Statics: Buckling

Example 4: Bistability of a slap band

Bistability is a fundamental phenomenon in nature. A slap band that is bistable can be at rest in two equilibrium states. By default, the band will be in the state with the minimum energy as shown on the right side in Figure 10.A1a. A transition from the state of minimal energy to the other state of equilibrium that has maximum energy requires some form of activation energy to be provided. If one stretches the band into a straight position, it can be held as shown in Figure 10.A1b. If a little disturbance is given to the straight band which corresponds to the state of maximum energy, the band will relax into the state of lowest energy again.

a) Equilibrium with the smallest energy                                             b) Equilibrium with the largest energy
Figure 10.A1: A slap band at its two equilibrium states with the largest and smallest energies

Reflective slap bands, as shown in Figure 10.A1, have high visibility and became a safety product, which can be wrapped round wrists, arms and legs. Due to the interesting nature of bistability and low cost, slap bands are also used as a promotion product.