טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYalon Stav
SubjectVoids Interactions in a Mode I Field
DepartmentDepartment of Mechanical Engineering
Supervisor Dr. Shmuel Osovski
Full Thesis textFull thesis text - English Version


Abstract

Most ductile structural alloys have been observed to fail through a mechanism involving the nucleation, growth and coalescence of voids. As such, it has been a problem of longstanding research and investigation aiming to gain a better grasp of the physical mechanism involved. The failure of ductile materials under medium and high stress triaxialities has been extensively studied both analytically and numerically. Various damage models describing the nucleation, growth and coalescence of voids exist in the literature and have proven to be very successful in describing the fracture process of ductile materials. While these models are based on extensive analytical and computational work, most experimental work done in this field up to date was strictly aimed at calibrating those models and obtaining material specific constants.  In this research, we propose to study specimens with a designed population of voids similar to that used in previous studies. A single edge notched tensile specimen, with a row of voids located at fixed spacing ahead of the notch tip. By changing the size of the voids, the initial porosity level is controlled.  Numerical calculations of this geometry reported in the paper by V. Tvergaard and J. W. Hutchinson in 2002 demonstrate a transition between two crack growth mechanisms, i.e. void-by void crack growth and multiple voids interaction. These mechanisms, also described as the Single-void and Multi-void interaction mechanisms, will be simulated numerically using finite element software. The transition between the interactions in under different loading conditions and plastic hardenings will be investigated. Based on the simulated results we intend to design an experiment to validate the existence of both void-interaction mechanisms and show the transition between them for materials with different plastic hardenings.