On the inception of leakage : Effect of hydrostatic pressure on the sealing interface

• As the move towards sustainability continues,  attention needs to be paid to the development of new machinery with high performance and low environmental impact. It places increasing demands on low/zero-emission sealing with a long lifetime. The seal, as a machine element used to prevent leakage and maintain fluid pressure, is consistently subjected to the hydrostatic load from the pressurized fluid. On the one hand, the fluid pressure applied to the seal is utilized as a complementary source to tighten the sealing surfaces, because seal installation and the design of the contact interface limit the tightening that can be generated by pre-tensioning. On the other hand, an elevated sealed fluid pressure might proceed the fluid front at the contact interface, which may eventually lead to leakage.Besides the usual seal failure modes such as aging, material degradation, and extrusion damage, there is one failure mode that has raised the attention of researchers and engineers in recent years, where the leakage transition is in connection with little material damage. It often happens when the sealed fluid pressure passes a particular critical value. The change from no-leakage to leakage is not continuous, accompanied by significant fluid flow. It is a geometrical design problem, thus closely related to the contact pressure distribution at the sealing interface. The critical pressure, at which leakage is initiated, is closely associated with the hydrostatic load from the sealed fluid, and it is essential for the seal design.In this work, the contact mechanics problem at the sealing interface is studied by means of modeling and numerical simulation, incorporating the hydrostatic load from the sealed fluid. The main research interest is how the contact state is affected by variations in the sealed fluid pressure, and, more specifically, the magnitude of the sealed fluid pressure that opens up the contact and initializes the leakage, i.e., the critical pressure. A 2D contact problem, in which the sealed fluid pressure contributes to the total contact load and the contact opening force, is first studied with the finite element method. The results show that the hydrostatic pressure from the sealed fluid can enhance the sealing. Meanwhile, it may also proceed the fluid front and open up the contact, which occurs when elevated sealed fluid pressure does not provide a high enough increase of the total contact load.Incorporating the hydrostatic load at the contact interface for arbitrary 3D contact problems is challenging and requires an accurate and efficient numerical simulation method. Therefore, an approach based on the boundary element method is developed and implemented in this work. The resulting novel method is computationally efficient, and can be applied to study the contact problem with a hydrostatic fluid load between surfaces with complicated geometries. It is utilized to study the critical pressure of the sealed fluid that leads to leakage for both 2D and 3D contact interfaces. The outcomes of the simulations have been fitted into some empirical equations to ease their use for engineers. On top of that, a new dimensionless number, called the critical pressure factor, is introduced. It allows one to simplify the computation of the critical pressure by using only the physics quantities from the surface's dry contact conditions.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Tribologi (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Tribology (hsv//eng)

Nyckelord

static seal

contact mechanics

hydrostatic

critical pressure

leakage

Maskinelement

Machine Elements

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