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The mechanical behaviour of a material can be established by an analytic expression called the constitutive relation that shows stress as a function of plastic strain, strain rate, temperature, and possibly other thermo-mechanical variables. The constitutive relation usually includes such parameters as coefficients or exponents that must be determined. At a high strain rate, the heat generated during the deformation process is directly related to the plastic deformation energy of the material. This energy can be calculated from the plastic work, resulting in an expression that includes the constitutive relation parameters as variables. The heat generated can also be estimated by measuring the temperature surface of the specimen during compressive tests using the technique of infrared thermography. The objective of this paper is to present a procedure for determining the constitutive relation parameters by measuring the temperature increase associated with plastic strain in compressive Hopkinson tests. The procedure was applied to estimate the parameters of the Johnson&-Cook constitutive relation of an aluminium alloy (Al6082).