Compute Strain in Copper Bars  
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The figure shows the free body diagram of the aluminum bar sandwiched between copper bars. The free body diagram cuts across the three bars. The forces on the copper bars at the top and bottom are F subscript 1 directed rightwards. The force on the aluminum bar is F subscript 2 directed rightwards.

Temperature change

ΔT = +65°C

Copper bars (1)

A1 = 360 mm2
E1 = 120 GPa
α1 = 16.0 × 10-6/°C

Aluminum bar (2)

A2 = 720 mm2
E2 = 70 GPa
α2 = 23.0 × 10-6/°C

To compute the strain in the copper bars, recall that normal strain is defined as the change in length divided by the initial length. The change in length of the copper bars is deformation δ1:

Dividing this expression by the initial length L1 gives an expression for the normal strain in the copper bars: