Deflection shape of a turbine blade

Figure 2: Deflection shape of a turbine blade

Unravelling the Importance of High-Cycle Fatigue Testing with Polytec’s Cutting-edge Solutions

In our fast-paced world where technology drives progress, understanding the limits of the materials that power our lives is more critical than ever. Any engineered material, a piece of metal, a stretch of composite, or a slice of alloy might seem indestructible at first glance, but how do they react under strain and repetitive stress? Enter the realm of High-Cycle Fatigue (HCF) testing. This crucial test analyses the endurance and resilience of materials when subjected to a large number of stress cycles. In this blog, we'll uncover the significance of HCF and VHCF testing and highlight how Polytec's innovative solutions are revolutionising this domain.

Why is High-Cycle Fatigue Testing So Vital?

Safety at the Helm

Think of an aeroplane soaring above the clouds. Each component, down to the tiniest bolt, plays a pivotal role in ensuring the aircraft's integrity. Now, imagine these components experiencing millions of repetitive stresses during their lifetime. One minor failure due to repeated stress, and the outcome could be disastrous.

And it’s not just about the force exerted on these materials but also the frequency with which they are subjected to this force. HCF testing aims to mimic these conditions, ensuring materials can endure the repeated stresses of real-world applications without compromising safety.

Guaranteed Durability

Replacing aerospace components is not as simple as changing a light bulb. It can be cumbersome and time-consuming, so knowing how much these parts can withstand is vital. Safety is arguably the most important topic when it comes to aerospace components’ lifecycles, but the economic implications of replacements and repairs are not trivial either.  

Modern consumers are increasingly conscious of the longevity of products they invest in. No one wishes to replace their car's components or home appliances frequently. With HCF and VHCF testing, industries can ascertain the durability of materials, promising customers a longer and trouble-free product lifespan with confidence.

Economic Impact

A product recall or frequent after-sales service due to material failure is not just detrimental to a brand's reputation but also to its financial health. HCF and VHCF testing is a proactive approach to avert such unforeseen costs, acting as a shield against potential economic pitfalls.

Increasing fatigue test requirements

Standard tests are mainly defined for low-cycle fatigue, and traditionally, an HCF test (10^7 cycles) has been sufficient to pass safety checks. However, the introduction of new materials and alloys, together with the ever-increasing emphasis on safety and reliability, have brought to the forefront very high cycle fatigue (VHCF) tests, which run 10^9 cycles.

Polytec: Elevating the Standard of HCF and VHCF Testing

While the relevance of HCF testing is now universally accepted, the precision and efficiency of these tests are often contingent on the equipment and methodologies employed. This is where Polytec's innovations come to the forefront.

Non-contact Precision with Laser Vibrometry

Traditional testing methods, like strain gauges, often involve contact-based measurements, which might alter the natural response of the material. Polytec’s laser Doppler vibrometers are game-changers in this realm. These devices measure vibrations and strains in test materials without any physical contact and at speeds that the strain gauges are unable to handle. The result? A more authentic representation of how materials would respond in real-world conditions.

From High-Cycle Fatigue Testing to Very High Cycle Fatigue Testing

Polytec’s innovations don’t stop there. As mentioned earlier, new materials and alloys require an even higher number of cycles in testing to ensure safety. However, VHCF testing poses unique challenges. Repeated compressive and tensile stress has a deteriorating effect on the fatigue strength, which reduces with number of cycles for homogeneous materials. To keep the testing time to an acceptable level, VHCF typically uses much higher frequencies than what traditional gauges are capable of handling over the test’s duration.

Higher frequencies, although necessary for maintaining reasonable testing times, limit the capabilities of existing sensors. Also, it becomes a bigger challenge to excite the sample at higher frequencies while still dealing with resulting high temperatures. Consequently, this creates a need for an alternative strain measurement technique. Laser Doppler vibrometers have already been proven suitable for High-Cycle Fatigue testing. So, Polytec took things one step further and tested a new setup called multi-path laser Doppler vibrometers (MDV), which combines four LDVs on a fixed structure and image processing techniques for alignment and calibration. This setup proved ideal to meet even the substantial demands of VHCF testing.

Accelerated Analysis for Faster Outcomes

The multi-path version is compatible with the MDE (Multi-point Data Evaluation) software, as it allows agnostic connections. That means that it works more seamlessly with any configuration, including VibroFlex or VibroGo vibrometers. Another revolutionary aspect of the MDE software is that it even allows the combination of non-contact and contact sensors in a common data and geometry model.

Given that VHCF involves potentially billions of stress cycles, time is a quintessential factor, and Polytec's systems are engineered for speed without compromising on accuracy. Rapid data acquisition coupled with swift computational capabilities ensures that industries can get timely insights into material behaviours.

Adaptable to Diverse Needs

Every industry, be it automotive, aerospace, or renewable energy, has unique testing requirements. Materials come in varied sizes, shapes, and compositions. Polytec’s extensive range of top-quality equipment showcases commendable versatility, catering to a broad spectrum of testing needs. Whether you wish to use our MDV setup for aerodynamic testing in a wind tunnel, shock testing, speed sweeps in electric motors, tissue tension measurement, or VHCF testing of fragile structures, we can optimise it to your needs. Our equipment’s adaptability ensures that regardless of the testing challenge, there's a Polytec solution ready to address it.

In Conclusion

In an age where the integrity of materials is paramount, High-Cycle Fatigue testing stands as the unsung hero, working behind the scenes to ensure the products we use daily are safe, durable, and economically sustainable. Within this landscape, Polytec emerges as a torchbearer, propelling the domain of HCF testing with its cutting-edge solutions and even taking on challenges posed by VHCF testing.

Embracing Polytec’s innovations is not just about getting accurate test results; it's about securing a safer, more efficient, and economically vibrant future. As industries continue to push the boundaries of material capabilities, having a reliable partner like Polytec becomes indispensable. With our unwavering commitment to precision and innovation, Polytec is undeniably setting the gold standard in High-Cycle Fatigue testing.