# Thermal load in static analysis - confusing results when ALPHX is T dependant

Question asked by Stefan Rutzinger on Apr 3, 2014
Latest reply on Dec 15, 2015 by Neil Glasson

Hello folks,

I'm using static analysis with external thermal load and want to calculate thermal expansion dl/l. The point is that T_load goes to cryogenic temperatures where ALPHX(T) is strictly not constant and not linear with T and I get confusing results. Example:

A cube with 1mm edges

Material with ALPHX(T)=

T[K]     ALPHX(T)[1e-6]

300     10

250     9.5

200     9

150     7.5

100     5

65     0

50    -3

Study -> Reference Temperature T_ref = 300K

External load -> Temperature - applied to the whole body - T_load = 65K

What I expect by physics is dl/l = SUM_i (T_ref -> T_load) [ 0.5*(ALPHX(T_i)+ALPHX(T_(i+1))) * (T_i - T_(i+1)) ] = ~0,0018 - should be UX=1.8micron

What I get is exactly dl/l = 0 / UX=0 !?

Is it possible SIMULATION does not integrate ALPHX(T) dT in order to calculate dl/l but instead uses something like dl/l = APLHX(T_load) * (T_load - T_ref)

which physicaly is not very useful.

Could somebody please verify and explain what's my mistake?

Stefan