CD Laboratory for Defect Tolerance of Steels in the High and Very High Cycle Fatigue Regime

In this CD laboratory, the influence of defects on the cyclic strength of steels is investigated. The results should contribute to a fundamental understanding of the fatigue mechanisms in the regime of high and very high number of load cycles and thus enable the prediction and extension of the service life of cyclically stressed components.

The development of steels with ever higher strength opens up new possibilities to increase energy efficiency by reducing weight. However, the increase in static strength is usually accompanied by a reduction in defect tolerance under cyclic loading conditions. As a consequence, even very small defects can lead to the formation of fatigue cracks and failure. Defects can never be completely avoided and occur both inherently (e.g. non-metallic inclusions, material inhomogeneities, pores) and production or application related (e.g. surface roughness and damage, corrosion pits). A comprehensive understanding of the material´s defect tolerance is therefore of the utmost importance for the safe design of a cyclically stressed part, enabling the design and use of durable and energy-efficient components. This can make a significant contribution to the sustainable use of resources and to ensuring a competitive economy.

The research concept focuses on investigating the fatigue properties of high-strength steels. In addition to characterising the defect tolerance, the influences of surface treatment, welding and environment on the cyclic strength are investigated. The use of innovative testing methods, such as the ultrasonic fatigue testing technique, enables the time-efficient performance of comprehensive test series as a basis for the simulation of relevant operating conditions. The experimentally determined data will be utilised to develop physics-based models for predicting the fatigue strength. The aim is to develop competitive, resource- and cost-efficient components based on the knowledge gained in the CD laboratory.

Figure 1: In the CD laboratory DefTol at BOKU University, the research group led by Bernd Schönbauer is investigating the influence of defects on fatigue strength.

Figure 2: In the very high cycle fatigue range, crack initiation preferentially occurs in the interior of a material.

Figure 3: The high-accuracy ultrasonic fatigue testing equipment developed at the Institute of Physics and Materials Science enables extensive test series to be carried out in a time-efficient manner.