Investigation of load bearing and shape morphing capacities of lattice materials

Lattice materials are cellular solids with periodically repeating unit cells. They offer unique solutions to vibration isolation, morphing structures and many other engineering applications because of their lightweight structure. In this study which focuses on load bearing and shape morphing capacities of lattice materials, two different application fields are investigated. First application field is investigation of the lattice material faults on the actuation performance and the second one is usage of lattice structures on Capacitive Micromachined Ultrasonic Transducer (CMUT) devices. In the lattice fault investigation chapter, lattice structures large enough to neglect boundary condition effects are taken into consideration. Kagome structure, which proves its effectiveness in actuation application is investigated with two of its variants namely Dual Kagome and Kagome Triangular lattice, with an actuator in the middle of the structure, taking attenuation distance and actuation energy as actuation performance criterion. Effects of single fault on defined locations on the actuation corridor and multiple faults randomly distributed over defined areas on the structure are investigated in terms of actuation performance and general stiffness of the structure. Fractured cell wall, missing cell, cell wall waviness, cell wall misalignment and non-uniform wall thickness faults which are commonly encountered in lattice manufacturing are studied. As a result of this study, in case when there is a fault on the actuation corridor, the fault stops the motion if its closer than the attenuation distance of the perfect structure, otherwise it carries the actuation motion forward. In case of randomly distributed faults over the structure, effectiveness of different types of faults are the same for different lattice types. The most important effect comes with fractured cell wall fault, followed by missing cells and cell wall waviness. Cell wall misalignment has its own random behavior due to tis random parameters but its less effective. Non uniform wall thickness has the least significant effect. Order of effectiveness for different types of faults is related how faults reduce the overall connectivity of the lattice structure. Fractured cell wall, which reduces the overall connectivity of the lattice structure the most has the largest effect while non-uniform wall thickness which noes not change the connectivity has an insignificant effect. CMUT device is an electro-acoustic energy transducer which vibrates due to capacitive forces as a result of applied electric field and interacts with the surrounding acoustic medium due to its vibration. In this device an encastered plate with vacuum on one side is vibrated at its natural frequency and waves are generated on the acoustic medium on the other side of the plate. Nonlinear effects due to motion of the encastered plate are generated and become apparent with increased motion, yet the device is desired to be operated at the linear regime. In this study it is shown that designs having the same natural frequency with the solid plate with 3 times larger linear working regime and reduced mechanical impedance are possible thanks to negative Poisson's ratio lattice stiffener structures applied to the CMUT plate. Thanks to this study despite solid plate designs, plate motion is increased in the linear regime with smaller forces without altering the dynamic behavior, allowing groundbreaking CMUT device designs to be made.