PSI - Issue 32

3

Artem Udartsev et al. / Procedia Structural Integrity 32 (2021) 187–193 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

189

Experiments on uniaxial and volumetric compression were carried out using an MTS-815 servo-hydraulic complex with a maximum load of 1600 kN (Fig. 2) according to the Karman scheme ( σ 1 > σ 2 = σ 3 ) (Stavrogin and Tarasov, 2001). The tests were carried out at the lateral pressure equal to σ 3 = 0; 5.0 and 7.5 MPa. All the studies were carried out with an automatic registration of the experimental results. For long-term tests under uniaxial and volumetric loading, hydraulic rheological facilities with a maximum force of 150 kN (Fig. 3) were used, which load was constant due to a controlled oil pressure in the hydraulic system. The facilities for uniaxial compression made it possible to test up to 3 specimens simultaneously (Fig. 3,a). Experiments on creep under volumetric compression were carried out using volumetric hydraulic units (Fig. 3,b), which made it possible to have independent loading of the specimens with respect to lateral and axial forces. The maximum allowable pressure in the volumetric loading chamber was 40 MPa. In accordance with the research program, the creep experiments were carried out at a lateral pressure equal to σ 3 = 0; 5.0 and 7.5 MPa.

(a)

(b)

Fig. 3. Facilities for continuous loading: a) uniaxial creep; b) bulk creep

For specimens of all series, the creep experiments were done at different load levels, i.e. 0.3 σ str ; 0.4 σ str ; 0.5 σ str ; 0.6 σ str ; 0.7 σ str and 0.8 σ str . The total number of the creep specimens tested was 60 pcs. The maximum experimental time for the sylvinite specimens was 35 days, and for the carnallite specimens it was 95 days. 3. Results of Studies Based on the experimental results, complete deformation curves were obtained (Fig. 4). Average values of the determined mechanical parameters of sylvinite and carnallite obtained during the instantaneous tests for various lateral pressures are presented in Table 1.