scholarly journals INVERSE COMPUTATIONAL DETERMINATION OF JOHNSON-COOK PARAMETERS USING THE SHPB TEST APPARATUS

2019 ◽  
Vol 25 ◽  
pp. 64-67
Author(s):  
Anja Mauko ◽  
Branko Nečemer ◽  
Zoran Ren
Keyword(s):  
Base Material ◽  
Impact Testing ◽  
Strain Rates ◽  
Sample Material ◽  
Hardening Material ◽  
Material Parameters ◽  
Digital Twin ◽  
Twin Model ◽  
Shpb Test

The paper describes determination of the material parameters of the Johnson-Cook constitutive model of steel S235 JR sample material by applying the inverse computational methodology using the digital twin model of the SHPB. A quasi-static tensile testing of bulk material was conducted first to determine the base material parameters. This was followed by dynamic impact testing at two different strain rates using the SHPB. A digital twin computational model was built next in the LS-Dyna explicit finite element system to carry out the necessary computer simulations of the SHPB test. The inverse determination of strain hardening material parameter of Johnson-Cook model was done by using the Nelder-Mead simplex optimisation by comparing the measured and computed stress to time signals on incident and transmission bars. The obtained Johnson-Cook material parameters much better describe the sample material behaviour at very high strain-rates in computational simulations, if compared to the parameters derived by the classic, one-dimensional wave propagation Hopkinson procedure.

Automated procedures for the determination of high temperature viscoplastic damage constitutive equations

1992 ◽  
Vol 437 (1901) ◽  
pp. 527-544 ◽  
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Cyclic Plasticity ◽  
Parameter Determination ◽  
Nominal Composition ◽  
Strain Rates ◽  
Material Parameters ◽  
The Matrix

Methods have been developed for the determination of the material parameters in the Chaboche viscoplasticity model, and in the evolution equation for cyclic plasticity damage. The matrix of cyclic plasticity tests required for parameter determination consists of nine tests to be carried out for three strain ranges, and for each strain range, three strain rates. A programme of uni-axial cyclic plasticity tests has been carried out on cast copper (nominal composition: 99.99% Cu, 0.005% O 2 , B. S. 1035-1037) at strain ranges ± 0.3%, ± 0.6%, and ± 1.0%, each at strain rates 0.6% s -1 , 0.06% s -1 , and 0.006% s -1 . The matrix of tests has been carried out at each of the following temperatures: 20, 50, 150, 250 and 500 °C. At elevated temperature, strain rate has been found to have a significant effect on specimen lifetime. Low strain rates lead to increased creep damage evolution at high temperature, and hence lead to reduced cycles to failure. Cast copper has been found to be a rate sensitive material at temperatures above 150 °C. No strain rate effect was observed at temperatures below 150 °C. Ratchetting tests have been carried out at 20, 150, 250 and 500 °C. The effect of mean stress and stress rate on ratchet rates and lifetimes has been examined. Mean stresses of the order of 1 % of the applied stress range have been found to lead to significant ratchet rates for this material, resulting in failure by plastic collapse at elevated temperature. The methods presented for the determination of the material parameters and the results of the cyclic plasticity testing programme have enabled the viscoplastic damage model to be developed.

Mechanical Behaviour of CoCrMo Alloy with Si Content

2015 ◽  
Vol 754-755 ◽  
pp. 1017-1022 ◽  
Author(s):  
Petrică Vizureanu ◽  
Mirabela Georgiana Minciună ◽  
Dragoş Cristian Achiţei ◽  
Andrei Victor Sandu ◽  
Kamarudin Hussin
Keyword(s):  
Tensile Strength ◽  
Chemical Composition ◽  
Testing Machine ◽  
Base Material ◽  
Optical Emission ◽  
Experimental Tests ◽  
Optical Emission Spectrometry ◽  
Emission Spectrometry ◽  
Standard Samples

.The paper present aspects about the obtaining of non-precious dental alloys (type CoCrMo and CoCrMoSi7), the determination of chemical composition by optical emission spectrometry and the experimental tests for determining the tensile strength, made on standard plate samples. The base material used in experiments was a commercial alloy, from CoCrMo system, which belongs to the class of dental non-precious alloys, intended to medical applications. The obtaining of studied alloy was made on arc re-melting installation, under vacuum, type MRF ABJ 900. The process followed to realize a rapid melting, with a maximum admissible current intensity. The samples for tests were obtained by casting in an electric arc furnace, under vacuum, in optimal conditions for melting and solidification and processing by electro-erosion, to eliminate all the disturbing factors which come by processing conditions for the samples. The determination of chemical composition for cobalt based alloys, by optical emission spectrometry, was made on SpectromaxX equipment with spark. The electrical discharge is made with the elimination of an energy quantity, fact which determine plasma forming and light issue. Tensile tests for standard samples, made from cobalt based alloy, was made on Instron 3382 testing machine, and assisted by computer. The obtained results are: elongation, elasticity modulus, tensile strength and offer complete information about the analyzed mechanical properties. For the certitude of obtained experimental results, the tests were made on samples with specific dimensions according ISO 6892-1:2009(E) standard, both for the tensile strength, and also machine operation.

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