American units
American units
(OP)
Hi guys,
I have to built a FE Model using the following units:
length -> in
force -> lbf
time -> s
I am not very used with american units and I am looking for the corresponding unit of mass (lbf s²/in ??) and its conversion with lb.
I found that 1 lbf s² /in = 386.1 lb.
Is that correct?
Thank you.
I have to built a FE Model using the following units:
length -> in
force -> lbf
time -> s
I am not very used with american units and I am looking for the corresponding unit of mass (lbf s²/in ??) and its conversion with lb.
I found that 1 lbf s² /in = 386.1 lb.
Is that correct?
Thank you.





RE: American units
1 g is 32.2 f/s/s
1 lbf = force that one g exerts on one lb mass
one lb mass is accelerated at 32.2*12 (=386) inches per second per second, by 1 lbf
so...
1 lb mass = 1 lbf/(386 in/s/s)
which is what you said, so I think you are good to go. When in doubt convert it all back to proper units (grin)
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: American units
I did the calculation you mentionned and it confirms my results.
Bye.
RE: American units
1 in = 2.54 cm
1 s = 1 s (hey, at least we Americans got ONE unit right
Many people have NO IDEA how to do what you just did, but your conversion is correct.
Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
Magnitude The Finite Element Analysis Magazine for the Engineering Community
RE: American units
It was slugs that confused me at University.
Like Greg said, for complex problems it's sometimes easier to work in 'native' units and convert to the other system at the end.
RE: American units
as Kenat says, if you don't feel totally comfortable with coherent unit systems other than metric, then the best you can do is to express/build (it depends on how the CAD "interprets" the "units") the model in metric units, do all the FEA in metric units, and then express the whole in imperial units: simply do the equivalences mm -> in and MPa -> lbf/sqin. The stress/strain/force field obviously remains the same !!! Most FE programs have a function to "scale" the stress results (more generally: the "summable quantities"), so you can have the plots "expressed" in imperial units only in postprocessing, if you need to include them in reports.
Regards
RE: American units
http://www.onlineconversion.com/
http://www.unitconversion.org/
I suggest you work the model in Metric and convert the results afterwards. Or you can work them once in both English and Metric and see if the units are ok.
RE: American units
If all you are doing is a static analysis, then the time shouldn't enter in, and it would just be inches and lbs and psi for everything.
If it's any more involved than that, you need to make sure the units are all consistent regardless of whether it's metric or not- that doesn't just automatically eliminate all problems.
RE: American units
btw, they're "imperial" units, not "american" ... tho' america is the last hold-out !
RE: American units
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: American units
Here in Canada we use Imperial units when not being metric.
RE: American units
Imperial Units = platoons of stormtroopers
Meanwhile back at the ranch.
Unlike in metric, there is no difference in imperial between a Force and a weight, both are in pounds. So there is no multiplying by gravity.
csd
RE: American units