Sizing of partially closed surface-breaking microcracks with broadband Rayleigh waves

Abstract

Sizing of cracks in the range of tens of micrometers by laser-generated surface acoustic wave (SAW) pulses with a bandwidth of up to 200 MHz is reported. The radius of a semicircular surface-breaking crack was evaluated using two methods, one based on the experimentally measured reflection coefficient and the other on the frequency dependence of the phase lag of the transmitted wave. These quantities were also simulated numerically by means of the finite differences method and fitted to the experimental ones by varying the assumed size of the crack. In both cases the interaction between crack faces was taken into account by an effective interfacial stiffness parameter and the crack sizes obtained acoustically were compared with those measured by optical microscopy. Nondestructive evaluation was extended to the characterization of real microcracks in the range of tens of micrometers with the laser-based pump-probe technique. The microcracks studied were generated in fused silica by strongly nonlinear SAW pulses with shocks in a separate experiment.

Acoustic Enhancement of Surface Diffusion

“…The corresponding natural limit of γ eff e 0 < E d 0 * is also outlined by a dashed line in Figure 3. The upper limit for e 0 is determined by the onset of surface damage 2,3 and is on the order of 10…”

Detection of open and partially closed surface defects in plates using ultrasonic enhancement

“…These additional wave modes are expected to produce a distinctive high frequency signal in the near field of the defect when the laser source passes over the defect, from which an enhancement factor can be obtained to accurately position the defect, and to give a measure of its geometric alignment relative to the scan direction. The transmission coefficients of partially closed defects for surface acoustic waves are very high [13] and therefore it is expected that there will generally be insufficient reflected signal to produce the constructive interference needed to form a significant near field enhancement when the laser detector passes over the defect.…”

Second-harmonic generation in a multilayered structure with nonlinear spring-type interfaces embedded between two semi-infinite media

“…In Eqs. (15) and (16), and denote the complex-valued amplitude reflection and transmission coefficients, respectively. These are calculated by applying the transfer-matrix method [54], [55] to Eqs.…”

“…Spring-type interface models have been utilized extensively to characterize a contacting interface between rough surfaces of solid bodies [8]- [13], a partially closed crack [14], [15], concentration of microcracks [16]- [18], a fracture in rock mass [19]- [23], adhesion at double interfaces between an adhesive layer and two adherents [24]- [28], multiple interlayer thin resin-rich zones of polymer-based composite laminates [29]- [33], and multiple rock joints [34], [35].…”