推土机平衡梁全尺寸疲劳试验及疲劳断口分析

在ＭＴＳ上完成平衡梁全尺寸疲劳试验后，研究了试验断口上疲劳裂纹萌生、发展的原因、过程和特点；获得箱形焊接结构的３种寿命预测模型；对选择异材设计的平衡梁，提出了改进意见。

FATIGUE EXPERIMENT OF THE FULL SCALEEQUALIZING BAR OF BULLDOZER ANDANALYSIS OF THE FATIGUE FRACTURE

Using the equalizing bar of bulldozer as an example, the fatigue design technology of boxsectioned welded structure is studied systematically. The fatigue experiments of two full scale equalizing bars, which materials of cover plates are different, are finished with test stress spectrum on the MTS Vehicle Dynamical Test System. And it is found that the lives of the two equalizing bar are almost equal. On the basis of the macroexamination and the microexamination of the fracture with the S 360 scanning electron microscope, the cause, the process, the characteristics of the fatigue crack initiation and propagation on the fatigue fracture of the two boxsectioned welded structures are studied. According to the different propagation modes of the crack, the crack process is divided into two phases. In the two different phases, the quantitative relationships between the crack length a and the crack propagation life N , between the crack propagation rate d a /d N and the crack propagation life N are established, the main stresses which cause the crack propagation are determined in detail. On the basis of the fatigue experiments and the fracture examination, there is the conclusion that the same kind of material should be chosen for the cover plate and the web of boxsectioned welded structures under bending load, such construction design is more reasonable. The models of fatigue life prediction for boxsectioned welded structures are presented, and those models also can be used to estimate the remaining life of the structures.