Journal of Japan Foundry Engineering Society
Online ISSN : 2185-5374
Print ISSN : 1342-0429
ISSN-L : 1342-0429
Volume 79, Issue 2
Displaying 1-7 of 7 articles from this issue
Research Articles
  • Naoto Shiraki, Yoshiyuki Atsumi
    2007 Volume 79 Issue 2 Pages 83-89
    Published: February 25, 2007
    Released on J-STAGE: December 26, 2012
    JOURNAL FREE ACCESS
      The purpose of this study was to investigate the effects of humidity on the characteristics of fatigue crack propagation in spheroidal graphite cast iron with two phases which is ferrite and bainitic-ferrite. First, using spheroidal graphite cast iron (FCD400) as a specimen, two kinds of heat treatments were conducted; one was austempering (ADI, FADI82 and FADI55), and the other was ferrite haploidization processing (FDI). Fatigue crack propagation test was then carried out using these resultant four materials. The experiment conformed to ASTM. Stress ratio R was 0.1, and the specimen used was of the 1CT type with a thickness of 12.5mm. The test was carried out at room temperature and under three kinds of humidity: 0, 40, and 80%. The relationship between the characteristics of fatigue crack propagation and the crack closure generated on the fracture surface was investigated.
      Threshold stress intensity factor range, ΔKth of all materials increased with increasing humidity. In high ΔK regions of FADI and ADI, the fatigue crack propagation speed was accelerated because this seems to be effect of a phenomenon similar to the water embrittlement of bainitic-ferrite included in the matrix. In low ΔK regions of ADI, FADI and FDI, the fatigue crack propagation speed was lower because of the oxide-induced crack closure of the ferrite included in the matrix. Consequently, although the phenomenon similar to water embrittlement occurred also in the low ΔK regions of FADI82 and FADI55, the oxide-induced crack closure was also found to occur markedly. This confirmed the superior characteristics of fatigue crack propagation of specimens containing ferrite and bainitic ferrite.
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  • Kiyomi Konagaya, Tatsuya Yamahata, Shunzo Aoyama, Naoya Suzuki, Kazuki ...
    2007 Volume 79 Issue 2 Pages 90-94
    Published: February 25, 2007
    Released on J-STAGE: December 26, 2012
    JOURNAL FREE ACCESS
      Fatigue cracks are often generated in aluminum alloy die castings subject to repeated cyclic load as casting defects, which propagate and causes final fracture. This process can be formulated by the properties of fatigue crack propagation, the position of defect and cyclic load, because fatigue cracks propagate following the relation between stress intensity factor range ΔK and crack propagation rate da/dN, especially Paris equation which can be obtained by a fatigue crack propagation test using CT specimens.
      The authors have already proposed a prediction method of fatigue life based on the cross section of casting defect, tensile stress at the origin, and ΔK-da/dN relation.
      In the paper, the effectiveness of the prediction method was examined, focusing on the initiation process in the fatigue phenomenon of aluminum alloy die castings using artificial cracks instead of natural casting defects.
      First the influence of crack, processing method on the cyclic number initiation was examined and it was found out that cracks induced by the electric discharged wire machining has the minimum number of initiations due to less residual stress at the crack tip.
      Next the fatigue life of the actual suspension part of aluminum alloy AC4CH die casting with artificial crack was examined under several conditions.
      Based on the results, a new correction method is proposed which takes the initiation process from artificial defect to fatigue crack into account.
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  • Yoshihito Kinoshita, Yoshiki Tunekawa, Masahiro Okumiya
    2007 Volume 79 Issue 2 Pages 95-100
    Published: February 25, 2007
    Released on J-STAGE: December 26, 2012
    JOURNAL FREE ACCESS
      Ultrasound has been successfully applied to the grain refinement of various cast metals through frequent nucleation, as well as degassing, and inclusion removal from molten metals. In the present study, in order to broaden applications of semi-solid castings, grain refinement and formation of granular primary solid solution were examined by applying ultrasonic radiation to a molten aluminum alloy (AC4CH) surface during the solidification period, instead of inserting the ultrasonic radiator into molten metal. The ultrasound was radiated from a vibrating end surface with a vibration amplitude of 60μm and resonant frequency of 20kHz. Prior to the solidifying experiments of molten aluminum alloy, a transparent substance of succinonitrile was visibly solidified with ultrasonic radiation. According to successive observations, solid crystals generated near the heaved liquid surface were found to settle at the bottom by the forced convection due to the ultrasonic radiation, which is known as acoustic streaming. Primary aluminum solid solution vigorously nucleated right next to the vibrating surface, so that granular primary crystals accumulated at the mold bottom, instead of forming a dendrite structure. The granularity of primary solid solution depends on the irradiation period of ultrasound, that is, slow solidification rate is desired in the solid/liquid coexisting temperature zone. In the compressive shaping of semi-solid slurry, the form ability improves with the degree of primary crystal granularity.
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  • Kazuki Shouyama, Hiroyuki Toda, Tomomi Ohgaki, Toshiro Kobayashi
    2007 Volume 79 Issue 2 Pages 101-106
    Published: February 25, 2007
    Released on J-STAGE: December 26, 2012
    JOURNAL FREE ACCESS
      Closed cell aluminum foams (Al-Zn-Mg alloy foams) before and after heat treatment were visualized for three dimensions utilizing the high resolution Synchrotron X-ray computed tomography (CT) at SPring-8. Influence of heat treatment on the microstructure in the aluminum foams was quantitatively investigated. The sizes of the micropores after heat treatment were larger than those before and the shape after heat treatment was more heterogeneous than that before. After heat treatment, the intermetallic compound particles became coarse with some crystal orientation and the sphericity distribution of the particles became widespread. It was concluded that mezzo-structural transformation by the heattreatment mentioned above has small effects on materials for shock absorption of automobiles.
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