Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

Chinese Journal of Mechanical Engineering

Table 3 Presentation of the THz-TDS measured results for the different delamination defects before and after the denoising operation by the SWT

ROI	Real thickness (µm)	The thickness of the top delamination defect				The thickness of the middle delamination defect				The thickness of the bottom delamination defect
ROI	Real thickness (µm)	Thickness before SWT	Thickness after SWT	RE before SWT (%)	RE after SWT (%)	Thickness before SWT	Thickness after SWT	RE before SWT (%)	RE after SWT (%)	Thickness before SWT	Thickness after SWT	RE before SWT (%)	RE after SWT (%)
1	130	134.084	132.405	3.142	1.850	134.565	134.825	3.512	3.712	136.305	131.665	4.850	1.281
2	130	137.465	130.245	5.742	2.496	139.725	129.085	7.481	− 0.704	138.985	131.505	6.912	1.158
3	130	145.585	130.505	11.988	0.388	137.465	130.515	5.742	0.396	136.305	128.925	4.850	− 0.827
4	130	141.885	130.344	9.142	0.265	151.305	132.184	16.388	1.680	139.205	130.605	7.081	0.465
5	130	132.245	129.505	1.727	− 0.381	141.405	128.934	8.773	− 0.820	152.505	130.205	17.312	0.158
Mean±SE	130 ± 0	138.253 ± 2.460	130.601 ± 0.483	–	–	140.893 ± 2.845	131.109 ± 1.099	–	–	140.661 ± 3.026	130.581 ± 0.496	–	–

Note: The acronym ROI stands for “region of interest” and RE for “relative error”