Hi,
Does anyone have experience with fatigue analysis within Pro/Mechanica. I have analyzed some structure on fatigue. Pro/Mechanica calculates and displays following results:
- log life: log of number of oycles to failure. FOr example, Mechanica calculates a minimum value of log life to be 6. This simply means that the failure will occur at 10^6 loading cycles
- factor of safety: the ratio between the number of loading cycles you specifiy (desired durability) and the number of cycles to failure. Value > 1 indicates failure.
- Confidence factor: a similar definition to factor of safety (I don't the exact meaning)
- log damage: ?
In damage mechanics, the damage parameter D is the variable which indicates the number of accumulated damage and can have values between 0 en 1. Zero means no damage, 1 means complete damage (failure).
Now, log damage should simply be log(D) en dus it should be a negative number or zero for failure. However, Pro/Mechanica displayes values which equal to values voor log life, only the sign is different: log life has positive values and log damage ahs negative values.
For example, if the number of cycles to failure is 10^6 and the user speifies a desired number of cycles of 10^6, log lige will have an upper bound of 6 and the factor of safety of 1. If we now specify a desired life of 10^7 cycles, the log life will again be 6 of course (the life is still 10^6 cycles), but the factor of safety will become less then 1, which is logical. However, the calculated log damage remains unchanged. This can not be true, as the structure is definetely more damaged than in the previous case.
Does somebody know how Pro/Mechanica calculates the log damage and what it exactly means?
Does anyone have experience with fatigue analysis within Pro/Mechanica. I have analyzed some structure on fatigue. Pro/Mechanica calculates and displays following results:
- log life: log of number of oycles to failure. FOr example, Mechanica calculates a minimum value of log life to be 6. This simply means that the failure will occur at 10^6 loading cycles
- factor of safety: the ratio between the number of loading cycles you specifiy (desired durability) and the number of cycles to failure. Value > 1 indicates failure.
- Confidence factor: a similar definition to factor of safety (I don't the exact meaning)
- log damage: ?
In damage mechanics, the damage parameter D is the variable which indicates the number of accumulated damage and can have values between 0 en 1. Zero means no damage, 1 means complete damage (failure).
Now, log damage should simply be log(D) en dus it should be a negative number or zero for failure. However, Pro/Mechanica displayes values which equal to values voor log life, only the sign is different: log life has positive values and log damage ahs negative values.
For example, if the number of cycles to failure is 10^6 and the user speifies a desired number of cycles of 10^6, log lige will have an upper bound of 6 and the factor of safety of 1. If we now specify a desired life of 10^7 cycles, the log life will again be 6 of course (the life is still 10^6 cycles), but the factor of safety will become less then 1, which is logical. However, the calculated log damage remains unchanged. This can not be true, as the structure is definetely more damaged than in the previous case.
Does somebody know how Pro/Mechanica calculates the log damage and what it exactly means?