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[dbt2dariomn]

Hi all,

I am trying to run a simple analysis that consists of an arm that has a torch. They come from a transient thermal analysis, so they are at 150ºC aprox.

However, when I see the solution, I find it has a displacement on the positive axis (+Y axis) instead of the negative direction. How is that possible? I have also considered the standard earth gravity for the analisys, and my model weights about 250kg...I cannot understand why it moves upwards...

 

[Aniket]

Could this be due to difference in coef of thermal expansion of different materials similar to a bimetallic strip?

Try without added temperatures, and only with standard earth gravity to verify that.

-Aniket

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[dbt2dariomn]

 

Doing the analysis only with earth gravity and without temperature makes sense, as it moves downwards (expected). The materialas are the same both thermal and structural analysis (structural steel)

Why is there such difference with/without temperature? I think I am doing something wrong…

 

[peteroznewman]

Please reply with a plot of the Temperature load that came from Transient Thermal. If the beam is hotter on the bottom and cooler on the top, thermal expansion will cause the arm to curve up.

[dbt2dariomn]

Indeed Peter, it is hotter on the bottom, but only a few degreees more..what I do not understand is why the influence of the temperature is higher than the influence of the weight of the own beam if it weights 250kg.

Remark: In SS, when imported body temperature, I placed time at t=20 min (1200s); source time =analysis time = 1200s and then the arm curves down. But, if I place source time =1200s and analysis time = 1s the arm curves up. Does this has to do with the final results?

[peteroznewman]

The force of gravity is smaller than the force of thermal expansion, so when there is a delta Temperature betweeen the bottom and top surfaces, the arm will curve up.

If you set analysis time to 1200s, is that where there is a very small delta Temperature?  If you set analysis time to 1s, is that where there is a very large delta Temperature?  That would explain the difference in curvature. 

[dbt2dariomn]

There is a delta temperature of aprox 10ºC, that is to say, hotter in the bottom surface. But I still find it difficult to understand how a 10ºC difference can overcome 250kg of weight...

[peteroznewman]

250kg is a force of about 2,500N due to gravity.

Do a hand calculation of the force created in the bottom half of the beam due to a 10C temperature increase.

For a beam that is fixed at both ends with cross-sectional area of A in m^2, a Modulus of Elasticity of E in N/m^2, a CTE in units of /C, you can compute the axial Force in N in the beam as A*E*CTE*10