工業的試験法としての曲げCOD試験について : 第2報

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The industrial material test must be simple. In this sense, COD bend test is thought to be an effective testing method. But one of the troubles in the conventional COD bend test is that the clip gauge readings(Vg) must be converted to the notch tip COD by means of rotational factor γ which is to be experimentally determined as a function of Vg or the fracture load for a given material. The authors proposed in the previous paper^<1)> that the critical COD could be evaluated simply from fracture load and yield stress with the use of the relation of EΦ/dσ_Y vs. σ_N/σ_Y (E : Young'S modulus, Φ : notch tip COD value, d : specimen depth, σ_N : nominal skin stress at the notched section, σ_Y : yield stress) obtained from FEM. In this paper, it is newly proposed that the method using FEM is to be applied with the limitation of σ_N/σ_Y≲1.5. For the range of σ_N/σ_Y≳2.0,the rotational factor γ=1/3 is to be used taking advantage of the constancy of γ when considerable deformation occurs prior to fracture. Thus the experimental determination of γ is not needed. For the intermediate range of 1.5≲σ_N/σ_Y≳2.0,the above two methods are to be combined, i. e. Φ_c for bend test may be estimated by a fair curve connecting the points of Φ_c obtained by using FEM at σN_/σ_Y=1.5 and Φ_c obtained by using rotational factor at σ_N/σ_Y=2.0. (Φ_c : critical COD value) The proposed standard specimen size is identical to ASTM recommendation^<2)>. It was confirmed that COD bend test is one of the most effective and useful test methods from the fact that critical COD obtained from bend test compares very well with that obtained from tension test.
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工業的試験法としての曲げCOD試験について : 第2報

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