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Finding Stresses AND Factor of Safety Calculations on 3D jig

Finding Stresses AND Factor of Safety Calculations on 3D jig

(OP)
Hello,
I had an interview where I had to figure out the FOS at the point where the jig was most likely going fail. Didn't get all the way through the problem and didn't know if if i started out the problem correctly. Could I get some help with working through the problem? The attachment has the information given in the problem that I can remember.
Thanks,
Reuben Huddleston

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

i've corrected their (maybe intentional) spelling mistake ... its AL not LE.

do they really need 5 decimal places ? maybe for tooling, but ??

that's a lot for an interview calc !

i'd look at the two ends of the inclined flange.

another day in paradise, or is paradise one day closer ?

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

(OP)
Hi,
Thanks for responding! No they didn't ask for 5 dec. places that was just my settings in AutoCad

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

ok, what failure modes did you consider ?

another day in paradise, or is paradise one day closer ?

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

(OP)
Are you asking in terms of how failure occurred like bending and shearing failure? or failure theories?

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

failure by bending or shear ... how/where could this fail ?
where would you analyze the structure ?

another day in paradise, or is paradise one day closer ?

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

at point C, do you think 3.75in2 of steel is going to be worried by 60 lbs ? (not sure if that is the sum of the loads or each individual load; not much difference either way) Just like do you see a tension problem with the green area ?

point B or A sure ... there's a subtle difference between the two. The moment at A is clearly higher, but ...

another day in paradise, or is paradise one day closer ?

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

(OP)
Correct the piece wouldn't actually fail, the main point was to use static failure theories to find the lowest FOS. Having this at an interview I wasn't sure how to proceed with the problem.

RE: Finding Stresses AND Factor of Safety Calculations on 3D jig

I think the logic of the interview question was to see how quickly you could assess the structure, to deduce where the structure is likely to fail.

I suspect section C will have the highest margins, and so therefore not critical. Just like a tension failure in the green web area isn't likely to be critical.

Section A has the higher bending moment, but there's a twist in the calcs that makes it stronger than section B and so it isn't really obvious which is critical.

another day in paradise, or is paradise one day closer ?

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