Active damage control is a new technique which mimics the self-repairing capability of biological beings and can be used to greatly increase the structural integrity and fatigue life. This thesis describes two approaches used in active damage control: direct stress cancellation and indirect stress cancellation. Direct stress cancellation is illustrated using an example of active crack damage control with embedded shape memory alloy actuators. Both experimental and theoretical investigations have been conducted to analyze the damage control mechanism. The approach of indirect stress cancellation is demonstrated with active fatigue damage control of adhesive joints. The damage and active control mechanisms of the adhesive joints have been experimentally and theoretically investigated. / Master of Science

Polyrotaxanes are new polymers. Macrocyclic molecules, such as crown ethers, are threaded by linear or branched polymer chains. There is no covalent bond between the crown ethers and the polymer backbone. After the crown ethers are threaded onto the polymer backbone, both ends of the polymer can be blocked by large end groups. Polyrotaxanes are the topological isomers of blends of crown ethers and polymers. This architectural modification will produce interesting chemical and physical property changes in the polymer such as T_g and T_m, solubility, tensile strength, flexibility of the polymer. The study include crown ethers, blocking groups, poly(azomethine)s A and B, poly(azomethine)rotaxanes A and B synthesis, characterization, and property research. Crown ethers, 21-crown-7, 30-crown-10, 42-crown-14, and 60-crown-20, were synthesized from oligo(ethylene glycol)s and oligo(ethylene glycol) ditosylates with 22-40% yield. The high temperature synthetic method was developed so that the percentage yield of large crown and the small crowns in the same reaction could be controlled. A new purification method, low temperature recrystallization method was developed. The crown ethers properties included melting points, decomposition temperature, chemical shift on NMR spectra were studied. A series of blocking groups were synthesized and characterized. Several synthetic routes were studied, and the best route was the Grignard synthesis. The purification method was improved by recrystallization in cyclohexane or carbon tetrachloride. A by-product, bis(p-t-butylphenyl)methanol, was obtained. The new compounds, p-tri(p-t-butylphenyl)methylaniline and p-tri{(p-t-butylphenyl)methylphenol, were identified by ¹H NMR, FTIR, and elemental analysis. Poly(azomethine)s A and B are liquid crystalline polymers. They are rigid and strong. They have high T_m's and do not dissolve in general solvents. To check the reported information, the synthesis and characterization of these polymers were repeated. They precipitated from the reaction solution when their degree of polymerization reached 3-5. They were not thermally stable and were easily hydrolyzed in strong acids and in GPC column. In order to establish the effectiveness of the blocking groups, a monomeric rotaxane, a di(azomethine)rotaxane, was designed and synthesized. The compound was successfully isolated by multiple reprecipitations and recrystallizations. A 12% yield of this compound was obtained. The largest crown ether that the blocking group could block was 42-crown-14. / Master of Science

Reciprocity in friendship has been identified as necessary to developmental stages of friendship formation in children and adolescents. Studies of young adults and older adults in reciprocal friendships have focused on gender differences, communication, and social satisfaction, including social supports. There has been little research on the role of reciprocity in same-sex close friendships of middle aged women. Eighteen interviews of women ages 40 to 56 years were qualitatively analyzed to explore the importance of reciprocity and how it is expressed in middle aged same-sex close friendships. The Jones and Vaughan (1990) categories of self-disclosure, emotional support, tangible assistance, and social initiatives were used as a starting point for coding the interview responses. Shared values, acceptance and trust, feedback, and similarity/mutuality over time were additional themes that emerged from the data. The women in this study expected reciprocity from close friends. Tangible assistance and social initiatives did not seem to be important whereas shared values and self-disclosure were the foundations of their friendships. However, there were contradictions and reservations about sharing problems and successes. Self-disclosure, feedback, emotional support, and acceptance and trust were found to be interrelated and reciprocal. Two different levels of listening emerged from the data. The first level was expressed as listening when a close friend self-disclosed with the expectation of being "heard" and "accepted." The second level was expressed as listening when a close friend shared with the expectation of providing feedback. Acceptance and trust emerged as being reciprocally related, while similarity and mutuality emerged as being developmental over time. A relationship between feedback and self-esteem also became evident. The middle aged participants valued reciprocity in their friendships and expressed it with complexity and richness that was multi-dimensional. / Master of Science

