ilfrau
Mechanical
- Oct 1, 2012
- 2
Hello everyone,
I want to ask you how facing the following problem:
analysing the fatigue life of a mechanical component critical point stressed by two or more stresses (ex: bending+torque) acting with different cicles.
I premise that I have studied on Shygley: Mechanical engineering design, and about the book the following aspects are considered:
combination of loads: are applied at the same time different kind of load
energetic method is used, combining with the Von Mises formula of the strain energy, the different σ and τ.
The method is further split:
utilizing each of the obtained "equivalent" stress in one of the fatigue failure method like Goodman, Gerber, ASME,etc...obtaining the fatigue safety coefficient
combining the two values to obtain a Smax to verify the yield strength at the first cicle
damage for cumulative fatigue: no more a only load periodicity, but we have more load cicles.
using the Palmgreen-Miner rule in this case
About the book there isn't reference about "the union" of the two circumstances.
What to do so?
The Miner rule says to calculate how many cicles the material can support if it is subjected to a σ1 tension; after it is calculated the difference with the real cicles done and it's used that value to verify with the next S2, ect...
But can I do in this way though the nature of σ1 and σ2 is different?
Example: I have 3000 bending cicles and subsequently 2000 tensile cicles?
And if I have 3000 bending-torque cicles with a certain intensity and subsequently 2000 cicles at different intensity?
I have to consider those in separate manner, or considering an ideal tension for each one?
Regards
I want to ask you how facing the following problem:
analysing the fatigue life of a mechanical component critical point stressed by two or more stresses (ex: bending+torque) acting with different cicles.
I premise that I have studied on Shygley: Mechanical engineering design, and about the book the following aspects are considered:
combination of loads: are applied at the same time different kind of load
energetic method is used, combining with the Von Mises formula of the strain energy, the different σ and τ.
The method is further split:
utilizing each of the obtained "equivalent" stress in one of the fatigue failure method like Goodman, Gerber, ASME,etc...obtaining the fatigue safety coefficient
combining the two values to obtain a Smax to verify the yield strength at the first cicle
damage for cumulative fatigue: no more a only load periodicity, but we have more load cicles.
using the Palmgreen-Miner rule in this case
About the book there isn't reference about "the union" of the two circumstances.
What to do so?
The Miner rule says to calculate how many cicles the material can support if it is subjected to a σ1 tension; after it is calculated the difference with the real cicles done and it's used that value to verify with the next S2, ect...
But can I do in this way though the nature of σ1 and σ2 is different?
Example: I have 3000 bending cicles and subsequently 2000 tensile cicles?
And if I have 3000 bending-torque cicles with a certain intensity and subsequently 2000 cicles at different intensity?
I have to consider those in separate manner, or considering an ideal tension for each one?
Regards
