International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 07 Issue: 05 | May 2020 www.irjet.net p-ISSN: 2395-0072 © 2020, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page 1476 Evaluation of Johnson-Cook Material Model Parameters of AA6063-T6 Devesh Rajput 1 , Ankit Singh 2 , Arpit 3 , Sanjay Kumar 4 1,2,3 Student, Mechanical Engineering Department, Delhi Technological University, Delhi, India 4 Assistant Professor, Mechanical Engineering Department, Delhi Technological University, Delhi, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - The present work deals with the stimulus of strain rate on the behaviour of commercial aluminium alloy 6063-Temper 6. It is a medium strength alloy commonly referred to as architectural alloy and expected to have a low strain rate sensitivity. Consistent and judicious characterization of the material behaviour under the coupled effects of strain, strain rate, and temperature on the material flow stress is remarkably crucial to design as well as optimize the process parameters for industrial practice. Tensile tests were performed at room temperature at strain rates starting from 10 -4 to 10 -1 s -1 . The alloy exhibited a low but positive strain rate dependence of material strength at the investigated strain rates. The stress-strain relations obtained through these tests were employed for calibrating Johnson- Cook (J-C) material model. An empirical constitutive relation stated by Johnson and Cook (J–C) is extensively used to capture the strain rate sensitivity of the metals. In this work, model constants of J–C constitutive relation have been determined experimentally from the uni-axial tensile test. Key Words: Johnson-Cook, Material model, AA6063-T6, Strain rate, flow stress, ASTM – E8M. 1. INTRODUCTION Aluminium alloys have developed as a strong candidate material for defence, aeronautical and automotive applications due to their low density, tremendous strength, and high corrosion resistance. But their mechanical behaviour has to be thoroughly understood to utilize their potential for such demanding applications. This requires a more profound understanding of the material properties, which is very complex due to the relationship between large plastic deformations, high strain rates, thermal softening as a result of adiabatic heating of materials, material deterioration, and fracture. The theory in continuum mechanics referred to as viscoplasticity [5] explains the rate- dependent inelastic response of solids. Rate-dependence in this setting means that the deformation of the material depends on the rate at which loads are employed. Numerical techniques have surfaced as an efficient and cost- effective tool for investigating material behaviour. The reliability of numerical results depends massively on the exactness of material models used to interpret the dynamic behaviour of materials under consideration. The Johnson- Cook material model [1] is one of the most manageable models with five parameters, which can describe the material response at high temperatures, high strains, and high strain-rates and is often used in simulations. In addition to the material model, a failure model introduced by Johnson and Cook is used to model the damage progression and foretell failure in many engineering materials. 2. LITERATURE SURVEY Johnson and Cook (1983) suggested a simple model to describe the plastic behaviour of metals under dynamic loading. The model defines the equivalent flow stress as a function of strain, strain rate, and temperature. * * ( )(1 ln )(1 ) n m eq eq eq A B C T        (1) where A is Yield stress, B is Hardening modulus, C is Strain rate coefficient, n is Hardening exponent and m is thermal softening parameter. These are to be determined experimentally. eq  is equivalent plastic strain, * eq  is the ratio of equivalent plastic strain rate to a reference plastic strain rate. T * is the homologous temperature and is defined as * r m r T T T T T    (2) where T is the current temperature of the material, Tm is the melting temperature of material and Tr is room temperature. The first, second and third set of brackets in equation (1) picture the effect of isotropic strain hardening, strain rate hardening and thermal softening sequentially in an uncoupled manner. Dislocation dynamics based material models like Zerilli- Armstrong model (1987) and Mechanical Threshold Stress model (Follansbee and Cocks 1988) have been introduced to judge linked nature of strain rate and thermal sensitivity but they have not been able to overtake Johnson-Cook (J-C) model due to complexity in the calibration of constants. 3. JOHNSON-COOK MATERIAL MODEL A review study of material parameters of Johnson-Cook constitutive and failure model (Johnson and Cook 1983, 1985) for some regularly used aluminium alloys acknowledges that various researchers have obtained different parameters for the same alloy. Therefore, it is very important for researchers working in crucial areas to be self- governing in the calibration of dynamic material models. 3.1 Method for calibration of J-C material model The fundamental concept in the quantification of J-C material model is to isolate the effect of strain hardening, strain rate hardening and thermal softening on the plastic behaviour of