hysteresis loop. The major difference is given by the macroscopic ratcheting. A posteriori it has been found that this phenomenon can occur in SA537 steel under very low strain rate since at this deformation rate viscoplastic behavior becomes manifested. Experimental test has been stopped after 20 cycles. According to finite element prediction only a limited amount of damage should be generated in the specimen minimum section without failure in this cycling. In figure 3 the deformed mesh showing damage contours after 7 cycles is given as a sample. Figure 2a – RNB(T) specimen geometry and dimensions 2b- cyclic response: comparison between FEM results and experimental data Figure 3 – Damage contours along the minimum section after 7 cycles. REFERENCES 1. Bonora, N., (1997), Eng. Frac. Mech.,, 58, pp. 11-28 2. Bonora, N., (1998), Int. J. Frac., 88, pp.359-371 3. Bonora, N., and Milella, P.P. (2001), J. of Impact Engng., to appear. 4. Bonora N., and Newaz, G., (1998), Int. J. Solids and Struc., 35 , pp. 1881-1894 5. Lemaitre, J., (1986), Engng. Fract. Mech., 25, No. 5/6, pp.523-537 6. Bonora, N, (1999), J. Strain Analysis, 34, 6, pp. 463-478 7. Brocks, W., Bonora, N., O’Dowd, N. and Steglich, D., (2000), personal discussion at GKSS
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