Influence of loading direction on the static and fatigue fracture properties of the long term operated metallic materials

In this paper, the problem of fatigue crack growth resistance and fracture toughness in steel structural components have been discussed. For investigation were extracted parts of bridges made of 19th century puddled steel and early 20th century mild steel. The object of interest of the authors were fragments of steel structures from ancient bridges located in Warsaw (Poland): Most pod Cytadelą (marked as “C” material); Most Kierbedzia (marked as “W”); and, a parts from the Main Railway Station hall in Wroclaw, Poland (marked as “B”). In all cases, the metallographic analyses were performed. It has been proofed the presence of degradation processes in such old steel. The mentioned processes consisted mainly in precipitations of the brittle phases inside the ferrite grains, as well on the grain boundaries. The mechanical properties and crack growth resistance, as well as fracture toughness expressed by the J-integral method have been determined for the specimens collected from the Main Railway Station hall in Wroclaw (Poland). It has been shown that crack resistance – expressed with the critical value of J-integral – in the rolling direction is significantly higher than in the direction perpendicular to rolling. For fatigue analysis, fatigue crack growth experiments were performed for all materials in rolling direction as well as in transversal direction. Based on the experimental results is worth to notice that, the obtained values are far lower than the critical values of the J-integrals characterizing the modern low-carbon constructional steels (S235JR or S355JR steels).