Thesis (M.S.)--Missouri University of Science and Technology, 2010. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed June 29, 2010) Includes bibliographical references (p. 77-78).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on July 5, 2006). PDF text: viii, 166 p. : ill. ; 2.03Mb. UMI publication number: AAT 3205393. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 212-228).

<p> HNBR is a widely used oil resistant polymer with good tear strength. Due to these properties, HNBR is used in oil wells. However, harsh working environments require high equipment maintenance fees and HNBR will be degraded when contacted with H₂S. This study aims to improve the mechanical properties and H₂S resistance of HNBR through molecular dynamics simulations. Some of the simulation results are compared with experimental results and literature values. In this study, the solubility parameters and densities of pure HNBR with varying acrylonitrile content, FKM and three surfactants (KBM503, a trimethoxysilane methacrylate, A10, a perfluoroalkoxy bis(alkylamide), and Capstone-62MA, a semifluorinated methacrylate) are calculated by molecular dynamics simulation. The cohesive energy densities of 50/50 HNBR/FKM blends with different kinds and content of surfactants are calculated. The diffusion of H₂S and CO₂ are predicted by molecular dynamics simulation. The solubility coefficients of H₂S and CO₂ are predicted by Grand Canonical Monte Carlo (GCMC) simulations. A series of NPT simulations (constant of number of atoms, pressure and temperature) are used to estimate the glass-transition temperature of Capstone-62MA grafted HNBR. Dissipative Particles Dynamics (DPD) simulations are used to obtain the micro phase separation of Capstone-62MA grafted HNBR. The results shows that the solubility parameter values and densities we obtained from molecular dynamics simulations are fitted very well with literature values. According to our calculation of energy of mixing for HNBR/FKM blends with three surfactant (KBM503, A10 and Capstone-62MA), KBM503 has the largest effect. Based on the experiment results for HNBR/FKM blends with different mass fractions of KBM503, the tensile stress at break and elongation at break increases with the increases of KBM503 content until the mass fraction KBM503 is equal to 5%. When the mass fraction of KBM503 is 5%, adding more KBM503 decreases both mechanical properties. However, the tear strength keeps increasing when the mass fraction of KBM503 increases. The conclusion obtained from these experiments and simulations indicates that mixing HNBR with FKM can improve some mechanical properties but this method has disadvantages due the large discrepancy between the solubility parameters of HNBR and FKM. Gas diffusion and solubility calculations indicate that the diffusion and solubility of H₂S decrease with the content of Capstone-62MA increases. The gas diffusion of H₂S also decreases with increasing content of acrylonitrile in HNBR. However, the solubility of H₂S also increases with the content of acrylonitrile in HNBR. For comparison with H₂S, the diffusivity and solubility of CO₂ are calculated. The diffusion of CO₂ increases with the increase of Capstone-62MA content. The solubility of CO₂ decreases with increases of Capstone-62MA in HNBR with 17 wt% acrylonitrile content. For HNBR with 36 wt% acrylonitrile content, increasing the content of Capstone-62MA first increases the solubility of CO₂ and then reduces it when the content of Capstone-62MA is larger than 2%. The calculation also indicates that diffusion and solubility coefficient are reduced when the content of acrylonitrile increases in HNBR. Calculations for the glass-transition temperature of HNBR with different numbers of Capstone-62MA chains suggest that the glass-transition temperature is not changed by grafting Capstone-62MA onto the backbone of HNBR. These results are compared with experimental results. Although the glass-transition temperatures obtained from simulations are higher than those obtained from experiment, they have the same trend as the content of Capstone-62MA is changed. DPD simulations suggest that micro phase separation exists in the Capstone-62MA grafted HNBR and this phenomenon improves the mechanical performance of polymers. In summary, we have used computer modeling to design new polymer materials and perform molecular dynamics simulations, Monte Carlo simulations and DPD simulations to predict some properties of these new materials. Some simulation results are compared with experimental results indicating that we indeed obtain a newly a polymer material with improved properties with the help of computer simulations.</p><p>

The new research described in this dissertation created systems and methods to assist wheelchair users and provide them with new realistic and interesting driving opportunities. The work also created and applied novel effort reduction and collision avoidance systems and some new electronic interactive devices. A Scanning Collision Avoidance Device (SCAD) was created that attached to standard powered wheelchairs to help prevent children from driving into things. Initially, mechanical bumpers were used but they made many wheelchairs unwieldy, so a novel system that rotated a single ultra-sonic transducer was created. The SCAD provided wheelchair guidance and assisted with steering. Optical side object detectors were included to cover blind spots and also assist with doorway navigation. A steering lockout mode was also included for training, which stopped the wheelchair from driving towards a detected object. Some drivers did not have sufficient manual dexterity to operate a reverse control. A reverse turn manoeuvring mode was added that applied a sequential reverse and turn function, enabling a driver to escape from a confined situation by operating a single turn control. A new generation of Proportional SCAD was created that operated with proportional control inputs rather than switches and new systems were created to reduce veer, including effort reduction systems. New variable switches were created that provided variable speed control in place of standard digital switches and all that research reduced the number of control actions required by a driver. Finally, some new systems were created to motivate individuals to try new activities. These included a track guided train and an adventure playground that including new interactive systems. The research was initially inspired by the needs of young people at Chailey Heritage, the novel systems provided new and more autonomous driving opportunities for many powered wheelchair users in less structured environments.

