Flexural Mechanics of Creased Thin Metallic Strips
The introduction of creases into thin sheets has a dramatic effect on their global mechanical properties. This can be observed by manipulating a crumpled piece of paper which has been unfolded; it no longer deforms in the same way as the original sheet. Creases have typically been modelled as singular hinge lines, often accompanied by a torsional spring to provide some opening resistance; however, the appropriate stiffness of these springs is unclear. In reality, creases have a discrete geometry based on the method they were formed. This dissertation investigates the flexural behaviour of a creased thin metallic strip and the influence of the crease geometry.
When a strip is bent perpendicular to the crease, putting the crease region in tension and the strip edges in compression, initially torsional deformations occur which ultimately coalesce into a central localised flattened region. An analytical model of this flexural behaviour is developed, which idealises the crease as an initially circular segment. Predictions show the bending resistance increases as the crease decreases in size. The model predictions are compared to finite element analysis and experimental results showing excellent agreement. When a strip is bent in the opposite direction, with the crease region in compression and the strip edges in tension, a bistable snap-through occurs. The deformed shape is characterised by a sharp vertex on the crease line. An analytical model is developed by generalising a Gauss mapping approach, and used to predict the deformed shape. These predictions match experimental results well.
This dissertation provides an understanding of the mechanics of creased thin strips, where the crease is given a discrete geometry, and explores the nature of localisation. It also provides the foundation to explore the mechanics of thin sheets featuring a network of creases. This offers the opportunity to improve the efficiency of thin shell structures by using creasing to optimise the mechanics, leading to reduced material use, more sustainable construction, and fuel savings from lighter vehicles.