100 150 200 250 300 1.5 2.0 2.5 3.0 v, ms-1 Jc d, kJm-2 ME test PD test Power (ME test) Power (PD test) 100 150 200 250 300 4.6 5.0 5.4 5.8 ao, mm Jc d, kJm-2 Figure 4. Jc d–v dependence for MF and PD tests Figure 5. J c d–a o dependence for MF and PD tests CONCLUSIONS Results shown in Figs. 4 and 5 have been statistically interpreted by power curves, although the result is the same if fitted by a linear, exponential, or logarithmic curve. This indicates an increasing tendency of the dynamic J-integral (Jc d) with impact load rate (v), and a decreasing tendency for larger initial cracks (ao). Fitted power curves J=ƒ(vx), J=ƒ(ao x), show very small difference in J-integral, indicating good agreement between ME and PD techniques on evaluation of ductile crack growth initiation. The ME power curve is constantly located above the PD power curve indicating slightly higher J-integral. In the average this is true, since PD evaluated time-to-fracture (ti) is usually shorter than its ME equivalent (Table 2). So, the released energies U(t) are smaller, and dynamic J-integral values are smaller too, Eq. (1). Multiple peaks in F(t)-ME(t) and F(t)-PD(t) diagrams are probably related to complex development of crack initiation and propagation. Analyses indicate that ME peaks follow PD peaks by a small delay, and both peaks usually precede F(t) peaks. This is still not clear, but the delay is probably related to specimen–strain gauge, or specimen–probe interaction, or hysteresis in electric and magnetic properties of the tested material. ACKNOWLEDGEMENTS The authors gratefully acknowledge the support of the OTKA T 030057 project. REFERENCES 1. Winkler, S.R. (1990). ASTM STP 1074, Philadelphia, pp.178-192. 2. Lenkey, Gy.B. (1997). In: 7th Summer School of Frac. Mech., Velika Plana, Yugoslavia, pp.39-50 3. Lenkey, Gy.B. and Winkler, S.R. (1997) Fatigue and Fract. of Engng. Mater. and Struct. 20, 143. 4. Lenkey, Gy.B. and Tóth, L. (2000). In: Fracture Mechanics: Applications and Challenges, Fuentes, M., Elices, M., Martin-Meizoso, A., and Martínez-Esnaola, J.M. (Eds.), Elsevier, Oxford. 5. Radakovic, Z., Lenkey, Gy.B. and Sedmak, A. (1998). In Fracture from Defects, Vol.III, pp.1267-1272, Brown, M.W., Rios, E.R. and Miller, K.J. (Eds.) 6. Glover, A.P., Johnson, F.A., Radon, J.C. and Turner, C.E. (1977). In: ASM Int. Conf. on Dynamic Frac. Tough., Vol. 1, pp.63-75, The Welding Institute. 7. MacGillivray, H.J. and Turner, C.E. (1989). In: Fourth Int. Conf. on the Mech. Properties of Mater. at High Rates of Strain, Oxford. 8. Grabulov, V., MacGillivray, H.J., Tomic, D. and Jovanic, P. (1992). In: Reliab. and struct. integ. of adv. materials, pp.315-320, Sedmak, S., Sedmak, A. and Ruzic, D. (Eds.), EMAS, Warley West Midlands. 9. Grabulov, V. (1995). PhD Thesis, University of Belgrade, Depart. of Tech. and Metallurgy, Yugoslavia. 10. Radakovic, Z., Lenkey, Gy.B., Grabulov, V. and Sedmak, A. (1999) Internat. Jour. of Frac. 96, L23. 11. Yoon, J.H., Lee, B.S., Oh, Y.J. and Hong, J.H. (1999). Inter. Jour. of Pres. Vessels and Piping 76, 663.
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