Simulation is widely used for research and development in engineering. Advanced testing tools and software are utilized in numerous industries for product development, such as large-sized bearings in the wind energy sector. Replicating realistic conditions in an artificial environment significantly accelerates the development process and components do not have to be repeatedly manufactured and tested. Nonetheless, the behavior of materials used to make industrial seals is much more difficult to simulate.
Rubber is the most common sealing material because it enables the seals to follow the movements of the counter surfaces they are in contact with, such as shafts, rods, or bearings.
Source: evolution.skf.com
Challenges of seal simulation:
1. A conventional linear model is not enough
The majority of modern engineering calculations are conducted on the premise that materials will behave linearly and elastically. Simply put, force and displacements linearly relate to one factor: stiffness. The common sealing material rubber generally does not follow this linear classification. To accurately simulate how rubber will perform requires more complex models that can support non-linearity.
2. Rubber is generally incompressible
The material behavior of rubber differs from standard elastic substances. The fact that it is nearly incompressible means that the volume of a compressed piece of rubber before and after deformation is approximately zero. This is known as volumetric locking, which creates numerical instabilities. An alternative approach is needed to understand how rubber will behave.
3. Contact mechanics are required to deal with interference
Seals face significant interference from other components, such as the bore and shaft, when in operation. It is not only the behavior of the rubber in isolation that needs to be simulated, but also how it interacts with materials it comes into contact with. Including these factors in simulation poses an additional challenge.
Rising to the challenges with advanced methods
To effectively recreate the properties of rubber, a hyperelastic model is required. Hyperelastic simulation still recreates elasticity but incorporates non-linear behavior of stress and strain. This enables research and development departments to accurately analyze the effects of deformations in numerous orientations—representing rubber under realistic conditions.
When it comes to the challenge of incompressibility, the F-bar method provides an effective option, which modifies the conventional integration methods. Based on detailed algorithms, this approach delivers more stable findings that overcome the hurdle of volumetric locking. To rise to the challenge of replicating contact stress, simulation software can include contact mechanics. Methods, such as the Lagrange multiplier, can mathematically match the deformation to the constraints provided by the surrounding counter surfaces. This is preferable to methods like the penalty method where certain functions are only triggered once a constraint is exceeded. As a result, testing technicians gain more comprehensive and precise results.
A single solution for multiple challenges
All of these factors for enhancing seal simulation are combined in the finite element method (FEM). This meets the requirements for testing hyperelasticity, deformations, and contact mechanics. Based on this principle, SKF developed SKF Seal Designer, which its product engineers use for testing. The calculation tool enables SKF to deliver reliable results for both manufacturing and performance—helping provide various industries with seals that are up to the task of long-term operation.