Master of Science in Mechanical Engineering (MSME)
In this study, a novel hybrid sandwich structure with an integrated, iso-grid stiffened syntactic foam core was fabricated and evaluated by impact test and static test. Sandwich beams with different grid cell areas were prepared using a pin-guided dry weaving process. Low velocity impact test on different locations (rib, node, and bay) was conducted with varying hammer weight and impact velocities by an instrumented impact testing machine. Ultrasonic C-scan was utilized before and after impact to identify the damage induced by impact. Scanning Electron Microscopy observation was also implemented to visualize the impact damage at micro- length scale. Compressions after impact (CAI) tests per an anti-buckling test fixture were conducted to evaluate the residual strength and stiffness of the impact damaged sandwich plate specimens. In order to validate the experimental results, Finite Element Analysis was conducted on unimpacted specimens of different Groups. Parametric study was also conducted to study how different parameters affect the strength of the iso-grid stiffened sandwich structures. The test results show that the novel sandwich structure has a higher capacity to transfer impact energy elastically. It leads the sandwich plate towards quasi-static impact response. The propagation energy, the energy absorbed for damage creation and propagation, is reduced. The damage is more localized and confined to the bay directly under impact or adjacent bays. It is found that the bay area is one of the most important design parameters for the iso-grid pattern investigated. The residual strength and residual modulus of iso-grid structures is found to be higher than that of laminates. Impact damage on iso-grid structures is confined to a smaller area when compared to laminates.
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Chakka, Venkata Sandeep, "Quasi-Static and Impact Characterization of Sandwich Structures with an Iso-Grid Stiffened Syntactic Foam Core" (2008). LSU Master's Theses. 3424.