14 Influence of Dynamic Multiaxial Transverse Loading on Dyneema® SK76 Single Fiber Failure 87 Fig. 14.2 Indenter geometry comparison Fig. 14.3 Experimental image analysis. (a) Progressive loading of single fiber. Images range from undeformed state (far left) to final ultimate tensile strain before failure (far right). (b) Angle measurement in final frame before failure. (c) Fiber motion post-failure at approximately 20.0 μm. The blunt indenter is one order of magnitude larger with a radius of 200.0 μm, and the razor indenter is one order smaller at approximately 2.0 μm radius. The indenters as produced are depicted in Fig. 14.2. For each loading geometry, a minimum of 10 successful tests at each loading velocity were performed. 14.3 Results and Discussion Tests are split into 6 groups based on a combination of impact velocity (fast or slow) and indenter geometry (blunt, sharp, or razor). Each test group contains a minimum of 10 samples in each. Figure 14.3 represents a typical test progression as used for measuring velocity and failure strain. Fast tests correspond to velocities of approximately 20 m/s with a pressure set point of 15 psi, and slow tests correspond to an impacting velocity of approximately 10 m/s with a pressure set point of 5 psi. Average velocities for all groups with standard deviation are displayed in Fig. 14.4. Sanborn et al. have performed tensile testing of Dyneema®SK76 single fibers at varying gage lengths and strain rates, the results of which are included in Fig. 14.5 [3]. Based on this study, as strain rate increases in uniaxial tension, failure strain decreases, but apparent strength increases, presumably due to rate-dependent stiffness increase. Average experimental strain
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