## 3 Testing Program  
### Tensile Response of Fibers  
Fiber tension tests were conducted under displacement control mode to measure elastic modulus, strain capacity, ultimate strength, toughness, and mode of failure. The setup is shown in Figure 3 with a specimen under the applied load. An actuator displacement rate of 0.4 mm/min was used. Preliminary tests were conducted using fiber lengths of 150, 200, and 250 mm to address the length effect. Follow up studies used a sample length of 150 mm and a minimum of five replicate samples per series. The load was measured using a load cell rated at a capacity of 1300 N, while the elongation was recorded by an extensometer with a 50 mm gage length. A close-up view of the failed specimens with the extensometer attached is shown in Figure 3b,c. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Type** & **Yarm Type** & **Sample Variables** & **Curing** & **Yarm V\({}_{\text{f}}\)\%** \\ \hline Fiber Tension & MAC & 150, 200, and 250 mm & N/A & \\ Fiber Tension & MF40 & 150, 200, and 250 mm & N/A & \\ Composite Tension & MAC & Volume fraction & 28 days & 1.0, 2.5, 4.0 \\ Composite Tension & MF40 & Volume fraction & 7, 28 days & 1.0, 2.5, 4.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of Tension specimens with continuous fibers. Figure 3: (**a**) Test setup for yarn tension tests, (**b**) failed MAC fiber, and (**c**) failed MF40 fiber. Stress-strain behavior for the two types of MAC and MF fiber yarns are presented in Figure 4 and a summary of test results is given in Table 2. The initial stress-strain curve started with a stiff response up to a stress level of about 5-7 MPa.Beyond that level, the stiffness decreased due to fiber yielding. The general behavior was linear for the monofilament samples up to the failure; however, significant nonlinearity was observed for the microfiber yarn. Gradual transition of the stress-strain response of microfiber yarns to a nonlinear behavior started from 50% ultimate strain capacity without a clearly marked yield point. Beyond this level, the stiffness reduced gradually until failure. Table 2 summarizes the single fiber tensile test results for both fiber types representing values of initial elastic modulus, E\({}_{1}\), and a post yield modulus, E\({}_{2}\). The macro-synthetic fiber, MAC, hadcomparatively higher initial and post-yield modulus, and showed a sudden failure compared to a progressive failure of the individual filaments of MF40 yarn. The ultimate strength was reached in a gradual manner for MF40 as opposed to a sharp end for MAC. Figure 3b,c show the failed MAC and MF40 specimens, respectively. With a strain capacity in the range of 12%, microfibers deformation was almost twice as much as the monofilament fibers, as shown in Figure 4. Compared to MAC, the MF40 microfiber exhibited significant crazing. This response was more pronounced when the strain wasmeasured using the actuator signal, as shown in Figure 4b, which also included the relative slipping of the individual filaments past each another, resulting in an apparent tensile strain as high as 75% for the MF series. These slip mechanisms lead to a higher strain capacity of the MF compared to MAC fibers. The difference in strain capacity between the two fiber compositions resulted in the toughness of MF being twice that of MAC and is attributed to the structure of multifilament yarns, which by