PSI - Issue 16

Yaroslav Ivanytskyi et al. / Procedia Structural Integrity 16 (2019) 126–133 Yaroslav Ivanytskyi et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The load Р – elongation Δ l balanced curves for two batches of samples at tensile testing were recorded (Fig. 2a). Registration of elongation of specimens and reduction on the basis of 0.5 mm were carried out in place of maximum deformations using an optodigital system (Ivanyts ’ kyi et al., 2014). The true stresses S were determined by changing the cross-section of the sample F, i F S   . Determined the true deformation by the elongation value Δ l , i l l    . From the built diagram (Fig. 2b), the fracture energy for the steel was determined according to 0 ( ) W d       .

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Fig. 2. “ Load – elongation” curves (a); Determination of the critical specific energy of deformation (b).

Studies on steel creep in hydrogen were carried out in a special chamber with a viewing window (Fig. 1c). The sample was heated by a passed current to a temperature of 640 ° C, which was maintained constant during the experiment. The sample was subjected to loading to deformation of 0.2. Hydrogen pressure in the chamber was 3 MPa. During the experiment, a deformation gain was determined after a certain period. According to the obtained research results data, the creep and energy deformation diagrams were built. The same diagram was built for the samples tested in air.

4. Numerical modeling and results

1.1. Modelling of the stress-deformed state of Bridgman sample with the finite element method

Testing of the proposed approach was carried out earlier (Qin et al., 2018). Here are the results of numerical studies for the Bridgman sample (Fig. 3) made of steel 0.5Cr0.5Mo0.25V, under uniaxial tension at loading P = 54 MPa and temperature 640 ºC , after hydrogenation at different pressure of hydrogen: P 1H = 1, P 2H =3, P 3H =32 MPa. Dimensions of the sample are shown in Fig. 2a.

Fig 3. General view of the Bridgman sample and the finite-element partitioning.

The problem was solved by the finite element method using the MSC MarcMentat 2014.0.0 software package and proprietary software. Sample was divided into 14093 elements of tetrahedron-shaped form. Finite element model contained 22,282 nodes totally. The grid was thickened near stress concentrator. The constants of the kinetic equations for creep and long-term durability of the studied steel are obtained by processing the curves of creep and the long-term strength of the steel. The values of the coefficients are given in Table 2.