Method for determining the strain rate sensitivity factor for the Johnson-Cook model in Charpy tests

Abstract The basis for the study was the necessity to design a supporting structure of the road infrastructure subjected to high strain rates occurring during vehicle accidents. Mathematical models of hardening due to the high strain rates are reviewed. Commonly used methods for determining constants for one of the models, i. e., Johnson-Cook model are characterized. The main section of the study presents a proposed method for determining the strain rate sensitivity of the material. It is a hybrid method which requires Charpy tests using unnotched specimens and a series of calculations using the finite element method to simulate the tests. Several variants of strain measurement of specimen subjected to failure in Charpy tests, as required for the proposed method are analyzed. Using the suggested method, a strain rate sensitivity factor was obtained with a value similar to the value obtained using the split Hopkinson pressure bar technique. The advantages of the suggested method compared to the existing methods are the high availability of the instruments, simple and quick processing of the results and significantly lower costs.

[1]  D. Dini,et al.  The mechanisms governing the activation of dislocation sources in aluminum at different strain rates , 2015 .

[2]  Zbigniew L. Kowalewski,et al.  DYNAMIC PROPERTIES OF ALUMINIUM ALLOYS USED IN AUTOMOTIVE INDUSTRY , 2015 .

[3]  H. Kolsky.  An Investigation of the Mechanical Properties of Materials at very High Rates of Loading , 1949 .

[4]  R. Armstrong,et al.  Dislocation Mechanics of Shock-Induced Plasticity , 2007 .

[5]  J. D. Campbell,et al.  Tensile Testing of Materials at Impact Rates of Strain , 1960 .

[6]  Daniel Rittel,et al.  Determination of the Johnson–Cook Material Parameters Using the SCS Specimen , 2009 .

[7]  J. Lewis,et al.  The development and use of a torsional Hopkinson-bar apparatus , 1972 .

[8]  Dariusz Skibicki,et al.  Phenomena and Computational Models of Non-Proportional Fatigue of Materials , 2014 .

[9]  R. Armstrong,et al.  A constitutive equation for the dynamic deformation behavior of polymers , 2007 .

[10]  G. Gray.  High-Strain-Rate Deformation: Mechanical Behavior and Deformation Substructures Induced , 2012 .

[11]  Martin Bäker,et al.  Determination of Johnson–Cook parameters from machining simulations , 2012 .

[12]  G. R. Johnson,et al.  Fracture characteristics of three metals subjected to various strains, strain rates, temperatures and pressures , 1985 .

[13]  D. Eakins,et al.  Attenuation of the dynamic yield point of shocked aluminum using elastodynamic simulations of dislocation dynamics. , 2015, Physical review letters.

[14]  W. Grzesik,et al.  Numerical and Experimental Analysis of Residual Stresses Generated in the Machining of Ti6Al4V Titanium Alloy , 2014 .

[15]  E. Lucon.  Experimental Assessment of the Equivalent Strain Rate for an Instrumented Charpy Test. , 2016, Journal of research of the National Institute of Standards and Technology.

[16]  Bilge Yildiz,et al.  Mapping strain rate dependence of dislocation-defect interactions by atomistic simulations , 2013, Proceedings of the National Academy of Sciences.

[17]  Amos Gilat,et al.  A direct-tension split Hopkinson bar for high strain-rate testing , 1991 .