All material are susceptible to
, smaller the amount the larger the stress per unit amount when used at same point leading to material fatigue. It is known that For some materials, notably
and
, there is a theoretical value for stress amplitude below which the material will not fail for any number of cycles, called a
, but to go beyond this limit you need to make the parts bulky defeating the use of Titanium to replace Aluminum.
I understand what you are saying But whether the material will fail or not, is also based on the calculated stress higher or lower than allowable stress( limit)
What fatigue analysis does is basically derating the allowable stress by factor depending on the number of cycle.
Assuming you have 2 black box, one of them you inputted with your design condition like load, constraint, material,geometry etc then it will spit out the calculated stress
Then you have another box where you inputted the allowable stress and number of cycle It will spit out the limit stress.
You then compare the 2 If your calculated stress is lower than your limit you are okay
the last black box is reversible it also can spit out the number of cycle if you inputted the limit and the calculated stress
So if you have either low enough calculates stress or high enough limit stress It will spit 10 to the power of 6 or 7 cycle Which is basically infinite number of cycle or in other word indestructible. So it not true that all material will fail if subjected to cyclic load Depend on your design, material loading etc
