Multiscale Modeling of Light Activated Shape Memory Polymer

Presented is the development of a multi-scale model predicting the material response of a light activated shape memory polymer. Rotational Isomeric State (RIS) theory is used to build a molecular scale model of the polymer chain backbone, tracking the distances between cross-links. Cross-link to cross-link distances are then used with Boltzmann statistical mechanics to predict material response, generating Young’s modulus and stress-strain relation predictions. Young’s modulus is predicted by the model to be 0.049 and 3.2 MPa for the soft and hard states of the polymer respectively. Experimentally determined properties are also presented with reported moduli of 2.0 and 11.4 MPa in the soft and hard states respectively.

Broadband Vibration Suppression Assessment of Negative Impedance Shunts

Piezoelectric materials allow for the manipulation of stiffness and damping properties of host structures by the application of electrical shunting networks. The use of piezoelectric patches for broadband control of vibration using a negative impedance shunt has been shown to be an effective active control solution. The wave-tuning and minimization of reactive input power shunt selection methodologies require the use a negative capacitance. This paper shows that the two theories are comparative and obtain the same shunt parameters. The results of the theoretical shunt selection and simulation are compared to experimental results of tip vibration suppression, spatial average vibration, and reactive input power minimization.

Analysis of Clustering and Interphase Region Effects on the Electrical Conductivity of Carbon Nanotube-Polymer Nanocomposites via Computational Micromechanics

In the present work, computational micromechanics techniques are applied towards predicting the effective electrical conductivities of polymer nanocomposites containing aligned bundles of SWCNTs at wide range of volume fractions. Periodic arrangements of well-dispersed and clustered/bundled SWCNTs are studied using the commercially available finite element software COMSOL Multiphysics 3.4. The volume averaged electric field and electric flux obtained are used to calculate the effective electrical conductivity of nanocomposites in both cases, therefore indicating the influence of clustering on the effective electrical conductivity. In addition, the influence of the presence of an interphase region on the effective electrical conductivity is considered in a parametric study in terms of both interphase thickness and conductivity for both the well dispersed case and for the clustered arrangements. Comparing the well-dispersed case with an interphase layer to the same arrangement without the interphase layer allows for the assessment of the influence of the interphase layer on the effective electrical conductivities, while similar comparisons for the clustered arrangements yield information about the combined effects of clustering and interphase regions. Initial results indicate that there is very little influence of the interphase layer on the effective conductivity prior to what is identified as the interphase percolation concentration, and that there is an appreciable combined effect of clustering in the presence of interphase regions which leads to increases in conductivity larger than the sum of the two effects independently.

Measurement of the Thermal Expansion for Space Structures Using Fiber Bragg Grating Sensors and Displacement Measuring Interferometers

Dimensional stability of the space structures, such as large telescope mirrors or metering substructures, is very important because even extremely small deformations of these structures might degrade the optical performances. Therefore, precise deformation data of the space structures according to environment change are required to design these structures correctly. Also, real-time deformation monitoring of these structures in space environment is demanded to verify whether these structures are properly designed or manufactured. FBG (fiber Bragg grating) sensors are applicable to real time monitoring of the space structure because they can be embedded onto the structures with minimal weight penalty. In this research, therefore, thermal deformation measurement system for the space structures, composed of FBG sensors for real time strain measurement and DMI (displacement measuring interferometers) for accurate specimen expansion data acquisition, is developed. Thermal strains measured by distributed FBG sensors are evaluated by the comparison with the strains obtained by highly accurate DMI.

Testing and Simulation of Stress-Stiffening Extreme Poisson’s Ratio Twisted Fiber-Reinforced Elastomer Composites

Laminates that exhibit high and negative Poisson’s ratios can be used as solid-state actuators, passive and active vibration dampers, and for morphing aircraft structures. Recently, fiber-reinforced elastomer (FRE) laminates have been fabricated that exhibit extreme (high and negative) Poisson’s ratios [1]. The current research explores twisted fiber bundle elastomeric laminates (both single and double helix) which are being investigated using experimentation, linear and non-linear finite element analysis (FEA). Twisted fiber bundles can be made from carbon fibers, fiberglass, etc, but for simplicity the current work uses twisted cotton string. It is observed that uniaxial fiber-reinforced elastomer laminates, where the fibers are twisted as shown in Figure 1, exhibit stress stiffening. Negative Poisson’s ratios may be produced if the fiber bundles have a double helical path as simulated by a series of laminated tubes. Future auxetic FRE laminates may be developed that do experience extreme shear.

Energy Harvesting From Pneumatic Tires Using Piezoelectric Transducers

The concept of harvesting energy in our surrounding has recently drawn global attention. Harvesting the ambient energy of the deflected tire and convert it to electricity is discussed in this paper. An Elastic pneumatic tire deflects due to the load it carries. This deflection appears as a contact patch to the road surface. Initially, the concept of the tire deflection will be discussed. This deflection is then related to the wasted energy used for deflection. The dependency of this energy to some important parameters such as the tire air pressure, vehicle speed and tire geometry and forces are primarily discussed. To harvest the deflection energy different well established methods are exists. Due to the tire environment, piezoelectric transducers can serve as the best option. Those transducers are traditionally used to produce mechanical motion due to the applied electrical charges. This material is also capable of generating electrical charges by mechanical motion and deflections. For the tire energy harvesting application, the piezoelectric stacks can be mounted inside a tire structure such that electric charge is generated therein as the wheel assembly moves along a ground surface. For this application, lead-zirconate-titanate (PZT) is selected. The PZT inside the tire is modeled as a cantilever beam vibration in its first mode of vibration. The frequency of vibration is calculated based on the car speed, tire size, and PZT stack length. A mathematical model for this energy harvesting application is derived. Based on this model, the optimum load of the electrical circuit is also found. Finally the amount of energy harvested from tire using PZT is calculated. Although this energy is not significantly high, it will be enough to provide power for wireless sensors applications.

