Issue 29

M. Marino, Frattura ed Integrità Strutturale, 29 (2014) 96-110; DOI: 10.3221/IGF-ESIS.29.10

R ESULTS

A

loading-unloading displacement-based uniaxial test at constant temperature T is simulated. Starting from =0  , a constant strain-rate | |= e    is applied with maximum and minimum strain max  and max   , respectively. Accordingly, introducing 1 = / max t e   , applied strain-time law is (see Fig. 2).

1 for =[0, ] = ( ) = 2 for = ( , 3 ] 4 for = (3 , 4 ] max max e t e t t e t t                       1 1 1 1

(17)

1 [0, ] t   and

1 1 [2 , 3 ] t t   , while unloading conditions are addressed for

Therefore, the material element is loaded for

1 1 [ , 2 ] t t   and 1 1 [3 , 4 ] t t   . Two cases are preliminary distinguished: the high-temperature response for > af mf T T . Accordingly, in the former case, the alloy is fully austenitic (that is, 1 =1 in  characterized by a multi-variant martensitic lattice arrangement (namely, 4 =1 in  <

T T and the low-temperature one for

), while in the latter the alloy is

). Moreover, the response of the model at

< < af T T T , where the co-existence of multi-variant martensite and austenite is admissible, is described. Finally, relationships for setting the value of reverse transformation strains in function of experimental residual strains are given. mf

Figure 3 : Stress  vs. strain  predicted by present model in a displacement-driven traction loading-unloading test at the high temperature 2 > af T T . The applied strain is depicted in Fig. 2 for 1 [0, 2 ] t   .

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