Palmgren - Miner's Rule exponent P query
Palmgren - Miner's Rule exponent P query
(OP)
Dear Experts,
I wish to know is it possible use Palmgren's - Miner's rule to calculate the equivalent torque for a given group of torques / cycles.
We have sufficient data in terms of these torque load cases but I am not sure how I may obtain the exponent p. I understand that I am using the Marco and Starkey Method which augments Miner's rule via the exponent p.
Does anyone know how I may obtain this parameter? Is this a specific material constant? Is there an approximate value we can use for ADI (Austempered Ductile Iron) and Aluminium materials for this exponent?
Any information will be greatly appreciated.
Kind Regards
Eddie
I wish to know is it possible use Palmgren's - Miner's rule to calculate the equivalent torque for a given group of torques / cycles.
We have sufficient data in terms of these torque load cases but I am not sure how I may obtain the exponent p. I understand that I am using the Marco and Starkey Method which augments Miner's rule via the exponent p.
Does anyone know how I may obtain this parameter? Is this a specific material constant? Is there an approximate value we can use for ADI (Austempered Ductile Iron) and Aluminium materials for this exponent?
Any information will be greatly appreciated.
Kind Regards
Eddie





RE: Palmgren - Miner's Rule exponent P query
There are several papers from NASA that cover the subject covering metals.
http://www
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RE: Palmgren - Miner's Rule exponent P query
I see that the value for p varies between 0 and 1, however, I have seen values of 3 and above been used....
Perhaps there is a different version of Miners rule used to calculate the equivalent torque from the cumulative torques / cycles.
Regards
Eddie
RE: Palmgren - Miner's Rule exponent P query
We made an attempt to use this approach on some H11 fasteners that we use by thousands in our process and as I recall there was a lot of work to set the value of "p". It ended up that we had made some assumptions concerning our input data on loading the fasteners that created too much scatter. The problems weren't resolved until our mathematician got involved to work on the input data.
RE: Palmgren - Miner's Rule exponent P query
Thank you for your response. I guess I could be opening up a can of worms trying to get a value for P. This is not necessarily a material constant is it?
Here is the equation that I have seen....
Torque equivalent = (((No Cycles(1)*Applied Torque)^P + (No Cycles(2)*Applied Torque)^P +...... (No Cycles(n)*Applied Torque)^P)^1/p)/total number of cycles
I cant imagine that P for this equation would be a material constant?...
Determining this equivalent torque appears to be more difficult than I thought! Any suggestions will be appreciated.
Kind Regards
Eddie
RE: Palmgren - Miner's Rule exponent P query
RE: Palmgren - Miner's Rule exponent P query
The value of P is considered to be greater than 0.0 and less than or equal to 1.0, with the value increasing with stress level. Note that with P = 1.0, this method is equivalent to Miner's Rule.
I would contact the Linda Hall Libary or the ASME to see if you can get a copy of this paper.
Marco, S.M. and Starkey, W.L. (1954) "A Concept of Fatigue Damage," Trans. ASME, Vol. 76, No. 4, pp. 627-632.
http://www.lindahall.org/
RE: Palmgren - Miner's Rule exponent P query
I can't vouch for the veracity of the statements, however you might note at website
http://www
that the author(s) state that "The nonlinear method described has good correlation to observed material behavior and can be used to sum damage in high temperature applications where there is interaction between creep and fatigue. However, like all nonlinear theories, it requires a material constant that requires a considerable amount of testing to determine and may not be available for a given material or application." So 'p' appears to me to be material dependent at least.
RE: Palmgren - Miner's Rule exponent P query
Now for nonlinear cumulative damage, the Marco-Starkey theory uses an exponent in the Miner's equation. The exponent is a function of STRESS level. This is a derived quantity based on curves of damage fraction versus cycle ratio plotted as a function of stress levels.
So, in other words, you have to conduct fatigue tests to determine the exponent for use. Here sequence of loading does impact damage fraction curves and provides a better correlation to experimental data.
RE: Palmgren - Miner's Rule exponent P query
I meant that the p in the "torque equivalent" equation is not a material constant (see third post by morris9791. P is essentially a material constant in the proper Marco-Starkey equation.
RE: Palmgren - Miner's Rule exponent P query
I understoond P to be a material constant for the Marco-Starkey eqn but for the torque equivalent equation I am trying to determine what p is. There is no sufficient reference given with the equation.
Regards
Eddie
RE: Palmgren - Miner's Rule exponent P query
In your torque equivalent equation the p is a fitting parameter that must be determined by experimental testing. You won't find this type of information in a handbook, on a website, etc.