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本文提出了确定疲劳裂纹扩展速率曲线转折点的数学方法——曲率判定法。其原理是:根据y=f(x)的相对曲率τ=y_x~n/(1+y_x~(′2))~(3/2)的正负和大小来判定曲线的转折点,这里x=1g(△K),y=Ig(da/dN)。给出了y′_x和y″_x的计算方法。用六种金属材料的实验数据进行了验证,并与其他数学方法进行了对比,结果表明:曲率判定法优于其他方法,其准确性比其他方法好得多。
In this paper, a mathematical method to determine the turning point of the fatigue crack growth rate curve-curvature method is proposed. The principle is to determine the turning point of the curve according to the positive and negative values of the relative curvature y = f (x) = y_x ~ n / (1 + y_x ~ (2)) ~ (3/2) 1g (ΔK), y = Ig (da / dN). The calculation methods of y’_x and y "_x are given.Experimental data of six kinds of metallic materials are validated and compared with other mathematical methods. The results show that the method of curvature determination is superior to other methods, and its accuracy ratio Other methods are much better.