Carbon fiber sheet

Tanahashi, I., Yoshida, A. and Nishino, A., Activated carbon fiber sheets as polarizable electrodes of electric double layer capacitors, Carbon, 1990, 28(4), 477 482. 

Concrete structure. Retrofitting, Carbon fiber sheet. Adhesive interface, Mixed mode. Fracture toughness. Fracture criterion... 

Fig. i. Schematic drawing of retrofitting method for concrete beams with tensioned carbon fiber sheets. 

Fig. 2. Experimental results of 4-point bending test for concrete beams with and without bonding of carbon fiber sheets.

In the present work, a novel experimental method was proposed to evaluate the modes I-fll fracture toughness of the adhesive interface between concrete and carbon fiber sheets. The validity of the evaluation formula was studied on the basis of the results of finite element analysis. The mixed mode fracture toughness and fracture criterion of the adhesive interface were also studied on the basis of the results of fracture toughness test using the proposed method. 

The MMD (Mixed Mode Disk) specimen was proposed to investigate the modes I+II fracture behavior of the adhesive interface between concrete and carbon fiber sheets. This specimen, which consists of two concrete blocks inserted carbon fiber sheets and steel jigs, is basically similar to the Arcan specimen, as shown in Fig. 3 [12]. However, the evaluation formula for the Arcan specimen can not be directly applied to the MMD specimen owing to the difference of geometries and the existence of carbon fiber sheets. For the present specimen, the adhesive region was set to be smaller than the face of... 

Eq = 20-40 GPa for = 30 GPa). The cases with and without carbon fiber sheets... 

Figures 5-7 shows the effects of the geometric parameters, a, p, y, on the evaluation of the mixed mode energy release rate, G, which was calculated by Eqn (7) and normalized by (P/Bq) ( tF)/( qTo). where F = f 6 + f CO 6. All the results are for the case without carbon fiber sheets.

Fig. 6. Effect of the geometric parameter, p, on evaluation of the mixed mode energy release rate, G without carbon fiber sheets, a= 1.00, 7=0.50, = 1.00.

As shown in Fig. 9, the theoretical prediction did not agree with the finite elemenl results, which corresponds to the tendency discussed in the previous section. The finite elements results with and without bonding of carbon fiber sheets did not also agree each... 

Figure 10 shows the relationship between the loading angle, 0, and the mode ratio, G,/(Gi + G[]). The open and solid circles with broken lines represent the finite element results for the case with bonding of carbon fiber sheets on upper and lower sides of the crack, respectively. The solid triangles with broken line represent the finite element results for the case without bonding of carbon fiber sheets. The open triangles with solid line represents the theoretical prediction by Eqn (1). All the results are for a = 0.44, P = 0.50, y = 0.50 and = 30 GPa. 

Table 1 shows the specifications of the concrete, carbon fiber sheet and adhesive resin investigated in the present work. The concrete blocks of 30 x 20 x 90 mm were made of normal grade Portland cement and cured in water for 4 weeks. The carbon fiber sheet (UT70-30, Toray) was a unidirectional cloth bound with a few lateral fibers. The adhesive resin (DK-530, Denka) was a modified acrylic resin of two component system. 

Two concrete blocks were carefully bonded by inserting a carbon fiber sheet with the adhesive resin and cured at room temperature for 48 hours as the manufacturer s recommendation. A thin releasing film was inserted between the concrete blocks and carbon fiber sheet to introduce an artificial crack and to make an adhesive region of 20 x 10 mm The blocks were then bonded to the steel jigs with the same adhesive resin, as shown in Fig. 11. A liquid type primer was used to gain the adhesiveness of the interface between the concrete and carbon fiber sheet. 

As shown in Fig. 14, a thin concrete layer always remained on the adhesive region the crack path was inside the concrete blocks. Hence, the experimental results did not strictly indicate the properties of the adhesive interface. However, this behavior totally agreed with the actual fracture behavior of the RC beam reinforced with carbon fiber sheets [6]. This behavior was also consistent with the finite element results, where the principal stress in the concrete blocks partially exceeded their tensile strength. 

Fig. 15. Mixed mode fracture toughness of the adhesive interface between concrete and carbon fiber sheets each plot is the average value of 5-10 test data.

In order to apply the characterization and structural design of the concrete bridge structures retrofitted with tensioned carbon fiber sheets, the mixed mode disk specimen was proposed and applied to the mixed mode fracture toughness tests. The following conclusions were derived from the results and discussions ... 

Table 4,5 Compar ng properties of glass and carbon fiber sheet molding compounds...

Keywords epoxy resin, seismic retrofit, steel jacketing method, carbon fiber sheet jacketing method, unseating prevention... 

When the pier has an irregular shape such as I-shaped cross section, carbon fiber sheets cannot be adhered continuously around the pier. Thus, the edges of these fiber sheets have to be fixed with some effective methods such as use of steel angles and anchor bolts, or application of carbon fiber anchor as shown in Fig. 5. 

Figure 5 Special anchors of edge of carbon fiber sheets for irregular shaped cross section...

Marsh G,Seismic retrofit provides opportunities for FRP, Reinforced Plastics, 38-43, Mar 1998. Meier U, Rehabilitation and retrofitting of existing structures through external bonding of thin carbon-fiber sheets. Materials and Structures, 28(176), 105-106, 1995. 

Mitsui Y, Murakami K, Takeda K, Sakai H, Study on shear reinforcement of reinforced concrete beams externally bonded with carbon fiber sheets. Composite Interfaces, 5(4), 285-295, 1998. 

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