<p>High-performance fibers used for ballistic protection are characterized by having outstanding mechanical properties such high modulus and strength. These mechanical properties are granted by the fiber’s chemical and physical structure as well as their high degree of orientation. Twaron fibers are one of the most commonly used fibers on soft body armors such as bulletproof vests. They are made from poly (p-phenylene terephthalamide) (PPTA), a rigid-rod and highly crystalline polymer. Although these fibers are crystalline and have great mechanical properties, their performance can decrease when they are exposed to different degradation factors. Free volume is the unoccupied space between the polymer molecules. It is responsible for characteristics such as diffusion and viscosity. Hence, the free volume changes as the polymer degrades. This thesis focuses on the effects of sonication, pH changes, and sweat on the free volume of PPTA fibers. </p><p><br></p> <p>A non-destructive technique known as positron annihilation lifetime spectroscopy (PALS) was used to measure the free volume in PPTA. Changes in the free volume of fibers degraded under different conditions were compared to their mechanical performance. Degradation in DI water, pH 4 and pH 10 aqueous solutions was conducted for 10 weeks at 80^oC. Sweat degradation of PPTA fibers was also conducted for 10 weeks at 25^oC, 50^oC, and 100^oC. Fibers degraded in pH4 and sweat solutions had greater loss of mechanical performance and changes in the free volume. PALS was able to detect changes in the nanostructure of PPTA fibers at early stages of degradation. This data was supported by mechanical tests and is complementary to other characterization techniques such as small angle X-ray scattering (SAXS). Results of this research are a steppingstone for future studies on lifetime predictions of bulletproof vests and the development of the next generation of soft body armors. </p>

This master thesis is aimed at computational modeling of ballistic resistant layered laminate. The introductory sections of the thesis are aimed at understanding the individual topics that are closely related to the interaction of the projectile and target and computational modeling of this process. The main goal of this thesis was to create a computational model that is able to reflect the behavior of aramid fabric during the interaction with the projectile. During the development of the computational model were used more methods of modeling and also more material models were used. For the purposes of the development of the computational model were used the available data of the companies SVS FEM s.r.o. and VVÚ s.p. The outcome of the diploma thesis is a computational model of aramid fabric which is designed for ballistic protection simulations. This model is validated on the basis of available experiments. The validated computational model is then applied to the simulation of ballistic protection.