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Accurate material constitutive modeling is critical for the quality and reliability of the simulation of dynamic impact processes. Under dynamic loading ductile structural components can experience very large deformation that, in terms of equivalent plastic strain, can be well beyond the strain at which necking would occur in uniaxial tensile tests. Unfortunately, the material flow curve for ductile metals can only be measured over a limited strain range while at large strain it is either extrapolated or corrected in some way. In this paper the role of the approximation of the material flow law in the post-necking range is investigated with particular reference to the Taylor test. Result seems to indicate that the flow law governs the shape of the mushroom region while temperature and strain rate have a more important role in the resulting deformed shape of the intermediate and rear portion of the specimen geometry. In particular, the temperature effect exponent in the J&C expression can be calibrated based on the final length of the impacted cylinder. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]