Small zipper elements are manufactured by successive plastic deformations of a preformed wire. However, when designing a new zipper chain, it is difficult to obtain an optimal zipper element shape without having to conduct several forming tests. To reveal deformation behavior from a preformed wire processed into zipper elements, we aim to clarify the shearing mechanism of a preformed wire. Using the results of observations with an optical microscope, SEM and X ray CT on the sheared surface, we elucidated how the shearing of a preformed wire occurs. First, a crack is initiated at the leg area from both punch and die sides. Second, as the shearing progresses, the crack expands, and dimples on the fractured surface on the punch side are compressed by contact with the die surface. Finally, the head part is broken by the moment from the punch to leave a rough dimpled surface.
