Punching Holes: Piercing and Perforating, Arms and Armour

Publisher Summary This chapter focuses on a variety of processes where holes are made by different processes. Solid punches driven into the surface of a brittle solid produce craters with the displaced material removed as radially broken-up lumps like slices of a cake. The action of flat-ended solid punches when making holes in floppy or ductile materials is by pushing a plug of material from the near (proximal) surface through to the far (distal) side of the workpiece. Separation of the center portion from the rest of the sheet can either be by scissor-like cutting or by ductile shear in a narrow band around the separated edges. A fid is a heavy-duty needle used in, for example, sailmaking with canvas, or with leather, and adapted to industrial sewing machines. A pin used to pop a balloon or blister probably causes fracture not by cutting but by facilitating, through its sharpness, crack initiation in the stretched membrane at the strain induced in the balloon by the particular inflation pressure. It is possible to sit on an inflated balloon without bursting it.