This project will focus on the fabrication and testing of composite sandwich structures for marine and hydrokinetic (MHK) turbine rotor blades. MHK rotor blades need to be carefully designed to survive in the harsh environments associated with producing power from ocean currents. These blades convert the kinetic energy contained in ocean currents into mechanical torque, which can then be converted to electric power. Although the rotation (rpm) of the blade is slow, blades have to carry a large torque to produce a reasonable amount of power. During operation, these blades withstand large hydrodynamic loads which are random and also cyclic in nature. This give rise to cumulative fatigue loading in addition to regular rotation of the blade. Life assessment under such loading is key to the design of the blade. On the top of this complex loading scenario, turbine blades need to be neutrally buoyant and resist hydrostatic pressure if submerged, and also survive for a prolonged period of time under salt and marine environment. A composite structure is ideal for such applications.
The idea in this project is to try out a composite sandwich construction for blade materials. The sandwich will be made of polyurethane foam core with face-sheets of E-glass/Vinyl ester composites. Several test coupons of this material will be fabricated using a VARTM (Vacuum Assisted Resin Transfer Molding) process. Sandwich test specimens will then be subjected to static and fatigue tests. Both static and fatigue tests will be conducted under a 4-point bend configuration. Since foam core is very weak in shear, the goal of these tests will be to subject the specimens to core shear failure. Fatigue tests will be run under displacement control, at a stress ratio (R) of 0.1, and a frequency of 5 Hz. Once static and fatigue tests are complete, load-displacement and S-N curves will be generated. In addition, Weibull statistical analysis of both static and fatigue data will be performed to assess dispersion and reliability. If time permits, fractured specimens will be examined under a microscope to determine modes of failures.