NECKING AND RADIAL CRACKING AROUND PERFORATIONS IN THIN SHEETS AT NORMAL INCIDENCE

The Formation of multiple necks and cracks around perforations in duct ile materials is investigated. Expressions are obtained for the number of plane-strain radial necks formed by conical penetrators (with or w ithout starter holes in the flat target), and also by round-ended proj ectiles into flat targets having starter holes or, in plain targets wi th no starter holes, after fracture of the initial circumferential nec k has detached a circular cap of material (''discing''). Likewise, exp ressions are derived for the number of radial cracks which form subseq uently in both cases and lead to ''petalling''. The number of cracks i s smaller than the number of necks. Experiments seem to agree with the analyses, although accurate counting of necks in thin sheets is illus ory. (C) 1998 Elsevier Science Ltd. All rights reserved.