Application of a New, Energy-Based Δ Crack Driving Force for Fatigue Crack Growth Rate Description.

This paper presents the problem of the description of fatigue cracking development in metallic constructional materials. Fatigue crack growth models (mostly empirical) are usually constructed using a stress intensity factor Δ in linear-elastic fracture mechanics. Contrary to the kinetic fatigue fracture diagrams (KFFDs) based on stress intensity factor , new energy KFFDs show no sensitivity to mean stress effect expressed by the stress ratio . However, in the literature there is a lack of analytical description and interpretation of this parameter in order to promote this approach in engineering practice. Therefore, based on a dimensional analysis approach, Δ is replaced by elastic-plastic fracture mechanics parameter-the Δintegral range. In this case, the invariance from stress is not clear. Hence, the main goal of this paper is the application of the new averaged (geometrically) strain energy density parameter Δ based on the relationship of the maximal value of integral and its range Δ. The usefulness and invariance of this parameter have been confirmed for three different metallic materials, 10HNAP, 18G2A, and 19th century puddle iron from the Eiffel bridge.