3 mm-PMMA plate with a circular FBH (radius 1 cm, depth 2 mm) meshed (a) and vibration pattern at 1.5 kHz plate eigenfrequency (b).
FEM simulation of LDR vibration patterns in PMMA plate shown in Fig. 1 : a fundamental LDR (10.4 kHz) (a) and higher-order LDR (23.25 kHz) (b).
Amplitude spectrum and vibration patterns at resonance peaks for the FBH in PMMA plate shown in Figs. 1 and 2 .
Fundamental frequency of LDR for a circular FBH ( = 0.7 mm; = 1 cm) in a PMMA plate (200 × 30 × 3 mm3) determined by different approaches.
Normalized LDR fundamental frequency as a function of normalized FBH thickness in a PMMA plate: FE-simulation for a FBH with 10 mm.
LDR fundamental frequencies as functions of FBH thickness calculated for different boundary conditions and measured for a 5 mm-radius FBH in 1 cm-thick PMMA specimen.
LDR fundamental frequencies as functions of FBH radius calculated for different boundary conditions and measured for a set of defects with = 0.5 mm in 3 mm epoxy specimen.
(a) LDR vibration patterns for a circular FBH (radius 1 cm; thickness 1 mm) in a 3 mm-thick PMMA plate: fundamental LDR. (b) Zoom-in fundamental LDR frequency response for this FBH (resonance frequency 11 kHz, Q-factor is 100).
Vibration patterns at the GFRP specimen eigenfrequency (3.4 kHz, (a)) and the fundamental LDR frequency (20.9 kHz, (b)) of the delamination.
LDR vibration patterns for a 50 μm-wide and 10 cm-long crack in GFR-concrete specimen (frequency 4.19 kHz, (a)) and for an impact induced loss of fibres (area 25 × 2 mm2) in a CFRP plate (frequency 3.66 kHz, (b)).
A PMMA specimen with many FBH of different thicknesses . The bottom row is marked to refer to Fig. 12 .
Laser vibrometry images of FBH from a bottom row of Fig. 11 obtained in a sweep excitation mode at different LDR frequencies.
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