Compression testing of martensitic stainless steel with superimposed ultrasonic vibration

Abstract The expanding use of materials with high strength in cold forging and the associated force increases as well as the limited formability present a major challenge for conventional process technology. One method to respond to this challenge is the use of high frequently oscillating forming tools which lead to a decrease of the required forces. Previous research on this topic has focused on fairly soft materials, such as aluminum. Materials with higher strength have only been analyzed to a very limited extent. This study addresses the ultrasonic-assisted compression testing of high strength martensitic stainless steel with 20 kHz oscillation frequency aiming at the identification of relevant process parameters and the partial separation of occurring effects. Experimental investigations are carried out to analyze the effect of ultrasonic-assistance during compression testing with varying oscillation duration and amplitude on the maximum forming force and on specimen heating. To isolate the proportional force reduction due to material heating from other oscillation induced causes, a comparison with conventional warm compression tests is performed. Finally, a simplified numerical simulation which is able to model the ultrasonic-assisted compression test is proposed. The experimental results reveal a strong influence of the oscillation amplitude on the reduction of maximum forces and on specimen heating. The oscillation duration presents a minor influence on the maximum forces, but strongly affects the heat generation. The developed simulation model is in good accordance with experimental force displacement curves and allows the separation between stress superposition and other ultrasonic-induced effects.