Experimental investigations and modelling of strain rate and temperature effects on the flow behaviour of 1045 steel

If structures have to be designed to sustain low and high loading rates, the appropriate constitutive equations are essential for the accurate modelling of the structural response. However, a lack of the required data is observed very often, especially, if a very wide range of strain rates has to be covered. Therefore, the flow behaviour of the steel 1045 (C45E) was investigated with defined chemical composition and microstructure in a very wide range of strain rates between 10 -4 and 10 5 1/s and different temperatures. The rate-dependent thermomechanical behaviour was determined using low strain rate (10 -4 to 10 0 1/s) servo-hydraulic compression testing, high strain rate (∼10 2 1/s and 10 3 1/s) compression drop weight testing and split Hopkinson pressure bar testing, and for very high strain rates (10 5 1/s) the plate-impact test. Additionally, strain rate jump tests at relatively low strain rates and different temperatures were performed to determine the activation volume at constant temperature and deformation. The measured flow stresses as well as the strain and strain rate hardening behaviour as a function of strain rate and test temperature are discussed in terms of the microstructural deformation processes. The theory of thermally activated flow is applied and compared to the widely used models like the Johnson-Cook model and a dislocation drag model. The occurrence of possible dislocation drag effects is discussed in conjunction with the measured data. Our results show, that the strain rate dependence of the flow stress of 1045 steel can be described completely by the theory of thermal activation up to strain rates of 10 5 1/s.