In-plane local defect resonances for efficient vibrothermography of impacted carbon fiber-reinforced polymers (CFRP)

Abstract

It is well known that the efficiency of the vibrothermographic non-destructive testing (NDT) technique can be enhanced by taking advantage of local defect resonance (LDR) frequencies. Recently, the classical out-of-plane local defect resonance was extended towards in-plane LDR for enhanced efficiency of vibrometric NDT. This paper further couples the concept of this in-plane LDR to vibrothermography, on the basis of the promising potential of in-plane LDRs to enhance the rubbing (tangential) interaction and viscoelastic damping of defects. Carbon fiber-reinforced composites (CFRPs) with barely visible impact damage (BVID) are inspected and the significant contribution of in-plane LDRs in vibrational heating is demonstrated. Moreover, it is shown that the defect thermal contrast induced by in-plane LDRs is so high that it allows for easy detection of BVID by live monitoring of infrared thermal images during a single broadband sweep excitation. Thermal and vibrational spectra of the inspected surface are studied and the dominant contribution of in-plane LDR in vibration-induced heating is demonstrated.

Vibrothermographic spectroscopy with thermal latency compensation for effective identification of local defect resonance frequencies of a CFRP with BVID

“…In a recent study by the current authors [22], the significant contribution of in-plane LDRs in vibration induced heating was demonstrated. Broadband sweep excitation was applied to impacted CFRP coupons with barely visible impact damage (BVID) and the LDR frequencies with distinct out-of-plane and in-plane vibrational characteristic were identified using 3D-SLDV measurements.…”

“…The measured impact energy of 6.3 J introduced BVID including a hair-like surface crack at the backside (see the inset of Figure 1(a)). BVID includes a complex combination of various damage features [24], leading to the existence of multiple in-plane and out-of-plane LDRs at the BVID area [22,25]. The ultrasonic C-scan timeof-flight (TOF) and amplitude images ( Figure 1(b,c)) of the impacted CFRP, clearly show the extent and the complex nature of the BVID.…”

“…Broadband sweep excitation was applied to impacted CFRP coupons with barely visible impact damage (BVID) and the LDR frequencies with distinct out-of-plane and in-plane vibrational characteristic were identified using 3D-SLDV measurements. It was shown that the in-plane LDRs can be detected through live monitoring of the surface temperature during the sweep excitation (see supplementary information of [22]).…”

Backside delamination detection in composites through local defect resonance induced nonlinear source behavior

“…Which of these mechanisms is dominant depends on the properties of the defect as well as the characteristics of the vibration field (e.g. dominant in-plane versus out-of-plane) [11,12]. However, until now deep defect detection in monolithic composite components has not been demonstrated under LDR condition.…”

Vibration-Based In-Situ Detection and Quantification of Delamination in Composite Plates

“…However, only low-frequency (modal) excitation using PWAS transducers has been conducted in the above-mentioned literature. To overcome this issue, the concept of local defect resonance, as first described by Solodov in [44], has recently gained considerable attention for the detection of delamination in composites [45,46,47,48,49,50]. High-frequency excitations were used to obtain a localized resonant activation of the defected zones [45].…”