Self-folding metal origami: Mechano-activated shape morphing of aluminum-plastic laminate composites

Many “metallized plastic” packaging films bend if stretched and released. Such behavior can be reproduced in laminate composites prepared by bonding aluminum foil to an adhesive polymer sheet. We show that such bending occurs because stretching deforms the aluminum layer permanently (i.e. plastically), whereas the polymer layer deforms elastically. Upon releasing, the aluminum-polymer composite then resolves the strain mismatch by bending, with the aluminum on the convex side of the bend. The curvature is found to increase linearly with the applied strain and found to reduce as the aluminum thickness increases. The theory of fully-elastic bilayers with strain mismatch is in qualitative agreement with the results, but underpredicts the curvatures. We show how such bilayers can be patterned with defects such as holes or slits to realize more complex shape morphing, and also how one may achieve bidirectional bending. Such aluminum-polymer layered composites provide an inexpensive platform suitable for rapid-prototyping of self-folding origami structures using robust materials. Using well-established and scalable manufacturing techniques, even meter-scale origami may be created.