Please consider attending the following: MATERIALS ENGINEERING SEMINAR "Non-Destructive Method for the Detection of Degradation on Ballistic Fibers" By Nelyan López Pérez Purdue MSE Ph.D. Preliminary Exam Advisor: Professor John A. Howarter ABSTRACT Ensuring the performance and safety of body armors during service is crucial for institutions such as the United States National Institute of Justice (NIJ). The NIJ's commitment to safety prompts the research of the degradation of high performance fibers like Kevlar, Twaron and Dyneema. Degradation, the reduction of the mechanical properties such as strength and toughness, occurs when a material is exposed to various common environmental factors like sweat, humidity, temperature and sunlight. Currently, the effects of water and pH are studied in Twaron fibers. The amount of water and its effects on their mechanical properties are tested through tensile testing and dynamic mechanical analysis (DMA). However, early stages of degradation can be detected using a technique called positron annihilation lifetime spectroscopy (PALS), which measures the dimensions of free volume in polymers. As the fibers degrade, the dimensions of the free volume change. Hence, PALS can then be used as a complementary technique to the previously mention mechanical tests. Comparing the changes in free volume to those in the mechanical properties gives a broader understanding of the degradation process and rate for high performance fibers, and can later be implemented for the lifetime prediction of new and used body armors. Date: Monday, November 20, 2017 Time: 10:30 A.M. Place: ARMS 1021