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

Abstract

Due to the dispersive and multimode natures, only nonlinear Lamb waves with exact phase-velocity matching were generally used in previous studies to evaluate the evenly distributed microstructural evolution in the incipient stage of material degradation, because of the cumulative generation of second harmonics, which was also found within a significant propagation distance for mode pair S0-s0 with quasi phase-velocity matching at low frequency. To explore the feasibility of fatigue damage evaluation by using this mode pair and fully utilize its unique merits, the cumulative second harmonic analysis was performed on aluminum alloy specimens with various material damage produced by the continuous low cycle fatigue tests. Similar to mode pair S1-s2 with exact phase-velocity matching, a mountain shape curve between the normalized acoustic nonlinearity parameter and the fatigue life was also achieved with the peak point at about 0.65 fatigue life for mode pair S0-s0, even though a relatively higher sensitivity to fatigue damage was observed for mode pair S1-s2. The excited frequency selection was further analyzed in a certain frequency range, where the quasi phase-velocity matching condition was satisfied for mode pair S0-s0 owing to the less dispersive property. Results show that the fatigue damage can be effectively detected using the mode pair S0-s0, and a relatively lower excited frequency was preferred due to its higher sensitivity to microstructural evolution.

Nonlinear ultrasonic evaluation of disorderedly clustered pitting damage using an in situ sensor network

“…In the model, the nonlinearity is depicted using a three-dimensional (3-D) stress-strain relation with a second-order approximation 38 , as ( 1 2 ) Morphological analysis, conducted by the authors in their earlier study 6 , reveals that in a typical pitted region, on top of a large quantity of macro-scale craters and cracks, diverse microstructural changes, for instance micro-voids, micro-cracks, recrystallized fine grains and dislocations, co-exist, as observed in the example shown in Figure 2. These recrystallized fine grains, dislocation substructures and shock hardening jointly lead to an increase in material plasticity and hence intensification in material nonlinearity 35,36,42,43 . In general, such intensification in material nonlinearity incurred by the pitting damage imposes remarkable influence on probing wave propagation more than the intrinsic material nonlinearity does.…”

“…In general, such intensification in material nonlinearity incurred by the pitting damage imposes remarkable influence on probing wave propagation more than the intrinsic material nonlinearity does. In the analytical model, the localized intensification in the material nonlinearity in the pitted region is depicted using the increasing in the three TOE constants (i.e., A , B and C ,  is the scale factor) 43,45 . In addition, numerous micro-voids expand to form micro-cracks and then macroscopic cracks, as illuminated in Figure 3,…”

“…These recrystallized fine grains, dislocation substructures, and shock hardening jointly lead to an increase in material plasticity and hence intensification in material nonlinearity. 35,36,42,43 In general, such intensification in material nonlinearity incurred by the pitting damage imposes remarkable influence on probing wave propagation more than the intrinsic material nonlinearity does. In the analytical model, the localized intensification in the material nonlinearity in the pitted region is depicted using the increase in the three TOE constants (i.e.…”

“… α A , α B , and α C , α is the scale factor). 42,43 In addition, numerous micro-voids expand to form micro-cracks and then macroscopic cracks, as illustrated in Figure 3, interaction of a probing GUW with which gives rise to the generation of CAN.…”

Experimental and Numerical Study of Nonlinear Lamb Waves of a Low-Frequency S0 Mode in Plates with Quadratic Nonlinearity

“…However, nonlinear ultrasonic technologies [4,5,6,7,8,9,10,11,12,13,14] are dramatically sensitive to material microstructures, which could be promising in overcoming this problem. Especially nonlinear Lamb-wave detection techniques [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39], which can be employed for long-range monitoring and inspection in thin plate structures, have attracted extensive attention in the past two decades.…”