Thermal control - QuickField simulation example
The bimetallic thermal control is made of a brass bar and magnesium bar. The bars are arranged so that there is the gap between their ends at room temperature.
How to find bimetal strip contact temperature threshold?
Engineering answer Typical applications Geometry
Given Task
Solution The second part simulates bars after they came into contact. The deformed (elongated) bars geometry is used. In this problem the temperature increment T2 = ΔT - T1 is applied to the bars.
Results
Thermal stress at temperature T2 = 300 - 191 = 109 °F (61 K).
*James M. Gere, Stephen P. Timoshenko "Mechanics of materials", Third edition (1990), pp.26-27. ISBN: 0-534-92174-4.
Engineering question
Set up an axisymmetric QuickField Stress Analysis problem for a bimetal strip and evaluate contact temperature threshold from computed field results.
bimetal thermal switches, temperature control contacts, thermal expansion actuators
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Simulation problem
Problem Type
Axisymmetric problem of stress analysis
Brass bar length Lb = 0.75";
Young's modulus of the brass Eb = 15·106 psi (103 GPa);
Thermal expansion coefficient of the brass αb = 10·10-6 1/°F (18·10-6 1/K);
Magnesium bar length Lm = 1.3";
Young's modulus of the magnesium Em = 6.5·106 psi (44.8 GPa);
Thermal expansion coefficient of the magnesium αm = 14.5·10-6 1/°F (26.1·10-6 1/K);
Initial distance between bars δ=0.005".
First part is solved using serial analysis capability of LabelMover. Temperatures of the bars rise with the step of 1 K. Elongation of the bars is calculated for each temperature. The bars come into contact when the total elongation of bars reaches δ. This way the temperature of the contact T1 is determined. There is no stress in the bars before the contact takes place.
Temperature at which the contact takes place: T1 = 106 K (191 °F)
Contact temperature
Stress in the magnesium
QuickField
191 °F (106 K)
9170 psi (63.2 MPa)
Theory*
190 °F
9680 psi
Difference
0.5%
6%
Video
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