FIGURE 9 Schematic diagram of nonlinear damage accumulation.
Like constant, an empirical function is also constructed as follows:
where constants, , , and are obtained by best fitting. When the slop is zero, can be obtained, which means the slop is negative if . Constant will decrease with the increase of stress at a given temperature when the temperature is less than 727℃.
Eq. can also be arranged as the function of temperature :
Similarly, when the slop is zero, can also be calculated, which means the slop is negative if . Constant will decrease with the increase of temperature at a given stress when the stress is less than 1152MPa. Generally, the service temperature and stress of GH4169 are much lower than above ranges, which means that the total life will be reduced for those engineering structures made of GH4169 when high stress or high temperature loading condition is applied first.