The present work is an extension of a previously developed fracture mechanics cracking damage model and highlights the ability of that model to predict the fatigue lifetime of un-notched round specimens made of a ferrite–pearlite 0.4C-70/30 carbon steel in the cases of (a) two-step fully reversed axial loading with low-to-high and high-to-low sequences and (b) repeated application of fully reversed two-step axial loading blocks. This model numerically simulates the collective behavior of growing short fatigue cracks originating from the specimen surface. The surface roughness is assumed to resemble microcracks of different sizes and locations along the minimum specimen circumference. Material grains of different phases, sizes, and strengths are randomly distributed over that circumference. Possible activities of surface cracks are predicted against loading cycles till a fracture occurs. Published experimental data on ferritic-pearlitic steel specimens in fully reversed variable amplitude loading are utilized. Different specimen tests are randomly configured and simulated. The present predictions are in fair agreement with the corresponding experimental results.

中文翻译：

---

基于裂纹模拟的累积疲劳损伤评估

目前的工作是先前开发的断裂力学开裂损伤模型的扩展，并突出了该模型预测由铁素体-珠光体 0.4C-70/30 碳钢制成的无缺口圆形试样疲劳寿命的能力。 (a) 两步完全反向轴向加载低到高和高到低序列和 (b) 完全反向两步轴向加载块的重复应用。该模型对源自试样表面的不断增长的疲劳短裂纹的集体行为进行了数值模拟。假定表面粗糙度类似于沿最小试样周长的不同尺寸和位置的微裂纹。不同相、尺寸和强度的材料晶粒随机分布在该圆周上。根据加载循环预测表面裂纹的可能活动，直到发生断裂。已发表的关于铁素体-珠光体钢试样在完全反向可变振幅载荷下的实验数据被利用。不同的试样测试是随机配置和模拟的。目前的预测与相应的实验结果相当一致。