-FEM) was implemented in simulation, and verification was performed through experimental works. The S-FEM consists of virtual crack closure method and Paris law as a crack growth criterion for 3-dimensional problem with hexahedron elements was used. Auto-mesh generation technique with a fully automatic crack growth simulation system was employed in S-FEM simulation. Specimens with 0^o of crack surface angle were prepared and analysed for the mode I loading. A four-point bending fatigue test was conducted and simulated in order to gain crack path, fatigue crack growth and stress intensity factors value. Results from simulation and experiment showed good agreement with a certain condition. The implications from the results were discussed through the analysis of fatigue crack growth.

Abstract: This study evaluates effects of the diffusion layer thickness and the share stress on metal surface for the polarization curve under flow field on metal corrosion. We measure the polarization curves under the different diffusion boundary layer thickness and the wall share stress. Metal surface conditions are observed from microscopic and macroscopic view points to evaluate tendencty of corrosion and shape of corrosion product.

Abstract: This study presents a mesh generation technique considering the measurement accuracy of the potential on an inverse analysis using the boundary element analysis. We evaluate the effects of the distance between layered rebar and corrosion size on measured potential distribution on the concrete surface, and then propose a technique to select reasonable and efficient size of boundary element. A numerical simulation demonstrates the validity and efficiency of the proposed technique.

Abstract: Three-dimensional finite element method (FEM) is widely used as an effective numerical simulation technique to solve the complex engineering problem. Usually, the more complex engineering problem has more complex structure and shape; the FEM simulation technique is that needs to discrete the structure and shape of the problem by mesh. In addition, the correct generation of mesh is one of the most significant issues that directly affect to the accuracy of the FEM simulation. The hexahedral mesh is better than tetrahedral mesh in solving the complex engineering problem. The common methods of hexahedral automatic mesh generation have been used in some commercial soft already, but its adaptation is not enough to solve for practical applications of the complex engineering problems. A new method of mesh generation technique was proposed by improved waveform mesh generating method, and realized by C++ developing program in Linux OS. The method could generate some effective and smoothly mesh models by quadrilateral element or hexahedron element, and not only generated revolution curve surface meshes, but also generated random meshes according to free functions too. The results shown that the hexahedral mesh models of the complex shapes were generated as the shape function apply to regular mesh side as a waveform constraint.

Abstract: From a view point of engineering application, solid-liquid flow is one of the most practical phenomena, however MPS and other particle methods usually premises a constant size of all particles in the model.　In a realistic phenomenon, the size of those particles is different.　 Koshizuka et al. has proposed new algorithm for solid-liquid flow simulation which is multi-scale DEM-MPS method. The method can calculate solid -liquid flow with a large difference of the particle scale. However, its program code requires a DEM part and a MPS part, and actual phenomenon includes various scales of particles. In order to analyze solid-liquid flow with different particles, modified Laplacian model and variable cut-off radius MPS method is proposed. This modification can directly deals with small particles and large particles. Calculation cost is kept and visualization of the results has more reality by these modifications.

Abstract: This paper presents the dynamic growth behavior of the voids in ductile metals under dynamic loading condition. Started from energy conservation law, a dynamic damage model on void growth process is developed, in which inertial effect is taken into account. The proposed model on void growth is introduced into Gurson model through VUMAT subroutine, so the void growth behavior affected by inertial effect can be investigated and compared. Numerical analysis shows that inertial effect decreases the rate of void growth, and with the increasing of the loading rate, the decreasing effect becomes more remarkable. Inertial effect is very sensitive to the initial damage of the material and the distribution of the void density. The larger the initial damage and the sparser the void density, the stronger the inertial effect on the void growth.

Abstract: Crack propagating evaluation is needed to predict and prevent structural damages since many structure defects from numerous crack propagating. It is widely known that ductile fracture occurs when external load is exerted to the material, these load include strong and unpredictable load such as earthquakes and collision of objects. Ductile material fractures via nucleation of void, growth of void and coalescence of voids. Many studies have been conducted; Kikuchi and Sannoumaru have published papers on the studies of ductile fracture. In the first paper [1], the thickness effect on the microscopic fracture process and fracture toughness is studied experimentally. In the second paper [2], dimple fracture tests were performed using three point bending specimens. In the test, loading condition is changed from mode I to mixed mode condition to study the effect of the mixed mode loading. Numerical simulation is conducted using Gurson’s constitutive equation. It is found that crack growth direction is affected significantly by the loading condition. Ductile fracture of a pipe used in Light Water Reactor components is researched in this paper. Four point bending of a pipe experiment had been done by the Central Research Institute of Electric Power Industry [3]. They were experimented in two conditions; one at room temperature (23 ) and second at high temperature (300 ). As a result, crack propagation behavior differs largely form each other. At room temperature, crack propagates parallel from the pre crack, and at high temperature, crack propagates in a slanting direction from the pre crack. Results show that that difference from the two temperature distinction of a tensile test in a stress strain curve is very little. In this paper, this problem is studied at first by experiments, observation of fracture surface and numerical simulation.

Abstract: Recent development of crack propagation analysis is rapidly advanced and its applications are being extended. Usually finite element method is utilized for the analysis. One of the most important tasks is mesh generation which requires fully automated system and no failures. It is very difficult to meet all geometrical and mechanical requirements for a surface mesh generation. Recent studies show a factory roof is easily generated under mixed mode loading. How to generate surface crack tetrahedral mesh without failures and surface crack analysis with factory roof are presented.