Issue 43

B. Saadouki et alii, Frattura ed Integrità Strutturale, 43 (2018) 133-145; DOI: 10.3221/IGF-ESIS.43.10 139 Figure 8 : Comparison between monotonic and cyclic tensile curves for SICLANIC ® . It is the law of cyclic consolidation or cyclic hardening law, where ܭ ′ and n' are respectively the coefficient and the exponent of cyclic hardening. In Tab. 2, the monotonic and cyclic mechanical characteristics of SICLANIC ® are compared. The extent of variation of the hardening coefficient is due to the cyclic deformation. It goes from a relatively low value (0.034) to a higher value of 0.136. Monotonous n = 0.034 K = 591 MPa YS 0, 2% = 498 MPa Cyclic n ’ = 0.136 K ’ = 490 MPa YS’ 0, 2% = 350 MPa Table 2 : monotonic and cyclic mechanical characteristics of SICLANIC ® Prediction of softening or hardening phenomena According to Smith, Hirschberg and Manson [22], softening occurs when UTS / YS 0.2 < 1.2, while hardening appears for UTS / YS 0.2 ˃ 1.4. In the case where the ratio is between 1.2 and 1.4, one or the other of the softening and hardening phenomena can be observed. As a result of the examination of various materials, Morrow [23] finds that if the value of n is higher than 0.1, hardening or stability occurs; however, if n is less than 0.1 the softening happens during the material is cycling. In Tab. 3, we have compiled the predictions of SICLANIC ® cyclical behavior, the predictions are in agreement with experience, however, the criteria used consider the characteristics determined outside the deformation domain (<2%) such as UTS and n . A new definition of the hardening criteria is introduced by Lieurade [24], taking the ratio σ 1 / YS 0.2 , of which parameters correspond to the experience, since they are located in plastic deformation field. It has been shown in the case of steels that if σ 1 / YS 0. 2 is less than 1.3 there is softening, while if σ1 / YS 0.2 is higher than 1.5 there is hardening. Smith, Hirschberg, Manson Morrow Experience σ 1 / YS 0, 2 ∆σ 1 / σ 1 (%) UTS / YS 0. 2 Prediction n Prediction Observation σ 1 / YS 0. 2 Prediction 1.23 uncertainty 0.034 softening softening 1.18 softening 17.8 Table 3 : Analysis of SICLANIC ® hardening criteria. The ratio Δσ 1 / σ 1 defines the hardening rate.