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.
Highlights
An effective and reliable inspection technique for continuous monitoring and evaluation of early-stage nonlinearities in materials is necessary for engineering parts
It should simulate the wave in propagation a largely deformed medium be a powerful toolbetoa powerful simulate tool the to wave propagation a largely in deformed medium with the with the plasticity-driven material damage and its evolution process under tensile loading
The results show effectively employed to monitor and evaluate the plasticity drivendriven early stage material damage
Summary
An effective and reliable inspection technique for continuous monitoring and evaluation of early-stage nonlinearities in materials is necessary for engineering parts. Conventional linear ultrasonic evaluation and monitoring methods are not sensitive to early stage micro-damage or micro-plastic deformation [4], and the smallest crack that current linear ultrasonic based approaches can monitor or evaluate is only approximately 1 mm [5]. This drawback limits their applications and does not allow early preventive actions [5,6,7]. When a high-intensity ultrasonic wave passes through a nonlinear medium, the waveform may be distorted [8]. It is well-known that a linear solid medium may become a nonlinear one gradually in the process of fatigue damage [9], radiation damage [10], hardening [11], and thermal aging [12]
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