Magneto-Mechanics of Magnetic Shape-Memory Crystals with Micropeened Surfaces

Magnetic shape-memory (MSM) materials use magnetic energy to generate large deformation. Nickel-Manganese-Gallium is a prominent MSM crystal that can be strained to 6% of its length. The alloy degrades and breaks after repeated loading, a behavior called fatigue. Bombarding the surface of the material with minuscule glass beads (micropeening) increases the number of loading cycles thousandfold; however, this decreases the maximum strain. In this project, stress and strain were measured before and after micropeening at different pressures to identify a quantitative relationship between process parameters and the dynamic material properties. Preliminary results show that micropeening at 25 psi preserves a large part of the strain while micropeening at 30 psi suppresses most of the strain.