2.1.1. Carbon Textile

The carbon textile that was used in this study is manufactured in two orthogonal directions at a nominal spacing of 5 mm. Multifilament yarns consisting of 6000 monofilaments are used to produce the textile. The outer filaments (sleeve filaments) are in direct contact with the matrix and, therefore, have a greater effect on the bond properties than the inner filaments (core filaments). The inner filaments have no direct contact with the matrix because of the low penetration of the matrix. The force on the sleeve filaments is transformed to the core filaments via friction; thus, the untreated textiles exhibit little cooperative bearing ability between the sleeve and core filaments. A large number of experimental studies have shown that epoxy resin can fully penetrate all filaments within the yarns, thereby providing an intact unit reinforcing system [36,37]. Hence, impregnated carbon textiles are used in this study, and the warp yarns (along the length of the textile) are considered to be the reinforcing yarns, as shown in Figure 1a.

**Figure 1.** (**a**) Carbon textile impregnated with resin epoxy, (**b**) single yarn samples, (**c**) strip sample, and (**d**) steel fibers.

Details about the physical and mechanical properties of the impregnated carbon yarns (reinforcing direction) are presented in Table 1. The tensile strength, Young's modulus, and elongation of the carbon yarns were determined through direct tensile tests using 100-mm gauge length samples according to the Chinese specification GB/T 3362-2017 (Figure 1b). The cross-sectional area of a single yarn is 0.218 mm2, calculated as the ratio of tex (the linear density of this material) to its bulk density. Ten 40-mm wide strips of 100-mm gauge length samples were cut from the textiles (Figure 1c) to determine their tensile properties. The average tensile bearing capacity and tensile strength of the 10 test strips were 4 kN and 2293.6 MPa, respectively, as determined via tensile tests.


**Table 1.** Physical and mechanical properties of the warp carbon yarns (impregnated).

Note: 6K means that one multifilament yarn consists of 6000 monofilaments.