Surface Segregation of Sulfur and Its Effect on Surface-Energy-Induced Selective Grain Growth in Magnetostrictive Fe-Ga-B Alloy

The surface-energy-induced selective grain growth with a specific plane can be governed in polycrystalline Fe-Ga-B alloys doped with sulfur. The segregated sulfur during texture annealing played an important role in controlling the surface energy to induce the selective growth of {100} or {110} grains, corresponding to maximum magnetostrictive performance, along <001> orientation with respect to rolling direction. The results show that sulfur diffuses (adsorbs) from bulk interior (sulfur atmosphere) then segregates on the surface. The amount of segregated sulfur increases with an increase of annealing time at the temperature of 1200°C. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) data on the surface as well as selective development of {100}<001> and {110}<001> preferred textures are presented in this work. The XPS fitted peaks of S 2p3/2 at binding energy of 161.2 and 163.2 eV for annealed Fe-Ga-B doped with sulfur represent the presence of stoichiometric FeS and FeSn (polysulfide), respectively. For all of the sulfur-free Fe-Ga-B sheets annealed in the ampoule with sulfur element, XPS indicated contributions centered at approximately 161.7 (S 2p) that has been assigned to iron sulfide as well. The presence of FeS was clearly confirmed by XRD patterns and XPS fitted peak positions at 161.5 eV (S 2p3/2) and 710.2 eV (Fe 2p3/2). The segregation of sulfur and boron during annealing were also confirmed by AES depth profile results, which exhibited peak concentrations of 10 at.%S and 20 at.%B at the surface, respectively. The peak magnetostriction of 201 ppm was obtained at annealed (Fe81.3Ga18.7)99B1 alloy with near {100}<001> orientation under sulfur atmosphere containing the amounts of 6.4 mg S. On the other hand, the texture of sulfur-free Fe-Ga-B alloy was close to {110}<001> after annealing at 1200°C for 6h under flowing argon, corresponding to the magnetostriction of 160 ppm.

A Modified Micromechanical Model of Ionic Polymer-Metal Composite Actuation

Recent ionic polymer-metal composite (IPMC) research efforts have been directed at developing optimized electrode configurations, using novel solvents and cations, and modeling the actuation response. A micromechanical model of IPMC actuation has been developed by Nemat-Nasser [1]. In this work a similar approach is taken to model the electrochemomechanical transduction mechanisms in IPMC’s, specifically IPMC’s with ionic liquid as the solvent. An analysis of the electrostatic interactions, which are dominant in determining actuation response, is conducted in order to gain further insight into the mechanisms behind actuation. The ultimate goal of this research is to model the underlying mechanisms of IPMC actuation in order to direct the development of new transducers consisting of novel polymers and solvents. Changes to the actuation model are also implemented to describe free air actuation and to account for the finite volume of the mobile cations. Results are presented from the different calculations and the implications are discussed.

Active Vibration Control and Isolation for Micro-Machined Devices

Some harsh environments contain high frequency, high amplitude mechanical vibrations. Unfortunately some very useful components, such as MEMS gyroscopes, can be very sensitive to these high frequency mechanical vibrations. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. However, the performance of these filter structures is typically limited by low damping. This is especially true if operated in low pressure environments, which is often the optimal operating environment for the attached device that requires vibration isolation. An active micromachined vibration isolator can be realized by combining a state sensor, and electrostatic actuator and feedback electronics with the passive isolator. Using this approach, a prototype active micromachined vibration isolator is realized and used to decrease the filter Q from approximately 135 to approximately 60, when evaluated in a low pressure environment. The physical size of these active isolators is suitable for use in or as packaging for sensitive electronic and MEMS devices, such as MEMS vibratory gyros.

Fully Reversed Electric Fatigue Behavior of a Piezoelectric Composite Actuator

The aim of this study is to investigate fully reversed electric fatigue behavior of a piezoelectric composite actuator (PCA). For that purpose, fatigue tests with different loading conditions have been conducted and the performance degradation has been monitored. During a preset number of loading cycles, non-destructive acoustic emission (AE) tests were used for monitoring the damage evolution in real time. The displacement-cycle curves were obtained in fully reversed cyclic bending loading. The microstructures and fracture surfaces of PCA were examined to reveal their fatigue damage mechanism. The results indicated that the AE technique was applicable to fatigue damage assessment in the piezoelectric composite actuator. It was shown that the initial damage mechanism of PCAs under fully reversed electric cyclic loading originated from the transgranular fracture in the PZT ceramic layer; with increasing cycles, local intergranular cracking initiated and the either developed onto the surface of the PZT ceramic layer or propagated into the internal layer, which were some different depending on the drive frequencies and the lay-up sequence of the PCA.