ContiTech MEGI® News

Life cycle costing

Rubber adheres to material laws of its very own. At the very latest users become aware of these properties when an elastomer component fails unexpectedly. In the future surprises and risks like this can be reduced. ContiTech Vibration Control has developed a service life costing concept for elastomer components.

There is practically no getting around elastomer materials when power units, systems or assemblies, have to be suspended or supported. For the most part rubber is nonwearing – throughout its life. But how long is a product life? From a life cycle costing perspective it does make a difference, though, whether a component holds up for 200,000 or 400,000 operating hours. In the past it was very difficult to say anything meaningful in this regard. One thing is certain, though: The service life of a rubber material is limited. It is exposed to dynamic stressing, is stretched, is subjected to tension and becomes deformed. At some time or another, the material does fail.

Every time a product is developed, of course, technical requirements are defined. They are documented in the performance specifications. Among the requirements defined is that of minimal durability. The supplier will generally want to exceed what is required. This, however, does not really allow for any reliable statements on the actual service life of a product. And this can be of disadvantage, for sudden and, above all, premature product failures are very costly. ContiTech Vibration Control has thus developed a method that can be used to calculate the life expectancy of a product in a specific application area. The rubber expert is already making use of this life expectancy calculation in the product development area. “Especially customers from the rail industry want to know exactly how long the rubber suspension components can measure up to the trains’ requirements and the stress they are subjected to,” explains Rüdiger Meyer, engineer at ContiTech Vibration Control in Hamburg.

The methods developed by ContiTech establish a connection between track testing and test bench results. At the same time it improves product quality and accelerates development. “This reduces the time and expense required for experimental component trials,” notes Meyer. With the help of the finite element method (FEM) – a modern calculation process used in engineering – Rüdiger Meyer and his colleagues employ a virtual elastomer component (CAD model) to calculate the life expectancy of a given product. They play through different stress scenarios to determine how long the component – a hydromount, for instance – will hold up, or to determine where critical loads will occur and how destructive these are. “We feed typical driving signals into the FEM calculation program – for instance, the forces and force paths acting on an elastomer component situated in the bogey of a train over a specific length of track. “The calculation is complemented by the customer’s specification of just how long the elastomer component is to hold out.”

The different life cycle loads are simulated on a 3D computer model. The different load parameters show what stress the material – or the elastomer compound – is subjected to in the rail vehicle. The 3D model visualizes the deformations on the elastomer component. “The body of the model allows us to see exactly where the component risks being damaged or failing due to excessive stress or strain. Points with excessive stressing (tensile force or elongation) are referred to as critical," says Meyer. “They are then rectified by means of modifications in the computer model." In a follow-up step a damage calculation is carried out on the computer. One ends up with a diagram that illustrates the time history of very true-to-life product stressing through to the point of failure. “This allows us to draw up a good service life forecast for the respective elastomer component. Within the framework of experimental service life trials, we have, in the meantime, been able to attain a highly satisfactory concurrence between test and calculation,” says Meyer.

Conclusion: With relatively little expense, the ContiTech service life calculation process allows for a much improved prediction of elastomer component service life than was possible previous. At a very early stage, elastomer components now in development benefit from this product expertise. Before proceeding too far in development work, it is possible, for example, to determine whether the respective concept measures up to later requirements and can withstand the loads to which it will be subjected. Rüdiger Meyer is confident that: “The concept adds to the high degree of customer satisfaction that crucially underlies a sustained customer-supplier relationship.”

Life cycle costing
Life cycle costing
Life cycle costing