Buckling of inflatable pouch seams

Inflating a mylar balloon results in a pattern of wrinkles around its seams, and a shape with similarities to those of stuffed paper folders, tea bags, empanadas, and other objects in which the perimeters of thin sheets are attached to form a closed surface around a maximal volume. Our present interest in this problem stems from working with inflatable pouches for soft robotic actuators, made by layering textiles, plastics, and adhesives. We examine circular pouches with annular seams. Inflation of the pouch effectively provides a contractile planar constraint on the interior of the rim, leading to buckling reminiscent of prior results on swelling gel strips attached to rigid bodies. The buckling wavelength coarsens with the width of the seam, until it saturates at four cycles. We examine the effects of seam width, pouch radius, and sheet thickness on the buckling wavelength, through experiments and scaling arguments.