Hypervelocity impacts generate shockwaves causing catastrophic damage and failure of surrounding material and structures. Adaptive materials have been previously studied to mitigate shockwaves by providing diagnostics tools, wave steering, and dissipating mechanical energy. Numerous ferroelectric studies have been conducted, with less focus on ferromagnets, or magnetoelasticity. This presentation explores the response of magnetoelastic Galfenol (Fe81.6Ga18.4) to high strain-rate, high stress amplitude loading.
Experimentally, 2 GPa rarefacted shockwaves are generated in Galfenol using a Nd:YAG laser. Magnetization changes are recorded using inductive coils along the sample length and interferometry is used to infer the stress amplitude at the specimen’s back surface. The experimental results highlight how the shockwave evolves as it travels, including the onset of lateral release waves. Magnetic field control of the mechanical wave speed by 20% is observed, accompanied by large control of the measured magnetization changes. These changes highlight the coupled magnetoelastic nature of the effect. Furthermore, it is observed that the magnetization more strongly couples to lateral release waves than the incident compressive pulse. Last, magnetization changes are seen to precede the propagating mechanical wave, indicating dipolar coupling can transfer energy ahead of the mechanical wave front.
A numerical model has been developed to provide further insight into the experimental study. This model fully couples elastodynamics with magnetostatics using a nonlinear magnetoelastic constitutive behavior. The nonlinear model captures the main findings of the experimental study, including wave evolution, and strong magnetoelastic coupling to the release waves.
John P Domann, Ryan Crum, Vijay Gupta, and Greg P Carman, "Magnetoelastic shockwave response (Conference Presentation)," Proc. SPIE 10165, Behavior and Mechanics of Multifunctional Materials and Composites 2017, 1016514 (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 28, 2017; Published: 10 May 2017); https://doi.org/10.1117/12.2263254.5427319328001.
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