Oxidation damage, in conjunction with fatigue, is a concern for nickel-based superalloys utilised as disc rotors in high pressure compressor and turbine of aero-engines. A combined experimental and numerical study has been carried out for alloy RR1000, developed at Rolls-Royce plc through a powder metallurgy route to meet the demands for higher overall pressure ratios, compressor discharge temperatures and rotational speeds for the latest aero-engines. Cyclic experiments have been carried out for waisted specimens at selected temperatures (700°C-800°C), followed by microscopy examination using Focused Ion Beam (FIB). The results suggest that the major mechanism of oxidation damage consists of the formation of surface oxide scales and internal micro-voids and oxide particles beneath the oxide scales, which becomes more severe with the increase of temperature. Applying a cyclic stress does not change the nature of oxidation damage but tends to enhance the extent of oxidation damage for temperatures at 750°C and 800°C. Further energy dispersive X-ray (EDX) analyses show the enrichment of Cr and Ti, together with lower Ni and Co levels, in the surface oxide scales, suggesting the formation of brittle Cr2O3, TiO2, NiO and Co3O4 oxides on the specimen surface. Penetration of oxygen into the material and associated internal oxidation, which leads to further material embrittlement and associated failure, are evidenced from both secondary ion imaging and EDX analyses. Scanning electron microscopy (SEM) studies of fracture surfaces have been performed for dwell crack growth, and the results confirmed the transition from transgranular to predominant intergranular cracking in alloy RR1000 for increased dwell time. This change in fracture mode supports the oxidation-assisted crack growth mechanism via grain boundary embrittlement. Oxidation embrittlement has also been supported by the FIB analyses of fracture surfaces which confirmed the oxidation reaction for alloy RR1000 at high temperatures. A stress-assisted diffusion approach has been used to model oxygen penetration in the waisted specimen based on Fick’s first and second laws. Grain microstructures were considered explicitly in the model using a finite element submodelling technique, and the grain boundary was taken as the primary path for oxygen diffusion. The material constitutive behaviour was described by a crystal plasticity model to consider the effects of heterogeneous deformation at grain level on oxygen diffusion. Two essential diffusion parameters, i.e., oxygen diffusivity and pressure factor, have been obtained from the simulated oxygen penetration as well as the FIB measurements of internal oxidation depth. Using the obtained diffusion parameters, finite element analyses of a compact tension specimen have been carried out to model oxygen diffusion, coupled with viscoplastic deformation, near a fatigue crack tip. A failure curve for crack growth has been constructed based on the consideration of both oxygen concentration and accumulated inelastic strain near the crack tip. The failure curve was then utilized to predict crack growth rates under fatigue-oxidation conditions for selected loading frequencies and dwell periods, with comparison against the experimental results and those predicted from the viscoplastic model alone.

The central belief in lean systems (LS) is that the implementation of lean practices will reduce different type of wastes. However, LS implemented without an evaluation of organisational readiness may lead to failure. In this study, a measurement framework to evaluate the lean readiness (LR) and LS within Kuwaiti small and medium-sized manufacturing industries (K-SMMIs) has been developed. This measurement framework encompasses the quality and management practices related to LS (processes; planning and control; human resources (HR); top management and leadership; customer relations; and supplier relations) to assess the practices in K-SMMIs and determine whether they have the foundation to implement LS. Mixed methods are adopted in this study, including quantitative approaches (questionnaire administered to 50 K SMMIs and structured observation conducted in 27 K-SMMIs), and qualitative approaches (two case studies (observation and semi-structured interviews with staff of various levels), and semi-structured interviews with 27 managers of K-SMMIs and 26 experts). In addition, a comprehensive literature review has been carried out. The findings indicate that current quality and management practices within K-SMMIs are not very supportive towards LS. Many factors are revealed, both external and internal, that affect K-SMMIs with respect to LS readiness, including language barriers, and deficiencies in aspects including quality workers in terms of education and skills; technology; government attention; know-how regarding LS; market competitiveness; and urgency for adopting LS. This LS and LR measurement framework relating to K-SMMIs provides a unique effort in the area of lean system, and the study’s findings can be used as an internal checklist prior to and during LS implementation. However, this research study contains some obvious limitations, such as very limited information being available on LS and quality initiatives in Kuwait, and small sample size. Further, the LR framework should be tested in small and medium-sized manufacturing industries that have successfully used LS, in order to provide a benchmark.

