Fides programm enables to define mission profiles. It seems to be based EXCLUSIVELY on a yearly basis. When the total of hours drifts from 8760, FIT calculation reacts very strangely :
when the period is much smaller (about 2000 H) and temperature quite high (85°C), results are the same as for 8760 hours.
when the period is much bigger (about 160000H) and temperature (high 85°C), results are almost the same as for 1 year and hence 2000 hours !
There are lots of other examples, where it looks as if time is not the major factor but only temperature.
I am quite confused about this issue and would greatly appreciate your support,
All models in the FIDES Guide are described with a yearly life profile of 8760 calendar hours. But this is only a default value, and any longer or shorter duration may be used.
If the repartition of phase′s duration remains the same, the calendar failure rate is not a function of the total life profile duration. The total duration of the life profile is not a factor at all, because the result of the prediction is not a probability but a failure rate.
This is true for low or high temperatures, for benign or harsh life profiles.
On an other hand, temperature has a direct influence on failure rate. But temperature is not the sole contributing factor : thermal cycling, mechanical vibration, humidity are the other major physical factor taken into account in a FIDES calculation.
I hope this will help you,