Why should you care about tiny defects on rails? Tiny cracks on rail surfaces can grow and develop into breakouts in the rail if left unattended. In Austria's 5,700 km long rail network, which carries 328 million passengers a year, early detection of such cracks is crucial to ensure operational safety and efficiency.
Head checks and rail monitoring. Rolling contact fatigue (RCF) may lead to surface defects such as head checks, which pose a risk of rail failure. Fatigue-related problems are responsible for 50-90% of mechanical failures in rail systems. Conventional rail monitoring relies on train recording vehicles (TRVs) and fixed sensors. While TRVs provide periodic assessments, fixed installations continuously monitor vulnerable sections of track, significantly reducing maintenance costs and rail downtime over time.
Piezoelectric sensors and surface acoustic waves. At the Materials Center Leoben (MCL), piezoelectric sensors were used to generate surface acoustic waves (SAWs) to detect cracks in rails. SAWs interact with surface cracks, whereby the transmitted, reflected and scattered signals provide important information about the crack depth. Piezoelectric sensors were chosen for their compactness, low cost and ability to generate a wide frequency range.
System design and implementation. The system shown in the picture above consists of piezo sensors installed in pairs along the rail web. The sensors are connected to a switch box (“OptiSwitch”) that allows flexible transmitter-receiver configurations. This setup is connected to a sensor box for signal control and amplification, which is connected to a laptop for real-time analysis.
Signal processing and innovation. The MCL's customized signal processing removes noise from the measured signals, cross-correlates the signals and calculates the transmission coefficients to determine the crack depth. Unlike conventional systems that require fine-tuning, this plug-and-play solution only requires the sensor spacing to be entered, greatly simplifying installation and operation while optimizing the signal-to-noise ratio (SNR).
Performance validation. The system was extensively tested at voestalpine Rail Technology GmbH, using a test rig that simulates wheel-rail interactions under different conditions and with different rail types. The crack depths were validated using metallography and eddy current measurements. The results consistently showed a high level of agreement between measured and estimated crack depths, demonstrating the reliability and adaptability of the system for continuous rail monitoring.
Impact and effects
For rail operators, continuous monitoring reduces the need for reactive maintenance, minimizing downtime and operating costs. Passengers benefit from increased safety, fewer delays and potentially lower travel costs, underlining the value of this innovative solution. For the environment, the increased availability of the rail system leads to greater use of public transport by commuters, which in turn reduces CO2 emissions.
Project coordination (Story)
Dr. Mohsen Rezaei
Senior Researcher
Materials Center Leoben Forschung GmbH
T +43 (0) 3842 45922-0
Mohsen.Rezaei(at)mcl.at
IC-MPPE / COMET-Zentrum
Materials Center Leoben Forschung GmbH
Vordernberger Strasse 12
8700 Leoben
T +43 (0) 3842 45922-0
mclburo(at)mcl.at
www.mcl.at
Project partners
• Materials Center Leoben Forschung GmbH, Austria
• voestalpine Rail Technology GmbH, Austria
• voestalpine Signaling Austria GmbH, Austria
• Montanuniversität Leoben, Austria
• Technische Universität Graz, Austria