H. Fujiki

Muroran Institute of Technology, Муроран, Hokkaidō, Japan

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Publications (9)8.8 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The present study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of bolted joints used in a car body, which contributes to crash simulations by CAE. We focus our attention on the shear fracture of the jointed steel plates of lap-bolted joints in the suspension of a car under impact load. Members of lap-bolted joints are modelled as a pair of steel plates connected by a bolt. One of the plates is a specimen subjected to plastic deformation and fracture and the other is a jig subjected to elastic deformation only. Three kinds of steel plate specimens are examined, i.e., a common steel plate with a tensile strength of 270 MPa and high tensile strength steel plates of 440 and 590 MPa used for cars. The impact shear test was performed using the split Hopkinson bar technique for tension impact, together with the static test using a universal testing machine INSTRON 5586. The behaviour of the shear stress and deformation up to rupture taking place in the joint was discussed. The obtained results suggest that a stress-based fracture criterion may be developed for the impact fracture of jointed steel plates of a lap-bolted joint.
    Journal of Physics Conference Series 07/2013; 451(1):2007-.
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    ABSTRACT: This study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of a bolted joint used in a car body. For the accurate prediction of crash characteristics of car bodies by computer-aided engineering (CAE), it is also necessary to examine the behavior and fracture of jointed steel plates subjected to impact loads. Although the actual impact fracture of jointed steel plates of a bolted joint used in cars is complicated, for simplifying the problem it might be classified into the shear fracture and the extractive fracture of jointed steel plates. Attention is given to the extractive fracture of jointed steel plates in this study. The extractive behavior and fracture of three kinds of steel plates used for cars are examined in experiments and numerical simulations. The impact extraction test of steel plates jointed by a bolt is performed using the one-bar method, together with the static test. In order to understand the mechanism of extractive fracture process of jointed steel plates, numerical simulations by a FEM code LS-DYNA are also carried out. The obtained results suggest that a stress-based fracture criterion may be developed for the impact extractive fracture of jointed steel plates of a bolted joint used in a car body.
    08/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The tensile properties of YAG laser welded butt joints using different high strength steel sheets with a tensile strength of 270 MPa, 590 MPa and 980 MPa (denoted HR270, HR590 and HR980, respectively) were investigated at static and dynamic rates, together with the three kinds of laser welded joints made by the same steel sheets. The impact tensile tests were performed by using the vertical type of split Hopkinson tension bar apparatus, while the static tensile tests were carried out using a universal testing machine INSTRON5586. The impact tensile strengths were significantly increased in comparison with the static ones due to the effect of strain rate, which might be the contribution of the part of HR270 base metal. And in both of static and impact tests, the fracture strains of HR270-HR590 joint, HR270-HR980 joint and HR590-HR980 joint were about one half of the fracture strains observed in the same steel welded joints of HR270-HR270, HR270-HR270 and HR590-HR590, respectively.
    International Journal of Modern Physics B 01/2012; 22(09n11). · 0.46 Impact Factor
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    ABSTRACT: Coke drums are subjected to cyclic thermal stresses, thus their operational life is much shorter than other pressure equipment in oil refineries. It is known through surveys that one of major typical location of failure in coke drums is the shell-to-skirt junction. The main objective is to simulate crack propagation and to develop a remaining life assessment method for shell-to-skirt junction with crack. Operational temperatures and strains on a coke drum have been measured for 100 cycles. The selected operational temperatures will be applied as thermal boundary conditions in analyses. The crack propagation is then simulated to assess the remaining life.
    Journal of Thermal Stresses 01/2012; 35(12). · 0.73 Impact Factor
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    ABSTRACT: This study investigated the role of macrophage migration inhibitory factor (MIF) in fracture repair using MIF gene-deficient mice (MIF KO). Fracture healing was delayed in MIF KO, and this was mainly due to the delay in the mineralization of osteoid within the fracture callus. We previously reported that the expression of macrophage migration inhibitory factor (MIF) was up-regulated during the fracture healing process in rats. However, its role in the pathophysiology of this process remained unclear. The aim of the present study was to clarify the role of MIF in the fracture healing process using MIF gene-deficient mice (MIF KO). Bone repair in wild-type mice (WT) and MIF KO (n = 70, respectively) was investigated using a tibia fracture model. Radiographic, biomechanical, histological, bone histomorphometric, and molecular analyses were performed. Post-fracture biomechanical testing showed that maximum load and stiffness were significantly lower in MIF KO than in WT on day 42. However, similar levels were observed between the two groups on day 84. Bone histomorphometric analysis revealed significantly higher osteoid volume, a lower mineral apposition rate, and smaller numbers of osteoclasts in the MIF KO callus compared to the WT callus. The messenger ribonucleic acid expressions of matrix metalloproteinase (MMP)-2, membranous type 1-MMP, cathepsin K, and tissue nonspecific alkaline phosphatase were found to be significantly suppressed in the MIF KO callus. The results of the present study suggest that delayed fracture healing in MIF KO was mainly attributable to a delay in osteoid mineralization.
