摘要
应用扫频法对柴油机曲轴疲劳裂纹的扩展规律进行实测。该方法以谐振式疲劳试验机为平台,根据试验过程中曲轴裂纹扩展之后谐振系统共振频率下降这一现象,通过系统的扫频试验来动态跟踪裂纹扩展的参照信息。在试样发生断裂之后,再根据断口形貌对裂纹的形态和尺寸进行实测,辅助以谐振系统的有限元模态分析来对裂纹尺寸的确切值进行反推,实现裂纹尺寸的动态测量。试验结果综合反映了零部件的各种结构几何参数、加工精度、强化处理工艺等因素对裂纹扩展行为的影响。通过对4个试样进行测试,发现曲轴的裂纹扩展速率在Paris区呈现三分段规律。根据试件断口形貌的特征,对这种规律性的机理进行推论,认为这种规律是由于在曲轴圆角表层残余应力的影响下,其裂纹前沿的应力比在裂纹扩展过程中发生突变造成的。
The crack propagation characteristics of a kind of diesel crankshaft are studied by measuring the crack growth rate using the frequency sweep method. This method is based on resonant fatigue test rig. According to the regularity that the resonance frequency will drop as the crankshaft＇s crack growth, the method tracks the crack size＇s growth rate dynamically by scanning the spectra of the resonant system. After the crankshaft is broken and actual shape and size of the crack are available, finite element modal analyses are conducted to accurately calculate the crack size at various test-cycle time point. The frequency sweep method is a more capable method than normal methods. It can be directly applied to a component even with complex structure and has been treated by all kinds of technology processing. As a corresponding result, the crack growth rate curve plotted herein would synthetically reflect many influence factors on the crack propagation behavior, such as geometric parameters, precision of machine tooling and reinforcing treatments, etc. 4 crankshaft specimens are tested and the result shows that a 3-section feature exists in the Pads region of the curve. According to the specimens＇ fracture surface profile, it is concluded that the feature＇s formation is chiefly due to the stress ratio＇s sudden change during crack propagating, which is caused by surface residual stress of the crankshaft.
出处
《机械工程学报》
EI
CAS
CSCD
北大核心
2008年第1期238-242,共5页
Journal of Mechanical Engineering
关键词
内燃机曲轴
扫频法
裂纹扩展速率
残余应力
Engine crankshaft Frequency sweep method Crack growth rate Residual stress
