טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBlumer Dvir
SubjectThe Influence of Microstructure on the Static and Dynamic
Strenght of Transparent Magnesium
Aluminate Spinel(MgAl2O4)
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Daniel Rittel
Full Thesis textFull thesis text - English Version


Abstract

Transparent polycrystalline ceramics in general and Magnesium Aluminate Spinel (MgAl2O4) in particular, have a unique combination of properties which makes them a promising candidate for commercial and defense demanding applications.

The dynamic flexural strength of transparent ceramics is an important property for these demanding applications. However, the data on dynamic strength, especially tensile/flexural, is still very scarce. Moreover, detailed correlations between strength and microstructure (e.g. grain size) are not yet established.  Therefore, this work reports a systematic study of the grain size influence on the dynamic and static flexural strength of Magnesium Aluminate Spinel (MgAl2O4), utilizing a modified split Hopkinson (Kolsky) apparatus. An ultra-high-speed camera (8*106 frames/sec), was extensively used and provided precious insight of the dynamic crack initiation and propagation. A standard three point bending method was used to determine the static flexural strength. It was found that fine microstructure Spinel exhibits slightly higher static flexural strength than coarser microstructure. However, in the dynamic regime, no significant difference was found. Moreover, the fracture timing method, i.e. fracture gauge or high-speed camera, influences significantly the dynamic strength results. While the fracture gauges indicate complete fracture, the high-speed camera captures the onset of the fracture as a true material property. Consequently, Spinel’s dynamic flexural strength is not rate sensitive, based on high-speed imaging.