PSI - Issue 8

L. Landi et al. / Procedia Structural Integrity 8 (2018) 3–13 L. Landi et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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Table 2. Mechanical proprieties of steel DC01 Propriety Min

Max

Yield strength [MPa]

140 270

280 410

Hardening [MPa]

Elongation % (A80%)

28

-

Banabic (2010) executed various experimental tests on this material. We report below the average results obtained by the author in terms of yield point, necking coefficient, K and n parameters of the typical Hollomon constitutive equation (8). = (8) where: n = 0.208 K = 615 σ y = 210 By comparing this equation with the Johnson- Cook’s constitutive model (2), and considering as “minor” the effects of temperature and strain hardening, we can obtain some of the parameters of the Johnson- Cook’s constitutive model for DC01, Table 3 taken from Landi and Amici (2016).

Table 3. First DC01 JC constitutive model First model JC parameters

Data

̇ 0 c m

A, B [MPa] , 0 [K] n [s -1 ]

210, 360.3

0.0001

1792, 300

0.275

0.02

0.7

Not being possible to retrieve experimental data for DC01 JC’s failure model, we decided to employ the simple criterion on the maximum equivalent strain for failure model. Considering that the impact phenomena is mainly localized, in order to define a correct behaviour of material, it is fundamental to know the value of local deformation at fracture. Unfortunately, we could not find this value for steel DC01 on international scientific literature. Kpenyigba (2013), making tensile tests on a general-not well defined mild steel plates with 1 mm thickness, affirms that considering adiabatic phenomenon (very short time period) we can considered use ε f local = 0.80 . The Results of comparison with experimental data in Landi and Amici (2016) have confirmed that it is a good approach to reduce the uncertainty of the experimental results. In the following paragraph, some information to achieve a DC01 model improvement will be reported. The results presented by Landi and Amici (2016) shown that using a failure plastic strain close to 0.8 we were able to correctly reproduce the behavior of projectile of 0.625 kg. The approximation of the model was greater for heavier projectiles because direct impact zones waits were larger. Some preliminary results of tensile tests on three different kinds of non-alloy steels not yet published revealed that:  The most of true stress/true strain curves published in international journals are valid only from yield to necking of steel specimens, the reliability of these curves decreases when the plastic strain increases  The limit of plastic deformation used by Landi and Amici (2016) ε f local = 0.80, chosen by Kpenyigba, has proven to be excessive. The preliminary results of these attempts give a realistic value of the limit around ε f local = 0.5 − 0.6 for 3 mm thick plates 3.2 Modified model of a general DC01 steel non alloy steel