Correct thermal expansion coefficient unit in NX Nastran?

[Srki1982]

Hi,

I hope someone can help me out with units in FEMAP with NX Nastran.

I am working in (mm) scale and I use following material data for a simple model:

Youngs module E: 200000,
Poisson's Ratio, nu: 0,27
Expansion Coeff, a: 1,728E-5
Conductivity, k: 0,015
Specific Heat, Cp: 500000
Mass Density: 7,9E-9
Reference Temp: 20


When I apply nodal temperature load from output (from Steady-State Heat Transfer Analysis result with temperature loads 10 C and 100 C) to my load condition and run the static analysis the stress increases from 17 MPa to 132 MPa. This is according to me higher increase of stress then it should be. Rp0,2 at 20C is 220 MPa and 166 MPa at 100 C. So basicly it should be a increase of 33 % as a result.

What should I have as input because I cannot find any good information about this?

Best regards

/Srki

 

[Srki1982]

I can answer on this myself. Hope it can help anyone else

In my case I worked in mm scale. Thermal expansion coeff is usually stated in xx 10^-6 K^-1 and for stainless steel EN 1.4404 it is (16 x 10^-6 K^-1). K^-1 can be written as um/m K (micro meter/meter K)and because of that I needed to multiply with 10^-3 to obtain the value in um/mm K. When I changed the expansion coeff to (16x10^-9 x 90) in FEMAP the result was much better. Multiplication with 90 is there because of the temperature increase of 90 C or 90 K.