Inhaltszusammenfassung

Composite materials are essential in aerospace and automotive structures, yet their safety critical use demands reliable nondestructive testing (NDT). Ultrasonic inspection is well suited for carbon fiber reinforced plastics (CFRP) but struggles with glass fiber composites (GFRP) and structural foams because scattering and attenuation mask defect echoes. Terahertz testing, which uses electromagnetic waves between 0.1 and 1 THz and needs no coupling medium, overcomes these limits for non condu...Composite materials are essential in aerospace and automotive structures, yet their safety critical use demands reliable nondestructive testing (NDT). Ultrasonic inspection is well suited for carbon fiber reinforced plastics (CFRP) but struggles with glass fiber composites (GFRP) and structural foams because scattering and attenuation mask defect echoes. Terahertz testing, which uses electromagnetic waves between 0.1 and 1 THz and needs no coupling medium, overcomes these limits for non conductive materials. Ultrasound and terahertz are therefore complementary. This paper evaluates the best choice depending on frequency, defect size and depth. This study quantitatively compares signal to noise ratios (SNR) delivered by focused ultrasonic transducers (1, 2.25, 5 MHz) and continuous wave terahertz probes (100, 150, 300 GHz). Two specimens were prepared: a 50 mm pultruded GFRP block with blind holes 2.5 8 mm at nine depths, and a 15 mm expanded polypropylene foam slab with 2 12 mm holes at two depths. Water coupled pulse echo C scans and matching terahertz scans were recorded with 300 µm steps. The signal to noise ratio was defined as the maximum defect amplitude divided by the maximum surrounding echo. Ultrasonic testing detected most GFRP defects to 35 mm with the 2.25 MHz probe. 5 MHz resolved 2 mm holes but only to a depth of 15 mm, while 1 MHz penetrated the full block yet with blurred indications at higher depths. Terahertz produced higher SNR overall. 100 GHz was optimal for GFRP, imaging an 8 mm hole at 40 mm, whereas 300 GHz yielded the clearest foam images. The foam could not be inspected ultrasonically. The signal to noise ratio increases with flaw size and drops with depth and frequency. Its optimum shifts deeper as frequency falls. Terahertz is besides the more expensive computer tomography the only effective method for closed cell foams. For GFRP, 2.25 MHz ultrasound remains the most versatile for defects larger than 6 mm for ultrasonic testing, while terahertz offers superior signal to noise ratios. Combining both techniques maximizes defect detectability for non-carbon composite components. » weiterlesen» einklappen

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Klassifikation

DFG Fachgebiet:
4.31 - Werkstofftechnik

DDC Sachgruppe:
Ingenieurwissenschaften