Issue34

G. Lesiuk et alii, Frattura ed Integrità Strutturale, 34 (2015) 290-299; DOI: 10.3221/IGF-ESIS.34.31 298 also identified during the tensile static tests in changes of elongation and reduction in area in normalized state. The yield stress does not always correspond to the structural changes. For the S-steel, the complex low-cycle fatigue and fatigue crack growth resistance tests were performed. The results indicate the worsening of the cyclic properties and fatigue crack growth in accordance with the degradation processes level. According to the [2] and [9], the authors have proposed a new kinetic equation for description of fatigue crack growth rate for the puddled steel. Due to the low-material data consumption, the model (3) can explain the differences in fatigue fracture. The proposed new model (14) needs the complex data for cyclic properties. In this case, it seems that the degradation model (14) behavior (Fig. 7) is close to the experimental results. According to the [7], the kinetic fatigue fracture diagrams for B and W steels have been constructed. The differences in the fatigue crack growth rate have been identified. In comparison to the force approach and  K basis in fatigue fracture diagrams, the CTOD is more sensitive for degradation changes in kinetics of fatigue crack growth in the puddled steel. In the light of the experimental results and deliberations in the works [7-9], it seems that energy description for the fatigue crack growth rate and microstructural degradation influence is a promising approach. Figure 8 : Kinetic fatigue fracture diagram for steel B and W. A CKNOWLEDGMENTS his work has been supported in part by the project B40075/PWR/W10/K10. R EFERENCES [1] Lesiuk, G., Szata, M., Aspects of structural degradation in steels of old bridges by means of fatigue crack propagation, Materials Science (New York), 47 (1) (2011) 82-88. [2] Lesiuk, G., Mechanical and structural degradation of 19 th puddled steel, Wroclaw University of Technology, PhD Thesis, (2013), in Polish. [3] Bień, J., Damage to bridges and diagnostics, Wydawnictwo Komunikacji i Łączności, Warszawa, (2010), in Polish. [4] Björklund, A., Höglind, J., Strengthening of steel structures with bonded prestressed laminates. Master thesis, Department of Structural Engineering, Chalmers University of Technology, (2007) 1-8. [5] Helmerich, R., Kühn, B., Nussbaumer, A., Assessment of existing steel structures. A guideline for estimation of the remaining fatigue life, Structure and Infrastructure Engineering, 3(3) (2007) 245 – 255. T