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K. Nowak, Frattura ed Integrità Strutturale, 34 (2015) 507-514; DOI: 10.3221/IGF-ESIS.34.56 513 Analysis of critical lengths of cracks (Fig. 7) shows that the final crack growth acceleration for small values of H is only when the cracks meet together - the calculated critical length is close to half of the plate width. For larger values of H this length is not constant. Therefore, it is difficult to propose any formula for equivalent length. Thus in time dependent analysis and for multiple crack configurations the failure criterion based on critical length of the crack is meaningless. F INAL REMARKS he solutions obtained demonstrate ability of adopted methodology to show creep crack paths in the case of existence of interactive initial cracks. Different cracks behaviour like its merging, kinking and branching become possible. The next step one should consider influence of geometry of structure (width and length of a specimen under tension) as well as the length of initial cracks making this analysis useful in engineering practice. R EFERENCES [1] Bodnar, A., Chrzanowski, M., On creep rupture of rectangular plates, Zeitschrift für angewandte Mathematik und Mechanik, 82 (2002) 201-205. DOI: 10.1002/1521-4001(200203)82:3<201::AID-ZAMM201 >3.0.CO ;2-G [2] Bodnar, A., Chrzanowski, M., Nowak, K., Brittle failure lines in creeping plates, Int. J. Pres. Ves. & Piping, 66 (1996) 253-261. DOI: 10.1016/0308-0161(95)00100-X [3] Bodnar, A., Chrzanowski, M., Nowak, K., Latus, P., Influence of small variations of initial defects upon crack paths in creeping plates – Continuum Damage Mechanics description, Eng. Fract. Mech., 75 (2008) 526-533. DOI: 10.1016/j.engfracmech.2007.01.014 [4] Carpinteri, A., Brighenti, R., Vantadori, S., A numerical analysis on the interaction of twin coplanar flaws, Eng. Fract. Mech., 71 (2004) 485-499. DOI: 10.1016/S0013-7944(03)00040-7 [5] Daud, R., Ariffin, A.K., Abdullah, S. et al., Mathematical model of elastic crack interaction and two-dimensional finite element analysis based on Griffith energy release rate, Advanced Materials Research, 795 (2013) 587-590. DOI: 10.4028 /www.scientific.net/AMR.795.587 [6] Gope, P.C., Bisht, N., Singh, V.K., Influence of crack offset distance on interaction of multiple collinear and offset edge cracks in a rectangular plate, Theor. and Applied Fracture Mechanics, 70 (2014) 19-29. [7] Hayhurst, D.R., Brown, P.R., Morrison, C.J., The Role of Continuum Damage in Creep Crack Growth, Phil. Trans. R. Soc. Lond. A, 311 (1984) 131-158. [8] Kachanov L.M., On the time of the rupture in creep conditions (in Russian), Izv. Akad. Nauk. SSR, 8 (1958) 26-31. [9] Kachanov M., A simple technique of stress analysis in elastic solids with many cracks, Int. J. Fract., 28 (1985) R11- R19. [10] Kamaya M., Growth evaluation of multiple interacting surface cracks. Part II: Growth evaluation of parallel cracks, Eng. Fract. Mech., 75 (2008) 1350-1366. [11] Mizuno M., Murakami S., Analysis of creep crack growth under neutron irradiation, in: M. Jono T. Inoue (Eds.), Mechanical Behavior of Materials VI, 3, Pergamon Press, Oxford, (1991) 853-858. [12] Moussa W.A., Bell R., Tan C.L., The interaction of two parallel non-coplanar identical surface cracks under tension and bending, Int. J. Pres. Ves. & Piping, 76 (1999) 135-145. [13] Murakami S., Hirano T., Liu Y., Asymptotic fields of stress and damage of a mode I creep crack in steady-state growth, Int. J. Sol. Struct., 37 (2000) 6203–6220. [14] Murakami S., Liu Y., Mizuno M., Computational methods for creep fracture analysys by damage mechanics, Comput. Methods Appl. Mech. Engng, 183 (2000) 15-33. DOI: 10.1016/S0045-7825(99)00209-1 [15] Si, J., Xuan, F. Z., Tu S. T., Creep Crack Interaction of High Temperature Structure with Multiple Cracks, Key Engineering Materials, 327-325 (2006) 105-108. DOI: 10.4028 /www.scientific.net/KEM.324-325.105 [16] Tada, H., Paris, P.C., Irwin, G.R., The Stress Analysis of Cracks Handbook, ASME Press, (2000). [17] Xuan, F. Z., Si, J., Tu, S. T., Evaluation of C* integral for interacting cracks in plates under tension, Eng. Fract. Mech., 76 (2009) 2192-2201. DOI: 10.1016/j.engfracmech.2009.06.012 T