This article addresses an analysis relating K_OP to K_max,th (FCG threshold) using measured FCG threshold data at various load ratios from R = 0.1 to R = 0.9 under constant amplitude loading. K_OP is estimated at near threshold region, due to the low-resolution measurement limit. It is shown that threshold K_max,th is related to K_OP through a critical monotonic plastic strain. Key observation is that this relationship is independent of yield strength, ultimate tensile strength, Young’s modulus, specimen geometry and methods of pre-cracking. This trend in K_OP vs K_max,th seems to be linear and show a general behavior for many different structural materials, under different environments, and load ratios. The analysis suggests that that there are possible sources of the uncertainties in the measurement techniques of K_OP using nonlinear deviation in the load–displacement curves.

本文介绍了一种分析方法，该方法使用恒定振幅加载下从R = 0.1到R = 0.9的不同负载比下测得的FCG阈值数据，将K _OP与K _max，th（FCG阈值）相关。由于低分辨率测量限制，在接近阈值区域处估计了K _OP。结果表明，阈值K _max，th通过临界单调塑性应变与K _OP有关。关键观察结果是，这种关系与屈服强度，极限抗拉强度，杨氏模量，试样几何形状和预开裂方法无关。K _OP vs K _{max，th的趋势}似乎是线性的，并显示出许多不同结构材料在不同环境和负载比率下的一般行为。分析表明，使用载荷-位移曲线的非线性偏差，在K _OP测量技术中可能存在不确定性。