Operational strength

Operational strength

Operational strength is a 2nd semester elective specialised course held at University of Ljubljana, Slovenia.


2. semester - University of Ljubljana, Slovenia


prof.dr. Marko Nagode

Course Points (ECTS)


Contact Information

University of Ljubljana, Slovenia


Course Overview

Module objective

The students obtain specific knowledge as an upgrade to the basic knowledge of the R&D programme in mechanical engineering and the E&M field programme. This knowledge will enable them to execute developmental tasks in the field of developmental evaluations. The Operational strength course upgrades the knowledge obtained in the Science of the strength of materials and Advanced science of the strength of materials courses, qualifying the student in the developmental methods, dealing with the predictions of operating and loading states during the exploitation.

Knowledge outcome

The student learns the state-of-the-art of functionalities, and the developmental, manufacturing and operating specialties of basic building blocks of mechanical actuators. He or she understands the development, manufacturing and operation of elements and assemblies, as well as the principles of synthesis into machines and devices.

Syllabus outline

  • Describing time-variant operating conditions. Load classification. Statistical methods for the description of load states.
  • Deterministic and random load states, load spectra.
  • Experimental determination of operational strength: Wöhler tests, block diagrams for testing, random loading program, special program, validity of testing programs.
  • Modeling operational strength: loads, critical cross-section, stress, form factor, safety margin. Factors influencing the operational strength (the influence of loads, form, material, manufacturing process, temperature, chemical influences, corrosion, frequency and so forth).
  • Low-cycle strength, stress vs. cycles to failure (fatigue strength), fatigue limit. Multiaxiality of stresses: stress- and deformation-based approach. Basics of crack propagation theory and their influence on the component life. Calculations of safety and reliability.
  • Practical solutions: experimental support for the determination of operational strength, analysing the measurement results, processing the results, load spectra, constructing the load spectrum, statistical distribution of extreme values, load spectra spread, the dependence of load spectra form and extent on operating conditions, partial load spectrum, summary load spectrum, load spectrum growth, durability curves, durability curve spread. Tracking the operating conditions and the operating state during the operation and the whole life time.

Monitoring of student progress

  • Two colloquia
  • written examination


[1] Bahram Farahmand: Fatigue and Fracture Mechanics of High Risk Parts - Application of LEFM & FMDM, 1997
[2] S. Suresh: Fatigue of Materials, 1998
[3] Norman E. Dowling: Mechanical Behavior of Materials, 2006
[4] Manuela Sander: Sicherheit und Betriebsfestigkeit von Maschinen und Anlagen: Konzepte und Methoden zur Lebensdauervorhersage, 2008
[5] Dieter Radaj, Michael Vormwald: Ermüdungsfestigkeit: Grundlagen für Ingenieure, 2009
[6] Erwin Haibach: Betriebsfestigkeit: Verfahren und Daten zur Bauteilberechnung, 2002
[7] Otto Buxbaum: Betriebsfestigkeit, 1992