טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGolan Guy
SubjectEnergy Absorption of Encapsulated Granular Materials
under Impact Loading
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Itzhak Shmulevich
Dr. Zvi Anosh Asaf
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Granular materials have been researched for many years. According to the literature review, the granular material characterized by bulk of particles, behaves as a solid under certain conditions and as fluid under other conditions. Granular materials exhibit energy-absorbing capabilities during motion. Literature focuses on the study of granular systems under rigid boundary conditions or distant boundary conditions.

The current study focused on the influence of flexible boundary conditions on the ability of the granular material to absorb energy and to reduce forces, as a result of impact loading. The feasibility of the research hypotheses was examined by preliminary tests: using drop tower machine with granular materials samples packed in flexible and rigid boundaries.

The results have clearly shown that the energy absorption and force reduction in flexible boundary condition is greater than rigid boundary condition.

The research includes a parametric investigation of: coefficient of friction between the particles, cell size and flexible boundary conditions. The experimental system included building cylinder cells with flexible walls attached to perforated rigid cover to remove air pressure. The test cells included combination of three different volumes with three different flexibility of the boundary condition (achieved by different thickness of the latex).The experiment system allowed examining the effect of the following parameters: particle shape, particle friction coefficient, volume control, and different boundary conditions. The system tested under three loading rates: static, dynamic and impact.

The response was characterized by measuring the acceleration, force, displacement and velocity of the loading means.

A comparison of the results shows that:

(a)    Higher loading rate increases the energy absorbing capability

(b) Force reduction of flexible boundary conditions is high compared to rigid boundary conditions

(c) Control volume contributes to the force reduction more than the latex thickness parameter

To understand the phenomena better, a numerical simulation was performed, using LS-DYNA (dynamic finite element software). The simulation was calibrated and validated using tests results. The simulation results well predicted the tendency of the system response to dynamic and impact loadings.

In addition, tests have shown similar force reduction capabilities between granular materials and other energy absorption materials.

The main contribution of the research is by giving technical and numerical tools to predict the response of granular system to impact loading. Those tools  is a platform for extending the findings regarding different materials and geometry, by a numerical model followed by tests for verification.