Issue 43

M.P. Tretyakov et alii, Frattura ed Integrità Strutturale, 43 (2018) 146-154; DOI: 10.3221/IGF-ESIS.43.11 150 a e b f c g d h Figure 4 : The order of turning and testing of specimens in accordance with scheme 1 ( a - d ) and scheme 2 ( e - h ) . a b Figure 5 : Strain curves obtained in the tests of specimens turned by scheme 1 ( a ) and scheme 2 ( b ) after tension of initial specimens at level a (solid lines), at level 2 (dotted lines) and level 3 (dashed lines), and initial stages of strain curves in the range of zero to 400 MPa. Based on the obtained data, the values of the elasticity modulus at the initial linear sections of the strain curves were calculated in the stress range up to 400 MPa, which are shown on an enlarged scale in Fig. 5. The dependence of the values of the elastic modules of the tentative reached level of postcritical deformation and the scheme of specimens turning to the results of the tests was not revealed, which can be associated with a relatively small range of previously achieved deformations. The average value of the Young's modulus determined on the initial specimens was 204 GPa, and the average value after turning was 174 GPa. The deviation of experimental data obtained on the initial specimens by did not more than 5 %, and for all the turned specimens did not exceed 8 %. According to the test results, the maximum achieved stresses were calculated by the ratio of the maximum load to the initial cross-sectional area of the grooved specimens. The results reflecting the dependence of the ultimate stress upon stretching of samples turned along the entire gauge length ( a ) and turned in the necking zone ( b ) versus the degree of postcritical deformation reached at the moment of unloading, are shown in Fig. 6. The obtained results may indicate that, at the time of unloading, the material in the peripheral zones of the initial specimens was in a hardened state, since the maximum stresses averaged by 10 % higher than the tensile strength of the initial specimens. In this case, the maximum stresses obtained by stretching the specimens prepared according to scheme 2 rise