Thermomechanical response of DH-36 structural steel over a wide range of strain rates and temperatures

To understand and model the thermomechanical response of DH-36 Naval structural steel, uniaxial compression tests are performed on cylindrical samples, using an Instron servohydraulic testing machine and UCSD's enhanced Hopkinson technique. True strains exceeding 60% are achieved in these tests, over the range of strain rates from 0.001/s to about 8000/s, and at initial temperatures from 77 to 1000 K. The microstructure of the undeformed and deformed samples is examined through optical microscopy. The experimental results show: (1) DH-36 steel displays good ductility and plasticity (strain > 60%) at low temperatures (even at 77 K) and high strain rates; (2) at relatively high temperatures and low strain rates (especially below about 0.1/s), its strength is not temperature sensitive, indicating that the material has good weldability; (3) dynamic strain aging (DSA) occurs at temperatures between 500 and 1000 K and in the range of strain rates from 0.001/s to 3000/s, the peak value of the stress shifting to higher temperatures with increasing strain rates (it is about 600 K at 0.001/s, about 650 K at 0.1/s, and about 800 K at 3000/s); (4) adiabatic shearbands develop when the strain exceeds about 30% at 77 K, and at higher strains for higher temperatures; and (5) the microstructural evolution of the material is not very sensitive to changes in strain rates and temperatures. Finally, based on the mechanism of dislocation motion, and using our experimental data, the parameters of a physically-based model developed earlier for AL-6XN stainless steel [J. Mech. Phys. Solids 49 (2001) 1823] are estimated and the model predictions are compared with various experimental results, excluding the dynamic strain aging effects. Good agreement between the theoretical predictions and experimental results is obtained. In order to further verify the model independently of the experiments used in the modeling, additional compression tests at a strain rate of 8000/s and various initial temperatures are performed, and the results are compared with the model predictions. Good correlation is observed. As an alternative to this model, the experimental data are also used to estimate the parameters in the Johnson-Cook model [G.R. Johnson, W.H. Cook, 1983, in: Proceedings of the Seventh International Symposium on Ballistic, The Hague, The Netherlands, p. 5411 and the resulting model predictions are compared with the experimental data, again excluding the dynamic strain-aging effects. These and related results suggest that the physically based model has a better prediction capability over a broader strain rate and temperature range. (C) 2003 Elsevier Ltd. All rights reserved.