Issue 43

B. Saadouki et alii, Frattura ed Integrità Strutturale, 43 (2018) 133-145; DOI: 10.3221/IGF-ESIS.43.10

Figure 8 : Comparison between monotonic and cyclic tensile curves for SICLANIC ® .

ܭ ′ and n' are respectively the coefficient and the

It is the law of cyclic consolidation or cyclic hardening law, where

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.

n = 0.034

YS 0, 2%

Monotonous

K = 591 MPa

= 498 MPa

n ’ = 0.136

YS’ 0, 2%

Cyclic

K ’ = 490 MPa

= 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.

/ YS 0, 2

Smith, Hirschberg, Manson

Morrow

Experience

σ 1

∆σ 1

/ σ 1

(%)

UTS / YS 0. 2

n

/ YS 0. 2

Prediction

Prediction

Observation

σ 1

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.

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