Figure 3.

Deformation cross-section. This figure illustrates the deformation geometry of a circular, linear elastic tube neglecting the bending stress inside the wall. Cross-section B - B (left) shows circular expansion under pressure and the cross-section C - C illustrates the geometry under external deformation (right). The equilibrium cross-sectional area A_d is shaded in light grey, while the perturbation area A' is shaded in dark grey. The dashed lines indicate expansion under pressure.