This study proposes a novel methodology to model the fatigue crack growth acceleration under underloads using a phase field fracture framework. In this model, fatigue crack growth is characterized by the degradation of fracture toughness, with an emphasis on employing a representative loading strategy instead of explicit cyclic loading, thus accelerating simulations of high-cycle fatigue. The model integrates a zone-based crack acceleration approach that responds to single-cycle underload. Notably, the model adeptly captures the dynamics described by the Paris-Erdogan law. Post-underload crack growth acceleration is simulated by identifying an acceleration zone near the crack tip, inspired by existing models based on the plastic zone. This zone is defined by a strain energy density threshold, and the underload ratio governs the rate of fatigue damage accumulation attenuation within this area. The implementation leverages the UMAT user subroutine in Abaqus, utilizing coupled temperature-displacement elements where temperature analogously represents the phase field parameter. Experimental validation of the model confirms its ability to accurately reflect the loss of fatigue life and the acceleration of crack growth rates in compact tension and middle tension specimens. Additionally, the model shows promise for extension to periodic underloads, highlighting its potential for simulating real-world fatigue scenarios effectively.

中文翻译：

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欠载引起的疲劳裂纹加速的相场建模


本研究提出了一种使用相场断裂框架来模拟欠载下疲劳裂纹扩展加速度的新方法。在该模型中，疲劳裂纹扩展的特点是断裂韧性下降，重点是采用代表性加载策略而不是显式循环加载，从而加速高周疲劳的模拟。该模型集成了基于区域的裂纹加速方法，可响应单周期欠载。值得注意的是，该模型巧妙地捕捉了巴黎-埃尔多安法所描述的动态。受到基于塑性区域的现有模型的启发，通过识别裂纹尖端附近的加速区域来模拟欠载后裂纹扩展加速。该区域由应变能密度阈值定义，欠载比控制该区域内疲劳损伤累积衰减的速率。该实现利用 Abaqus 中的 UMAT 用户子例程，利用耦合温度位移元素，其中温度类似地代表相场参数。该模型的实验验证证实其能够准确反映紧凑拉伸和中等拉伸试样中疲劳寿命的损失和裂纹扩展速率的加速。此外，该模型有望扩展到周期性欠载，突显其有效模拟现实世界疲劳场景的潜力。