title: Stressed systems: reliability of physical systems under varying loads
topics: Dependability, security and performance
committee: Enno Ruijters ,
Mariƫlle Stoelinga


RAMS (Reliability, Availability, Maintenance, Safety) requirements are of utmost importance for safety-critical systems like nuclear power plants, power grids, and railroad infrastructure. These systems wear out as they are used, and require maintenance to keep them in working order. It is therefore important to understand how fast they wear out, and how much maintenance is required.

Physical systems typically wear out faster or slower depending on the intensity of their use: The tires on a racing car need to be replaced after a few laps, while the tires on your car can last for thousands of kilometres. Similarly, the failure of a component will depend on its use: if the treads on your tires are too worn, you can still drive just fine, right until it starts raining and you find that your tires lose grip. Similarly, a worn axle can stay intact until a strong bump snaps it.

A widely used standard for RAMS analysis is fault tree analysis (FTA), which we have recently extended to include degradation and maintenance through fault maintenance trees (FMTs). The current models, however, assume that components degrade over time regardless of how much they are used, and that components fail at a particular level of degradation regardless of stress. In this project you will extend this model to include a model of the load on the system, and the effects this has on the wear of the components.

Your tasks will include:

  • Study of the degradation of physical systems subject to varying loads
  • Integration of load-dependent degradation in the FMT framework
  • Case study to validate the extended model

As part of this project, you will visit NedTrain who will assist with the case study.


  1. W.E. Vesely, F.F. Goldberg, N.H. Roberts, D.F. Haasl, Fault Tree Handbook, Office of Nuclear Regulatory Research, US Nuclear Regulatory Commision, 1981 (Digital version available here)
  2. E. Ruijters, D. Guck, P. Drolenga, M. Stoelinga, Fault maintenance trees: reliability centered maintenance via statistical model checking. (Digital version available here)