In Fig. 3-4 plastic zone length, C, and crack opening displacement, COD, are presented. The results are normalised with respect to plastic zone length and COD of single crack. The analytical results are compared with finite element solution. a) 0.0 0.5 1.0 1.5 0 0.1 0.2 0.3 0.4 0.5 T / q C / CD FEM Theory b) 0.00 0.05 0.10 0.15 0.20 0.25 0 0.1 0.2 0.3 0.4 0.5 T / q C / 2a0 Dugdale FEM Theory Figure 3: Plastic zone length: a) results are normalised with respect to Dugdale solution, b) results are normalised with respect to the length of macrocrack. 0.8 1.0 1.2 1.4 0 0.1 0.2 0.3 0.4 0.5 T / q COD FEM Theory Figure 4: Crack opening displacement. CONCLUSION The pair of microcracks ahead of the crack tip increases the COD comparably with COD of a single crack whereas the plastic zone diminishes when it approaches to microcracks. So the defects ahead of the crack tip can enlarge the brittleness of material. REFERENCES 1. Dugdale, D.S. (1960) J. Mech. Phys. Solids. 8, 100. 2. Leonov, M.Ya. and Onishko, L.V. (1962) In: Teorija Plastin i Obolochek (in Russian). Izd. AN Ukr.SSR, Kiev, pp. 200-203. 3. Karihaloo, B.L. (1979) Eng. Frac. Mech. 12, 49. 4. Harrop, L.P. (1978) Eng. Frac. Mech. 10, 807. 5. Theocaris, P.S. (1983) Eng. Frac. Mech. 18, 545. 6. Romalis, N. and Tamuzh, V. (1984) Mechanics of Composite Materials. 20, 35. 7. Panasyuk, V.V., Savruk, M.P., Dacishin, A.P. (1976) Raspredelenie naprjazhenij okolo treschin v plastinah (in Russian). Kiev.
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