# Thermal FEA Calculations

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Thermal calculations in FEA include stresses and strains induced by temperature differentials.

## Introduction

NairnFEA can do thermoelastic calculations. In the presence of temperature differentials, the calculations will find thermal stresses and strains. This section is for FEA only; see separate help on thermal calculations when doing MPM calculations with NairnMPM.

## Temperature Settings

Thermal stresses and strains are induced when the temperature on the nodes differs from the stress free temperature. The temperature field (which may be non uniform) and the stress free temperature are set with the following commands. In scripted input files, the commands are:

Temperature (temp) StressFreeTemp (reftemp)

In `XML` input files, the commands must be in a `<Thermal>` block:

<Thermal> <Temperature>(temp)</Temperature> <StressFreeTemp>(reftemp)</StressFreeTemp> </Thermal>

where

`(temp)`is an temperature or a user defined function that gives the temperature on each node as a function of the coordinates of the node. The calculation will have residual stresses if it is a composite having materials with different thermal expansion coefficients or if the temperature field is non-uniform.`(reftemp)`is the stress free temperature in degrees. The default value is 0.

## Notes

- The thermal stresses and strains depend only of the
*difference*between temperature and the stress free temperature, which means the absolute values of these numbers does not matter. The difference, however, should be in degrees C (or K).