Analysis of two parameter identification methods for original and modified Johnson-Cook fracture strains, including numerical comparison and validation of a new blue-brittle dependent fracture model for free-cutting Steel 50SiB8

Gerstgrasser, Marcel and Smolenicki, Darko and Akbari, Mansur and Klippel, Hagen and Roelofs, Hans and Cadoni, Ezio and Wegener, Konrad (2021) Analysis of two parameter identification methods for original and modified Johnson-Cook fracture strains, including numerical comparison and validation of a new blue-brittle dependent fracture model for free-cutting Steel 50SiB8. Theoretical and Applied Fracture Mechanics. p. 102905.

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Abstract

A non-linear relation between fracture strain and temperature is observed in Split Hopkinson Tension Bar (SHTB) tests for free-cutting steel 50SiB8 at high strains and high temperatures, due to blue-brittleness. A fourth-degree polynomial function for the thermal parts of the original and modified Johnson-Cook (JC) fracture strain constitutive equation is suggested and the corresponding parameters are identified. Fracture modelling of 50SiB8 is not reported in literature. 50SiB8 is characterized under quasi-static, isothermal, high temperature and high strain rate conditions using smooth and notched tension specimens. For the calculation of the original and modified JC fracture parameters, two different parameter identification procedures, so-called forward and backward parameter identification methods are performed, compared with each other and explained in detail. For the stress triaxiality factor of the original and modified JC fracture model, the forward parameter identification method is suggested for the original JC fracture model, while backward parameter identification method is proposed for the modified JC fracture model. The effect of blue-brittleness in the temperature factor and the corresponding parameters are presented. Furthermore, FEM simulations of the original and the blue-brittleness including JC fracture model are compared with experiments. In the blue-brittle temperature range, the new adjusted JC model shows more accurate results, regarding fracture diameter and strain. Additionally, this work introduces a fracture model combining the Bai-Wierzbicki stress triaxiality dependent model, JC fracture models and the nonlinear temperature factor with blue-brittleness effect, while further experiments are required in order to determine its parameters.

Item Type:	Scientific journal article, Newspaper article or Magazine article
Uncontrolled Keywords:	Forward and Backward Parameter Identification Methods, Fracture, Constitutive behaviour, Rate-dependent material, Kolsky bar, blue-brittleness fracture model, FE simulations
Subjects:	Engineering Engineering > Mechanical engineering Engineering > Mechanical engineering > Mechanisms & machines
Department/unit:	Dipartimento ambiente costruzioni e design > Laboratorio SUPSI DYNAMAT
Depositing User:	Ezio Cadoni
Date Deposited:	11 Jan 2021 09:14
Last Modified:	24 Aug 2023 14:00
URI:	http://repository.supsi.ch/id/eprint/12255

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