טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBen Sahal Michal
SubjectContact Mechanics of Elastomeric O-Rings with Time
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Emeritus Izhak Etsion
Dr. Yuri Kligerman
Full Thesis textFull thesis text - English Version


Abstract

Elastomeric O-rings are widely used in hydraulic and pneumatic equipment to ensure sealing between a moving piston and stationary cylinder. During assembly the O-ring is squeezed between the inner wall of the cylinder and the piston. In some cases the system is stored for considerable time before operation. A plane strain numerical model was developed to simulate the problem. The theoretical contact model was studied numerically using a Finite Element Method, realized in the commercial software ANSYS 13.0.

Maxwell's constitutive model was selected to describe the viscoelastic material properties of the O-ring. The elasticity modulus was represented by a Prony series to describe the relaxation of a viscoelastic material. A validation of the numerical material model was performed for the uniaxial case by comparing ANSYS results to an analytical solution using the material properties of HT-6135 silicone rubber.

 An unrestrained radial loading model was built to simulate the O-ring assembly. The moving piston and the stationary cylinder were represented by two walls compressing the O-ring.  A normal displacement was applied to one of the walls compressing the O-ring, followed by a dwell time during which the structure remained in a strained condition, and stress relaxation was allowed to take place. Thereafter, tangential displacement was applied to one of the walls, which further increased the strains in the O-ring.

The main goals of this research were to study the effect of O-ring squeeze, mechanical properties, and dwell time on contact parameters such as contact area, contact force, and stress distributions.