Shape memory alloys (SMA) have the unique ability to recover large strains and generate large recovery stresses via a repeatable martensitic transformation. Stress-strain and shape memory effect characteristics are needed in order to develop SMA force actuator design methods. Moreover, constitutive models able to quantitatively predict these characteristics and thus be useful as engineering design tools are also needed. An experimental apparatus designed to characterize the mechanical behavior of SMA was built and utilized. The apparatus is used specifically to gather stress-strain and shape memory effect characteristics from nitinol wire whereby mechanical properties associated with the material are determined. Phenomena such as the R-phase and stress induced martensite serration are investigated. A one-dimensional constitutive model is presented that quantitatively predicts stress-strain and shape memory effect behavior and was developed with the intention of being an engineering design tool for SMA force actuators. Experimental stress-strain and shape memory effect results are compared against that predicted by the model with the intention of verifying the model. The model displays the ability to predict stress-strain behavior that is in good quantitative agreement with experiment. The model also displays the ability to predict hysteric shape memory effect behavior for free, controlled, and restrained recovery cases of selected prestrains that is in good quantitative agreement with experiment. The model is unable to predict shape memory effect behavior such as the R-phase. Demonstrating the ability to experimentally investigate a constitutive model will hopefully inspire further combined experimental and theoretical SMA research. / Master of Science

Acid/base modifiers are sometimes used as additives in the elution on columns packed with amylose tris(3,5-dimethylphenylcarbamate) stationary phase to separate enantiomers. When modifiers are removed from the mobile phase, the stationary phase is affected in ways that are not understood because of the lack of systematic studies, making the scale-up of preparative separations difficult to predict. Once a column has been exposed to these modifiers, the selectivity of certain pairs of enantiomers may change, for the better or the worse. Numerous pairs of molecules affected by this phenomenon are listed in the literature. Five pairs of these molecules were chosen, the selectivity of which changes after an acidic or basic solutions has been percolated through the column. The selectivity of the ketoprofen, 4-chlorophenylalanine methyl and ethyl esters improves after a solution of ethanesulfonic acid is percolated through the column. The selectivity of the propranolol HCl and Troger’s base increases after a solution of diiospropylethylamine is percolated through the column. The selectivity of these the 4-chlorophenylalanine ethyl ester, propranolol and Troger's base enantiomers are inversely affected by percolation of the opposite acid/base solution. This residual change in certain enantiomeric separations has been named the Memory Effect. In contrast, trans-stilbene oxide (TSO) was used as a standard to determine the column's stability because no Memory Effect is observed for this separation (the retention, enantioselectivity, and resolution remain constant). Karl Fischer titrations showed that only slight changes in the mobile phase's water content occurred, and that the water to polymer repeat unit ratio is important. Analytical studies of the stationary phase suggest that slow protonation/deprotonation of water bounded to the carbamate moiety may be responsible for the Memory Effect. It has been shown that the Memory Effect can be minimized by percolating through the column a sufficiently concentrated solution of the appropriate acid or base. Thus, columns that were unreliable for method development, due to the Memory Effect, can now be used. As a result, the scale-up of separations can be predicted and successfully performed. Finally, a test was devised to determine if a column was under the influence of the Memory Effect.

Burrs severely inhibit the performance and aesthetics in machined parts besides posing a safety risk to the user and manufacturer. Abrasive assisted brushing presents a fast and effective method for deburring these parts but is difficult to control. The dependence of deburring rate on the workpiece material, abrasive grit size, type and rotational speed of the brush is studied. It is found that deburring rate is proportional to initial burr height indicating fracture of the burr at the root. Deburring rate increases with spindle speed and is higher for diamond than SiC. The formation of burrs in micromilling of a thin nickel-titanium alloy (nitinol or NiTi) foil used in implantable biomedical device applications is analyzed as a function of micromilling process parameters such as spindle speed, feed, tool wear, backing material and adhesive used to attach the foil to the backing material. All factors except spindle speed are found to affect burr size. If initial penetration is sufficient to cause the foil to fail in tension, the foil tears with the crack starting closer to the upmilling side and thereby resulting in larger downmilling burrs. If penetration is insufficient, the foil plastically deforms until it tears typically in the middle of the cutter tooth path. A kinematic model that captures this behavior is used to predict burr widths and is verified through experiments. The thesis also presents an investigation of the abrasive impregnated brush deburring process for thin NiTi foils. Models based on Hertzian indentation and fracture mechanics are proposed to predict the rates of indentation and deburring during brushing and are validated using experiments. The predictions of the models are within the experimental variation. Burrs can be removed with this process within 12 minutes for a 6 mm long groove with no more than a micron change in foil thickness. Knowledge of burr formation and deburring is applied to a novel micromilled thin shape memory based NiTi foil device used for the surgical correction of Age-related Macular Degeneration (AMD), a leading cause of blindness in the western world in those over age 50. Burrs on the surface of the structure are used successfully to mechanically constrain and translocate an autograft to replace the diseased RPE-Bruch's membrane under the macula. The shape memory device is analyzed using experiments and simulations.

