Bistable fiber composite laminates have promising capabilities for shape morphing and have found applications in advanced airframes, energy harvesting, and robotics. Their bistability originates from an asymmetric ply layout and can create highly complex deformations during the snap-through from one stable state to the other. There- fore, it is essential to understand the transient behaviors of these laminates under different loading conditions. Although simple symmetric loading conditions are well understood, asymmetric loading conditions received far less attention. In this study, we investigate the transient deformation of a [0°/90°] square laminate subjected to an asymmetric point load at different locations. Finite element simulation and experimental testing both show that, depending on the loading position, snap-through can either be a one-step or two-step process, while each step is related to the curvature change of a laminate edge. Also, at some loading positions, snap-through is unattainable regardless of the input magnitude. The results of this study would help us obtain a more comprehensive understanding of the nonlinear mechanics of bistable composite laminates showing transient response to different external forces.
This research investigates the methods of fabrication for non-traditional, non-rectangular bistable structures using Carbon Fiber Reinforced Polymers. Currently, the non-rectangular shapes that have been used are rhombi (diamonds), triangles, and circles. Each shape is cut from a 12x12 inch sheet of composite laminate. The shape, when cut, must maintain a 12-inch dimension in one aspect of height, diameter, or length. As these shapes are fabricated and postprocessed, it is observed that the boundary conditions, performance, curvature and options for fixturing vary significantly. It has also been observed that much of the remaining material from post-processing cutting methods also retain much of its disability, allowing for usage in alternative capacities.
Energy Harvesting is a powerful process that deals with exploring different possible ways of converting energy dispersed in the environment into more useful form of energy, essentially electrical energy. Piezoelectric materials are known for their ability of transferring mechanical energy into electrical energy or vice versa. Our work takes advantage of piezoelectric material’s properties to covert thermal energy into electrical energy in an oscillating heat pipe. Specific interest in an oscillating heat pipe has relevance to energy harvesting for low power generation suitable for remote electronics operation as well as low-power heat reclamation for electronic packaging. The aim of this paper is develop a 2D multi-physics design analysis model that aids in predicting electrical power generation inherent to an oscillating heat pipe. The experimental design shows a piezoelectric patch with fixed configuration, attached inside an oscillating heat pipe and its behavior when subjected to the oscillating fluid pressure was observed. Numerical analysis of the model depicting the similar behavior was done using a multiphysics FEA software. The numerical model consists of a threeway physics interaction that takes into account fluid flow, solid mechanics, and electrical response of the harvester circuit.
Selection of airfoil for better design of aerodynamic and aerodynamic performance is very important such as aircraft and wind turbine. Also, a number of military and civilian applications required efficient operation of airfoils in low Reynolds number, particularly for micro aerial vehicles. This work simulates a classical flow pattern (Von Karman street) that can form as fluid flows past a flapping NACA0012 airfoil, and S1223 airfoil at low Reynolds number. These two airfoils has been selected and investigated in computational analysis by using basic computational fluid dynamics and fluid-structure interaction modules. The S1223 airfoil, designed by University of Illinois at Urbana was selected for its high lift characteristics at low Reynolds number and the NACA0012 was chosen to check the lift at low Reynolds number. Velocity distributions are analyzed at different angles of attack for both airfoils. The results obtained from simulation have compared between the two airfoils. The magnitude and the frequencies of the oscillation generated by the fluid around the airfoils are computed and compared between the airfoils.
Devices with increased sensitivities are needed for various applications including the detection of chemical and biological agents. This paper presents the design of microelectromechanical systems (MEMS) devices that incorporate lead zirconate titanate (PZT) films in order to realize highly sensitive sensors. In this work, the piezoelectric properties of the PZT are exploited to produce sensors that perform optimally for mass sensing applications. The sensor is designed to operate as a thin-film bulk acoustic resonator (TFBAR) whereas a piezoelectric is sandwiched between electrodes and senses a change in mass by measuring a change in resonance frequency. Modeling of the TFBAR sensor, using finite element analysis software COMSOL, was performed to examine optimal device design parameters and is presented in this paper. The effect of the PZT thickness on device resonance is also presented. The piezoelectric properties of the PZT is based on its crystal structure, therefore, optimization of the PZT film growth parameters is also described in this work. A detailed description of the fabrication process flow developed based on the optimization of the device design and film growth is also given. The TFBAR sensor consists of 150 nm of PZT, 150nm of silicon dioxide, silicon substrate, titanium/platinum bottom electrodes, and aluminum top electrodes. The top electrodes are segmented to increase the sensitivity of the sensor. The resonance frequency of the device is 3.2 GHz.
The properties of highly magnetostictive materials, such as Terfenol-D, have opened the door to a wide variety of application possibilities. One such developing application is embedding magnetostictive particles (MSP) as sensors for determining the structural integrity of composite materials over the course of the operating life. The process of embedding these particles during the fabrication of the composite structure presents many challenges. This paper will briefly discuss and show the relationship between particle density and the output of a uni-axial induction based sensor. This relationship is critical for defining the goal of embedding process in this paper, to create a uniform uni-axial distribution of particles within the composite structure. Multiple methods of embedding magnetostrictive particles into a composite structure are detailed and then compared to determine their relative effectiveness. Methods included are: a simple by-hand spread of particles onto uncured prepreg composite, using the controlled adhesiveness of the prepreg to separate particles, applying the particles using a unidirectional application tool, introducing the particles into the epoxy mix to create a slurry during a VARTM layup, and spraying the particles onto a tacky composite surface during layup. Each method is used to embed particles into a composite beam or analog beam. That beam is then scanned with the uniaxial induction sensor to determine the effectiveness of the method. Results show promise for the adhesive method while the remaining processes show critical flaws.
This paper examines the mechanics of delamination, ply variation, and the fabrication on the sensing ability for magnetostrictive particles embedded in a carbon fiber reinforced polymer laminate. An analytical method is used to determine how delamination and ply variation affect the mechanical state and magnetic properties of the embedded terfenol-d particles. Numerical models are also used to simulate the effect of delamination and ply variation on the mechanical state. For the analytical method, the mechanical properties observed are the net strain and stress in a local particle section resulting from magnetostriction. A one dimensional load line equation and material property data are used to obtain approximate solutions. The magnitudes of the stress and magnetostriction drop in the laminates are observed. Based on the local mechanical and magnetic state, the magnetic permeability can be selected from experimental data. The analytical method reveals that the effect of a delamination is to reduce the resistance to particle actuation in a local area, which allows for variation in stress and magnetostriction magnitudes in damaged areas vs. nondamaged areas. This variation in the mechanical state subsequently affects the magnetic permeability, which changes the reluctance in the local particle layer. These results are compared to a numerical model of terfenol-d embedded in carbon fiber reinforced polymer laminate, which reveal a drop in stress and increase in magnetostriction in the delamination region. Finally, these results are projected to experimental results from health monitoring scans of carbon fiber reinforced polymer laminates with varied ply count and a delamination.
This paper details an experiment using MSP, embedded into the matrix of carbon fiber beams, to locate predetermined
damage in each sample. The fabrication process of the composite samples and the development of the data acquisition
system used for this experiment are heavily detailed, including our method of implementing a live data feed with
variable "snapshot" recording. Also included are preliminary results from the experiment. These preliminary results
suggest credible flaws and lead to improvements in the fabrication process. This work identifies potential obstacles
when fabricating composites embedded with MSP and proposes possible solutions.