Abstract
A fatigue test on the failure mode of flange shafts was conducted. The propagation characteristics of the initial crack at the junction between the shaft and the flange as well as its angle effect were studied. This study developed an analysis program of fatigue crack propagation, based on the APDL (ANSYS Parametric Design Language). It obtained the effective angle interval within which the initial crack is able to propagate. The fitting calculation formula was derived and the results showed that: (1) The initial crack at the junction between the shaft and the flange would propagate in the radial and axial directions; the unstable crack propagation would cause an abrupt fracture of the cross-section, failing connection; and the angle of initial crack was uncertain. (2) The crack followed the I-II-III mixed mode, which was dominated by mode I. An initial crack with a larger angle showed more noticeable II-III characteristics; KII and KIII affected the crack’s propagation angle in the radial and axial directions and they also affected the structure’s surface direction. (3) The deepest point A of the crack was located at the junction between the shaft and the flange. Its crack propagation can be divided into three stages: rapid growth (stage 1), steady decline (stage 2, buffer stage), and instability (stage 3). The initial crack angle not only affected the propagation rate at stage 1 but also influenced the fatigue life distribution of the structure during propagation. The larger the initial crack angle was, the smaller the proportion of buffer stage in the total fatigue life would be. Moreover, the propagation of crack with a larger initial angle reached instability faster after stage 1, which would cause an abrupt fracture of the cross-section. This was unfavorable for deciding the crack detection time or carrying out maintenance and reinforcement. (4) The crack propagation at the junction between the shaft and the flange was determined by the size relation between ΔKI and ΔKth, instead of the effective stress intensity factor. The effective stress intensity factor can partly reflect the law of crack propagation, but cannot serve as the only criterion for crack propagation; it must be combined with the effective angle interval, which was negatively correlated with the crack’s shape ratio, to determine whether the crack would propagate.
Highlights
As the support of the transmission parts, a flange shaft can transfer the torque and bear the load
The effective stress intensity factor can partly reflect the law of crack propagation, but cannot serve as the only criterion for crack propagation; it must be combined with the effective angle interval, which was negatively correlated with the crack’s shape ratio, to determine whether the crack would propagate
Where: ∆Keq and ∆Ke f f were the amplitudes of equivalent stress intensity factor and effective stress intensity factor, respectively; ∆KI, ∆KII and ∆KIII were the amplitudes of stress intensity factor of modes I, II, and III cracks; ∆Keq,max was the maximum value of the equivalent stress intensity factor, v was the Poisson’s ratio and here we adopted 0.3, and α was the weight coefficient, for which we took 1.0 for safety [30]
Summary
As the support of the transmission parts, a flange shaft can transfer the torque and bear the load. Atanasovska et al carried out finite element analysis of corrosion fatigue crack and turbine shaft damage based on actual turbine shaft failure cases and proposed a new method to calculate the stress concentration coefficient [8]. Zhou conducted a fatigue test of a flange shaft under bending stress and obtained the curve of the crack propagation rate and the residual strength model [13]. Many scholars have fully studied the propagation characteristics of fatigue cracks on welding components of shafts based on the numerical simulation of fracture mechanics [27]. Based on the theory of 3D fracture mechanics, the author studied the propagation characteristics of fatigue crack at the junction between shaft and flange and the focus of the study was on the impact of the initial crack angle. The study aims to help researchers understand more about the propagation characteristics of the fatigue crack on the flange shaft and to provide a reference for related research
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