Application of high-speed video extensometry for high-temperature tensile characterization of boron heat-treated steels

The increased desire to use advanced, high-strength steels for lightweight automotive structural components requires better understanding of thermo-mechanical behavior and appropriate experimental data for developing constitutive models. Thermo-mechanical studies are particularly important for understanding and optimizing hot-stamping processes which produce both complex and high-strength components. The experimental setup presented herein is capable of characterizing the thermo-mechanical behavior of such steels with strain rates up to approximately 1 s(-1) and temperatures as high as 850 degrees C. The main parts of the apparatus are a high-speed camera, a load frame, and a box furnace. For the determination of strain, a simple image-processing program was developed. The strain was determined in three sections that span the entire gauge length of the specimen. Thus, the onset of localization could be more accurately determined. Stress versus strain data for various strain rates and temperatures are presented.