Identifier

etd-11142008-093201

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

Syntactic foams are composite materials in which the matrix phase is reinforced with hollow particles called microballoons. They possess low moisture absorption, low thermal conductivity and high damage tolerance because of their compositions. Traditionally, syntactic foams are used in many high strength applications such as in aerospace and marine industries, thus there is a need to achieve both high compressive strength and high fracture strain with minimal increase in density. This research studies the effect of nanoclay on the high strain rate mechanical properties of syntactic foams. Nanoclay reinforced syntactic foams are fabricated by adding 1, 2 and 5% volume fraction of Nanomer I.30E nanoclay in syntactic foams having 10, 30 and 60% microballoon volume fraction. Transmission electron microscopy is performed to determine the dispersion of nanoclay in matrix. To compare the effect of nanoclay, plain syntactic foams without nanoclay are fabricated with same microballoon volume fraction. Two types of glass microballoons, S22 and K46, having different wall thickness are used in plain and nanoclay syntactic foams. High strain rate tests using split Hopkinson pressure bar (SHPB)apparatus are conducted on all types of plain and nanoclay syntactic foams and dynamic strength and modulus values are calculated. Also, quasi-static tests are conducted using MTS-810 machine and results are compared with dynamic SHPB results. The results demonstrated the importance of strain rate, nanoclay volume fraction and microballoon wall thickness in determination of syntactic foam properties. It is found that inclusion of 1% nanoclay gives the optimum enhancement in strength and modulus of nanoclay syntactic foams at all three microballoon volume fractions. The behavior of strength and modulus dependence on nanoclay volume fraction is found to be similar in both composite foams having S22 and K46 microballoons. Specimens exhibited higher strength and modulus at high strain rate than at lower strain rates. Based on stress-strain behavior of composite foams, energy absorption is also calculated. It is found that thicker walled microballoons (K46) composite foams showed higher strength, modulus and energy absorption than those with thin walled (S22) microballoons. Scanning electron microscopy is performed to study the fracture behavior under different loading rates.

Date

2008

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Eyassu Woldesenbet

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