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首页> 外文期刊>Journal of the American Helicopter Society >In Search of a Rotorcraft Airframe Fatigue Assessment Methodology: Cracking Prediction under Service Loading
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In Search of a Rotorcraft Airframe Fatigue Assessment Methodology: Cracking Prediction under Service Loading

机译：寻找旋翼飞机机身疲劳评估方法：在服役载荷下的裂纹预测

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摘要

Rotorcraft hub loads are functions of main and tail rotor rotational frequencies and introduce n per revolution stresses into an airframe structure. Airframe fatigue life is currently computed using the stress-life method. This approach uses an S-N curve with an endurance limit where low-amplitude cycles below the endurance limit do not contribute to damage accumulation. This method does not consider the low-cycle (high stress) and high-cycle (low stress) interaction effects. To overcome these deficiencies, a strain-life isoprobability approach is proposed. The recorded strain/stress history was analyzed using Fourier analysis to identify n per revolution vibratory stress components. It was further analyzed with a peak-valley algorithm to extract once per maneuver and ground-air-ground cycle values. The field strain was recorded near a critical location. The ground strain was derived using the finite element analysis (FEA) ground strain, FEA strain range, and measured strain from ground to hover. The notch stress at critical location is computed using the stress concentration factor. The stress-life, mean strain-life, and proposed strain-life isoprobability approaches were utilized to compute stub wing fatigue lives with various probabilities of failure. The prediction was verified using 21 failures (cracked) and 293 nonfailures (uncracked) stub wings in the fleet. The probability of fleet stub wing failure was determined with a Weibull distribution. The analytical predicted fatigue life correlated well with the observed stub fatigue cracking in the fleet at 1.86% probability of failure. The strain-life isoprobability approach can predict fatigue cracking in fleet rotorcraft in comparison to significantly higher fatigue life predicted by stress-life and mean strain-life methods.
机译：旋翼飞机的轮毂载荷是主旋翼和尾旋翼旋转频率的函数，每旋转一圈的应力会向机身结构中引入n倍。机身疲劳寿命目前使用应力寿命法计算。此方法使用具有耐久极限的S-N曲线，其中低于耐久极限的低振幅循环不会导致损伤累积。此方法不考虑低周期（高应力）和高周期（低应力）相互作用的影响。为了克服这些缺陷，提出了一种应变寿命等概率方法。使用傅立叶分析对记录的应变/应力历史进行分析，以识别每转n个振动应力分量。使用峰谷算法对其进行了进一步分析，以提取每个操纵和地面-地面-地面循环值一次。在关键位置附近记录了现场应变。地面应变是使用有限元分析（FEA）地面应变，FEA应变范围以及从地面到悬停的测量应变得出的。使用应力集中系数计算关键位置的缺口应力。应力寿命，平均应变寿命和建议的应变寿命等概率方法被用于计算具有各种失效概率的短翼疲劳寿命。机群中有21个故障（破裂）和293个非故障（未破裂）短尾翼验证了这一预测。机群短翼失效的概率由韦布尔分布确定。分析性的预测疲劳寿命与车队中以1.86％的故障概率观察到的短管疲劳裂纹密切相关。与应力寿命和平均应变寿命方法预测的疲劳寿命相比，应变寿命等概率方法可以预测机队旋翼飞机的疲劳裂纹。

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