Slow Stress-Relaxation of Thin Sheet Folds

We measure the slowly relaxing force required to maintain a fold in thin sheets of aluminum, copper, Mylar, and paper. The relaxation is found to be best described by a Weibull distribution of relaxation times. The exponent $\beta$ of the Weibull distribution characterizes two distinct classes of relaxation observed in metallic ($\beta\simeq 2$) and polymeric materials ($\beta \simeq 1$) respectively.