13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- reflects shrinkage (expansion) in the 2x ( 3x , 3x )-direction due to tensile (compressive) stress in the 1x ( 2x , 1x )-direction. Table 1 Mechanical properties of the carbon fiber strand 3. Results and discussion Fig. 4 shows typical virgin and damaged load-displacement curves for reference FRP specimens with t =2mm. It was found that the critical fracture load of the damaged specimen ( damaged cP ) was almost the same as the value of residual cP . Typical virgin and healed load-displacement curves for the self-healing FRP specimens with t =2mm are shown in Fig. 5. The slope is initially the same as the virgin test and this indicates that the damage has healed. The healing efficiency for the specimen with t =2mm shown in Fig. 5 is 45%. A healing efficiency of 98% was also achieved for the self-healing FRP specimen with t =3mm, but the healing probability for the specimen with t =3mm was slightly lower than that for the specimen with t =2mm (data not shown). To investigate the damage progression behavior in the SENT specimen of the self-healing FRP, the finite element analysis coupled with damages was employed. In this analysis, the values of R=0.266mm and h=0.484mm were used. Fig. 6 shows the predicted damage progression in the SENT specimen with t =2mm at the applied displacement value of 0.4mm. The microcracking of the matrix initiated from the initial notch tip and propagated along the coated fiber strand. Moreover, the microcracking of the coating layer was followed by the microcracking of the matrix. This leads to the release of the healing agent from the microcapsules. The microcracking of the coating layer close to the fiber strand/coating layer interface also initiated and propagated, and could induce fiber strand/coating layer debonding. The corresponding result for the SENT specimen with t =3mm at applied displacement value of 0.5mm is shown in Fig. 7. The microcracking of the matrix initiated from the initial notch tip, and the microcracking of coating layer was followed by the 0.5 1 1.5 1 2 3 4 0 Displacement (mm) Load (kN) Self-healing FRP t=2mm Virgin Healed 0.5 1 1.5 1 2 3 4 0 Displacement (mm) Load (kN) Reference FRP t=2mm Virgin Damaged Figure 4 Measured load-displacement curves for reference FRP specimens with t=2mm Figure 5 Measured load-displacement curves for self-healing FRP specimens with t=2mm 147 Young’s modulus (GPa) 10.3 7.0 0.27 0.54 2280 Shear modulus (GPa) Poisson’s ratio Tensile strength (MPa) 3.7 1E 2 3 , E E 12 31 , G G 23 G 12 13 , ν ν 23ν f Tσ
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