טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentFadida Refael
SubjectThe Mechanical Response of Additively Manufactured
Ti6Al4V Specimens Containing Discrete Artificial
Voids
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Daniel Rittel
Dr. Amnon Shirizly
Full Thesis textFull thesis text - English Version


Abstract

The mechanics of void-containing solids is very well established nowadays, but experimental validation is basically largely unavailable.  Until the advent of 3D printing, the introduction of controlled fully enclosed 3D voids into a material was almost impossible.  The metal additive manufacturing technology enables the fabrication of internal features, such as embedded voids (porosity) in any shape, size and pattern for almost any type of metal and its alloys.  We report on the mechanical response of additively manufactured Ti6Al4V specimens containing discrete artificial voids under quasi-static and dynamic loading.  Different configurations of specimens containing voids with varying size, shape and distribution were tested under uniaxial tension and shear-dominated stress sates.  The research highlights two basic results: first, artificial voids can mimic the behavior of realistic flaws in the material, and second that their presence can substantially affect the mechanical properties of the material.  In addition, it was found that the effect of voids on the mechanical response in combined shear compression stress state, is sensitive to the shape of the void (i.e., spherical or prolate).  Additive manufacturing can therefore serve as a tool to validate or refine existing analytical models dealing with the effect of porosity on plastic flow of metals.  As for the fully-dense material it was found that in both loading rate regimes, the mechanical properties of the additively manufactured material are comparable or even superior compared to conventional equivalent material, but the ductility of the latter is observed to be slightly higher.  Along with the experimental results, numerical and scanning electron fractographic analyses complement our understanding of the effect of voids on the structural mechanical response.