mhill700
Mechanical
- Jul 7, 2009
- 1
Hello Experts,
I have a test report detailing methods used to estimate the endurance limit of single components in a multiple step fatigue test.
In this test, the component undergoes one million cycles with a maximum load of 2000 N, another million cycles with a max load of 3000 N, and so on, for a total of five million cycles. This makes the graph of maximum load vs number of cycles a stepwise graph. The time of failure of each component tested is marked on this graph.
In estimating the endurance limit, the testers used the following formula:
FDL = Fo,L-1 + [(Fo,L - Fo,L-1) x (nL/del
)]
where
FDL = endurance limit
L = index of load level at which component fails (1-5)
Fo,L = max load level at which component fails
Fo,L-1 = max load on level L=1
nL = number of cycles to failure at Fo,L
del = number of cycles at one load level of test
This is the protocol outlined in the international standard ISO 7206-8, but I do not own rights to this protocol and would like to avoid having to purchase it if possible. The standard is titled Implants for surgery -- Partial and total hip joint prostheses -- Part 8: Endurance performance of stemmed femoral components with application of torsion.
I am interested in the research or proofs which led to the creation of this formula, as I have never seen it before and currently no indication as to how it was derived. I have been doing a lit search and so far I have not been able to find anything even remotely similar to this formula, though it seems that the part of the equation (nL/del) vaguely resembles the Palmgren-Miner linear damage hypothesis, as it is a ratio involving number of cycles to failure with number of cycles at a given stress magnitude. I am not certain that this correlation is valid, this was only my first guess.
Thank you for your time.
Mike
I have a test report detailing methods used to estimate the endurance limit of single components in a multiple step fatigue test.
In this test, the component undergoes one million cycles with a maximum load of 2000 N, another million cycles with a max load of 3000 N, and so on, for a total of five million cycles. This makes the graph of maximum load vs number of cycles a stepwise graph. The time of failure of each component tested is marked on this graph.
In estimating the endurance limit, the testers used the following formula:
FDL = Fo,L-1 + [(Fo,L - Fo,L-1) x (nL/del
)]where
FDL = endurance limit
L = index of load level at which component fails (1-5)
Fo,L = max load level at which component fails
Fo,L-1 = max load on level L=1
nL = number of cycles to failure at Fo,L
del
= number of cycles at one load level of testThis is the protocol outlined in the international standard ISO 7206-8, but I do not own rights to this protocol and would like to avoid having to purchase it if possible. The standard is titled Implants for surgery -- Partial and total hip joint prostheses -- Part 8: Endurance performance of stemmed femoral components with application of torsion.
I am interested in the research or proofs which led to the creation of this formula, as I have never seen it before and currently no indication as to how it was derived. I have been doing a lit search and so far I have not been able to find anything even remotely similar to this formula, though it seems that the part of the equation (nL/del
) vaguely resembles the Palmgren-Miner linear damage hypothesis, as it is a ratio involving number of cycles to failure with number of cycles at a given stress magnitude. I am not certain that this correlation is valid, this was only my first guess. Thank you for your time.
Mike
