Solution design

Fatigue Strength: advanced testing delivers significant benefits

Dr. Rudolf Randler, Head of Simulation at Datwyler, looks at advanced fatigue strength and endurance testing and how the automotive supply chain can benefit significantly from its insights

Dr. Rudolf Randler
Jan 8, 2025

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Mobility

 

Predictability is a valuable asset in any dynamic sealing application. From pump membranes to damping elements, for any rubber component under constant vibration, the ability to predict the fatigue strength and endurance of materials reduces prototyping costs, speeds up the validation process, and brings solutions to market sooner.

 

The exciting question is always: functionality, performance, endurance - where are the limits? Thanks to our strategic investments in the latest engineering expertise and a brand new, 384-core simulation server, we are able to communicate faster and to deliver more complex simulations for our customers.

These measures will enable us to exert greater influence on aligning material properties with component design ahead of serial production, ultimately accelerating the product development process itself. Our goal is to achieve 95% certainty in predicting how our materials and products will behave in an operational environment.

Fatigue strength and endurance testing

We develop components for dynamic sealing applications with low stress designs and materials that exhibit high endurance stability. However, if we take a pump diaphragm as an example, to put a figure on how many load, pressure or deformation cycles it can withstand would historically be difficult to achieve.

Customers would have to test the parts to destruction, usually at high or low temperatures, and at higher pressures than the application would normally run at. If we run a pump membrane at 50 Hertz for 8 hours per day over one year, for example, it is possible to calculate the number of cycles it could reasonably achieve before needing to be replaced. This approach is time consuming, costly, and requires the use of testing facilities that are often difficult to access due to high utilization. 

At Datwyler, to improve the accuracy of our simulations we test materials for stress-strain behavior and also for crack growth propagation. Test specimens with small, well-defined cracks, acting as defects in the system, are placed on the test rig, and tensile strain cycles are applied to measure the crack growth rate. The resulting data is  then used to formulate a failure model applicable to finite element simulations. This approach enables us to predict the fatigue life of our components, based solely on the material properties and the specified boundary conditions.

Enhanced software raises the bar

To perform these calculations we have implemented a new software called Endurica®. It serves to bridge the gap between testing and Finite Element Simulation  allowing us to calculate fatigue life and failure location on a part, and to diagnose and resolve material, geometry and loading issues to get durability right – all based on specific customer requirements. Recording models for different materials facilitates comparison and allows for efficient evaluation of different design variants. These calculations also permit the part geometries and designs to be modified before they go to serial production, which can save customers a great deal of money. 

Customers will of course have to run their own tests ahead of application use, but if we can promise a certain endurance limit in advance, they can be sure that any failures will not be due to our material or component. We are certain that our simulation capabilities will allow us to predict with 95% certainty that our materials will not cause a failure. This ability to pre-select materials also removes risk to customers when they come to reserve expensive testing facilities. As we are sure about the materials we propose, we know the development process will be faster as the amount of testing rounds required will reduce.

Real world benefits for Tier 1 suppliers

Dynamic, system-critical parts developed with fatigue strength and endurance testing methods in mind offer several benefits for Tier 1 suppliers. The information gathered is crucial for ensuring the reliability and durability of rubber components in mobility applications. Additionally, it also provides a quantitative measure of a material's resistance to fatigue failure for quality control purposes - ensuring that final products meet specified performance criteria and standards.

Testing fatigue strength and endurance allows engineers to identify weaknesses in rubber materials or component designs early in the development process. By understanding how different factors such as material composition, processing methods, or geometry affect fatigue performance, designers can optimise product designs for enhanced durability and longevity.

Identifying potential failure points under cyclic loading conditions also delivers benefits from a safety and reliability perspective, as there are no surprises in terms of when a material is expected to require replacement. Suppliers can also mitigate the risk of costly recalls for their customers, warranty claims, and reputational damage as a result of unexpected component failures in the field.

The path to innovation

Overall, fatigue strength and endurance testing plays a vital role in the development, quality assurance, and performance validation of rubber materials and components in mobility applications, contributing to enhanced product reliability, safety and longevity. At Datwyler we continue to innovate in this area, particularly through our work in partnership with academic institutions such as the Tomas Bata University in Zlín (CZ), for example.

A recent project conducted by the university in collaboration with experts from Datwyler focused on analyzing the mechanical properties of two different rubber compounds before and after exposure to three distinct aging conditions. The aim was to compare the fatigue strength of the two compounds and determine the impact of chemical aging in brake fluid on their fatigue behavior. Ultimately, our primary objective is to utilize these measured material parameters in conjunction with Finite Element Analysis (FEA) to predict the durability of rubber components under the specific loading and boundary conditions of the customer application. 

A series of tests were planned, utilising the latest Intrinsic Strength Analyzer (ISA) to measure intrinsic strength and critical tearing energy, along with Tear and Fatigue Analyzer (TFA) technology to assess fatigue growth rate and fatigue to failure. Additionally, a universal testing system was deployed to measure the hyperelastic properties of both compounds under cyclic loading conditions and the results are currently being collated.

The ability to evaluate the fatigue strength and endurance of materials and to forecast the durability of rubber components manufactured from these materials via FEA confers considerable benefits upon Tier 1 suppliers to the mobility sector. For instance, the degree of predictability it offers facilitates the streamlining of the prototyping and testing process, thereby enabling fully compliant products to be scaled and brought to market faster.

Watch this space for the full results of this exciting collaboration.

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