A problem defining material properties... HELP!
A problem defining material properties... HELP!
(OP)
Hi again everybody.
As usual, the way ANSYS handles units is a good source of confusion. In my model i'm asuming that my dimensions are in meters, so if i have to input a node coordinate in (1x;2y) milimeters, i input (0.001x;0.002y) for being consistent with my units. But when i'm defining the material properties i don't get any results in a modal analysis. I guess maybe it's because the units i'm using at the time i'm defining material properties.
An example of what i'm doing at defining is this:
Preprocessor - Material Models - Material Model Number 1 - Density
Here for aluminium i input in SI: 2700 (kg/m^3)
And again:
Preprocessor - Material Models - Material Model Number 1 - Linear Isotropic - EX
Here, for aluminium, i input in SI: 70000 (MPa)
But the modal analysis doesn't returns any result!
Anyone can tell me what's wrong here???
Thank you very much.
As usual, the way ANSYS handles units is a good source of confusion. In my model i'm asuming that my dimensions are in meters, so if i have to input a node coordinate in (1x;2y) milimeters, i input (0.001x;0.002y) for being consistent with my units. But when i'm defining the material properties i don't get any results in a modal analysis. I guess maybe it's because the units i'm using at the time i'm defining material properties.
An example of what i'm doing at defining is this:
Preprocessor - Material Models - Material Model Number 1 - Density
Here for aluminium i input in SI: 2700 (kg/m^3)
And again:
Preprocessor - Material Models - Material Model Number 1 - Linear Isotropic - EX
Here, for aluminium, i input in SI: 70000 (MPa)
But the modal analysis doesn't returns any result!
Anyone can tell me what's wrong here???
Thank you very much.





RE: A problem defining material properties... HELP!
Or better, check the listing of the *.err file in List>Files>Error File.
Second, after defining the material, check list>properties>all materials and see if the density is really defined.
For aluminium you should see:
MATERIAL NUMBER = 1 EVALUATED AT TEMPERATURE OF 0.0000
EX = 0.70000E+11
NUXY = 0.30000
DENS = 2700.0
Regards
Alex
RE: A problem defining material properties... HELP!
the mistake is in the E unit: you mustn't use [MPa] but [Pa], so that the unit of force is [N]:
[pressure] = [force]/[surface] = [force]/([length]*[length] = [N]/[m^2] = [Pa].
Btw: the unit for acceleration is coherently [m/s^2].
Regards
RE: A problem defining material properties... HELP!
sorry for the post in two pieces... I forgot:
also make sure that the size of your model does match the dimensional system you are using: list the keypoints' or nodes' coordinates and see if they are coherent with "meters" (no coordinates such as "12640"...).
If you have volumes defined, check their properties with VSUM.
If your model comes from CAD in [mm], you'd better drop the SI system and use:
native [mm] for length
[N] for force
[MPa] for pressure (and pressure-like units)
[mm/s^2] for acceleration
[tonne] = [10^3 kg] for mass
[tonne/mm^3] for density
Regards
RE: A problem defining material properties... HELP!
I don't have any idea of what's happening here. The software only gives results for Aluminium if:
1 - I draw my model being consistent with SI: In this case is a rectangular rod 6mm x 3mm area and 20mm long. I command it this way to ANSYS: 0.006 x 0.003 and extrude 0.02
2 - I define the material properties like this:
EX = 70 (In fact, Elastic modulus for Al is 70GPa - SI))
PRXY = 2,8 (It doesn't changes at all)
Silly that ANSYS only give me results if i'm inconsistent with the units i'm using. So, as i said before, i don't have any idea of what's happening here.
Thanks.
RE: A problem defining material properties... HELP!
Did you really input MP,PRXY,,2.8 ??? Then that is your problem. I don't know any material with such a huge PRXY (Major Poisson's ratio)
Try for aluminium: PRXY=0.3
Alex
RE: A problem defining material properties... HELP!
for isotropic materials PRXY must be lower then 0.5.
Alex
RE: A problem defining material properties... HELP!
By the other hand, i still got the problem with the units... only if i make my aluminium rod become a jelly rod, i can see any result in the results summary.
That issue still is there.
RE: A problem defining material properties... HELP!