6. Discussion
6.1. The stress and temperature dependence of constant
To ensure experimental damage is unity when failure occurs, the constant
is defined as . The constant shows the dependence on stress and
temperature as described in Figure 6. With the decrease of stress, the
constant increases. Cano23 tried to use Eyring
function to account for the stress dependence at a single temperature.
However, Eyring function is not suitable to describe the co-dependence
of constant on stress and temperature in this study. Hence, an empirical
function is constructed as follows
where , , , and are fitting constants. And above constants obtained by
fitting constant of specimens 1-12 are ,,,. Using this empirical
function, the critical experimental damage values of specimens 13-18 are
listed in Table 5. It can be observed that the critical experimental
damage values are close to unity, which indicates that the selected
empirical function is reasonable. After careful observation, the
critical experimental damage value of specimen 15 is relatively far from
unity, which can be attributed to the abrupt failure and lower rupture
strain as shown in Figure 1.