+ 2015 EMP – Introduction of compressive residual stresses by Electro Magnetic Pulses

The aim of the project is to build a prototype for the mitigation of metallic mechanical parts by electro-mechanic pulsed current. This relatively new technique is mostly used these days for the forming of thin plates.

The main idea consists of the use of higher frequency for the pulsed current, several hundreds of kHz instead of a few tens of kHz, in order to activate inertial forces at each material point within the volume. However the output energy is lower, in the order of one kJ, compared to the 10 to 50 kJ for EMP forming process. It will permit to introduce plastic strains, which in turns will generate compressive residual stresses, up to 10 mm deep or even below for thick parts. The level of plastic strains hence generated and the affected depth can be monitored by the frequency of the pulsed current as well as by the output energy, which can be estimated by numerical simulation. This constitutes the main advantage of this technique compared to conventional processes such as shot blast peening, ultrasonic shot peening, low plasticity burnishing, etc. This process should permit to enhance the material performances against crack initiation and propagation, as well as against corrosion and corrosion assisted cracking due to the introduction of dislocations.
To the best of our knowledge only one and recent patent has been published in the US in 2012, no paper has been found. Three I@L laboratories are partners in this project: LaMCoS for its expertise in the field of innovative processes and the simulation of thermomechanical processes, Ampère for its expertise in the field of power electronics and electro-magnetics, and Mateis with experts in the field of plasticity at the scale of dislocations and in the field of electrochemistry and corrosion resistant materials. The main outcomes expected are related to industries dealing with assembly of thick plates, such as for pressurized vessels, ship construction or nuclear industry.