The fatigue load spectrum is one of the most important parts in accelerated durability testing of agricultural machinery; however, the traditional editing approach just focuses on influence of load amplitude on mechanical components, which is not suitable for the agricultural machinery, the loads of which are broad in frequency bandwidth and time-varying in stress amplitude. Therefore, considering the comprehensive influence of load amplitude and frequency on the fatigue life of materials, a power-density-based fatigue load spectrum editing (PD-LSD) approach for accelerated durability testing is proposed ensuring that fatigue load spectrum for accelerated durability testing of tractor components can reproduce operation load characteristics of components. The concept of power density is introduced, and a fatigue analysis method based on power density and short-time Fourier transform (STFT) is discussed. For the approach of this study, STFT and stress-life (S–N) curve were used to derive accumulative power density (AccPD) of the load signal. The AccPD identified and extracted high fatigue damage segments of original load signal and obtained reduced accelerated load spectrum of components. Based on the load signal of the 88-kW tractor front axle, this approach and the time damage editing approach were applied to edit the load signal. The results show that, the accelerated load Signal Ⅰ based on the PD-LSD approach with a shorter length of time contained almost same damage of the original load signal, and the statistical parameters (mean value, root mean square and kurtosis coefficient) and the signal amplitude domain of the accelerated load Signal Ⅰ were more consistent with the original load signal, which verifies the acceleration, accuracy and effectiveness of the approach. This research supports fatigue testing and durability analysis for a key component of agricultural machinery.

中文翻译：

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基于功率密度的疲劳载荷谱编辑，用于拖拉机前轴的加速耐久性测试

疲劳载荷谱是农业机械加速耐久性试验中最重要的部分之一；然而，传统的编辑方法只关注载荷幅值对机械部件的影响，不适用于载荷频带宽宽、应力幅值随时间变化的农业机械。因此，考虑载荷幅值和频率对材料疲劳寿命的综合影响，提出一种基于功率密度的疲劳载荷谱编辑（PD-LSD）加速耐久性试验方法，确保疲劳载荷谱用于加速耐久性试验。拖拉机部件可以再现部件的运行负荷特性。引入功率密度的概念，讨论了一种基于功率密度和短时傅里叶变换（STFT）的疲劳分析方法。对于本研究的方法，STFT 和应力寿命 (S-N) 曲线用于推导负载信号的累积功率密度 (AccPD)。AccPD 识别和提取原始载荷信号的高疲劳损伤段，并获得组件的简化加速载荷谱。以88kW拖拉机前桥载荷信号为基础，采用该方法和时间损伤编辑方法对载荷信号进行编辑。结果表明，基于PD-LSD方法的加速载荷信号Ⅰ在较短的时间内包含与原始载荷信号几乎相同的损伤，统计参数（平均值，均方根和峰度系数）和加速载荷信号Ⅰ的信号幅值域与原始载荷信号更加一致，验证了该方法的加速度、精度和有效性。该研究支持农业机械关键部件的疲劳测试和耐久性分析。