Acoustic diagnostics – Defect detection | Signal evaluation | Quality assurance

Defect detection

Testing of parts and components is a critical task in transportation and environmental engineering. In rail and air transportation, passenger safety is the top priority. Spalling and other defects in wheel treads must be identified at an early stage. This requires continuous monitoring of wheels and wheel bearings in rail vehicles. High demands are also placed on aircraft structural elements, such as the fuselage shell, because they can suffer impact or fatigue damage while in flight.

As an example in the renewable energy sector, wind turbines are exposed to extreme loads. External influences, such as mechanical abrasions, weather events, and continuously fluctuating loads exerted on the rotor blades lead to wear and aging over time. Production-related flaws can also lastingly interfere with or even prevent operation.

The sooner damage or wear effects are determined, the better the chances of repair and avoidance of consequential damage (or catastrophe) are.

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Rail transportation

 

Fraunhofer IKTS offers a robust, autonomous solution for monitoring wheels and wheel bearings as well as detecting blocked brakes, damaged springs, and impermissible inclinations (e.g., due to improper loading) in rail vehicles.

Monitoring is based on acceleration and temperature data as well as the structure-borne sound signals generated by contact between the train wheels and the rails. These data are recorded and evaluated with customer-specifically adapted sensor nodes consisting of modules for sensor technology as well as signal processing and radio processors. Instrumentation and support for trial runs round off the offering for this monitoring solution.

For monitoring ICE wheels, Fraunhofer IKTS offers a measurement system that is permanently installed in the hollow shaft of the wheel set. This enables processing of high-frequency structure-borne sound signals generated by the wheel-to-rail contact and monitoring of both the wheels and the track for detection of damage.

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Rotor blades

 

An integrated system for the monitoring of rotor blades in wind power plants allows for condition-dependent component maintenance. The passive method of acoustic emission (AE) testing is used for detection of damage, such as structural damage, ice formation, and aerodynamic imbalances or lightning strikes.

This method utilizes special ultrasonic waves arising in the structure as a result of loading (acoustic emissions). Piezoelectric sensors detect these emissions. The frequency and the distribution of the acoustic emission events represent the current damage. Optical energy and data transmission are implemented to eliminate the risk of lightning strikes posed through use of metal conductors in the wind turbine rotor blades.

The IKTS system allows the evaluation of the component condition until the next inspection, thus optimizing maintenance planning.

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Aircraft structures

 

Aircraft developers rely on lightweight materials to reduce aircraft weight. However, the carbon fiber composites (CFRP) used require special processing, quality control, and inspection.

To ensure safety in consideration of the high loads experienced by aircrafts in flight, early detection of cracks and impact damages is crucial. With the help of active and passive ultrasonic diagnostics, damages can be rapidly detected and the severity assessed automatically.

Testing and monitoring of material properties, such as the structural integrity of the aircraft fuselage, are currently performed on the ground in load tests. In the future, monitoring should be able to take place in the air.