High Strain Rate Behavior and Failure Analysis of Nanoclay Reinforced Vinyl Ester Based Syntactic Foams Subjected to Hygrothermal Conditioning

摘要

Syntactic foams are widely used as core materials for composite sandwich applications, especially in applications where weight is a major factor. Understanding the dynamic response and failure mechanisms of syntactic foams under high strain rate testing is of great importance in designing proper core structures capable of sustaining catastrophic failure. Vinyl ester polymeric systems are studied extensively as an alternative to epoxy based syntactic foam systems, primarily due to their low density, high modulus of elasticity, low coefficient of thermal expansion, low cost and enhanced ductility. This study is aimed at addressing the high strain rate properties of vinyl ester based syntactic foams reinforced with nanoclay platelets. High strain rate compressive response of the syntactic foam is measured using split Hopkinson pressure bar (SHPB). The high strain rate testing was conducted at two different strain rates and on three different specimens. Volume fraction of glass microballoons was fixed at 60% and the weight fraction of nanoclay was 1%, 2% and 5%. Quasi-static, uniaxial compression tests were also conducted on the nanoclay reinforced vinyl ester syntactic foams for comparison purposes. Hygrothermal studies were performed on these foams by subjecting them to different environmental conditions, viz: de-ionized water and salt water. The effect of environmental conditioning on high strain and quasi-static properties were analyzed. This is very important owing to the application of vinyl ester based syntactic foam systems in marine applications. A microstructural failure analysis was also conducted to study the fracture behavior of these syntactic foams when subjected to dynamic compressive loads.