A prediction method for fatigue life of large moving components as function of scale factor: A case of motor‐generator rotor

Abstract

With the development of science and technology, more and more large moving components have been used in industry, and their service lives have become an important issue. After analysis of the previous results, considering the scale factor, a prediction method for fatigue life of large moving components based on the Basquin relation was proposed at first, and then the magnet pole part of motor‐generator rotor was chosen to make simulation parts with different scale factors mainly in terms of their S‐N curves and fractographies. It was found that with the change of specimen scale factor, the stress concentration factor at transition arc is almost unchanged as well as the fatigue strength exponent, and the fatigue strength coefficient changes linearly. Based on those results, a life prediction method was validated, and the results show that this method is a simple but more precise relation. After fatigue fracture surface and crack growth angle observations and quantitative analyses, the fatigue damage mechanisms associated with the relation among fatigue strength exponent and coefficient and scale factors were explained well. Those studies will provide a new clue to the prediction of the service life for those large moving components.

A fatigue life prediction method from magnetic pole material to simulation part

“…As shown in Figure 2(b), the maximum stress appears at the T tail structure, so it is the key part of the motor-generator rotor. Therefore, the simulation part was designed for fatigue testing according to the key part features and mainly based on the three similarity principles (Pan et al., 2017).

Figure 2.(a) The diagram of 1/12 rotor; (b) Von-Mises stress of 1/12 rotor; (c) FE mesh of the simulation part; (d) Von-Mises stress of the simulation part.

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“…However, as indicated in equation (21), it is interesting to find that for the scaled simulation parts, the r 1 / r n is the ratio of their overall dimensions, so it can be rewritten as follows: where s is the scale factor (Pan et al., 2017).…”

“…As shown in Figure 2(b), the maximum stress appears at the T tail structure, so it is the key part of the motor-generator rotor. Therefore, the simulation part was designed for fatigue testing according to the key part features and mainly based on the three similarity principles (Pan et al, 2017). Geometry similarity: According to the FE analysis, the key part of the rotor was the T tail structure, and an independent T tail can reflect the stress characteristics and fatigue life of the magnetic pole and was prepared as simulation part for fatigue testing.…”

“…where s is the scale factor (Pan et al, 2017). The C D generally refers as to the change of the fatigue strength for materials or conventional specimen, while the scale factor s refers as to the dimensional change between components.…”