Harmonic Scattering of Nonlinear Waves from Layered Materials that mimics Additively Manufactured Metals

Recent developments in additively manufactured materials show its capabilities towards designing single and multi-material layered metallic structured materials. Additively manufactured structures perform efficiently towards the targeted performance at the macro-scale level. However, their structural health monitoring using nonlinear ultrasonic techniques becomes challenging and complex due to multiple layers deposited during additive manufacturing and the various microscale damages such as micro-voids, micro-cracks, accumulation of local plasticity at the interfaces, etc. In this study, various numerical experiments are conducted using the finite element method to gain insight into the interaction of nonlinear elastic waves with such additively manufactured metallic materials. The presence of backscattered harmonic waves along with the forward scattered waves and their properties is demonstrated through studies such as the interaction of monochromatic waves, one-way two-wave mixing, and two-way two-wave mixing. Similarly, the harmonic scattering of waves from an additively manufactured bi-metallic material is demonstrated and discussed in detail. The interplay between linear and nonlinear impedance-mismatch leads to interesting forward and backscattered wave responses. Amplitudes of backscattered waves are nearly equal to the forward scattered waves in some case studies.