טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGodinger Adam
SubjectThe Influence of Confining Stress on the Ballistic
Properties of Soda Lime Glass
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Daniel Rittel
Dr. Avraham Dorogoy
Full Thesis textFull thesis text - English Version


Abstract

  Brittle transparent materials such as glass and ceramics are commonly used in armored windows and sensor protection for both civilian and military application. These materials are usually very tough under compression, but are fragile under tension. They can absorb high energy when impacted by a projectile, but have very low resistance to tensile load. When transparent protection is needed, the ability to optimize the energy absorption and the ability to endure different loads can be crucial. 

  One of the approaches to improve the energy absorption of a brittle armor is to compressively pre-stress the protective plate. This type of pre-stress improves the resistance to tensile stress and suppresses crack growth that would weaken the armor and reduce its transparency.

  This study investigates the influence of confining stress on the ballistic properties/performance of Soda lime glass using experimental and numerical tools. The projectile velocity range that was tested varied between 250[m/s] to 1000[m/s], well below the speed of sound in soda lima glass around 5000[m/s].  The specimens include a round plate, around 100[mm] in diameter and with a thickness of 8 [mm], which is impacted normally by flat tip projectiles that are accelerated by a 6 [meter] gas canon.

This study consists of three primary stages: a. the design of a device for application of uniform confining pressure; b. ballistic tests of confined and unconfined specimens; and c. simulations of steps a-b. 

 The achieved radial confinement pressure is ~100 [MPa] and was only limited by the press performance (15 [KN]). The experiments were successfully simulated, thus enabling us to predict the residual velocities and the damage shape that will help to minimize the need for experimental tests in the future.

This study revealed great improvements in terms of ballistic performance of the confined targets in comparison to the unconfined. The ballistic limits tended to increase by at least 50%, and the plate displayed better structural integrity compared to the unconfined.