Dual-mode second-harmonic (DMSH) generation on plate and cylinder guided media

Nonlinear ultrasonic guided waves have have shown promising prospects for early stage crack detection in structural components. In this work, we discuss a novel observation of simultaneously propagating dual-mode second-harmonic (DMSH) generation in guided media such as plates and cylinders which are fundamental building blocks for majority of structural components. When excited with nondispersive fundamental shear horizontal (SH0) mode on plate and fundamental torsional (T(0,1)) mode on cylinders two wave packets of different wave velocities were noticed and reported. Second harmonic symmetric (s0) mode and an orthogonal-shear horizontal mode were generated on a weakly nonlinear plate. Whereas second harmonic longitudinal (l(0,1)) mode and orthogonal torsional (t(0,1)
^┴
) mode were generated on a cylindrical wave guide. The observation from numerical simulateions were validated experimentally. The DMSH modes possesses different group velocities and thus, each wave packet were observed as separate wave modes after a short cut-off distance around 40λ. This article looks at the DMSH generation in plate and cylinder and compares the observations. The understanding of wave modes generated at second harmonics shall provide important insights during early-state defect detection in structural health monitoring and non-destructive evaluation applications of critical structures.