# X-ring Seal

An x-ring, also called quad ring, is an elastomeric seal with four contact lips designed to be seated in a groove.  The simulation model consists of three axisymmetric parts: piston, housing and x-ring. The x-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 four 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. In the fourth step fluid pressure is held constant for 1000 minutes and viscoelastic effects are considered.

Note: This exercise is part of the Solving Non-linear Problems with Abaqus course.

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 pushes the seal upward. As  compared to an o-ring, the x-ring does not roll in the groove instead it slides. This results in longer life of the x-ring.

Due to the squeeze of the x-ring between the piston and housing, initial sealing is achieved. As the lips can bend during the housing movement, it results in less friction and wear of the seal.

In the third step, a fluid pressure is applied. As the fluid pressure acts on the seal, it is pushed upward.

In the fourth step, fluid pressure is held constant for 1000 minutes to study the creep.  It can be seen that at the end of step, extrusion occurs.

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 x-ring.

As the fluid pressure acts on the seal, the contact pressure increases significantly. This figure shows the contact pressure distribution at the end of fourth step.

The following animation shows the evolution of von Mises stresses and contact pressure.