Apply the disp_x boundary condition to the entire bottom surface again and observe what happens. Undo that change before you move on to the next question.

The thermal expansion eigenstrain added in this input is isotropic, meaning the material expands not just in the y direction, but also in the x-direction. If we constrain the x displacement along the entire bottom boundary we will inhibit x expansion there and thus introduce a strong concentrated stress.

This scenario would model a strip that is "welded" to an infinitely stiff substrate at the bottom.