含天然与人工内部缺陷轮盘裂纹扩展特性对比分析

Crack Propagation Comparison of Disks with Natural or Preset Inclusion

关键词:  钛合金  离心叶轮  裂纹扩展  人工缺陷  内部缺陷

Key words:  Titanium alloy  Centrifugal impeller  Crack propagation  Pre-set defect  Internal inclusion

摘要:

为达到应用人工内部缺陷获得轮盘裂纹扩展特性，开展了含天然与人工内部缺陷轮盘高速旋转低周疲劳裂纹扩展对比试验，并通过无损检测分析、断口分析研究了裂纹扩展特性的差异，提出了含人工缺陷轮盘损伤容限分析思路。无损检测更易识别人工内部缺陷的特征及其变化；人工缺陷区呈碎裂状，有大量的晶间断裂，与天然缺陷区有明显差异；非缺陷区两者无明显差异。天然与人工缺陷区的裂纹扩展速率分别为0.2~0.4μm/次、0.6~1.2μm/次，均远大于基体材料理论值；1#盘加载突变区外断口反推寿命与第二加载阶段循环数的最大误差是12%；2#盘缺陷区外断口反推寿命占总循环数的44.9%~51.9%。基于人工缺陷区定义初始裂纹，排除人工与天然缺陷差异的影响，可获得轮盘裂纹扩展特性。

Abstract:

In order to obtain the crack growth characteristics of disk with artificial internal defects， the low-cycle fatigue crack propagation experiments under high-speed rotating condition were carried out on the disks with natural or artificial defect. Through the non-destructive testing analysis and fracture analysis， the difference of crack growth characteristics was studied， and the idea of damage tolerance analysis of disc with artificial defects is proposed. Nondestructive testing is easier to identify the artificial internal defects’ characteristics and its changes. The artificial defect area is fragmented， and has a lot of brittle intergranular， it is obviously different from the natural defect area， but there is no significant difference in the non-defect area. The crack growth rates in the natural and artificial defect areas are 0.2~0.4μm/cycle and 0.6~1.2μm/cycle， respectively， which are much higher than the theoretical value of the matrix material. The maximum error between the reverse life of the fracture outside the load mutation area of disc 1 and the cycle number in the second loading stage is 12%. The reverse life of the fracture outside the defect area of disc 2 accounts for 44.9%~51.9% of the total cycle number. Based on the artificial defect area， the initial crack of disk is defined to eliminate the influence of the difference between artificial and natural defects， so that the crack propagation characteristics of disk can be obtained by using artificial defects.