Simulations on Monitoring and Evaluation of Plasticity-Driven Material Damage Based on Second Harmonic of S0 Mode Lamb Waves in Metallic Plates

Abstract

In this study, a numerical approach—the discontinuous Meshless Local Petrov-Galerkin-Eshelby Method (MLPGEM)—was adopted to simulate and measure material plasticity in an Al 7075-T651 plate. The plate was modeled in two dimensions by assemblies of small particles that interact with each other through bonding stiffness. The material plasticity of the model loaded to produce different levels of strain is evaluated with the Lamb waves of S0 mode. A tone burst at the center frequency of 200 kHz was used as excitation. Second-order nonlinear wave was extracted from the spectrogram of a signal receiving point. Tensile-driven plastic deformation and cumulative second harmonic generation of S0 mode were observed in the simulation. Simulated measurement of the acoustic nonlinearity increased monotonically with the level of tensile-driven plastic strain captured by MLPGEM, whereas achieving this state by other numerical methods is comparatively more difficult. This result indicates that the second harmonics of S0 mode can be employed to monitor and evaluate the material or structural early-stage damage induced by plasticity.

Interaction of Lamb Wave Modes with Weak Material Nonlinearity: Generation of Symmetric Zero-Frequency Mode

“…According to previous studies [ 7 , 8 , 9 , 10 , 12 , 13 , 14 , 18 , 19 , 20 , 23 , 24 ], the measured acoustic nonlinearity parameter of Lamb waves can be expressed as , where, and are the measured amplitudes of the fundamental and the second harmonic signals, respectively. Here, the expressions and are adopted to measure the acoustic nonlinearity, where, is the measured amplitude of the zero-frequency mode.…”

“…Previous works have shown that the techniques based on nonlinear Lamb waves can be utilized for long-range and in-depth inspection [ 7 , 8 , 9 ] through characterizing acoustic nonlinearity, which in turn can be regarded as an indicator of the early-stage material nonlinearity caused by fatigue plasticity, precipitation hardening of thermal aging, corrosion, etc. [ 10 , 11 , 12 , 13 , 14 ]. In general, a nonlinear response is generated in the region where the early-stage material nonlinearity occurs and then several nonlinear wave components may appear including subharmonics or higher-order harmonics.…”

“…All of these possible nonlinear components can be used to evaluate or monitor the material nonlinearity by exploiting their higher sensitivity to the changes of the material microstructure [ 15 ] compared with the conventional techniques based on linear waves [ 7 , 16 ]. In the research field of the nonlinear Lamb waves, the observation and utilization of the second harmonic is the focus [ 1 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. However, an accurate experimental implementation of nonlinear Lamb waves is difficult due to the inherent multi-mode and dispersive nature.…”

Fatigue Damage Evaluation Using Nonlinear Lamb Waves with Quasi Phase-Velocity Matching at Low Frequency

“…Nonlinear ultrasound has been found to be a useful indicator of the material damage within large plate-like structures for nondestructive evaluation and structural health monitoring, since they are sensitive to microstructural evolution at the early stage of material degradation when compared with the conventional linear ultrasounds [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. The long propagation distance and the interrogation of the entire thickness of plate-like structures make nonlinear Lamb wave a highly efficient inspection method.…”

“…[ 1 , 2 ]. Recently, many studies focused on the second harmonic generation (SHG) to characterize the material nonlinearity [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Due to the dispersive and multimode natures, the propagation of Lamb waves is complex and the double frequency Lamb waves (DFLWs) are generally weak.…”