两种终加工工艺下LZ50车轴钢疲劳短裂纹扩展行为对比研究

Comparative Study on Short Fatigue Crack Growth Behavior of Axle Steel LZ50 with Two Final Processing Methods

为研究两种常用终加工工艺对LZ50车轴钢疲劳短裂纹扩展行为的影响,分别进行7个精车试样和6个表面滚压试样的短裂纹复型实验。观察结果表明:精车与滚压试样的主导短裂纹扩展率在微观结构短裂纹(MSC)阶段均出现2次明显下降,这一现象源于两种不同微观结构障碍的固有约束;此外,在MSC阶段,给定主导短裂纹尺度下的精车试样裂纹扩展率明显高于表面滚压试样,随着裂纹尺度和扩展驱动力的增加,这种差异逐渐减小。通过比较5种常用的统计分布函数,确定极小值分布为主导短裂纹尺度-扩展率关系的良好假设分布函数,并对相关统计演化规律进行阐述。最后,获得典型试样的短裂纹扩展率曲线。这些曲线反映了主导短裂纹在整个扩展过程中的周期性减速特征,与实验数据吻合良好。

To study the effects of two commonly used final processing methods on the short fatigue crack growth behavior, totally 7 finish turning （FT） specimens and 6 surface rolling （SR） specimens of Axle Steel LZ50 were tested by a replica technique, respectively. Observation results show as follows：The growth rate of dominant short cracks decelerates twice significantly in the micro-structural short crack （MSC） stage for both FT and SR specimens, this phenomenon roots in the intrinsic constraints from two different micro-structural barriers; the dominant short crack growth rate of FT specimen is much faster than that of SR specimen with a given dominant crack size in the MSC stage, their difference reduces gradually with increasing of the crack size and growth driving force. Taking five commonly employed distributions into account, the reasonable assumed distribution for data of dominant crack size and dominant crack growth rate was determined, and relevant statistical evolutionary laws were depicted. Furthermore, the short crack growth rate curves for typical specimens were obtained. These curves reflect the test data well, and can describe the periodic wave behavior of short fatigue crack growth reasonably.