U-cup Seal

U-cup seals are usually used in pneumatic and low-pressure hydraulic applications. A u-cup seal consists of two sealing lips which are forced towards walls as the pressure builds up. The major advantage of u-cup seals is that as the fluid pressure increases so does the force on sealing lips, enhancing the sealing capability of the seal.

The model consists of three axisymmetric parts: piston, housing and u-cup. The u-cup 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. This reduces the computational time significantly.

The analysis is performed in three steps. In the first step, interference is resolved and in the second step a pressure load is applied on the sealing lips. In the third step, a fluid pressure is applied.

As the fluid pressure increases on the seal, it is pushed upwards. Extrusion occurs when fluid pressure forces the seal material into the gap between sealing surfaces. Extruded material can break away, creating leak paths.

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 other parts. 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, a pressure load is applied on the sealing lips.

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In the third step, a fluid pressure is applied. As the fluid pressure increases on the seal, it is pushed further up.

During the second step, as the pressure load is applied on the sealing lips , the contact pressure builds on all sides of seal.

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.