The fatigue life and damage tolerance of composite stiffened panels with indentation damage are investigated experimentally using single-stringer compression specimens. The indentation damage was induced to one of the two flanges of the stringer of every panel. The advantages of indentation compared to impact are the simplicity of application, less dependence on boundary conditions, better controllability, and repeatability of the imparted damage. The tests were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in situ ultrasonic scanning. Specimens with initial indentation damage ranging between 32 and 56 mm in length were tested quasi-statically and in fatigue, and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed. The stress intensity measure provides the means to compare the collapse loads of specimens with different damage types and damage sizes, while the Paris law is used to compare the damage propagation rates in specimens subjected to different cyclic loads. This approach enables a comparison of different tests and the potential identification of the effects that influence the fatigue lives and damage tolerance of postbuckled structures with defects.

中文翻译：

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具有压痕损伤的后屈曲复合材料加筋结构的疲劳寿命和损伤容限

使用单纵梁压缩试样对具有压痕损伤的复合材料加筋板的疲劳寿命和损伤容限进行了实验研究。每块面板纵梁的两个凸缘之一都会产生压痕损坏。与冲击相比，压痕的优点是应用简单、对边界条件的依赖性较小、所造成的损伤具有更好的可控性和可重复性。测试是使用先进的仪器进行的，包括数字图像相关、被动热成像和原位超声波扫描。对长度在 32 至 56 mm 之间的初始压痕损伤的试样进行了准静态和疲劳测试，并研究了循环载荷幅度和损伤尺寸的影响。提出了一种基于应力强度测量和巴黎定律的损伤传播速率和倒塌载荷的比较方法。应力强度测量提供了比较不同损伤类型和损伤大小的试件的倒塌载荷的方法，而巴黎定律用于比较不同循环载荷下试件的损伤扩展速率。这种方法可以比较不同的测试，并潜在地识别影响有缺陷的后屈曲结构的疲劳寿命和损伤容限的影响。