## 4 Results and Discussion
### Dynamic Tensile Testing  
The deformation mechanisms were analysed by DIC. The left hand side of Figure 9 shows the evolution of the longitudinal strain at different stages of the experiment and Figure 10a plots the local longitudinal strain distribution at the dashed mid-line. The input bar pulled the nonwoven fabric from the right side. At the initial stage of the loading process (\(t~{}=~{}0.2\) ms), the material acquired an  
Figure 8: Validation of DIC measurements. (**a**) Velocities at the input and output interfaces registered by the strain gauges. Corresponding contour plots of longitudinal velocities at (**b**) \(t=0.6\) ms, (**c**) \(t=0.8\) ms, (**d**) \(t=1.0\) ms and (**e**) \(t=1.4\) ms.  
oscillating deformation around the 10% as a result of the wave reflection process. The magnitude of the applied strain continued to increase progressively in time (\(t~{}=~{}0.4\) ms) up to \(\approx\)20% of deformation, maintaining the original distribution. After a certain instant in time (\(t~{}=~{}0.6\) ms) the evolution of the strain nearby the output bar froze at a maximum value of 18% deformation leading to a heterogeneous strain field across the specimen (see Figure 9e,g) with an steep increment of deformation located at the input interface once onset of damage was attained at \(\approx\)40% of deformation; see Figure 10a. These strain gradients developed even at low strain values before the onset of damage, in contrast to the characteristic homogeneous strain distributions obtained at quasi-static loading regimes. Nevertheless, the strain gradients and damage localisation generated during dynamic testing were in agreement with the response registered during ballistic impact, where larger deformation and final fabric tearing were localised at the impact point, and did not further propagate through the target [19; 21]. Figure 10: Evolution of spacial distribution of local longitudinal (**a**) strain and (**b**) strain rate. \(X~{}=~{}0\) mm stand for the material particles at the output interface, meanwhile \(X~{}\approx~{}34\) mm stand for the material particles at the input interface. Figure 9: Evolution of the longitudinal strain \(\varepsilon_{x}\) (**a,c,e,g**) and lateral strain \(\varepsilon_{y}\) (**b,d,f,h**). (**a,b**) \(t~{}=~{}0.2\) ms, (**c,d**) \(t~{}=~{}0.4\) ms, (**e,f**) \(t~{}=~{}0.6\) ms, (**g,h**) \(t~{}=~{}0.9\) ms. Dashed line represents the mid-line used to monitor longitudinal strains and strain rates in Figure 10.  
The lateral strain was analysed, showing evidence of a biaxial stress state across the specimen, see the right hand side of Figure 9. The biaxial stresses were triggered by the large Poisson's ratio of the material, inducing higher deformations (longitudinal and lateral) at the outer edges of the fabric with respect to the mid-line region. This resulted in an heterogeneous transverse contraction of the material with lower influence of biaxillity at the mid-line region of the sample, where quasi-constant lateral strains developed. The lateral strain was also directly proportional to the longitudinal strain and the contraction decreased with the distance from the input face. The strain rate was not constant along the specimen during the dynamic testing. The average strain rate was registered by the strain gauges as \(\dot{\epsilon}\approx 400\) s\({}^{-1}\), in agreement with the local DIC measurements; see Figure 10b. These values were four orders of magnitude higher than the previous quasi-static experiments. Overall, the strain rate decreased with the distance from the input interface. The final stage of the experiment (\(t~{}=0.9\) ms) presented a different trend in strain rate distribution due to damage localisation, showing a drastic increment near by the input interface. The deformation was accommodated by the same micromechanisms observed during the quasi-static uniaxial deformation; fibre straightening, rotation and sliding towards the loading direction [15].