Life factor for long life in ISO 6336-2 standard

[meemouk]

The ISO 6336-2 standard mentions that the life factor for long life should range between 0.85 and 1; where 1 stands for optimum conditions and 0.85 stands for critical service where pitting lust be minimal. Does anyone know why 0.85 is the minimum value? can you take a lower value like 0.7 or 0.6? and how to decide that?

 

[RolMec]

Hello,
the numbers / values are based on the specified standard reference test gears, having run (long life) up to 10 exp10 cycles. Referenced to an optimum condition and a cycle limit of e.g. 2x 10 exp6, 5x 10 exp7 or 10 exp9 , the respective decrease in load bearing capacity versus non - optimum conditions amounted to -15%, this is then the limit of 0.85 given in the table 2 as well as figure 6.
However, non - optimum conditions are in themselves already demanding a minimum of technical environment, and then there's fast running gears that may exceed the 10 by 10 cycles limit. For those circumstances, you need to find additional input / do your specific tests, see chapter 5.4.
Regards

 

[meemouk]

Thank you RolMec for your answer. Just to double check I understood you correctly, if I am deriving an S-N curve for a new material/heat-treatment that was not included in the ISO standard and I got a value of the life factor below 0.85 for long life, should I accept it?