Experimental assessment of barely visible impact damage carbon fibre reinforced epoxy composite using ultrasound method

Abstract

Background: Carbon fibre reinforced epoxy (CFRP) is susceptible to impact damage which could resulted in reduction of the mechanical properties. This paper studies the architecture of barely visible impact damage (BVID) to comprehend the extent of damage on quasi-isotropic CFRP laminates of varying thickness (i.e. 16, 24 and 32-ply laminates of 3, 4 and 5 mm respectively). Methods: Quasi-static indentation is chosen to produce BVID on CFRP laminates, followed by using non-destruction evaluation method, namely conventional contact-type ultrasonic testing (UT) and C-mode scanning acoustic microscopy (C-SAM) method. Results: The findings revealed (1) the size and shapes of the BVID on CFRP laminates, (2) no damage found at the point of damage, and (3) the bridging between the point of impact to the outer damaged diameter due to the consequence of diverse orientation of carbon fibre strips which exhibit excellent mechanical properties before structural failure. Conclusions: The results concluded that the UT and C-SAM method can identify both the pristine region and the internal damaged structures in CFRP laminates.

In situ resin‐injection approach for repairing barely visible impact damaged carbon‐fiber reinforced epoxy laminates: Optimizing the repair parameters using Taguchi method

“…Although the QSI test resulted in barely visible damage to the specimens (i.e., 16-and 24-ply laminates), the size of the subsurface damage in the 24-ply laminate was about two times that of the 16-ply laminate. [30] This was not surprising given that the amount of impact energy needed to create the BVID in the former was higher than the latter. In addition, with regard to the morphology of the subsurface damage at the front and rear surface as seen from the thermal images, it was concluded that the damage could prevail across several laminas, which is consistent with findings from other reports.…”

“…In addition, with regard to the morphology of the subsurface damage at the front and rear surface as seen from the thermal images, it was concluded that the damage could prevail across several laminas, which is consistent with findings from other reports. [21,30,31] Altogether, these may have practical implications during inspection: for a given barely visible damage observed at the impacted surface, the subsurface damage in a thick laminate could be much more extensive compared to a thin laminate. [30] T A B L E 5 An orthogonal array L 12 (mixed-level design) of Taguchi with the repair efficiency derived based on the mechanical properties of the CFRP laminates in repaired state to pristine state (η P ) and repair efficiency derived based on the residual mechanical properties between the repaired and damage states and between the pristine and damaged states (η D ).…”

“…[32,33] The complexity and randomness of the crack network could differ among the laminates. [30] Low connectivity in the BVID may cause blockage to the adhesive pathway during resin-injection. Thus, only a small volume of adhesive could penetrate through the crack network, and this could affect the efficiency of the repair.…”