曲げCOD試験片におけるNotch Acuity効果の定量化に関する一提案

概要

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The conventional COD bend tests are frequently used for the purpose of obtaining a critical COD(δ_c). But it is well known that δ_c shows various values depending on notch acuities. Accordingly, COD bend test specimens have usually a fatigue notch. However the industrial material tests are desired to be simple. In this sense, it is desirable that COD bend test specimens have only machined notch. In this paper, the transformation equations of a mouth COD (V_<total>) for a machined notch to δ_c for a fatigue notch are proposed by considering the machined notch root displacement. These transformation equations are expressed as follows: [numerical formura] where V'=(γσ_YW(1-ν^2))/E : limit elastic clip gauge COD defined by Wells, W : specimen width, a : crack depth, Z : distance from free surface to positions setting a clip gauge, d : initial notch root width (d⪇0.4mm) The above proposed equations are obtained from results of F.E.M. analysis, and it was confirmed that the relation between δ by the above equations and the plastic zone size is not different in the case of various notch acuities of the specimens. These equations are engineeringly satisfactory in the range of d⪇0.4mm for various materials.
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