An O-ring is a mechanical gasket in the shape of a torus designed to be seated in a groove. It is used to create a seal at the interface. The model consists of three axisymmetric parts: piston, housing and o-ring. The o-ring sits inside the gland, cut into the piston. This is a challenging problems as it involves multiple nonlinearities: material nonlinearity, geometric nonlinearity and contact between multiple components. As the geometries and loads are axisymmetric, the problem is analyzed using an axisymmetric model.
The analysis is performed in three steps. In the first step, interference is resolved and in the second step housing is moved upwards. In the third step, a fluid pressure is applied.
As the geometries and loads are axisymmetric, the problem is analyzed using an axisymmetric model.
At the beginning of the analysis, an interference exists between seal and piston. During the first step, interference is resolved which results in stresses in the seal.
(Note: Click on the figure for closer view)
During second step, as the housing moves upward, it also pulls the seal upward.
A certain amount of squeeze is required to maintain contact with the sealing surfaces. This is necessary to prevent fluid leakage.
In the third step, a fluid pressure is applied. As the fluid pressure acts on the seal, it is pushed into the gap between piston and housing.
Extrusion occurs when fluid pressure forces the seal material into the gap between sealing surfaces. Extruded material can break away, creating leak paths. Furthermore, heat generated from friction can cause a seal to be compression set, shortening its life. Optimizing clearance gaps and selecting a proper material based on the temperature and pressure involved are necessary to reduce the risk of extrusion.
During the second step, as the housing moves upward, the contact pressure builds on all sides of the o-ring.
As the fluid pressure acts on the seal, the contact pressure increases significantly.
The following animation shows the evolution of von Mises stresses and contact pressure.