Numerical simulation of the reflected acoustic wave components in the near field of surface defects

Abstract

The interaction of a laser generated surface acoustic wave with a surface crack has been simulated in detail by the finite element method, where a surface notch of rectangular shape has been introduced to represent the fatigue crack for the convenience of modelling. It is shown that four distinct reflected components are present in the captured waveforms; the first component is the direct reflection of a compressive pulse from the left side of the notch, while the second one is assumed to be the Rayleigh wave converted from the laser generated compressive wave when it impacts the left face of the notch. The arrival time of the third peak has demonstrated clearly that it comes from the direct reflection of an initial Rayleigh wave on the near side of the notch. The origin of the last component has been assumed to be the mode conversion occurring at the base of the notch, which is based on the fact that the deeper the notch the longer the arrival time of the fourth peak.

Numerical Study on Signal Enhancement of the Rayleigh Wave in the Near-Field of Surface Defects

“…4(a) and had been discussed completely in previous paper. 12) Due to the opposite polarity of displacement signals of two components, the amplitude of merge signal reduced evidently as shown in Fig. 4(c).…”

“…This paper employs thermoelastic coupling model to simulate the procedure of laser generated surface acoustic waves in an aluminum half-space, which has been previously used to obtain many useful results. [11][12][13][14] 3. Numerical Results and Discussion Figure 2 shows calculated displacement signals of the scattered surface acoustic waves from a surface slot of 80 mm deep in an aluminum half-space, where the displacement signals of Rayleigh wave demonstrate the obvious signal enhancement for the out-of-and in-plane components in the near field of the slot.…”

Depth Evaluation of Fretting Fatigue Crack Appearing at Bolt Joints of Aluminum Alloy Plates by Synchronized Surface Acoustic Wave Measurement

“…18) Masserey et al 14,15) used the time-offlight method with the Rayleigh wave to estimate the depth of the crack in steel, and showed that various modes of the ultrasonic wave is superimposed and scattered at the crack. Guan et al 16) also estimated the depth of the slot by the laser generated surface acoustic wave. Rokhlin and Kim 9,10) reported that there are different types of mode conversion of the surface acoustic wave at the root of the pit, and they estimated the depth of the pit by using the converted wave.…”

An analysis of angled surface-breaking crack detection by dual-laser source generated ultrasound

“…The result agreed with the theoretical calculation and experimental data. In 2004, Guan et al [16,17] used FEM to simulate the physical process of the SLLS technique in detecting surface-breaking notches and sub-surface notches in aluminium. The simulation result shows agreement with the theoretical results and the experimental data.…”