I picked up some material files from one of the ProE sites. The tension for all of the ductile irons has the yeild properties in it. Now my boss has ask why did it not use the tensile strength? ie 65000
45000 12% In the tension feild the yeild of 45000 was used. Now this is for all the Ductile Irons. What do you think. Is there a reason that ProE need this? Or Should it be 65000 instead of 45000?
Ok guy that is where I picked up these files. You really did not answer the question. MATERIAL A536_65-45-12_DUCTILE_IRON This file may be edited using available editor. Just type on the necessary lines appropriate values after the "=" sign. Comments are not permitted on lines containing material properties names.
YOUNG_MODULUS = 2.270000E+07 POISSON_RATIO = 2.900000E-01 SHEAR_MODULUS = 9.300000E+06 MASS_DENSITY = 2.570000E-01 THERMAL_EXPANSION_COEFFICIENT = 6.000000E-06 THERM_EXPANSION_REF_TEMPERATURE = 7.000000E+01 STRUCTURAL_DAMPING_COEFFICIENT = 8.316000E-04 STRESS_LIMIT_FOR_TENSION = 4.500000E+04 STRESS_LIMIT_FOR_COMPRESSION = 1.500000E+05 STRESS_LIMIT_FOR_SHEAR = THERMAL_CONDUCTIVITY = EMISSIVITY = SPECIFIC_HEAT = 1.300000E-01 HARDNESS = 1.985000E+02 CONDITION = A536_65-45-12 INITIAL_BEND_Y_FACTOR = 5.000000E-01 BEND_TABLE = PRO_UNIT_MASS = UNIT_POUND PRO_UNIT_LENGTH = UNIT_INCH PRO_UNIT_SYS = PROE_DEF
Look at this and tell me if the STRESS_LIMIT_FOR_TENSION is right. Or Should it be 65000?
Depends if you read "STRESS_LIMIT_FOR_TENSION" to mean "UTS" or "Yield Strength". The way it's worded it sounds like "Yield Strength". I'm not sure if and how Mechanica interprets these files. When I designed lifting structures I always used UTS in my hand calcs, then applied a f.o.s. afterwards depending on the application. If you apply the same f.o.s. after using Yield Strength in the calcs your structures will be over designed. You will have to find out how this information is used by the software to decide.
Mechanica added failure crition a while back. So while most FEA only requireds poisson ratio & Modulus to run they allow you to specify a failure limit and a failure model (Last I knew they had 3 in there) It's up to you to pick the numbers and the right criterion. I'd have to root around on internet for a while to answer which number ...
Yeah - I didn't either... that's the beauty of newsgroups :-)
Agreed on the F.O.S... I thought that Yield was where it first starts breaking and Ultimate where it comes apart.. There's probably a textbook on all of our shelves that explains this... So the lower number is probably better... I'd argue with optimization you should be able to move stresses around and still save money so that you don't have to design on the hairy edge.
-meld
Exceeding yield strength will result in permanent deformation.
The yield point is where the relationship between stress and strain is no longer linear and plastic flow occurs. It's not a failure point in the sense of the material breaking but there *is* permanent deformation and the material will not return to its original state when the load is removed.
The Ultimate Tensile Strength (UTS) is the point, above the yield point, where rupture occurs.
Generally, Engineers are interested in the behaviour of the material in its linear region - that is up to the yield point - and the yield point is what is used in stress calculations along with an appropriate safety factor. I can't imagine that Mechanica would be interested outside this region either.
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