As submitted by the proposer. The life of many men and women that dedicate to protect this country depend on the performance of body armors. This essential protective gear relies on the properties of the materials they are made of.
High performance fibers like Kevlar are polymeric materials that are commonly used in soft body armors. Their outstanding mechanical and chemical properties have been engineered to make them ideal for applications under extreme dynamic conditions (i.e. stopping a ballistic projectile).
However, many chemical and physical factors during the lifetime of these materials can contribute to their degradation resulting in loss of their performance. The onset of these degradation events starts at smaller length scales on the polymer chains that compose the fibers, and in the initial stages may be undetectable at the macroscale. Changes on the molecular structure like chain scission and cross-linking due to degradation affect the size and shape of areas like the free volume (empty space) between the polymer chains.
In order to model degradation experimentally, ballistic fiber samples will be subjected to accelerated degradation conditions to determine in a shorter range of time how different factors affect the performance of the materials. The proposed research offers a non-destructive method of characterization that detects changes in the distribution of the free volume, known as positron annihilation lifetime spectroscopy (PALS). Comparing the results obtained with this technique with data acquired of chemical a mechanical characterization methods, the aging process of these material can be understood in more detail.
With this information, an empirical model which will relate the free volume distribution of the material with its mechanical performance, assessed by dynamic mechanical analysis (DMA). DMA is a mechanical characterization method that is able to submit the samples to compression, tension and induce fatigue by oscillation of the sample at a specific or a range of frequencies.
Information obtained from PALS and methods like the DMA is complementary to each other and will provide the nanostructural basis for premature fiber failure in next generation ballistic materials. Results from this study will allow National Institute of Justice (NIJ) to create standards for soft body armors. Moreover, it will establish a foundation for the synthesis of better materials that can outperform Kevlar and improve those that already exist by developing coatings that prevent their degradation at accelerated rates.
This project contains a research and/or development component, as defined in the applicable law, and complies with Part 200 Uniform Requirements 2 CFR 200.210(a) (14). nca/ncf
