Fatigue Life Optimization Of Y-560 Electromotor Axes And Ribs Weldment

Several electromotor axes ruptured at the weld toe of the axes and the face of the free end of the rib just one year after putting into operation, which affected the regular service of the electromotor seriously. For the problem, with the theory of welding mechanics, numerical simulation technology as well as fracture mechanics, this paper first analyzed the stress distribution and calculated the fatigue strength of the structure, then put forward the optimization design of making-up welding at the face of the ribs, which was proved to be an effective way to reduce the local stress concentration. To improve the efficiency and lower the cost of the axes, another design was also developed—reducing the original weld dimension.By the large engineering software MSC.Marc, the load of this electromotor axes were classified into two types: mean stress(constant load) and stress amplitude(alternation load). To make a full analysis, assumed that there was a elliptic-chip crack with 0.5mm in depth pre-existed at the welding toe of the electromotor axes. Thus, theⅠ-type crack, which propagated along the radial direction, are driven by the constant longitudinal welding residual stress and orthogonal variable axial stress caused by the gravitational force under high speed rotation of 2340 r/min; while the loading spectrum of theⅢ-type crack were the superimposition of constant transverse welding residual stress at weld toe and shear stress when impact torque were stroked.By the comparison of the calculated fatigue lives of the duty end and the free end respectively, theⅠ-type crack propagated much faster than theⅢ-type crack, which means a shorter service life. So the reason for the failure of the electromotor axes was the axial tensile stress, which was generated by the gravitational force loaded on the unequal distance between the end and its relative bearing. Obviously, the free end was 150mm longer to the bearing one, thus gave birth to the peak axial tensile stress at the weld toe of the face of the free end. With the making-up welding at the faces of the rib, the fatigue life could be prolonged 2.32~3.35 year at the free end, that was 54%~121% net increment, which proved this optimization design was very practical and acceptable. Under the same working conditions, the design of reducing the weld dimension could also prolong the service life of the structure by about 0.81~1.29 year at the free end, however, compared with the first scheme, this design was less satisfactory.