*3.3. Discussion*

Many simulations were carried out with differing failure types, as shown in Table 2, and the change rules between the spring stiffness coefficient and the amplitude variation coefficient were obtained, as shown in Table 3.


**Table 3.** The change rules between the spring stiffness coefficient and the amplitude variation coefficient.

1 decrease; 2 increase; 3 indeterminate.

As shown in Table 3, the amplitude variation coefficient probably increased, decreased or was indeterminate under different spring failures. The change rules of the amplitude variation coefficient are the same as the change rules of the amplitudes, according to Formula (30). Hence, the change rules of the amplitudes of four elastic support points in the *x*, *y*, and *z* directions can be summarized, as follows:


The change rules for amplitudes, obtained above, indicated that the spring failures would lead to amplitude change of the four elastic support points in the *x*, *y*, and *z* directions, and the amplitude change rules can reveal certain spring failures. Hence, the amplitude change rules can provide useful information for spring failure diagnosis.
