This article details a procedure for sizing single cantilever beam (SCB) test specimens that are used to characterize facesheet–core debonding in sandwich structure. The characterization is accomplished by measuring the critical strain energy release rate, Gc, associated with the debonding process. The sizing procedure is based on an analytical representation of the SCB specimen, which models the specimen as a cantilever beam partially supported on an elastic foundation. This results in an approximate, closed-form solution for the compliance–debond length relationship of the specimen. The solution provides a series of limitations that can be imposed on the specimen dimensions to help ensure the specimen behaviour does not violate assumptions made in the derivation of the data reduction method used to calculate Gc. Application of the sizing procedure to actual sandwich systems yielded SCB specimen dimensions that would be practical for use. The method is specifically configured for incorporation into a draft testing protocol to be developed into an ASTM International testing standard.

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Single wall carbon nanotubes (SWCNTs) were introduced in the interlaminar region of woven carbon fiber—epoxy composites and the mode-I delamination behavior was investigated. Pristine (P-SWCNT) and functionalized (F-SWCNT) nanotubes were sprayed in the mid-plane of these laminates and delamination was initiated using a teflon pre-crack insert. The composite laminates were produced using vacuum-assisted resin transfer molding process. The interlaminar fracture toughness (ILFT) represented by mode-I critical strain energy release rate (GIc) for the initiation of delamination was measured using double cantilever beam tests. The specimens with pristine nanotubes and functionalized nanotubes showed a small effect on the ILFT. The specimens with P-SWCNTs showed stable crack growth and the potential for enhanced crack bridging along with slightly higher GIc than F-SWCNT specimens. Scanning electron microscopy images showed enhanced fiber—matrix interfacial bonding in the specimens with F-SWCNTs. However, large unstable crack propagation was observed in these F-SWCNT specimens from load—displacement curves and crack propagation videos. This research helps in understanding the differences in mechanisms by addition of functionalized and unfunctionalized (pristine) nanotubes to the woven carbon fiber—epoxy matrix composite laminates.

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