Master of Science (MS)
Syntactic foams are comprised of hollow microballoons in matrix systems. The superior mechanical and physical properties of syntactic foams such as light weight, high compressive strength, and low moisture absorption make them attractive materials for structural applications. As these materials are used in high mechanical performance applications, there is a need to achieve both high compressive strength and high energy absorption with minimal or no increase in density. In this study, the effect of gradient configuration of syntactic foams on the energy absorption and compressive strength is studied. Functionally Gradient Syntactic Foams (FGSFs) in five different layer sequencings are fabricated using layer over layer integrated technique called integrated FGSFs (IFGSFs). Each syntactic foam layer in IFGSF is fabricated using one of the four different types of glass microballoons namely, S22, S32, S38 and K46. In the present study, gradient structures are created with the variation of microballoon wall thickness. In order to maintain uniformity in the structure, volume fraction of the microballoons in each layer of IFGSF is maintained constant at 60%. The different layers of IFGSFs are integrated before major solidification takes place. Five different layer sequencing IFGSFs are fabricated to understand the effect of layer sequencing on the compressive properties of gradient structures. IFGSFs have tested for flat-wise and edge-wise compression properties on MTS-810 servo hydraulic machine. Also, flat-wise compression results are compared with adhesively bonded FGSF and found that FGSFs fabricated with layer over layer integrated technique show dramatic improvement in compressive properties. Furthermore, the IFGSF results are compared to one another for understanding the effect of layer sequencing on flat-wise and edge-wise compressive behavior. Layer sequencing effect on crack propagation behavior of IFGSFs is carefully monitored and analyzed with Optical Microscope (OM) and Scanning Electron Microscope (SEM). In order to understand the dynamic properties of gradient structures, low velocity impact analysis is performed on the IFGSF structures. Impact testing of IFGSFs is conducted at velocities 1 m/s, 2 m/s and 3 m/s on Dynatup 8250 impact testing machine. The initiation energy, propagation energy and maximum load values of IFGSFs are compared to one another to understand the layer sequencing effect on impact properties.
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Chittineni, Kanakaji, "Functionally gradient syntactic foams" (2009). LSU Master's Theses. 943.