Temperature effect on EX for modal analysis

[harshn]

Hi All,

I am trying to induce temperature dependent isotropic modulus of elasticity in Modal analysis of a structure.

For this I followed the following steps. I defined a SOLID45 structural element and added a temperature DOF, specified the material property using MP command in which modulust of elasticity was specified as

MP,ex,1,500e6*(1+0.001*25),-0.001*500e6
and used physics,write,struct to write structure settings.

Then I changed to thermal element using ETCHG, following which I specified the thermal properties and wrote the physics of thermal problem using physics,write,thermal. Then I entered static thermal analysis solution mode specified the boundary conditions and solved for temperature by reading the the thermal physics.

Now I re-enter the solution phase read the structural settings and used ldread to apply temperature on the added temperature DOF using
ldread,temp,,,,1,,rth
I am not seeing the effect of -0.001*500e6 factor in the modal solution. Moreover description of MP command states "A polynomial input is not valid in an explicit dynamic analysis. C1, C2, C3, and C4 are ignored."

HOW CAN I iNCORPORATE TEMPERATURE EFFECTS ON EX VALUE FOR MODAL ANALYSIS ?

 

[Stringmaker]

Firstly have you issued the LDREAD command and plotted temperatures within your structural analysis to verify the correct distribution has been applied? Next I'm not entirely sure that you're definining modulus vs. temperature correctly. Have you plotted modulus to verify? Does it show temperature dependency? To define a temperature dependent property you'll want to use the MPTEMP command and the MPDATA command subsequently. Once you've done this and you've verified that your temperature are applied as BF's you should be set to solve your modal analysis.

-Brian

 

[harshn]

Hi Brian,

I appreciate you reply, I am a novice in using ANSYS. So I may ask some basic questions.

1. When I try to plot temperature variation over the structure after modal analysis I see no distribution. But when if I try to do static analysis and then plot the temperature distribution then I can see the exact and temperature distribution over the structure.

2. The ANSYS documentation indicates that "MP - Defines a linear material property as a constant or a function of temperature." using the following format.

MP, Lab, MAT, C0, C1, C2, C3, C4
where,
Lab Property = C0 + C1(T) + C2(T)^2 + C3(T)^3 + C4(T)^4

I specify the material property as

MP,EX,1,40,-10 (simple value for understanding)
thereafter plotting Ex using:
mpplot,Ex,1,0,40

but it still shows me a constatnt temperature variation with Ex value at 40. Should not the variation of EX applied automatically as explained in the manual.

Can you help me with these 2 observations?

3. When I use
LDREAD,temp,,,,,,rth
temperature as body loading and not as nodal constarined which you suggested I can see that when I change the last value in MP command the modal frequency do changes.

I will appreciate your suggestions.

Regards
Harsh