3. MECHANICAL PROPERTIES OF SPRAYED FRP
A total of sixty coupon specimens of each sprayed FRP were prepared as Type A (JIS K7054) test pieces. Thirty specimens were made with carbon fiber (CF-SU), and the other thirty specimens for glass fiber (GF-SU). Based on a tensile test method for plastics reinforced by glass fiber (JIS K7054), a tensile test was carried out for these Type A test pieces. In order to compare the differences of characteristics between sprayed FRP and fiber sheets, another sixty Type B (JIS K7054) test pieces were also prepared and tested in the same tensile test. Thirty of them were made by carbon fiber sheet (300g/m2) with one layer (CF-HU). The other thirty were made by glass fiber sheet (444g/m2) with 4 layers (GF-HU). The specified thickness of sprayed FRP for CF-SU and GF-SU is 3.0mm and 4.5mm, respectively.
Table 1 and Figure 2 show the tensile test results and the typical stress-strain (σ – ε ) diagram, respectively. The measured sectional areas including resin are applied, and elastic modulus is a secant stiffness of the 10%-50% tensile strength. The tensile strength of CF-SU is about one tenth of the one of CF-HU. GF-SU is about one fifth of GF-HU. The tensile strength of CF-SU is approximately the same as the one of GF-SU. Regarding elastic modulus, CF-SU is about one forth of CF-HU. GF-SU is also about one forth of GF-HU. The elastic modulus of CF-SU is approximately twice as large as the one of GF-SU. From these results, the thickness of sprayed CFRP needs to be about 6.5mm in order to expect the similar strength of specimens with one layer of carbon sheet (300g/m2). As shown in Figure 2, σ – ε relationships for sprayed FRP is not perfect linear.