Abstract : |
Advanced structural Fiber Reinforced Polymer (FRP) composites are elegant and promising materials in today’s high performance and reliability oriented material world with better eco-efficiency. Their outstanding mechanical properties as high strength to weight ratio, corrosion resistance, good impact resistance, better damping characteristics and improved fatigue properties enables their use in diversified fields. Widespread application spectrum covers civil engineering structures, aerospace and aircraft components, automobile parts, sporting goods, marine structures and chemical industry structures. All these structures and components are exposed to some environment. The environmental conditions can be high and low temperatures, high humidity, UV light exposure, alkaline environment and may be more severe if there is cyclic variation of temperature, hygrothermal environment and low earth orbit space environment.Polymer matrix composites are susceptible to damage in these environments. The mechanical behavior of FRP composites are dominated by the interfacial adhesion at the fiber-matrixinterface. The presence of moisture at the interface can modify the interfacial adhesion thereby affecting the mechanical performance of the FRP composites. Differential thermal expansion of fiber and matrix at elevated temperature can degrade the interface which leads to the lower interlaminar shear strength of the composite. At low temperature most polymer matrix behaves in brittle manner and do not allow the relaxation of residual stresses or stress concentration. These residual stresses at cryogenic temperature may results in larger debonded interfaces. Interlaminar shear behaviour can be used to characterize FRP composite materials. Loading rate has significant effect on the interlaminar shear strength of polymer composite and rate of loading can possibly change the failure mode.Experimental investigations were carried out on glass fiber, carbon fiber and kevlar fiber reinforced with epoxy and polyester resin in different environments (i.e. hygrothermal, thermal shock, thermal spike, ultra-low temperature, freeze thaw, and seawater). Mechanical behavior of composites has been assessed by evaluating interlaminar shear strength (ILSS) in 3-point bend test under different environments. An investigation [1] was focused on the effect of thermal shock on the interlaminar shear strength (ILSS) of glass/epoxy composite and it is reported that there is increase in ILSS value with the increase in conditioning time. Here the effect of thermal shock is evident at less conditioning time (at 5 min.). But post curing and strengthening phenomena and shrinkage compressive forces dominates at higher conditioning time. Shrinkage compressive forces can improve the mechanical interlocking at the fiber matrix interface. Investigation [2] on glass fiber/polyester composite reveals that the degradation of the composite under hydrothermal shock cycle is less pronounced with the increase of fiber volume fraction. The damaging effects are also loading rate sensitive. ILSS values were found higher for higher loading rates. The decrease in ILSS value with the increase in hydrothermal shock cycles was also noticed. Influence of thermal shock on the mechanical behaviour of Kevlar fiber reinforced with epoxy and polyester resin matrix were also studied [3]. For Kevlar fiber/polyester system, the ILSS value decreases with increasing conditioning time. The weak interface between Kevlar fiber and polyester resin deteriorate by thermal shock. The interface may be unable to accommodate the unfavourable tensile stresses developed due to the radial expansion of Kevlar fiber. Effects of freezing of absorbed moisture on interlaminar shear strength of glass fiber/epoxy composite at different loading rate were also investigated [4]. This freezing treatment results in further damaging |
Biography : |
Dr Bankim Chandra Ray is a Professor of the Department of Metallurgical and Materials Engineering at National Institute of Technology, Rourkela, India .Prof. Ray’s research centers on the impact of extreme environmental conditions in FRP composites. He is at present pursuing the mechanistic origin of environmental damage phenomena of the engineered FRP materials. He has also worked on non-destructive evaluation of FRP materials during his academic visit to UK University. Professor Ray intends to further his expertise in the field of polymer nano-composites. He and his group have started an investigation on the effect of ultra-low temperatures on synthesis of nano-particles by sono-electro-chemical principle. He has also worked on solidification behaviour and structure-property relationship of especially Al-Si alloys. He is also investigating micro-examinations of interfaces and its implications on nano-composites in metal matrix systems. He has an experience on computer modelling of phase transformation of ferrous materials. Dr. Ray has recently been selected by UNESCO based on Science Citation Index. He is the author of more than 125 scientific papers out of which 60 in International Journals and regular reviewer of many high impact Journals of Composites and Materials Science areas. Prof. Ray’s research has been funded by different governmental agencies. |