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In Lighting the Path to Innovation Blog
authored by Enhancing Fatigue Testing with Fiber Optic Sensing

Material fatigue occurs when an engineering application is subjected to repeated loading and unloading. Fatigue is responsible for up to 90 percent of part and application failures that occur in industries. To test for fatigue, many engineers use a strain-controlled testing method which uses cyclic loading to predict the life of an application under fluctuating loads.

Understanding fatigue life is imperative when implementing R&D efforts for new materials; fatigue testing also helps to understand a product’s life cycle, which in turn prevents against application failures. Any solid material can be tested for fatigue, but most fatigue testing occurs in applications across the aerospace, energy, automotive and manufacturing industries which are held to higher quality standards to enhance safety and reliability. This ensures the safety of workers in these fields and civilians alike throughout the world.

The objective of a fatigue test is to determine the fatigue life of an application, i.e. the location of failure when a material is subjected to a prescribed sequence of stresses. There are a number of methods used to test against stress and strain, including strain gages. However, the lifecycle of strain gages themselves decreases dramatically as strains reach values of 2000-4000 µstrain. This means that strain gages are unable to accurately assess the fatigue over certain parameters.

FOS technology can provide engineers with accurate, real-time data on strain levels, its shape, and additional residual strains resulting from overloading. Sensuron’s optical sensing technology provides strain measurement using thousands of distributed sensors to ensure maximum coverage from a single lightweight optical fiber. Immune to EMF, RFI, or other electromagnetic influences, Sensuron’s systems are ideal for use in hazardous atmospheres and difficult physical environments. It also bypasses the significantly more cumbersome wiring harnesses required by other sensors.

Fatigue Testing in Aerospace

Stress and strain are the parameters that determine the longevity and operational safety of any flight-bound vehicle. With thousands of sensors contained in a single hair-thin fiber providing these measurements, Sensuron’s fiber optic solutions provide a detailed picture of the health of an aircraft. Optical fibers are also resistant to temperatures ranging from cryogenic to hundreds of degrees Celsius. This enables embedded fibers to be monitored during the high temperature cure phase of composite fabrication to determine the through-thickness residual stresses and strains. For these reasons, continuous monitoring of composite structures can be a far-reaching advancement. For example, commercial airlines will always know the state of fatigue damage on critical components, allowing them to fine-tune maintenance schedules and minimize aircraft downtime. Other industries can also benefit from knowledge of the physical state of structures or structural components such as composite rotor blades, skins, beams, and pressure vessels.

Structural Health Monitoring in Energy

Subsea risers are designed to withstand some of the most complex loads and harsh environments that engineers have ever faced. For this reason, accurate fatigue testing is imperative to monitor the structural stability of subsea risers. This data can impact the future design of risers to ensure both long-term efficiency and safety. The dynamic nature of the riser, its components, and its environment subjects it to structural stresses, fatigue stresses, material wear, mechanical degradation, impacts, and environmentally induced loads. Due to these and other factors, the ability of sensors and instrumentation to measure the riser’s structural response to loads is critical. Based on distributed strain sensing, Sensuron’s technology could provide real-time information on riser loads, shape, and performance. These are all factors that periodic inspections can miss.

By monitoring the changes in a network of hair-thin fibers, Sensuron can ensure the integrity, efficiency and long-term durability of equipment across demanding aerospace, medical and energy industries. In this way, Sensuron enables the monitoring of materials in demanding environments to ensure that people stay safe, while solving problems on a global scale and encouraging the sustainable development, operation and maintenance of equipment.

To read more on fatigue testing best practices, see Fatigue Testing and Analysis: Theory and Practice.

Sensuron is a leading global provider of fiber optic sensing systems that use light to test, measure, control, inspect, assist with operation and ensure safety of innovations across aerospace, medical and energy industries.

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