PSI - Issue 7

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R. Prochazka, J. Dzugan, P. Konopik / Structural Integrity Procedia 00 (2017) 000–000

R. Prochazka et al. / Procedia Structural Integrity 7 (2017) 315–320

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3. Results and discussion The comparison between standard procedure for fatigue limit evaluation and thermal procedure using graphic method was done for two materials and is summarized in Table 1. The base material showed very constant results of mechanical properties in all directions, which is perhaps one of the reasons for the very good match of stress–life fatigue results. While using a standard method, the loading stress levels around the endurance limit were tested very gently, as can be seen from Fig. 4. Also, in the case of a weld joint, a slight difference in the results in comparison with the standard method was observed. The higher standard deviation is probably caused by mechanical property non-homogeneity in a weld-join region. In Fig. 5, the thermo image sequence for base material shows the behavior of unloaded and loaded specimen from the beginning until the failure.

Table 1 Fatigue limit results and standard deviation values Material

Thermographic method ( MPa )

Standard method ( MPa )

Standard deviation (%)

Duplex steel

289.3

290.0

0.2 7.3

Duplex steel – weld joint

85.8

80.0

a

b

Fig. 4 (a) S-N curves for base material and (b) weld joint

Table 2 Thermal data

Duplex steel

Duplex steel – weld joint

σ /2 (MPa)

σ /2 (MPa)

N

ΔT max (°C)

ΔT max (°C)

50 55 60 65 70 75 80 85 90 95

-0.167 -0.224 -0.259 -0.185 -0.066 0.055 0.466 1.313 2.282 5.252

1 2 3 4 5 6 7 8 9

150 175 200 225 250 275 300 325 350

1.028 0.984 1.378 1.749 2.840 4.426 7.626

13.866 25.542

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