T. Adachi

Ishinomaki Senshu University, Ishinomachi, Miyagi, Japan

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Publications (8)6.8 Total impact

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    ABSTRACT: A testing method under creep-fatigue interaction conditions has been proposed as the ASTM standard E2714-09. In accordance with the ASTM standard, round bar smooth specimens have been recommended as a testing specimen. Additionally, creep-fatigue crack initiation and growth life are usually defined as the attainment of a specific rate of decrease in the maximum tensile stress or the modulus of elasticity ratios. However, these criterions of crack initiation and growth life on ASTM standard are not characterized in terms of physical crack size. In this study, the creep-fatigue crack initiation and growth tests for P92 were conducted using circular notched round bar specimens. An attempt is made to measure the crack length during the tests by the direct current potential drop method, which results in the establishment of a high accuracy crack length measurement. Additionally, the life of creep-fatigue crack growth was characterized by linear cumulative damage law combined with the Qconcept which has been proposed as fracture parameter to describe the life of creep crack growth.
    No preview · Article · Jan 2012 · Journal of ASTM International
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    ABSTRACT: In components under static creep loading condition, the multiaxial stress fields appear due to the plastic constraint and they produce a more brittle type cracking behavior. From a practical standpoint, the characterizations of creep crack growth rates under the multiaxial stress field are important to improve the methods for creep life extension. In this paper, creep crack growth tests were conducted using round bar specimens with sharp circular notches for tungsten-added 12%Cr ferritic heat-resistant steel (W12%Cr steel), and the effect of multiaxiality on creep ductility and creep crack growth rate were investigated. Furthermore, three-dimensional elastic-plastic creep finite element analyses were conducted to clarify the effect of multiaxiality on creep crack growth.
    No preview · Article · Jan 2009 · Journal of Engineering Materials and Technology
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    ABSTRACT: A circular notched round bar specimen produces multi-axial stress field when uni-axial stress is applied in the axial direction. This stress field is produced in practical component structure. Therefore the characterization of creep crack growth rate under this condition is important for practical use. In this paper, developed 12Cr ferritic heat resistant steel was noticed. High temperature creep crack growth tests were conducted for a circular notched specimen for 12Cr ferritic heat resistant steel. And in order to investigate multi-axial stress state of a circular notched specimen, we have conducted 3D FEM analysis. The stress multiaxiality of a circular notched specimen increased as compare with that of CT specimen. Q* parameter which predicts creep crack growth rate is derived for this specimen. On the bases of this Q* parameter, the algorithm of predicting the life of creep growth is proposed.
    No preview · Conference Paper · Jan 2005
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    ABSTRACT: Using a round bar circular notched specimen for Cr-Mo-V steel and the proposed equation predicting crack length on the basis of electric potential drop method, the creep crack growth tests were previously conducted to investigate the effect of multi-axial stress on creep crack growth rate (CCGR). In this paper, more detailed experiments and analyses on the creep crack growth were conducted and the Q* parameter which characterizes CCGR for this circular notched specimen was derived. Furthermore, using the Q* parameter, the prediction law of creep crack growth life was also derived.
    No preview · Article · May 2004 · Materials at High Temperatures
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    ABSTRACT: It is important to evaluate the effect of multiaxial stress conditions on initiation and growth of creep cracks, when the laboratory data are subsequently applied to structural components under the same or similar stress state. The round robin tests of creep crack growth using circular notched specimens of 1CrMoV steel at 538 and 594 °C and 12CrWCoB steel at 650 °C were conducted by the Japanese VAMAS TWA25 group. The effect of notch depth and specimen size, i.e. stress multiaxiality on crack growth properties was investigated. The test procedure including criteria for crack length measurement by electric potential drop was established. The circular notched specimens fractured intergranularly and showed different crack growth behaviour from that of a CT specimen due to the multiaxial stress field. The creep crack growth rate for the same C* value increased as the ratio of the notch depth to specimen diameter, i.e. stress multiaxiality increased. The Q* evaluation method based on the thermally activated process can also be applied to the circular notched specimen.
    No preview · Article · Jul 2003 · International Journal of Pressure Vessels and Piping
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    ABSTRACT: The relation between fatigue life and damage accumulation of fiber-reinforced polymer composite (FRP) is not yet clarified. For practical use of FRP, it is necessary to relate the fatigue life to the mechanism of damage accumulation. Damage formation is controlled by the mechanical behavior of the interface between the matrix and fiber. We used short glass fiber-reinforced polycarbonate composite in our experiments. By using an in situ (real time) observational fatigue testing machine, we investigated the relationship between fatigue life and damage accumulation. From these results, the fatigue life of this material was found to be dominated by damage accumulation which results from microfracture at the interface between the matrix and fiber. This microfracture is controlled by a cycle-dependent mechanism.
    No preview · Article · Jan 1996
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    ABSTRACT: The decrease in the fracture strength of alumina ceramics at room temperature has usually been assumed to be caused by the effect of stress corrosion. However, at high temperatures, a viscous deformation will occur due to a glass-like phase which exists in the grain boundary. A study of the relation of the fracture strength of an alumina ceramics smooth specimen at room temperature to the visco-elastic property was performed. Mechanical tests and visco-elastic analysis, has shown that the fracture strength of this kind is controlled by the visco-elasticity.
    No preview · Article · Jun 1993 · Journal of Materials Science
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    ABSTRACT: The strength of ceramics has been thought to be controlled by a stress corrosion mechanism, but experimental results which do not obey this mechanism have been reported recently. In this paper, dynamic fatigue test, static fatigue test, stress relaxation test and measurement of internal friction were carried out for the smooth specimens of alumina ceramics. Furthermore, we simulated the dynamic fatigue characteristics by using a viscoelastic model. From these results, it was shown that alumina ceramics have viscoelastic properties and their mechanical properties were also affected by this mechanism. In addition, we discuss the effects of added components and grain size on dynamic fatigue.
    No preview · Article · Dec 1991 · Engineering Fracture Mechanics