超高强度抽油杆P-S-N曲线拟合新方法

P-S-N曲线是超高强度抽油杆力学性能分析的主要依据，其拟合方法通常参照于普通抽油杆。然而实验数据表明，超高强度抽油杆并不满足普通抽油杆P-S-N曲线拟合模型的假设条件。为了研究适应于超高强度抽油杆的P-S-N曲线拟合方法，提出了基于Box-Cox变量变换法的三参数P-S-N曲线拟合模型，其中Box-Cox变量变换法解决了一定循环应力下，疲劳寿命不满足正态分布的问题；三参数P-S-N曲线模型更符合典型S-N曲线的趋势。实验计算结果表明，新方法下的P-S-N曲线拟合度更高，相对误差仅为1.46%~4.12%，仅为以往方法的11%~30%，新方法拟合的曲线更能体现超高强度抽油杆力学性能，精确度更高。

A new fitting method for P-S-N curve of ultra-high-strength sucker rod

P-S-N curve is one important basis for analyzing the mechanical performance of ultra-high-strength sucker rod, and its fitting method is generally referred to that of conventional sucker rods.Based on experimental data, however, ultra-high-strength sucker rod can't satisfy the assumptions of P-S-N curve fitting model which is used for conventional sucker rods.A three-parameter P-S-N curve fitting model based on Box-Cox variable transformation method was developed to search for a fitting method suitable for the P-S-N curve of ultra-high-strength sucker rod.By means of Box-Cox variable transformation method, fatigue life can satisfy normal distribution in a certain cyclic stress.The three-parameter P-S-N curve model is more accordant with the trend of typical S-N curve.It is indicated from experimental calculation results that by virtue of this new method, the fitting degree of P-S-N curve is higher with relative error only 1.46%-4.12%, which is just 11%-30% of the conventional value.The fitting based on this new method can embody the mechanical performance of ultra-high-strength sucker rod more accurately.