fatigue for simple-to-make-but-hard-to-get-right structure
fatigue for simple-to-make-but-hard-to-get-right structure
(OP)
For some time now I have been testing a new door stopper design for our products (refrigerators) and I figured I would see if an FE analysis would have helped us do this faster. However, I have one problem: the impact force is not known and neither is the impact deformation of the door stopper and the hinge (the door stopper is attached to the door and stops against the hinge). There is no equipment available here with which to measure this and I don't have access to any software which could help in obtaining this information either.
I figured I could just use a force and do a simple comparison of designs, but what if I wanted to do this 'for real'? I have a couple of designs which failed after half the test and one which passed the test with flying colors (but which is way too expensive), should I select a force based on this?
I figured I could just use a force and do a simple comparison of designs, but what if I wanted to do this 'for real'? I have a couple of designs which failed after half the test and one which passed the test with flying colors (but which is way too expensive), should I select a force based on this?





RE: fatigue for simple-to-make-but-hard-to-get-right structure
if it's the former (i doubt it tho') then there's no problem (hence my doubts), so i assume you're guessing your test loads. why not test an existing design and interpret the result based on the known performance of the test piece ?
i think too that you're trying to simplfy the testing. FE will allow you to compare designs under a nominal load.
back to testing, i think you should test several specimens (at least 3) at a couple of load levels (hi, medium, and lo).
good luck
RE: fatigue for simple-to-make-but-hard-to-get-right structure
So I should start with a design I know failed the test and modify the force, right, but what force do I set, considering I can only perform a static analysis? Would it be fair to set it high enough to reach the yield strength of the material for the failing door stops? Or should I try to find the Wöhler curve for the materials we are testing and find the stress value for ~15000 cycles and then dimension the force to reach this stress value?
RE: fatigue for simple-to-make-but-hard-to-get-right structure
what's your constraint ... can you do lots of FE modelling to reduce the amount of testing, or lots of testing 'cause you're limited on the structural analysis side ? ... no dig intended, but it'll help with suggestions.
btw, it looks like your load spectrum is a safe life (10 openings per day over 10 years, in round numbers). so you should get a test result of about 100,000 cycles to meet the requirement.
RE: fatigue for simple-to-make-but-hard-to-get-right structure
RE: fatigue for simple-to-make-but-hard-to-get-right structure
Then feed that peak load into your FE model.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: fatigue for simple-to-make-but-hard-to-get-right structure
www.ampstech.com
Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
RE: fatigue for simple-to-make-but-hard-to-get-right structure
anyway, how about this: if I managed to measure the deflection of one door stop, I could use this to find the proper force. Of course, I will have to find something to measure with. Either a real instrument or just something which deforms easily (and permanently)...
RE: fatigue for simple-to-make-but-hard-to-get-right structure
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: fatigue for simple-to-make-but-hard-to-get-right structure
to measure the you could load up your detail thru a load cell, and apply load untill you get your measured deflection
RE: fatigue for simple-to-make-but-hard-to-get-right structure
RE: fatigue for simple-to-make-but-hard-to-get-right structure
RE: fatigue for simple-to-make-but-hard-to-get-right structure
Something I didn't take into account is the fact that the part to which the stop is fastened actually deforms (although the measurement was taken between the screw and the vertical part of the doorstop).