疲劳裂纹扩展试验载荷谱加重方法研究

为探索缩短疲劳裂纹扩展试验周期的载荷谱处理方法,对多种裂纹扩展模型进行了综述,概括出一种通用的裂纹扩展预测模型表达式。提出了一种将峰谷值同时等比例放大的载荷谱加重方法,并推导出加重前后裂纹扩展寿命的转换关系。用一种随机谱和两种块谱的基准谱及对应四种比例加重谱进行了LY12CZ中心裂纹板裂纹扩展试验,用常幅载荷谱及其1.1倍加重谱进行了典型机身壁板结构裂纹扩展试验。试验结果表明载荷谱等比例加重方法可以有效缩短疲劳裂纹扩展试验周期而不改变结构破坏模式,而分析结果表明由该方法预测的裂纹扩展寿命与试验结果的误差在15%以内,满足工程精度要求。

RESEARCH ON LOAD ENHANCEMENT METHOD FOR FATIGUE CRACK GROWTH TEST

To explore approaches of shortening fatigue crack growth (FCG) test period by load spectrum simplification and enhancement, various FCG models were reviewed, and a generalized expression was acquired. A load enhancement method magnifying all the peak and valley loads simultaneously was proposed, and the relationship between FCG lives under baseline and enhanced spectra was derived. Crack propagation tests were conducted using middle-crack tension (M (T)) specimens made of AA LY12-CZ and typical fuselage panel specimens made of AA 2524-T3 and AA 7075-T62. M (T) specimens were tested respectively under one random spectrum, two block spectra and corresponding enhanced spectra with four enhancement factors. Fuselage panel specimens were tested respectively under constant amplitude spectrum and 1.1 times enhanced spectrum. The experimental results demonstrate that the proposed load enhancement method can shorten FCG test periods effectively without changing the failure mode. The analysis result indicates that the difference between predicted FCG lives and experimental data is less than 15%, which satisfies engineering accuracy requirement.