Pallet repair and reinforcement with metal connector plates (MCPs) may reduce wood waste while providing pallet users with quality, economical pallets. The study objectives were to evaluate the effect of MCP repair and reinforcement on pallet performance, and to evaluate preliminary standards for repair and reinforcement of pallets with MCPs. Whole pallets and pallet components were tested. Stringers and notched segments were tested in static bending, while end feet were tested for resistance to fork tine impact. Whole pallets were evaluated with a test protocol that simulated the effects of long-term handling. Stringers, repaired at notch corners, had greater strength, but less stiffness than the original stringers. Notch reinforcement with MCPs resulted in stringers with greater strength and stiffness than equivalent unreinforced stringers. No consistent species-width effect was found for strength of plated stringers. MCP-repair of above-notch failures did not restore the original strength or stiffness of notched segments. However, these repairs may be satisfactory since above-notch failures are secondary in frequency of occurrence. No differences were found between performance of plates used to repair stringers and notched segments. Both repaired and reinforced end feet had greater impact resistance than the equivalent original or unreinforced end feet. Wood species, rather than stringer width, had a greater influence on MCP performance. In general, tests of whole pallets supported the results from component tests which suggests that component testing may be a practical means of assessing the effect of repair and reinforcement techniques on pallet performance. / Master of Science

Active control is applied to reduce noise emission from a vibrating elastic cylinder by exerting forces on the cylinder that cancel the noise-generating vibration. This technique is called Active Structural Acoustic Control (ASAC) (Fuller, 1987). Sensors are implemented using piezoelectric film, and actuators are implemented using piezoceramic material. Both analog and digital noise cancellation control algorithms are used to reduce the noise emission from the cylinder. Two-cylinder boundary conditions are taken as case studies. The first boundary condition is the open cylinder case. The second boundary condition is where the cylinder has an end plate bolted to each end. Actuator placement and the sensor design are done by first obtaining the natural frequencies and mode shapes of the cylinder using both analytical and experimental methods. Modal sensors developed and tested in previous work (Lee, 1989) are applied. After preliminary control experiments with analog feedback loop show that control can be done with the sensors and the actuators, digital signal processing hardware programmed with the filtered-x Least-Mean-Square adaptive control algorithm is used to control the vibration of the cylinder. The excitation is single-tone on-resonance. Acoustic - testing demonstrates that ASAC reduces the sound pressure level generated by the vibrating cylinder by up to 29 dB in the reverberant field. Vibration measurement reveals that the reduction in sound emission from the cylinder is a result of reduction in vibration. The adaptive controller reduces the vibration level by up to 68 dB. / Master of Science

In a survey of parents, professionals, and college students in Northern Virginia, 123 adults indicated they had experienced child sexual abuse. Their responses were examined in an effort to identify characteristics of child sexual abuse which might be related to long term negative effects. The variables examined include (a) incestuous verses non-family abuse, (b) victim's reported feelings of responsibility about the sexual abuse, (c) victim's reported feelings of guilt about the sexual abuse, (d) the duration of the sexual abuse, (e) the age of the victim at time of the sexual abuse, and (f) whether or not the sexual abuse was kept secret. Only one of the six variables was found to be significantly related to long term negative effects. The research found evidence that keeping the child sexual abuse experience/s secret may be positively related to long term negative effects of child sexual abuse. Of the 83 participants who reported that the sexual abuse had remained a secret, 58 also reported long term negative effects. The importance of creating a safe and secure atmosphere in which children are able to disclose incidents of child sexual abuse is emphasized by the findings of this research. / Master of Science

