基于DIC的焊接钢轨疲劳裂纹扩展特性研究

Study on Fatigue Crack Growth Characteristics of Welded Rail Based on DIC Technology

位于焊接钢轨轮轨接触表面以下5~25 mm的次表面区域抗蠕滑载荷疲劳裂纹扩展能力的精确表征是合理制定钢轨打磨周期的基础。测试了焊接钢轨次表面母材及焊缝区域在不同应力比下的疲劳裂纹扩展速率,同时借助数字图像相关(DIC)技术捕获了不同条件下试样平面内实时应变特性,解析了母材及焊缝区域抗疲劳裂纹扩展能力及裂纹扩展过程中裂纹面及尖端变形特性。结果表明,相同条件下焊缝区域抗疲劳裂纹扩展能力更弱。低应力比条件下,裂纹扩展表现出更为显著的塑性诱导裂纹屏蔽效应。基于DIC测试获取试样面内变形特征,建立了疲劳裂纹扩展过程中裂纹面及尖端因塑性变形引起的局部应力受力模型。

The exact characterization of rail fatigue cracks growth ability under the creep load is the basis for formulating reasonable rail grinding plan,these cracks located in 5~25 mm below the rail tread.In this paper,fatigue crack growth rate of base metal and joints under different stress ratio were tested,real-time strain characteristics were captured by using DIC(Digital Image Correlation)technology,fatigue crack growth abilities between base metal and joints and characteristics of crack flanks and tips were analyzed.The results show that the fatigue crack growth ability of joint is weaker than that of base metal,obvious characteristics of plasticity-induced crack closure are shown under condition of small stress ratio.Then,a local stress model around crack flanks and tips led by a plastic zone is established based on the results of strain characteristics in the samples got by DIC technology.