PSI - Issue 13

Andrzej Neimitz et al. / Procedia Structural Integrity 13 (2018) 285–291 Author name / Structural Integrity Procedia 00 (2018) 000–000

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triaxiality parameters, η at the central part of these specimens are very high from the very beginning of the loading process; and they are higher in the specimen centers than at other locations. Also, effective plastic strains are high at this stage of loading and one can expect that many voids had already nucleated and grown before the critical stress was reached and cleavage at this location was not possible. One should also notice that effective plastic strain reaches the highest values at the specimen centre in the PN specimen and it is not so in the case of the C04 specimen. The Lode factor at this stage of loading was in the range 0.4-0.6 for the PN specimen and 1.0 for the C04 specimen. The answer for the first question is not so unambiguous. Distribution of equivalent plastic strains and Lode factors are different in both discussed specimens. In the case of PN and C04 specimens the plastic strains are distributed uniformly through the critical cross-section only at the beginning of loading. In the C04 specimen the Lode parameter is equal to one at the specimen centre during the whole loading history and this value decreases along the specimen radius. Different behavior is observed in the case of the PN specimen. Only the η parameter behaves similarly in both specimens. In Fig. 9 the distribution of the ΔR parameter (Eq. 1) is shown along the normalized distance from the specimens' centers. In all three specimens (C04, C1, PN) the specimens' surfaces to the left from ellipsis (Fig. 9) are covered by caverns. In two cases (specimens C04, PN) the specimens' fracture surfaces to the right of the ellipsis are the results of the cleavage fracture process. It is not so in the case of the C1 specimen. Thus, using the mechanical field parameters discussed in this paper, there is no strong reasonable explanation why the C04 specimen broke due to the cleavage mechanics not to the ductile one.

Fig.6a. Distribution of the mechanical parameters at the critical moment along the critical plane, measured from the specimen centre; temp. -50  C, material N, specimen PN

Fig.5. Stress vs. normalized distance computed at the critical moment

Fig.7a. Specimen PN, material N, temp.-50 0 C, history of the plastic strain distribution along longer axis

Fig.6b. Distribution of the mechanical parameters at the critical moment along the critical plane, measured from the specimen centre; temp. -50  C, material N, specimen C04