Fracture-mechanical crack growth parameters of historical mild steels

•Old mild steels have a strong correlation between the parameters of the Paris-law.•The stress ratio influences the Paris-exponent in historical steels.•Considering the stress ratio has an impact of the fatigue assessment of structures. At the beginning of the 20th century, a large number of steel structures were built in Europe. Many of these buildings—especially railway bridges—are still in use. These structures are mainly composed of rimmed steel. In addition to the stress–life concept, fracture mechanics is often used to assess the safety of these structures in terms of fatigue failure. Based on crack propagation calculations, it is possible to determine inspection intervals and, thus, ensure safe operation. For these calculations, suitable parameters of the Paris law, along with threshold values, are needed. The aim of this study is to experimentally determine a wide range of fracture mechanics parameters for old mild steel with reference to the stress ratio R. The experimental results were compared with values from the literature. Furthermore, the experimental results were fitted to several models considering the stress ratio R during crack growth. The investigated models were compared on the basis of the results for simulated crack growth calculations. The models are assessed according to how closely they represent the experimental results.

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