Zainuddin Shaik, Ph.D. (2009)

Dissertation Topic: Durability Studies of Nanophased Composites Subjected to Different Environmental Conditions

Major Professor: Dr. Mahesh Hosur, Research Professor of Materials Science & Engineering

M.S.:  Mechanical Engineering, Tuskegee University

Employment:   Assistant Professor of Materials Science & Engineering, Tuskegee University

Dissertation Abstract:

Behavior of fiber reinforced polymeric (FRP) composites is both time and environment dependent. Long term behavior of FRP composites is affected by factors like temperature, moisture, service load, creep, ultraviolet (UV) radiation, etc. For applications like military facilities and civil infrastructure, it is desired to have a design life of 15- 50 years. However, it is not practical to perform tests on either materials or structures for very long periods to cover the design lifetime. Therefore, there is a strong need for accelerated lifetime characterization methodologies which can predict the degradation of FRP composite materials in order to assure the integrity and safety of structural components. Since nanophased composites are of recent origin and have shown tremendous advantages in terms of strength and stiffness, it is essential to understand their durability issues before they can be used with confidence in structural applications. Hence, this research was focused on characterization of physical, chemical and mechanical degradation of epoxy and E-glass/epoxy composites infused with 1-2 wt. % nanoclay loading. Epoxy and E-glass/ epoxy composites were fabricated and the samples were subjected to different environmental conditions. The conditioned samples were tested for their flexural and dynamic compressive properties. Surface morphologies of the samples before and after the exposure were characterized through scanning electron and optical microscopy. Based on the experimental results, a nonlinear damage model was established to describe the stress–strain relationship of neat and nanocomposite. The parameters in this model are modulus E, Weibull scale parameter σo and Weibull shape parameter β. A relation between Weibull parameters, time, and temperature was established through which long term behavior of material can be predicted.