In the marine industry, designers utilize 5052-H32 marine grade series aluminum for its strength to weight ratio, and the ability of this series to resist marine corrosive environments. During the operating lifetime of a marine vessel, it experiences constant and variable amplitude loading conditions from the sea environment, plus overloads/underloads in the form of high frequency pulses. These high frequency pulses can influence the fatigue crack growth behavior of the aluminum structure. Foundational models like Wheeler and Willenborg have previously been used to predict effects of underloads/overloads on fatigue crack growth, but have proven to be inadequate for all high frequency pulse loading conditions. In this paper, we coupled observations of the crack growth path obtained using an optical microscope with detailed measurements of surface strain fields using Digital Image Correlation (DIC) to elucidate the effects resulting from these high frequency pulses. An experimental test matrix was developed for applying pulses of varying amplitude and frequency to gain fundamental understanding of the characteristics of the high frequency pulses on crack growth behavior. Experimental results indicated there is a novel crack kinking behavior which results in retardation of the fatigue crack growth. Using DIC, we identified changes in the plastic zone ahead of the crack tip that mimic a hard inclusion, affecting not only the crack path, but also the crack opening displacements and subsequent crack growth rates. This work provides a foundation for understanding effects of high frequency pulses on crack growth to enable future development of a model incorporating the effects of the plastic zone on the growth mechanisms.

在船舶行业，设计人员利用 5052-H32 船舶级系列铝的强度重量比以及该系列抵抗海洋腐蚀环境的能力。在船舶的使用寿命期间，它会经历来自海洋环境的恒定和可变振幅载荷条件，以及高频脉冲形式的过载/欠载。这些高频脉冲会影响铝结构的疲劳裂纹扩展行为。Wheeler 和 Willenborg 等基础模型以前曾被用于预测欠载/过载对疲劳裂纹扩展的影响，但已证明不适用于所有高频脉冲加载条件。在这篇论文中，我们将使用光学显微镜获得的裂纹扩展路径的观察与使用数字图像相关 (DIC) 的表面应变场的详细测量相结合，以阐明这些高频脉冲产生的影响。开发了一个实验测试矩阵，用于施加不同幅度和频率的脉冲，以从根本上了解高频脉冲对裂纹扩展行为的特征。实验结果表明，存在一种新的裂纹扭结行为，导致疲劳裂纹扩展延迟。使用 DIC，我们确定了模拟硬夹杂物的裂纹尖端之前塑性区的变化，不仅影响裂纹路径，而且影响裂纹张开位移和随后的裂纹扩展速率。