Issue 47

Yu. G. Matvienko et alii, Frattura ed Integrità Strutturale, 47 (2019) 303-320; DOI: 10.3221/IGF-ESIS.47.23 317 negative value of cycle asymmetry ratio slows down fatigue damage accumulation process for loading programs with the same stress range. a b Figure 11 : Normalized CMOD values 1   v (a) and 2   v (b) for cracks of 1  a and 2  a length as a function of lifetime percentage for specimens of T5-H1 and T5-H2 group. a b Figure 12: Normalized SIF values 2  I K (a) and 3  I K (b) for cracks of 1  a and 2  a length as a function of lifetime percentage for specimens of T5-H1 and T5-H2 group. The key point of the approach developed consists of the fact that specimens with cold-expanded holes are tested under real operation conditions without inserting initial notch to ensure fatigue crack growth. Deformation response to small notch length increment, made under constant external load, serves as an indicator of damage accumulation at different stages of fatigue loading. Thus, the first benefit of the crack compliance technique resides in a posteriori character of the experimental procedure. This means that crack length measurements and further determination of fracture mechanics parameters are performed after fatigue loading with a high degree of accuracy [36]. The second advantage is a capability of study of fatigue