Non-stationary motion of a cracked rotating shaft with accelerating or decelerating angular velocity Ω through a critical speed is studied. The shaft has a breathing transverse crack and a disk. There are two parts, which are the investigation of flexural response, neglecting the torsional vibrations, and the investigation of flexural-torsional response. In both studies the longitudinal vibration and the influence of shear deformation are neglected. The boundary conditions of the supports are simply supported for the transverse displacements and fixed-free in relation to torsion (for the flexural-torsional response only). The transverse surface crack, which causes a geometric discontinuity, is replaced by generalized moments at the crack location. The equations of motion follow the formulation of Wauer. Galerkin’s method and numerical integration are used to obtain approximate solutions. The maximum responses are determined. The effects of the acceleration and deceleration rate and the different parameters of the breathing cracked rotating shaft, such as crack depth, crack location, disk location, disk eccentricity, disk eccentricity angle, and disk mass, are studied. The influence of internal damping, external damping, and torsional external damping are investigated. Comparisons with an open cracked rotating shaft and an uncracked rotating shaft are also presented. The influence of torsional deformation is analyzed. The results are presented in tables and figures. / Master of Science

The kinetics of austenite decomposition were studied in high purity Fe-0.1 C-0.4 Mn-0.3 Si-X (concentrations in weight percent, X represents 3 Ni, 1 Cr, or 0.5 Mo) steels at temperatures between 500 and 675°C. The transformation stasis phenomenon was found in the Fe-C-Mn-Si-Mo and Fe-C-Mn-Si-Ni alloys isothermally transformed at 650°C and 675°C but not in the Fe-C-Mn-Si and Fe-C-Mn-Si-Cr alloys at any of the temperatures investigated. The occurrence of transformation stasis was explained by synergistic interactions among alloying elements. The paraequilibrium model was applied to calculate the metastable fraction of ferrite in each alloy. This fraction was shown to coincide with cessation of transformation in the Mo alloy transformed at 600°C. Transformation stasis was found in both the Ni and the Mo alloys isothermally reacted at 650°C and 675°C. The interactions among Mn, Si, and Mo as well as interactions among Mn, Si, and Ni appear to decrease the threshold concentrations for occurrence of transformation stasis in Fe-C-Mn-Si systems. The segregation of Mn and Mo to the α/γ boundary assisted by Si was suggested to enhance the drag force and led to transformation stasis. In the Ni alloy, lower driving force for ferite formation by addition of Ni could be responsible for occurrence of transformation stasis. / Master of Science

The objective of this thesis is to analyze the operational requirements of aircraft during the runway exiting maneuvers and the economic feasibility of high-speed runway exits. The motion of the aircraft is simulated by a computer program based on the appropriate equations of motion and steering inputs. The economic analysis of high-speed runway exits is based on a life cycle cost approach. Historical data of airline operating costs are also used in the cost estimations. The results show that high-speed runway exits are operationally feasible and economically profitable. The results are also presented graphically to show the effect of various steering commands on the vehicle turning maneuvering requirements and the effect of different economic parameters to the evaluation of high-speed exit utilizations. / Master of Science

Fiber optic sensors fabricated from standard silica fibers have many advantages over conventional sensors like small size, portability, durability and immunity to electromagnetic fields. Unfortunately, these sensors are not suitable for use in harsh environments where the temperatures are greater than 700°C and large working stresses are involved. Sapphire fiber-based sensors present an attractive alternative for use in such environments. The material properties of sapphire like high melting point, extreme hardness and relative imperviousness to chemical reactions, coupled with the advantages of optical fiber sensing, enhance the performance of these sensors for rugged use. Unfortunately, commercial sapphire fiber that is currently available has higher optical attenuation than silica fiber and is costlier. 0, it is prudent to use a small length of sapphire fiber as a sensor head, which is then spliced to a standard singlen10de silica fiber which acts a lead-in/lead-out fiber to the sapphire sensor head. This thesis investigates possible splicing techniques to fabricate such a sensor set-up. Comparative results from experiments performed on splices that have been obtained by each of these techniques, are presented. Furthermore, two different sensor configurations using a sapphire fiber, spliced to a silica fiber, are developed, and the results of preliminary tests are presented. / Master of Science