Ni50.6Ti49.4 single and Ni52Ti48 polycrystalline shape memory alloy samples were subjected to aging under a uniaxial stress, to form a single Ni4Ti3 precipitate variant and to investigate the effects of single versus multi-variant coherent precipitates on the shape memory characteristics including two-way shape memory effect (TWSME). Shape memory and superelasticity properties along with the effects of stress and temperature on the transformation temperatures, strain, hysteresis, dimensional stability, and R-phase formation were investigated. This was accomplished through the use of isobaric thermal cycling and superelasticity experiments and various microscopy techniques that included transmission electron microscopy (TEM), scanning electron microscopy, and optical microcopy. The results showed that it is feasible to use constrained aging to bias R-phase martensite variants upon cooling from austenite without any external stress, however, accomplishing this with B19’martensite was much harder as complete TWSME was only found in the Ni50.6Ti49.4 single crystalline sample oriented along the [112] direction. The onset of irrecoverable strain corresponded to the R-phase temperature hysteresis increase in the single crystalline samples regardless of the aging conditions. Through TEM analysis it was discovered that [112] and [114] twins were found in austenite due to plastic deformation of martensite during the superelasticity experiments. Since [112] twins are theoretically impossible to form in austenite, and since martensite was plastically deformed, [112] austenite twins were attributed to the transformation of compound twins in martensite, in particular [113] martensite twins formed during the plastic deformation of martensite, into austenite twins. In the Ni52Ti48 polycrystalline samples, a compressive R-phase variant was biased through constrained aging under 100 and 200 MPa uniaxial tensile stresses at 400°C and 450°C. Aging, in all conditions, produced a high density of Ni4Ti3 precipitates that was most likely responsible for the small transformation strain observed, less that 2%, upon transformation to martensite. In the future, samples with compositions between 50.8 and 51.5 Ni atomic percent, in addition to altered solution and aging heat treatments as compared to those used in this study should be investigated as it is believed that samples with these compositions will yield better and consistent TWSME responses through constrained aging.

none

Thesis (Ph.D.)--City University of Hong Kong, 2009. / "Submitted to Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [214]-224)

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references.

This master’s thesis deals with integrating simulations using Agilents Electronic Design Automation tool ADS with customized Matlab scripts, for solving complex analog and digital radio architectures. In particular, it addresses predistortion, realized in the digital domain, of power amplifiers, modeled in the analog domain. The former is implemented in Matlab while the latter is implemented in ADS. Two versions of integrating the two systems have been tested: 1) Iterative approach on sample basis and 2) Scheduled batch solution by matrix inversion. The concept has been tested on two different PA configurations: 1) a standard class-AB PA and 2) a Doherty PA architecture. Evaluation has also been done on ADS ability to correctly simulate memory effects in PAs and on the actual DPD-algorithms ability to compensate for these memory effects.  An integrated simulation environment for ADS and Matlab was successfully established within the work of this thesis. Matlab scripts, used in predistortion algorithms in the digital domain, could interact directly with component-based PA models, in an enclosed simulation system.  The simulation results show that sample basis method is the most accurate, fast and reliable method to linearize a PA. The PA1 proved to be easier than the DPA to linearize, except for when being close to saturation where better IMD-suppression was achieved with the DPA.  ADS is clearly able to simulate memory effects in the analog domain. At low gain-levels the applied compensating memory-algorithms showed a great improvement to the linearization of the output signal of the PA. At higher gain-levels though, the compensation for memory effects lost their efficiency because the non-linearity of the PA became too significant.

New materials always have the possibility of revolutionizing manufacturing processes and the way we live. Bronze, steel alloys, vulcanized rubber, ceramics, and fiber optic cables are just of few of the materials man has discovered which improved his quality of life. One of the more recent additions to the field of material science are materials that exhibit what is known as the shape memory effect. Both metals and synthetic polymers can acquire this property through processing and chemistry. However while shape memory polymers hold a lot of promise, it will require more research and development to make them affordable and useful in large scale applications. / text

Not available / text