TABLE 1 CALCULATED J0 VALUES Calculations of smooth specimen fc determined on smooth specimen J0 (kN/m) corresponding to the crack growth initiation in CT25 specimen using 4-noded FE 0.0611 352.1 using 8-noded FE 0.0428 325.8 The values of J0 determined in this way show certain deviation from the experimental value J0 = 229 kN/m [1]. Possible reasons for this deviation are: a) use of 4-noded instead of 8-noded FE (the later were not used due to convergence problems); b) insufficient mesh refinement near the crack tip: further calculations should be made so that size of FE in front of a crack tip corresponds to the mean free distance between non-metallic inclusions l » 0.2 mm determined by quantitative metallurgical analysis. CONCLUSION Based on the results of micromechanical modelling of ductile fracture of structural low-alloy steel, the following may be concluded: · experimental values and results obtained by FE calculation according to GTN model for smooth specimen are in very good agreement; critical value of void volume fraction fc was determined in the centre of the specimen in both calculations, using both 4-noded and 8-noded FE; · quantitative metallurgical analysis is necessary for determination of initial void volume fraction f0 and mean free distance l; · the value obtained for J0 using both values determined for fc exceeds experimental value and may be used for approximate prediction of ductile fracture initiation in CT specimen for tested steel; the calculations should be updated by more refined mesh and higher degree of FE interpolation functions. REFERENCES 1. Bernauer G. and Brocks W. (2000). Numerical round robin on micro-mechanical models - Results, ESIS TC8, Institute for Materials Research - GKSS Research Center, Geesthacht 2. Gurson A.L. (1977). Journal of Engineering Materials and Technology, 99, 2. 3. Tvergaard V. (1981). International Journal of Fracture, 17, 389. 4. Tvergaard V. and Needleman A. (1984). Acta Metallurgica, 32, 157. 5. Zhang Z. L. (1996). Fatigue & Fracture of Engineering Materials and Structures, 19, 561. 6. Zhang Z. L. and Niemi E. (1994). Engineering Fracture Mechanics, 48, 529. 7. Sun D-Z., Kienzler R., Voss B. and Schmitt W. (1992). In: Fracture Mechanics - Twenty - Second Symposium, ASTM STP 1131, II, pp. 368-378, Atluri S.N., Newman J.C., Raju Jr.I. and Epstein J.S. (Eds.), American Society for Testing and Materials, Philadelphia. 8. Thomason P.F. (1990). Ductile Fracture of Metals, Pergamon Press, Oxford. 9. Argon A.S. and Im J. (1975). Metallurgical Transactions, 6A, 839. 10. Gurland J. (1972). Acta Metallurgica, 20, 735. 11. Chu C.C. and Needleman A. (1980). Journal of Engineering and Materials Technology, 102, 249. 12. Underwood E. E., (1970). Quantitative Stereology, Adison-Welsey, Reading, Mass. 13. Rakin M., Sedmak A., Matejic P., Zrilic M., and Sedmak S. (2000). In: Proceedings of the ECF 13 'Fracture Mechanics: Applications and Challenges', printed on CD, M. Fuentes et al. (Eds.), ESIS Publication, Elsevier Science Ltd, Oxford. 14. ESIS P2/92 (1992), Procedure for Determining the Fracture Behaviour of Materials, ESIS Procedure
RkJQdWJsaXNoZXIy MjM0NDE=