A five-step process will be used to solve this problem:

Step 1. Equilibrium equation
Draw a free-body diagram (FBD) of the assembly and write the equilibrium equation.

Step 2. Geometry of deformation equation
Determine the relationship between the deformations in bars (1) and (2).

Step 3. Force-deformation relationships
Write the generic force-temperature-deformation relationships for bars (1) and (2).

Step 4. Compatibility equation
Substitute the force-temperature-deformation relationships into the geometry of deformation equation.

Step 5. Solve equations simultaneously
Solve the equilibrium and compatibility equations simultaneously for the unknown forces F₁ (in the copper) and F₂ (in the aluminum).