Swelling of bent rubber strips and recovery when the stresses are removed

Swelling of rubber is strongly affected by applied stress. For example, when rubber sheets are bent, they will swell more on the tension side and less on the compression side. When the bending constraint is removed, only partial recovery towards the flat state occurs, followed by slow further recovery as the swelling liquid migrates internally. These effects have been explored using strips of natural rubber swollen by dodecane (Nah et al. 2011). The "set" on release from bending was predicted by simple swelling theory, and the time dependence of later recovery was consistent with the rate of diffusion of dodecane in rubber. Thus, bending and recovery experiments provide a simple way of studying the internal mobility of compatible liquids. Other ways of studying recovery from an imposed bending deformation are also proposed. We infer that liquid migration can make a significant contribution to deformational energy losses.