Abstract
The goal of the authors’ investigations was determination of the fatigue crack growth in fragments of steel structures (of the puddled steel) and its cyclic behavior. Tested steel elements coming from the turn of the 19th and 20th were gained from still operating ancient steel construction (a main hall of Railway Station, bridges etc.). This work is a part of investigations devoted to the phenomenon of microstructural degradation and its potential influence on their strength properties. The analysis of the obtained results indicated that those long operating steels subject to microstructure degradation processes consisting mainly in precipitation of carbides and nitrides inside ferrite grains, precipitation of carbides at ferrite grain boundaries and degeneration of pearlite areas [1, 2]. It is worth noticing that resistance of the puddled steel to fatigue crack propagation in the normalized state was higher. The authors proposed the new kinetic equation of fatigue crack growth rate in such a steel. Thus the relationship between the kinetics of degradation processes and the fatigue crack growth rate also have been shown. It is also confirmed by the materials research of the viaduct from 1885, which has not shown any significant changes in microstructure. The non-classical kinetic fatigue fracture diagrams (KFFD) based on deformation (??) or energy (?W) approach was also considered. In conjunction with the results of low- and high-cycle fatigue and gradual loss of ductility as a consequence (due to the microstructural degradation processes) - it seems to be a promising construction of the new kinetics fatigue fracture diagrams with the energy approach.
Highlights
The rapid development of metallurgy in the 19th century resulted in intensive erection of numerous bridges
The relationship between impact resistance toughness and fatigue crack growth conditions with the structural degradation nature of puddled steels was demonstrated below by the following equation proposed by the authors: dα dΝ
All tested materials were identified for the puddled steel – commonly used at the turn of the 19th and 20th century
Summary
The rapid development of metallurgy in the 19th century resulted in intensive erection of numerous bridges. Fatigue crack growth rate model for puddled steel From the experimental results it can be concluded that the most sensitive markers of degradation are the impact resistance toughness and low cycle fatigue properties. The relationship between impact resistance toughness and fatigue crack growth conditions with the structural degradation nature of puddled steels was demonstrated below by the following equation proposed by the authors: dα dΝ. In the proposed model: A means non-dimensional constant (A=2457 for post-operating state, A=1871 for normalized state), KCV means the impact energy value (Charpy test value) in J/cm, KCV35 - required minimal energy value (35 J/cm2) for the modern steel, E represents Young modulus in MPa, pl – yield tensile strength in MPa. In several studies The fracture toughness of investigated S-steel was estimated using J-integral as a critical value of fracture toughness Kc converted from J-integral using formula: KI
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