Research and Infrastructure Support to Tuskegee University through Office of Naval Research

The ONR grant to Tuskegee has been in place since 1981. The first Center of Excellence grant was awarded in 1986 under the DoD University Research Initiative (URI) program for the development of SiC/SiC composites for high temperature applications. Current research is focused on developing nanophased composites materials and structures with improved properties for marine applications. ONR funding has helped Tuskegee University to establish state-of-the-art facilities in mechanical  characterization  of advanced materials particularly high velocity impact, high strain rate, NDE, high speed imaging. In addition, computational capability was also enhanced. ONR funding along with that from National Science Foundation has helped Tuskegee University in establishing its first PhD program in Materials Science and Engineering in 1998.  A total of seven PhD students have graduated to date with support from ONR funding.  

Tuskegee has been successful in leveraging funding from other sources to enhance its research as well as infrastructure. State-of-the-art facilities developed through these leveraged funding include transmission electron microscope, ultrasonic NDE, biaxial materials test systems, TA instruments rheometer, dynamic mechanical analyzer, thermomechanical analyzer, differential scanning calorimeter etc. In the last ten years, there have been over 100 peer reviewed journal publications as well as over 200 conference papers presented through this research a fourth of them were from ONR funded research. Over 20 MS students have graduated with supported from ONR funded research with at least half of them getting PhD elsewhere. Five of them have served at Tuskegee in the last ten years as faculty.

Continued support from ONR has helped in sustained development of infrastructure at Tuskegee and allowed minority students to conduct research in advanced materials and structures with state-of-the-art facilities. The broader impacts resulting from ONR funded research activities include the fact that a large number of African American graduates, including many at the PhD. level, were produced in emerging areas of materials science and engineering.

Recently funded grant

 Investigations on the Mechanical, Multifunctional and Environmental Behavior of Fiber Reinforced Polymer Nanocomposites for Marine Applications, Office of Naval Research (7/7/08-05/31/12), Grant Number: N00014-08-1-0665

 PI: Dr. Mahesh Hosur, Professor of Materials Science and Engineering

 Specific Tasks accomplished are as follows: 

  • Liquid molding processing of fiber-reinforced polymer and sandwich nanocomposites
  • Environmental conditioning
  • Thermal, electrical, thermomechanical, mechanical, and damping characterization of polymeric, fiber reinforced polymer and sandwich nanocomposites
  • Dynamic mechanical properties fiber reinforced polymeric and sandwich nanocomposites

 Following are brief outcomes of research carried out under this grant

Sandwich Composites

Sandwich structures are widely used in aerospace, marine, automotive, and other commercial applications due to their high strength to weight ratios, high bending stiffness, high energy absorptions capabilities, and light weight.  Traditionally polymer foams serve as the core material for sandwich composites, mainly because of their low density and energy absorption mechanisms due to their cellular structure.  The core is a very important component of sandwich composites because it enhances energy absorption during impact, deters failure modes during loading, and improves bending stiffness.   In this investigation, rigid polyurethane foam cores, of high and low densities were modified with four different types of fillers to evaluate their effects on the morphological, thermal, thermo-mechanical, and mechanical properties.  In an effort to use more environmentally friendly materials, as well as a transition towards the fabrication of more “greener” composites; the reinforcements chosen for this study are all derived from natural sources.  Three organically-modified nanoclays (Cloisite® 10A, Cloisite® 30B, and Nanomer® I.28E) and maple wood flour were the fillers of choice.  In term of low density modified foam cores, micro structural analysis of foams through scanning electron microscope showed an increase in cell density due to particle infusion which led to an increase in mechanical properties for nanophased and wood flour foam cores when compared to neat foam cores.  An increase thermal stability was observed up to 800 °C, for modified cores in comparison to neat cores.  Thermo-mechanical results showed improved stiffness and energy absorption capabilities, but not an increase in glass transition temperature for modified foam cores in comparison to neat foams. In terms of high density modified foam cores, only thermal stability of modified cores showed promising results.  However, enhancements in viscoelastic and mechanical properties were only observed for 10A/PU high density foam cores.  Impact studies of low density sandwich composites, showed enhancements in peak load values for nanophased cores in comparison to neat cores.  No significant enhancements were observed for nanophased high density foam cores in comparison to neat high density cores.

 Durability Studies

Due to viscoelastic nature of polymers, there have been major concerns about their durability of fiber reinforced polymer composites over long-term applications particularly when exposed to ever-changing environmental conditions. Effects of UV radiation and associated elevated temperatures on properties of polymeric composites have been well documented, limiting the scope of use in outdoor applications. Several attempts have been made in the past to extenuate these effects by addition of fillers including UV blockers and nanoparticles particularly nanoclays leading to diverse results. In the current study, diglycidyl ether bisphenol A based epoxy (SC15) was modified with 1 – 3 wt. % montmorillonite nanoclay (Nanomer® I.28E). Influence of nanoclay loadings on morphological and rheological properties leading to curing and subsequent developments of physical properties of each composite were evaluated along with thermal and thermo-mechanical properties. The study revealed that optimization of modified epoxy composite properties requires different curing cycle. Four set of samples were fabricated and subjected to 2500 hours of UV radiation conditioning using identical composition of SC15 epoxy and various amounts of montmorillonite nanoclay. Samples used for the study were neat, 1, 2 and 3 wt. % nanoclay fabricated using manufacturers’ recommended cycle, and identical sets cured to 70, 80 and 90% conversion using results from cure kinetic studies. The goal was to evaluate materials’ property response to UV radiation based on different composition and degree of cure. Thermal and thermo-mechanical properties along with 60 minute half-life and service life predictions were evaluated at intervals of 500 hours. Formation and promulgation of free radicals on exposed surfaces were also monitored at the same interval. Addition of nanoclay decreased the viscosity of SC15, and increased heat of reaction during curing. Onset and decomposition temperatures were least affected among samples cured to the same degree, however, decreased with lower degree of cure, while activation energy of decomposition increased with increasing clay content and exposure time. Addition of nanoclay increased the viscoelastic properties, and partially cured samples evolved over exposure time, while fully cured samples degraded over the same period. Samples cured to 70 and 80% showed delayed commencement of UV radiation effects. 

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