Cyclic Destructive Testing - Continuous vs. Segments

hogheavenfarm

Quite Involved in Discussions
#1
Just a question to throw out there.
We have to do a function test on a product that requires testing operation to 100,000 cycles. We are a fairly small organization, and have determined that this test will take several days of continous running. Since we do not have personnel here 24 hours, we want to break the test up into 8 hour segments, so someone will be availble to observe the test at all times.
Does this compromise the integrity of the test?

Some more data if it would be helpful, we are testing for fatigue of a large spring, and bushing wear at a hinge point.
 
Last edited:
Elsmar Forum Sponsor
#2
Re: cyclic destructive testing

Have you thought about sub contracting the test? Then you don't have to worry about personnel coverage or test integrity.......might even be cheaper!
 

Tim Folkerts

Super Moderator
#4
Re: cyclic destructive testing

Unless the test procedure specifically calls for continuous testing, I don't see how it would be a problem to break the test up into several intervals.

There might be some small change in results. Electronics for instance often work better once they are warmed up, so they might well last a little longer in on continuous test rather than turning on & off multiple times during the testing. Other items can "recover" while not it use and might last a little longer by letting them "rest" overnight.

For a spring I don't expect it will make a big difference either way. (But I have no specific experience with springs to back that up).


Tim F
 

Jim Wynne

Staff member
Admin
#5
Re: cyclic destructive testing

Just a question to throw out there.
We have to do a function test on a product that requires testing operation to 100,000 cycles. We are a fairly small organization, and have determined that this test will take several days of continous running. Since we do not have personnel here 24 hours, we want to break the test up into 8 hour segments, so someone will be availble to observe the test at all times.
Does this compromise the integrity of the test?

Some more data if it would be helpful, we are testing for fatigue of a large spring, and bushing wear at a hinge point.
It depends on what you expect the testing to show you. Obviously, if you want to know whether the thing will withstand 100,000 cycles in continuous operation, you wouldn't want to break it up. If knowing that it can take 100,000 cycles in intermittent operation is enough, then it shouldn't be a problem.
 

hogheavenfarm

Quite Involved in Discussions
#6
Re: cyclic destructive testing

You are correct Jim, The point is mechanical failure, not necessarily a result of continuous action, just specifying a limit to the duration.
 

Jim Wynne

Staff member
Admin
#7
Re: cyclic destructive testing

You are correct Jim, The point is mechanical failure, not necessarily a result of continuous action, just specifying a limit to the duration.
Something that's often done in these cases is allowing the testing to continue until failure does occur, even after 100,000 (or however many relevant cycles/acutations/whatever). I recall an instance of testing an automotive window regulator that went on continuously for about a year, and was ended when the motor that ran the apparatus failed (the test fixture failed before the assembly under test did).
 
U

Umang Vidyarthi

#8
Just a question to throw out there.
We have to do a function test on a product that requires testing operation to 100,000 cycles. We are a fairly small organization, and have determined that this test will take several days of continous running. Since we do not have personnel here 24 hours, we want to break the test up into 8 hour segments, so someone will be availble to observe the test at all times.
Does this compromise the integrity of the test?

Some more data if it would be helpful, we are testing for fatigue of a large spring, and bushing wear at a hinge point.
To the best of my knowledge and experience, continuous running till it gives way, is a pre-requisite for any 'Fatigue Test'. By permitting rest periods you are not permitting the 'Fatigue' to set in and in that case, the 'Fatigue test' becomes a misnomer. The definition of fatigue in engg. is "The rupture or break down of material subjected to series of stresses."

You are correct Jim, The point is mechanical failure, not necessarily a result of continuous action, just specifying a limit to the duration.
IMO your inference drawn from Jim's post is not his intended response, as is further clear from Jim's next post at #7. This happens when you are groping for an answer suitable to your convenience. My advise is that you should continuously run the test, if found not feasible then you may outsource the same, as Andy has suggested here.

Hope this helps.

Umang :D
 

hogheavenfarm

Quite Involved in Discussions
#9
OK, it was the thought that was lurking in the back of my mind, and why I posted this question. It makes sense viewed in that light.
 

Tim Folkerts

Super Moderator
#10
To the best of my knowledge and experience, continuous running till it gives way, is a pre-requisite for any 'Fatigue Test'. By permitting rest periods you are not permitting the 'Fatigue' to set in and in that case, the 'Fatigue test' becomes a misnomer. The definition of fatigue in engg. is "The rupture or break down of material subjected to series of stresses."
I'm not a metallurgist (although I have known a few).

I'm not sure what you mean by "permitting the fatigue to set in". The article on fatigue at Wikipedia (I know - it is not always a reliable source) says in part:


  • The process starts with dislocation movements, eventually forming persistent slip bands that nucleate short cracks.
  • Fatigue is a stochastic process, often showing considerable scatter even in controlled environments.
  • The greater the applied stress, the shorter the life.
  • Fatigue life scatter tends to increase for longer fatigue lives.
  • Damage is cumulative. Materials do not recover when rested.
  • ...
This last line indicates to me that continuous testing would not be required. If you do 50,000 cycles and then pause, the damage is done and the material should get neither better not worse the next day. So you should be able to continue the testing from there with little or no change in the final results.

AGAIN - I am not a professional metallurgist. If the answer to this question is critical, then I would strongly advise getting the opinion of a metallurgist, not the opinion of a quality engineer.


Tim F
 
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