A Preliminary Investigation On Cross-Foldable Design In 4d Printing

In 4D printing, a printed smart structure would fold or unfold upon an external stimulus. In prior research, the hinges in the smart structure always fold or unfold individually with no crossing or overlap. The design complexity of the smart structure is increased by increasing the total number of hinges. In this research, cross-folding is investigated. Here cross-folding is defined as two overlapping folds in a single hinge. In particular, this research investigates the effect of thickness on cross-folding smart structures. It is found that hinge thickness affects the repeatability of cross-folding. A hinge with a thickness of 0.5 mm could be cross-folded three times prior to fracture whilst a hinge with a thickness of 0.3 mm could be cross-folded only once prior to fracture. A hinge with a thickness of 0.1 mm could not even be cross-folded without cracking. The introduction of a physical hole in the centre of the folding/unfolding line provided stress relief and prevented fracture.