Thermal Stresses in Composite or Compound Bars and Tubes:

Here on stepped bars, we have seen one category of composite bar where bars of various materials are joined serially. Here, we should consider another type of compound bar, a bar constructed from two various materials rigidly joined together as display in Figure (a), or two bars of various materials but of equal length held among two rigid plates as shown in Figure (b).

Figure

If the individual bars were free to expand (or contract) because of temperature changes, they would do so to different amounts (for the similar change in temperature), as display above in figure(c) and (d), because of the difference in the coefficients of linear expansion of the two materials.