Rupture des tiges en flexion

When thin brittle rods such as dry spaghetti pasta are bent beyond their limit curvature, they often break into more than two pieces, typically three or four. With the aim to understand these multiple breakings, we study the dynamics of a rod bent just below its limit curvature and suddenly released at one end. We find that the sudden relaxation of the curvature at the newly freed end leads to a burst of flexural waves, whose dynamics are described by a self-similar solution with no adjustable parameter. These flexural waves locally increase the curvature in the rod and we argue that this counter-intuitive mechanism is responsible for the fragmentation of brittle rods under bending. A simple experiment supporting the claim is presented.