## 4 Results and Discussion
### Results of the Impact Tension Tests
#### 4.2.1 Dynamic Uniaxial Tension Tests
The strain-hardening behavior lasted until the composite with SHCC matrices reached their tensile strength, and afterwards, no new cracks developed while only the localization crack continued to open. It can be observed that for all types of composites, the DIF of the first crack stress is considerably higher than that of the tensile strength. The first crack of material occurs during the initial loading stage associated with increasing displacement rates; i.e., acceleration. Due to this, the structural inertia has a significant contribution to the apparent first crack stress; see also, [33]. The first crack occurrence attenuates the effect of strain rates in the rate sensitive matrix considerably. Average crack widths and crack spacings at critical strain levels of 0.1%, 0.3%, and 0.4% for representative specimens subjected to uniaxial impact tension (except localization crack) are given in Table 8, according to the nearest frame recorded. Though the average crack widths keep increasing, along with the deformation for all three materials, TRC-PE and TRC-PBO possess superior crack control behavior with a steady and moderate growth in average crack width. Figure 11: _Cont._  
Figure 11: Tensile stress–strain curve and corresponding average crack widths of a representative specimens of (**a**) TRC-M, (**b**) TRC-PE, and (**c**) TRC-PBO, with corresponding composite stresses and crack patterns under impact loading. Compared to the quasi-static tension tests, at the same strain level, the average crack width of TRC-PBO is higher than that of TRC-PE, which is the smallest among the three composites. Furthermore, the ultimate average crack spacing of TRC-PBO is larger. Even though TRC-PE still possesses a higher ultimate strain capacity of 1.2% comparing to 0.9% of TRC-PBO, its corresponding DIF of 0.4 reveals a pronounced loss in pre-peak strain capacity, leading to a slight decrease in the work-to-fracture; see Table 7. TRC-PBO, on the contrary, maintained strain capacity at the same level as under quasi-static loading, which led, along with the considerably higher tensile strength, to a significant increase in work-to-fracture, with the DIF being 1.8. The average crack-width-strain curve of TRC-M exhibits a considerably steeper slope after the formation of the first crack, indicating a more rapid degradation in the composite stiffness, as there is no contribution by short fibers. However, the improvement in the strain capacity (multiple cracking) indicates a better energy absorption behavior of this material under impact loading in comparison to its performance under quasi-static loading. The reason behind this improvement is the enhancement of the yarn-matrix bond under dynamic loading, which will be discussed in the next section. The stresses applied and the average crack width growth at the critical strain levels are plotted in Figure 12. Taking into consideration both the load-carrying capacity and the average crack width developed, TRC-PBO exhibits the highest stress levels and a favorable crack control behavior at each strain level. When comparing to TRC-M, a sudden loss in composite stiffness is avoided, which means that TRC-PBO is able to carry a higher impact load with a more steady development of cracks.