Deformation Behavior and Crack Formation in Two Neighboring Holes Perforated in Engineering Sheet Materials under Tension

To obtain basic information on the mechanical mechanism of ductile fracture, deformation behavior and crack formation in two neighboring holes perforated in sheet materials have been investigated. Experiments have been performed with variations in mechanical factors such as a relative inter-hole distance (ξ/d), an arranged angle of two holes (φ) and the applied plastic strain, and in material ones of an mean grain size and a strain hardening exponent in copper and SS-41. Holes introduced in a close distance to each other are deformed quite oddly under tension, depending mainly on the arranged angle. The deformed configuration of them is able to be expressed by an approximated ellipse with supplements of intrusion and/or protrusion. The linear distance connecting centers of two holes varies with plastic strain and is given in two different definitions of a geometrical center and a shifted original cross one. Cracking at and around two holes has happened in both ways of protrude and intrude cracking which may result in the linking mechanism of two neighboring holes depending on the variables studied.