REGULAR ISSUE www.iioab.org | Bhatia et al. 2018 | IIOABJ | Vol. 9 | 5 | 1-8 | 1 ENGINEERING KEY WORDS Hollow glass microspheres, composite, epoxy, environment, mechanical properties REVIEW A REVIEW ON THE MECHANICAL PROPERTIES AND ENVIRONMENTAL IMPACT OF HOLLOW GLASS MICROSPHERE EPOXY COMPOSITES Sunny Bhatia*, Moin Khan, Himanshu Sengar, Vivek Bhatia Department of Automobile Engineering, Manav Rachna International Institute of Research and Studies, Faridabad, INDIA ABSTRACT The use of hollow glass microspheres (HGM) in composites is creating new opportunities in the composites industry. HGM consists of stiff glass hollow sphere filled with inert gas resulting in some specific properties like low weight, reduced dielectric constant, and reduced thermal conductivity. The typical wall thickness of HGMs is lying in between 0.5-2.0 μm and diameter 10-200 μm. On the basis of these properties, HGMs have been employed in the manufacturing of various composites for diverse applications. Therefore, the need of light- weight and high-strength materials for modern engineering applications may fulfill by the HGM composites. HGMs not only amending the properties but also ensuring the stability of molded articles by reducing viscosity and shrinkage of the composites. In this work, a comprehensive review on the properties of hollow glass microsphere (HGM) reinforced epoxy composites is presented. The summary of the paper shows the appropriateness of HGM-epoxy composites as an encouraging material for aerospace, automotive and cryogenic applications. The main focus area of the present study is the mechanical and environmental performance of the HGM composites. INTRODUCTION Composites are the materials produced employing two or more materials with different properties which on joining having assorted properties of both the constituents. The composite materials possess the indispensable properties borrowed from the best features of the two joined constituents. This material has the high strength to weight ratio and firm, fragile and other privative attributes of one material are concealed by the other one. In recent times, polymer composites are rapidly substituting the standard materials in various designing and product development in the engineering sector. Traditional materials and their modifications have a limited set of properties with a minor chance of improvements. On the other hand, composite materials can provide better quality control and required assortment of characteristics as per the application requirement. A proper blend of materials properties like specific modulus, a certain quality, low thickness etc. is doable in composites. The applications of composite materials are not limited to some particular areas. It also marked its presence in the space industry besides other common engineering industries owing to its sturdiness and potentials [1,2]. A thin walled sphere filled with inert gas or vacuum inside and a hard glass at the periphery are termed as hollow glass microspheres (HGMs). It is also named as hollow glass bead or glass bubbles or microballoons [3,4]. Syntactic foam is an example of HGM filled polymer composites [5]. The hollow glass microspheres have properties like feathery light, high specific area, inexpensive, low dielectric constant, flexible and noncorrosive. Additionally, the fragile microbeads are chemically strong, inflammable, unyielded and have excellent water resistance. The microspheres can be used in coatings, putty, artificial stones, emulsion explosives etc. [6–10]. It can also be used in oil and gas extraction industries as drilling fluid owing to its low density. It is also used to make superior optical glasses for visual resonators. Presently, the HGM reinforced composites especially syntactic foam are used to fabricate the gadgets employed for marine applications, deep sea exploration, ship bodies, helicopter and jet engine parts, detector instruments, noise reduction materials, sports merchandises. In the recent time, there is an increasing demand for the materials with low density and a high Young's modulus for various engineering applications. Therefore, HGM reinforced ploymer composites are gaining attention day by day. Foam glass owed Young’s modulus and density of typically 1 GPa and 130 kgm -3 , respectively [11,12]. Moreover, it could be blown up to a full-size bubble of 2 mm diameter and frequently used to prepare HGM composite [12]. In the present article, the major focus of the study is the mechanical properties of the HGM reinforced composites reported in the various literatures. Additionally, the environmental and economic aspects of the same are also addressed in the article. MECHANICAL PROPERTIES OF HGM COMPOSITES In this paper, the mechanical properties of rarely reconnoitered HGM reinforced polymer composites are summarized. In the recent years, the structural properties of syntactic foams are studied by several researchers. Compressive strength The compressive strength of HGMs filled epoxy composites are decreased with increasing volume fractions of the reinforcements [Fig. 1]. Additionally, higher density HGMs stimulates higher compressive strength of the composites. It can be marked from the plots [Fig. 1] that a stress plateau/valley exists in the plastic deformation region. The valley indicated the presence of broken HGMs owing to the compressive loading. Received: 19 April 2018 Accepted: 26 May 2018 Published: 1 Oct 2018 *Corresponding Author Email: sunny576bhatia@gmail.com Tel.: +91-8826004666