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Analysing seal development

Published: 1 August 2012 - Rachael Morling

Trelleborg Sealing Solutions takes a look at why Finite Element Analysis is an essential tool when developing a seal in order to reduce development costs and ensure a better performing product for the end-user

Using Finite Element Analysis (FEA) software, computer-generated models of materials or designs are created which can then be subjected to simulated stresses. This enables engineers to predict material and product performance under a range of operating conditions, providing real cost benefits over manufacturing each sample and testing it.

It is assumed that with computer software perfect results will be generated every time without input, however the model is run by complex algorithms in a hypothetical and idealised world. As a result, real-world testing, expertise and human input are required to bring it to life and enhance the results.

For a model to be successful, numerous factors have to be understood and formulated. After all, a model is only as good as the conditions set, which relies on the expertise of engineers to understand a system as much as the programming and logic of the software.

Trelleborg Sealing Solutions has developed its standard FEA software to provide reliable seal-related modelling. This involved a clear, accurate and comprehensive plan of boundary conditions, such as hardware interaction with the product or seal. Understanding whether the seal needs to be stretched or contorted for installation is critical for the success of FEA; and the accurate modelling of the product or seal before other parameters like stresses are applied is paramount to a successful analysis.

Understanding the stresses

Once a detailed model of the seal has been developed, a comprehensive understanding of the forces and stresses the product or seal will be subjected to is required. Here, it is possible to calculate for a range of conditions – 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.

A library of accurately modelled materials, both metallic and non-metallic, is needed to provide results as close to real-world performance as possible. Trelleborg Sealing Solutions performs almost all of its analysis on non-metallic materials, which require non-linear modelling, but this relies heavily on the quality of the material properties used in the model. Therefore, all materials need to be extensively tested in the real world to determine stress-strain curves, Poisson ratios and all other physical material properties.

The FEA software needs to be robust and from a testing partner which offers the latest in modern technology and understands how to use it. It 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.

As mentioned earlier, a team of analysts from a range of specialities is the best complement to well designed software. No FEA analysis is routine, and an experienced team provides valuable input and ideas to circumvent potential pitfalls. In fact the best analyses are created when the FEA analysts work in close cooperation with design and product engineers.

Whether a 2D or 3D model is chosen depends on the application. 2D 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 applied. 3D models offer a more complete idealisation 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. Here, 3D analysis is needed to visualise more complex profiles, increasing reliability of results.

Ensuring seal life

FEA is extremely useful in ensuring maximum seal life in an application. Through its use, it is possible to predict seal failure from cracks, leaks or deformation or to ‘reverse-engineer’ existing problems to discover the root causes. Furthermore, assembly force requirements to install the seal can be calculated and determine if specific tooling is needed.

Various temperature conditions can also be simulated to see the effects on the seal materials. Thermo-viscoelasticity simulation can be studied for each material to analyse effects of creep, viscoelasticity, hyperelasticity and Mullin’s Effect over a period of 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 have FEA analysis as part of their offering – it shortens the design optimisation 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 cost, better performing product for the end-user.

Trelleborg          

www.tss.trelleborg.com



 
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