Tensile Properties of Glass Microballoon-Epoxy Resin Syntactic Foams Nikhil Gupta, Ruslan Nagorny Composite Materials and Mechanics Laboratory, Mechanical, Aerospace and Manufacturing Engineering Department, Polytechnic University, Brooklyn, New York 11201 Received 16 August 2005; accepted 24 October 2005 DOI 10.1002/app.23548 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The effect of hollow glass particle (microbal- loon) volume fraction in the range of 0.3– 0.6 on the tensile properties and fracture mode of syntactic foams is charac- terized in the present research. Sixteen types of syntactic foams have been fabricated and tested. Four types of glass microballoons, having 220, 320, 380, and 460 kg/m 3 density, are used with epoxy resin matrix for making the syntactic foam samples. These foams contain 30, 40, 50 and 60% microballoons by volume. All types of microballoons have the same size but different wall thickness, which reflects as a difference in their density. It is observed that the tensile strength increases with a decrease in the volume fraction of microballoons. All types of syntactic foams showed 60 – 80% decrease in the tensile strength compared with that of the neat resin. The foams containing low strength microballoons showed lower tensile modulus compared with that of the neat resin, but the presence of high strength microballoons led to an increase in the tensile modulus of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1254 –1261, 2006 Key words: composites; foams; mechanical properties; ten- sion; microballoon INTRODUCTION Hollow particles are used in a variety of applications ranging from piezoelectric transducers and sound ab- sorption to fabrication of lightweight composite mate- rials for aeronautical and marine structures. 1 Hollow glass particle (microballoon) filled polymeric compos- ites, known as syntactic foams, have been studied over the past two decades for a variety of mechanical prop- erties. The microstructure of a syntactic foam is shown in Figure 1, where glass microballoons are embedded in epoxy resin matrix. These lightweight materials are known for their high compressive strength, dimen- sional stability, and low moisture absorption com- pared to other types of foams. Syntactic foams are extensively studied in the pub- lished literature for compressive, flexural, and hygro- thermal properties. 2–5 However, studies on tensile strength of these materials are scarce. 6–8 Most of the applications of syntactic foams were limited to the ma- rine structures, where the light weight of these materials could be used to obtain high buoyancy. These applica- tions, where hydrostatic compression is the principal applied load on the material, gained advantage from high strength and energy absorption characteristics of these materials under compressive loading conditions. It is observed that the compressive properties of syntactic foams can be effectively modified either by changing the microballoon volume fraction in the foam 2 or by choosing microballoons of different wall thicknesses. 9 The strength of microballoons depends on their wall thickness. It is observed that the com- pressive strength shows an almost linearly increasing trend with increase in the syntactic foam density. However, the total energy absorption decreases be- cause of a decrease in the fracture strain in higher density foams. Interest in utilizing the advantage of low density of syntactic foams in other applications such as aero- space structures and sports equipment has made it necessary to characterize these materials for tensile loading and study various parameters affecting their properties. The existing studies on the tensile proper- ties of syntactic foams were carried out on foams containing low microballoon volume fractions (V mb ). 6,7,10 It was found that the tensile modulus in- creases with decrease in V mb . The present work char- acterizes syntactic foams containing high V mb (0.3– 0.6). The selection criterion for microballoons makes it possible to directly relate the microballoon properties with the tensile strength and modulus of syntactic foams. The present study selectively studies the effect of microballoon density and volume fraction on the tensile strength and modulus of syntactic foams. Selection of microballoons and porosity calculations Hollow particles can be characterized based on their wall thickness (). A parameter named “radius ratio” is defined for hollow particles as Correspondence to: N. Gupta (ngupta@poly.edu). Journal of Applied Polymer Science, Vol. 102, 1254 –1261 (2006) © 2006 Wiley Periodicals, Inc.