PSI - Issue 26

Vladimír Chmelko et al. / Procedia Structural Integrity 26 (2020) 417–421 Chmelko et al. / Structural Integrity Procedia 00 (2020) 000 – 000

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Fig. 2. Pipes after destruction involved by internal pressure: on the left – ideal pipe before and after destruction; on the right – real pipeline after multi-year service subjected to destructive test

Fig. 3. Stress-strain diagrams and bilinear model of the steel X52.

These are obtained as conventional values from the tensile test. The corresponding yield stress is the deformation calculated using the Young's modulus E . The corresponding strain to the limit strength, required to calculate the strength modulus E´ , depends on the shape of the non-linear part of the stress-strain diagram. For steels of type X52, X60, X70, and others whose ductility is more than 20%, this strain value is approximately 10%. As can be seen in (Fig. 3), the constructed bilinear material model in the region below the ultimate strength gives lower stress values at the same strain value and in the region above the ultimate strength gives higher stress values compared to the actual stress values.

2.2. Criterion of destruction

The second important parameter of numerical simulation is the destruction criterion. The condition that the maximum stress value reaches the strength limit value in a conventional tensile diagram is not an instant of pipe