13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- 2. Experimental procedures 2.1. Materials and specimen preparation Self-healing FRP and reference FRP plates made of unidirectional carbon fiber-reinforced polymer were prepared. For self-healing FRP plates as shown in Fig. 1, Torayca T300B (Toray Industries, Inc.) carbon fiber strands were coated by manually dipping them into the Epikote 828 (Japan Epoxy Resins Co. Ltd)/Ancamine K54 (Air Products and Chemicals, Inc.) epoxy mixture containing 30wt% microcapsules and 2.5wt% Grubbs catalyst (Sigma-Aldrich Co.). Healing is triggered by crack propagation (interfacial debonding) through the microcapsules, which then release the healing agent into the crack plane. Subsequent exposure of the healing agent to the catalyst initiates polymerization and bonding of the crack faces. The number of filaments in the fiber strand was 6000. The healing agent used in this study was dicyclopentadiene (DCPD) monomer. DCPD was microencapsulated using the previously described procedure [1]. The microcapsules with mean diameter of around 300μm were used. To aid inspection for the release of the healing agent from broken microcapsules, the microcapsules were also made from DCPD mixed with a UV fluorescent dye (Blenny Giken Ltd.). After coating, the coated fiber strands were held straight and cured for 24h at room temperature in order to obtain proper hardness. For reference FRP plates, coated carbon fiber strands without Grubbs catalyst were prepared using similar procedures. Figure 1 Self-healing system of interfacial debonding in unidirectional FRP The semi-cured fiber strands were placed in a mold and impregnated with the Epikote 828/diethylenetriamine. The coated fiber strands were aligned parallel to the long direction. The mold was then closed and the samples were molded into the plate for 24h at room temperature, followed by 24h at 40 Co . Once the plates were cured, they were machined using a water cooled diamond saw to produce SENT specimens as shown in Fig. 2. The SENT specimens had a nominal width Wof 20mm, a nominal thickness t of 2 or 3mm, a gage length L of 40mm and an overall length of 70mm. A notch was cut using a diamond wafering saw and a sharp pre-crack was created by gently tapping a razor blade into the notch in the specimens. All specimens had an initial notch length to specimen width ratio 0 / a Wof approximately 0.25. Aluminum alloy gripping tabs (approximately 1mm thickness) were mounted to the specimens to prevent crushing due to the serrated rip faces. The specimens with t =2 and 3mm contained a fiber volume fraction of about 3.4 and 5.1%, respectively. Catalyst Microcapsule Crack Healing agent Polymerized healing agent Fiber strand Microcapsule Catalyst Unidirectional FRP Matrix Coated fiber strands Crack （Interfacial debonding) Coated fiber strand
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