Hiroyuki Fujiki

Muroran Institute of Technology, Муроран, Hokkaidō, Japan

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Publications (12)3.55 Total impact

  • H. Ambarita · M. Daimaruya · H. Fujiki
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    ABSTRACT: The present study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of a lap bolted joint used in the suspension parts of 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 behaviour and fracture of the jointed steel plates subjected to impact loads. Although the actual impact fracture of jointed steel plates of a lap bolted joint in cars is complicated, for simplifying it is classified into the shear fracture and the extractive fracture of jointed steel plates. Three kinds of steel plates, i.e., common steel with the tensile strength of 270 MPa and two high tensile strength steels with the tensile strength of 440 and 590 MPa level used for vehicles, are examined. In the impact shear test, the specimens are made of two plates and jointed by a bolt, and in the impact extractive test the specimens are made of a plate and drilled in the centre for a bolt. The impact shear test of jointed steel plates of lap bolted joints is performed using a modified split Hopkinson bar apparatus, while the impact extractive one is performed using one-bar method. Numerical simulations by a FEM code LS-DYNA are also carried out in order to understand the mechanism of shearing and extractive fractures process of jointed steel plates. The obtained results suggest that a stress-based fracture criterion may be developed for the impact shearing and extractive fractures of jointed steel plates of lap bolted joints used in a car body.
    06/2014; 566:232-237. DOI:10.4028/www.scientific.net/AMM.566.232
  • [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-. DOI:10.1088/1742-6596/451/1/012007
  • M. Daimaruya · H. Fujiki · H. Ambarita
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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.
    The European Physical Journal Conferences 08/2012; 26:01013-. DOI:10.1051/epjconf/20122601013
  • [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). DOI:10.1142/S0217979208047304 · 0.94 Impact Factor
  • [Show abstract] [Hide abstract]
    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). DOI:10.1080/01495739.2012.720491 · 1.17 Impact Factor
  • Masaaki Oka · Himsar Ambarita · Masashi Daimaruya · Hiroyuki Fujiki
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    ABSTRACT: In spite of the fact that coke drums are subjected to cyclic thermal and mechanical loads, generally, they are not designed for cyclic loads. Thus, their operational life is much shorter than other pressure equipment in refineries. Due to information developed from surveys, it was determined that the major typical location of failure due to thermal fatigue in coke drums is the shell-to-skirt junction area. This paper focuses on temperature and stress characteristics and also the thermal fatigue life of the junction area. The main objective of this paper was to explore effect of the switching temperature on thermal fatigue life of the junction area. Four coke drums, currently in service have been considered in the analyses, named drums A, B, C, and D, identical in dimensions and with an operating cycle period of 48 h. Operational temperatures and strains have been measured and collected every minute. The number of measured cycles of coke drum A, B, C, and D were 52, 53, 53, and 54 cycles, respectively. Thus, a total of 212 cycles have been analyzed. The operational temperatures and strains were examined. Finite Element Method (FEM) analyses have been performed on the selected cycles in order to find the most severe location in the junction area. The strain history and FEM results were used to assess thermal fatigue life. The thermal fatigue lives were calculated based on low cycle fatigue properties using engineering steels for high temperature components issued by National Institute for Materials Sciences (NIMS) in Japan. The number of cycle to fracture versus switching temperature for the coke drums was then plotted. The curve best fitting criteria was then used to develop an equation relating the number of cycle to fracture as a function of switching temperature. The results show that the switching temperature strongly affects the number of cycle to fracture. These results can be used to provide the necessary information to operate coke drums safely in order to extend their useful lives. [DOI: 10.1115/1.4004564]
    Journal of Pressure Vessel Technology 12/2011; 133(6):061210. DOI:10.1115/1.4004564 · 0.27 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Coke drums are subjected to severe cyclic thermal and mechanical loads, thus their operational life is much shorter than other the conventional pressure equipments in oil refineries. Information developed from surveys indicates that one of major typical locations of failure due to thermal fatigue in coke drums is the shell-to-skirt juncture area. At the outer surface of the upper part of the skirt, there are two peak strains in every cycle which are tensile in the beginning of the filling stage and compressive in the cooling stage. The objective of the present paper is to develop a remaining life assessment method for shell-to-skirt juncture of coke drum with cracks propagated during cyclic operation. A coke drum currently in service with inside diameter of 8.55 m, height of 34.9 m, shell thickness varies from 28.5 mm to 34 mm, and skirt thickness of 24 mm is taken into analyses. In order to get the actual operational characteristics of the coke drum, temperatures and strains on the coke drum have been measured for 100 cycles. The selected operational temperatures will be employed as thermal boundary conditions for analyses. Propagations of 2 mm initial cracks depth at the inner surface of the upper part of the skirt, underneath the juncture as shown in Fig-3, is simulated on the basis of linear elastic fracture mechanics (LEFM). The relations of crack size with the number of operation cycles are plotted.
    ASME 2011 Pressure Vessels and Piping Conference; 01/2011
  • Journal of the Society of Materials Science Japan 01/2011; 60(7):662-667. DOI:10.2472/jsms.60.662
  • Masaaki Oka · Himsar Ambarita · Masashi Daimaruya · Hiroyuki Fujiki
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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(10-10):964-976. DOI:10.1080/01495739.2010.482385 · 1.17 Impact Factor
  • Source
    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.
  • Journal of the Society of Materials Science Japan 01/2009; 58(11):903-909. DOI:10.2472/jsms.58.903
  • Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 01/2007; 73(732):891-896. DOI:10.1299/kikaia.73.891

Publication Stats

3 Citations
3.55 Total Impact Points

Institutions

  • 2010–2013
    • Muroran Institute of Technology
      • Division of Mechanical Systems and Materials Engineering
      Муроран, Hokkaidō, Japan
  • 2011
    • University of Sumatera Utara
      • Department of Mechanical Engineering
      Medan, North Sumatra, Indonesia