    Osteoporosis International 06/2011; 22(6):1955-65. · 4.04 Impact Factor
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    ABSTRACT: Coke drums are equipments of an oil refinery system used to separate petroleum coke from lighter oils. During operations, a coke drum is subjected to cyclic heating and cooling also cyclic mechanical loads. Thus, the useful life of a coke drum is much shorter than the other equipments in the refinery. Bulges are commonly problems found in a coke drum. The initiation mechanisms of the bulges are not clear yet. However, there are two postulates have been proposed. First is that bulges are caused by contact stresses due to differential expansion between solid coke and steel. Second is that they are caused by thermal stresses due to presence of hot and cold spots in the coke drum wall. The present paper tends to agree with the second one. The main objective is to demonstrate that thermal stresses are sufficient to initiate the bulges. A coke drum with overall length, diameter, and thickness of 25.46 m, 6.4 m, and 42 mm, respectively has been taken into analysis. In order to provide actual temperature boundaries, operational temperatures of the coke drum have been measured and collected while it is operating. A cycle which shows the most severe operational temperature has been selected to be analyzed. Two-dimensional axisymmetric model was developed and stresses analysis upon the model was carried out by using ANSYS FEM commercial code. The equivalent stresses and the yield strength as a function of time are plotted. The results show that the maximum equivalent stress can reach the yield strength of the coke drum material. This concludes that the bulges are mainly initiated by thermal stresses.
    Journal of Thermal Stresses 10/2010; 33(10):964-976. · 0.73 Impact Factor
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    ABSTRACT: This study evaluated the in vivo influence of a poly-(2-Acrylamido-2-methylpropane sulfonic acid)/poly-(N,N'-dimetyl acrylamide) (PAMPS/PDMAAm) double-network (DN) hydrogel on counterface cartilage in rabbit knee joints and its ex vivo friction properties on normal cartilage. In the first experiment, the DN gel was implanted in a surgically created defect in the femoral trochlea of rabbit knee joints and the left knee was used as the control. Evaluations using a confocal laser scanning microscopy demonstrated that the DN gel did not affect the surface microstructure (surface roughness, the number of small pits) of the counterface cartilage in vivo at 4 and 12 weeks. The histology also showed that the DN gel hadno pathological damage on the cartilage matrices and cells at 4 weeks. However, two of the five DN gel-implanted knees showed mild irregularity on the counterface cartilage surface at 12 weeks. In the second experiment, the friction property between the normal and the artificial cartilage was determined using a joint simulator apparatus. The ex vivo mean friction coefficient of the DN gel to normal cartilage was 0.029, while that of the normal-to-normal cartilage articulation was 0.188. The coefficient of the DN gel-to-normal cartilage articulation was significantly lower than that of the normal-to-normal cartilage articulation (p < 0.0001). This study suggested that the PAMPS/PDMAAm DN gel has very low friction coefficient on normal cartilage and has no significant detrimental effects on counterface cartilage in vivo, and can be a promising material to develop the artificial cartilage.
    Journal of Biomedical Materials Research Part A 09/2009; 93(3):1160-8. · 2.83 Impact Factor
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    M. Daimaruya, H. Fujiki, Y. Uemura
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    ABSTRACT: The present study is concerned with the impact behavior and fracture of jointed steel plates used in cars. The strength and failure of joint parts subjected to impact loads are examined for an accurate prediction of crash characteristics of car bodies by CAE. Members of lap-bolted joints in the suspension of a car are modeled as a pair of steel plates connected by a bolt. One of the plates is the specimen subjected to plastic deformation and fracture and the other is a jig which is subjected to elastic deformation only. We focus our attention on the impact shear deformation and fracture of the specimen plate. The specimens are made of a steel plate with a tensile strength of 270 MPa, while the jig plate is made of high tensile strength steel of 780 MPa. The impact shear test was performed using the Split Hopkinson bar technique for tensile impact. The behavior of the shear stress and deformation up to rupture taking place in the joint. Numerical simulations were also carried out to compare with experimental results and to understand the mechanism of the fracture process in plates of a bolted joint.
    http://dx.doi.org/10.1051/dymat/2009121. 01/2009;
  • Journal of the Society of Materials Science Japan 01/2009; 58(11):903-909.