PSI - Issue 5

Hołowaty J. et al. / Procedia Structural Integrity 5 (2017) 1043 – 1050 Hołowaty / Structural Integrity Procedia 00 ( 2017) 000 – 000

1049

7

Similar ageing effects were found when assessing elongation A5. For the steels from bridges Nos. 1 and 2, ageing had increased elongation while for bridges Nos. 3, 4 and 5 ageing had lowered it. As a result of ageing, all the bridge steels had reduced ultimate tensile strength f u . In the case of bridges Nos. 1 ÷ 4 the decrease was from 0.2 to 5.1 % and for bridge No. 5 it was up to 17.5 %. The hardness values and ultimate strengths f uB , given in Table 3 often have practical significance. There may be circumstances when cutting out samples for tensile testing is impossible and hardness tests are a good alternative. Impact toughness tests were carried out on standard Charpy specimens with dimensions 10×10×55 mm and V notch machined according to EN ISO 148-1:2016. As with the tensile testing, two types of specimens were used for all the bridges, naturally-aged S and normalized N. Annealed specimens A were only used for bridge No. 3. In Table 4, the average values of impact energy KV(T) at a given temperature are shown. The values were obtained from tests on 198 specimens. The results are given graphically in Fig. 3, with the horizontal line marking the 27 J impact energy which has been set as a limit value in EC3 for new structures. The low carbon steels from bridges Nos. 2 ÷ 5 with carbon content C ≤ 0.037 % revealed very low impact en ergy values. In the case of subgrade J0, at temperature 0 °C, the impact energy was from 5.5 to 12.1 J, which is only 20.3 and 44.4 % of the required 27 J value. 5. Toughness of the bridge steels

Fig. 3. Average impact energy for the naturally-aged S and normalized N steels from five railway bridges (Picture of three specimens after fracture with delamination at temperature 20  C) .