A new method to determine isothermal flow curves for integrated process and microstructural simulation in metal forming

Reliable isothermal flow curve data are often needed for the process simulations in metal forming technology. As a rule of thumb, at strain rates above 10−3 s −1 even isothermal compression tests are affected by deformation heating, such that the flow stress data should be corrected for stress decrease due to the temperature increase in the specimen. However, if the temperature increase during testing is larger than the interval of the nominal testing temperatures foreseen for individual tests, the compensated flow curves may show undesired kinks. When it comes to high strength materials, this phenomenon will be even more pronounced. The occurrence of kinks in compensated flow curves can be attributed to the interpolation methods used in the existing temperature compensation methods. As a remedy, an alternative strategy based on Thin Plate Spline interpolation is proposed on the example of two high strength materials. It is shown that this new strategy can be generally adopted to derive reliable isothermal flow curves over a wide range of temperatures and strain rates, especially for high strength materials.