Reliable seal-related modeling

Finite element analysis (FEA) is a method, typically performed by software, used to create models of materials or designs that can then be subjected to simulated stresses. Engineers can use the model to predict material and product performance under a range of operating conditions, providing real cost benefits over manufacturing and testing prototypes and providing fascinating insights into the behavior of seals.

However, the model is run by complex algorithms in a hypothetical and idealized world. Real-world testing, expertise, and human input is required to bring it to life and significantly enhance the reliability of the results. Perfect results are not always generated.

“For a model to be successful, numerous factors have to be understood and formulated. A model is only as good as the conditions set, which rely on the expertise of engineers to understand a system as much as the programming and logic of the software,” says Matthias Keck, manager development portfolio R&D Europe for Trelleborg Sealing Solutions.
 

Setting the stage

Trelleborg engineers have developed its FEA software to provide reliable, seal-related modeling on a per-application basis. This involves a clear, accurate, and comprehensive plan of boundary conditions to be created, taking into account hardware interaction with the product or whether the seal needs to be stretched or contorted for installation. In addition, a library of accurately modeled materials, both metallic and non-metallic, is needed to provide results as close to real-world performance as possible.

Trelleborg engineers perform the majority of their analyses on non-metallic materials, which require non-linear modeling. This relies heavily on the quality of the material properties used in the model. Therefore, all materials need to be tested extensively in the real world to determine stress-strain curves, Poisson ratios, and all other physical material properties.

The accurate modeling of the seal before parameters – such as stresses – are applied is paramount to a successful analysis.

“The data used to plan the analysis benefits from decades of experience – drawing from diverse knowledge sources such as sales engineers, polymer testing laboratories, real-world experimentation, and applications” Matthias explains.
 

A step further

Once a detailed model of the seal has been developed, a comprehensive understanding is required of the forces and stresses to which the product or seal will be subjected. A range of operational conditions can be calculated, such as flat or varying temperature and pressure conditions or dynamic movement of the hardware surrounding the seal. Accounting for the myriad possibilities can be complex and must be done on a case-by-case basis, requiring human analysis and experienced operators.

The FEA software needs to be robust and must be capable of contact, large strain, and multi-physics analysis for static and dynamic non-linear problems. Flexibility is also crucial to allow for adaption or a new direction in analysis.
 

The human touch

“No FEA analysis is routine and a team of experienced people provide valuable input and ideas to circumvent potential pitfalls. The best analyses are created when the FEA analysts work in close cooperation with design and product engineers,” Matthias says.

Whether a 2D or 3D model is chosen depends on the application. Two-dimensional models are for axi-symmetrical, plane strain and plane stress analysis, which help to demonstrate how a product will install, grow from thermal expansion, and react to forces or pressures applied.

Three-dimensional models offer a more complete idealization of a product, such as a seal that operates under complex and frequently varying stresses, allowing for non-uniform profiles or voids. For example, for a gasket with holes stamped into it for bolts to pass through, 2D analysis would not capture both cross-sections with and without the holes. Therefore, 3D analysis is needed to visualize more complex profiles, increase the reliability of the results obtained, and for simulating eccentric positioning of loads for axi-symmetrical geometries.
 

What can FEA do?

FEA is extremely useful in ensuring maximum seal life in an application. It is possible to predict seal deformation under load, the sealing contact forces, or the contact pressure distribution. The latter is especially useful for optimizing dynamic seals – or to reverse-engineer existing problems to discover the root causes.

Assembly force requirements to install the seal can be calculated and determine if specific tooling is needed. Various temperature conditions can be simulated to see the effects on the sealing system. Thermo-viscoelasticity simulation can be studied for each material to analyze effects of creep, viscoelasticity, hyperelasticity, and Mullins’ effect across time to ascertain sealing load long after installation. Frictional analysis uncovers breakout torque and running torque of rotary seals, or actuation force of linear seals.

Any seal manufacturer you work with should offer FEA analysis. It shortens the design optimization process, while improving design and seal performance through integrated software simulation. Reliable seal analysis capabilities reduce development costs and lead times and lead to a lower-costing, better-performing product for the end user.

Trelleborg Sealing Solutions
www.tss.trelleborg.com