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; Smolenicki, Darko; Akbari, Mansur; Klippel, Hagen; Roelofs, H.; Cadoni, Ezio; Wegener, Konrad

doi:10.1016/j.tafmec.2021.102905

Cited by 20 publications

(6 citation statements)

References 32 publications

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“…giving the coefficient m. The fitted curve is shown in red in figure 7. For the temperatures T = 20 • C and T = 200 • C the fit lies in the scatter band of the measured data, while it predicts higher yield stresses at T = 400 • C and T = 800 • C. At T = 600 • C the yield stress is predicted too low as the scatter of the experimental data is very large and ranges from ≈ 65% to 100% of the yield stress at T = 20 • C. This issue is probably due to blue brittleness as discussed in [7]. The classic Johnson-Cook temperature term is not able to correctly describe this behaviour and the curve fit is worsened before and after this peak.…”

Section: Parameter Mmentioning

confidence: 86%

“…• The thermal softening is captured well, except for temperatures around T = 600 • C. Using a modified temperature dependent term, as for example in [14] or [7], could potentially capture this peak as well.…”

Section: Discussionmentioning

confidence: 99%

“…A least squares fit is used to fit the parameters A, B and n from equation (7) to the experimental data, by minimizing the sum of the squared error of the model prediction [3]:…”

Section: Assessment Of True Stress and True Strainmentioning

confidence: 99%

“…The idea is to exchange lead by graphite inclusions in order to keep the good machinability of free cuttings steels. As the data basis for numerical simulations of this material is rather small [13,1,7], this report is initiated in support to [7], where the results of quasi-static tensile tests and Split Hopkinson Tension Bar (SHTB) tests were used to derive a modified Johnson-Cook fracture strain model for the free cutting steel 50SiB8. Here, the same test results are used to deduce the parameters for a flow stress model according to Johnson and Cook [8].…”

Section: Introductionmentioning

confidence: 99%

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Johnson Cook Flow Stress Parameter for Free Cutting Steel 50SiB8

Klippel,

Gerstgrasser,

Smolenicki

et al. 2020

Preprint

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The present publication deals with the material characterization of the free cutting steel 50SiB8 for numerical simulations. Quasi-static tensile tests as well as Split Hopkinson Tension Bar (SHTB) tests at various strain rates and temperatures are used to deduce the parameters for a Johnson-Cook flow stress model. These parameters are then verified against the SHTBexperiments within a finite element model (FEM) of the SHTB-test within ABAQUS c .

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Section: Parameter Mmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

“…A least squares fit is used to fit the parameters A, B and n from equation (7) to the experimental data, by minimizing the sum of the squared error of the model prediction [3]:…”

Section: Assessment Of True Stress and True Strainmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Johnson Cook Flow Stress Parameter for Free Cutting Steel 50SiB8

Klippel,

Gerstgrasser,

Smolenicki

et al. 2020

Preprint

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“…Therefore, the process and laser parameter in conjunction with the experimentally measured Archimedean density, melt pool depth and crack density are used from section 3.2, to find the corresponding function between each of the Π -terms with curve fitting. Further information about the least square fit approach for curve fitting can be found in the research of Gerstgrasser et al [39]. In case of the first system, a linear relation between the dimensionless 1 Π and 2 Π -term is observed, as presented in Fig.…”

Section: Crack Density Modelmentioning

confidence: 88%

High power selective laser melting of crack sensitive nickel-base alloy CM247LC, including dimensional analysis and modelling

Gerstgrasser

Cloots²,

Jakob³

et al. 2021

Preprint

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Compared to reference parameters in the low power and scan velocity range, which lead to dense and crack-free CM247LC LPBF samples due to in-situ crack healing, high power, high scan velocities and increased laser beam diameters are investigated, to decrease the production time further. By keeping the maximum laser intensity from the reference and the laser power to scan velocity ratio constant, the intensity approach provides an initial estimation for the laser spot size regarding the measured Archimedean density and crack density in the high power and high scan velocity range. The investigated cracks are identified as re-melting cracks. Solidification or hot cracks are not observed, since the crack healing effect for those kinds of cracks still occurs. Furthermore, a melt pool depth range is discovered, where not only solidification cracks can be avoided, but also re-melting cracks, which are resulting from higher laser power inputs. This theory can be proven by further laser spot size optimization, where the melt pool depth comes closer to the mentioned range. The Archimedean density and crack density results, in case of the 600 W power parameter with 2400 mm/s scan velocity and a beam diameter of 164 µm, are close to the one obtained from the reference with 200 W, a scan velocity of 800 mm/s and a laser spot of 90 µm. With the intensity approach and laser beam diameter optimization, the production time can be reduced by 300%. Based on dimensional analysis, a model, which combines the samples density with the crack density through the melt pool depth, is presented. Six main and two additional process and laser parameters are taken into relation. The result from the model and the measured values from experiments are in good agreement. Additionally, the influence of the doubled layer thickness and an increased hatch distance by 50% with varying scan velocities on the Archimedean density and crack density is analysed.

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Study on formation mechanism of serrated chip of Ti-6Al-4V titanium alloy based on shear slip theory

Zhu

Shi

Liu

et al. 2022

Int J Adv Manuf Technol

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Titanium alloy is a typical hard-to-machine metal and a lot of serrated chips are often formed in the cutting process. The appearance of serrated chips will not only cause the fluctuation of cutting force, resulting in the decline of cutting accuracy, but also lead to the rapid wear of tools. In this study, the formation mechanism of serrated chip of Ti-6Al-4V titanium alloy was investigated by a two-dimensional cutting simulation model of Ti-6Al-4V titanium alloy, which was established by using the Johnson-Cook constitutive model and Johnson-Cook fracture model. It is found that shear slip occurs with the decrease of the shear band and the overall stress during the formation of serrated chips.The peak temperature is reached at the end of the shear band. Meanwhile, the "dead zone" of temperature and stress is formed near the edge of the tool, which has an obvious periodic alternating trend in the cutting process, resulting in the macro curl and micro serration of chips.

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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

Cited by 20 publications

References 32 publications

Johnson Cook Flow Stress Parameter for Free Cutting Steel 50SiB8

Johnson Cook Flow Stress Parameter for Free Cutting Steel 50SiB8

High power selective laser melting of crack sensitive nickel-base alloy CM247LC, including dimensional analysis and modelling

Study on formation mechanism of serrated chip of Ti-6Al-4V titanium alloy based on shear slip theory

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