In the figure to the left a rod is installed in between two walls the distance
between which will remain at L for good.
The rod is made out of two sections which both have the same cross-section,
A, and initially the same length, L/2. They are made out
of different material, i.e. Young's modulus E1 and
E2 and coefficients of thermal expansion
&alpha1 and &alpha2, respectively.
The two sections are intially installed in a stress-free manner but then the
temperature changes by an amount ΔT.