Zdzisław Marciniak

Bio: Zdzisław Marciniak is an academic researcher from Warsaw University of Technology. The author has contributed to research in topics: Forming limit diagram & Sheet metal. The author has an hindex of 3, co-authored 5 publications receiving 2139 citations.

O różnych formach utraty stateczności blachy poddawanej rozciąganiu w stanie plastycznym

Abstract: Ogolną cechą utraty stateczności blachy poddanej jedno- lub dwuosiowemu rozciąganiu w zakresie plastycznym jest to, ze mimo istnienia np. w pewnym obszarze jednorodnego stanu naprezen, powstac w nim moze niejednorodne pole odksztalcen. Z chwilą utraty stateczności odksztalcenia koncentrują sie w pewnych tylko obszarach ciala, podczas gdy pozostale obszary, lezące poza zasiegiem koncentracji odksztalcen, są bądź odciązane i przechodzą w stan sprezysty, bądź tez doznają stopniowo zanikających odksztalcen plastycznych. Ta koncentracja odksztalcen zaleznie od warunkow moze przybierac rozne formy. W niniejszej pracy zanalizowano trzy najwazniejsze formy utraty stateczności rozciąganych powlok plastycznych. ON VARIOUS FORMS OF INSTABILITY IN SHEET MATERIAL UNDERGOING PLASTIC TENSION The loss of stability of sheet material undergoing plastic tension may take various forms: necking occuring for example in specimens loaded by uniaxial tension, a line of kinematical discontinuity or necking line connected with progressively diminishing plastic deformation in neighbouring portions of material. The present paper contains an analysis of conditions associated with each of these forms of instability. For principal stress ratio σ2/σ1 0.5 the deformation takes the form of a necking-line perpendicular to the direction of the greater principal stress. The course of stability loss is also considered for various processes of metal forming. Theoretical results are later compared with experimental observations.

Utrata stateczności rozciąganych powłok plastycznych

Abstract: W przypadku jednoosiowego rozciągania pretow i wąskich pasow mozna wyodrebnic w procesie rozciągania dwie fazy: 1) faze stateczności, charakteryzującą sie rownomiernym rozkladem wydluzenia wzdluz osi probki; 2) faze niestateczności, w czasie ktorej nastepuje koncentracja odksztalcen na pewnym obszarze probki, podczas gdy pozostale jej cześci, lezące dostatecznie daleko od miejsca przewezenia, nie tylko nie doznają dalszych odksztalcen plastycznych, lecz nawet zostają odciązone. THE LOSS OF STABILITY OF PLASTIC SHELLS UNDER TENSILE LOADING General condition of stability of a thin-walled plastic shell, loaded by tension in plane stress conditions is formulated. A number of particular cases of coupling of kinematic and static boundary conditions is considered. Moreover, a relation between conditions of plastic flow involved and the point of Joss of stability is derived. In the second part of the paper the formation process of a neck beyond of the stability range is analysed. It is shown, moreover, that in certain boundary conditions, an additional, intermediate, so-called quasi-stable stage occurs, connected with plastic deformation of the shell outside the neck in spite of the stability point being exceeded.

Void Nucleation Effects in Biaxially Stretched Sheets

Abstract: The effects of void nucleation occurring during the deformation history on forming limit curves are considered for both in-plane and punch stretching employing a constitutive model of a porous plastic solid. Both plastic strain controlled and stress controlled nucleation processes are simulated by a two parameter void nucleation criterion. For in-plane stretching, plastic strain controlled nucleation can have, in certain circumstances, a significantly destabilizing effect on the forming limit curve. However, within the framework of plane stress theory which neglects the enhance­ ment of the hydrostatic stress due to necking, a stress controlled nucleation process is not found to be significantly destabilizing. In punch stretching a ductile rupture criterion, which limits the maximum volume fraction of voids, as well as the ap­ pearance of a well defined thickness trough, is adopted as a localized necking criterion. Only plastic strain controlled void nucleation is considered here in out-ofplane stretching. The resulting forming limit curves have the same shape as those obtained previously with void nucleation neglected.