In this research, various concentrations of layered silicate based on vinyl ester nanocomposites were prepared and the effect of the incorporation of layered silicate into the polymer matrix on the different properties was investigated. The characterisations of interlaminar structure of the nanocomposites by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectrometry and Transmission Electron Microscopy are undertaken. This study revealed that the incorporation of layered silicate into the polymer matrix formed uniformly distributed nanocomposites structure at low clay content (i.e. 1, 2, and 3 wt.%). At 4 wt.% clay loading, the partially intercalated / exfoliated nanocomposites system was observed as proved by the different characterisations' results. However, the addition of more clay such as 5 wt.% resulted in decreasing the overall intercalation level due to the existence of aggregation layers. The addition of layered silicate into the vinyl ester matrix increased the environmental, mechanical and thermal properties, and the enhancements were correlated to the results of the characterisations' outputs. The mechanical properties such as flexural, tensile, nanoindentation, impact, and creep properties of neat samples were improved by the incorporation of layered silicate. The presence of layered silicate into the polymer matrix increased the tensile strength and modulus and flexural strength and modulus up to 4 wt.% clay content. The level of intercalation of nanocomposites played an important role in the improvements of the mechanical properties. So, the tensile and flexural properties were correlated to the characterisations' results. At 5 wt.% clay content, the modulus and strength of both tensile and flexural were reduced due to the effect of aggregation layers where the interfacial interaction between the layered silicate and the polymer is reduced. The nanoindentation test showed that the addition of layered silicate increased the reduced modulus and hardness of the nanocomposites compared to the neat vinyl ester. The presence of only 1 wt.% clay loading increased the hardness and reduced modulus at up to 13% and 11% respectively compared to the pristine polymer. The improvement percentage of hardness and modulus at 2 wt.% were 31% and 19% respectively. The ultimate improvements were observed at 4 wt.% clay loading, where the enhancements in hardness and modulus were 56 and 50% respectively compared to the neat vinyl ester. Further addition of clay resulted in marginal reductions in these properties. The impact properties of the neat vinyl ester and the nanocomposites were investigated using a low velocity impact testing. The addition of layered silicate into the polymer matrix showed that an optimum range of nanoclay reinforcement in the vinyl ester matrix can produce enhanced load bearing and energy absorption capability compared to the neat matrix. Likewise, the influence of the clay addition into the neat polymer on the creep relaxation behaviour at 25°C and 60°C was studied. In both cases, the presence of the layered silicate remarkably improved the creep behaviour. The strain reduction is related to the clay concentration level. The neat polymer illustrated higher strain compared to the nanocomposites samples. Moreover, the addition of layered silicate into the polymer matrix improved the thermal properties. Thermal Gravimetric Analysis (TGA) showed that the nanocomposites represent better stability compared to the neat polymer. The onset temperature of the nanocomposites was higher than the neat polymer. At 1, 2, 3, and 4, wt.% clay content, the improvements in onset temperature were 7 %, 4.2 %, 4 %, 2.5 % respectively compared to the virgin polymer. In addition, the incorporation of layered silicate into the polymer matrix increased the thermal conductivity. At 4 wt.% clay, the thermal conductivity was increased by 12% compared to the neat polymer. Differential Scanning Calorimetry (DSC) is also performed in order to study the effect of the addition of layered silicate into the polymer on the glass transition temperature. The level of intercalation is critical to the Tg values. The nanocomposites represented a marginal reduction in Tg, however at 4 wt.% clay loading the Tg was as same as the neat polymer which was traced to the well-dispersed structure. Furthermore, the study of environmental measurements, which included the water absorption behaviour and its effect on the nanoindentation test, was investigated. The improvement of the water repellence behaviour was observed for the nanocomposites. The enhancements in barrier properties were related to the clay content. At 5 wt.% clay loading, the reduction of water uptake was about 1266% compared to the neat polymer. The hardness and elastic moduli after water absorption was reduced due to the effect of water molecules entering into the polymer chains. However, the higher amount of clay reinforcement led to less reduction in hardness due to the formation of the barrier properties by the layered silicate. The hardness of neat polymer after immersing in water was reduced by 30% whereas the hardness of 5 wt.% nanocomposites showed only a reduction by 10.3% compared to the dry sample.

This research investigates detection and classification of surface defects in extruded aluminium profiles in order to replace the traditional eye inspection which is still the method widely used today. Through an extensive literature review it is evident that extruded aluminium surface is not investigated properly, while similar industrial products such as copper strips or rolled steel have attracted more interest. An experimental machine vision system is used to capture images from surfaces of extruded aluminium profiles. Extensive feature selection is investigated and appropriate statistical features from a novel technique based on Gradient-Only Co-occurrence Matrices are used to detect and classify defects. The methodology created in this research, makes use of the Sobel edge detector to obtain the gradient magnitude of the image and is followed by the extraction of statistical texture measures from the gradient, after a transformation of the gradient values. Comparisons are made between the statistical features extracted from the original image (Gray-Level Co-occurrence Matrix) and those extracted from the gradient magnitude using a novel approach (Gradient-Only Co-occurrence Matrix). The features extracted from the image processing are classified by feed-forward artificial neural networks. Experiments were conducted for a three class and a four class case study, with the first consisting of Good Surface, Blisters and Scratches, and the second introducing Die Lines to the classes of the first case study. The artificial neural network training is tested using different combinations of statistical features with different topologies. Features are compared individually and grouped, showing better classification accuracy for the novel technique (98.9%) compared to research standard methodology of gray-level co-occurrence matrices (55.9%).

Foreign Object Damage (FOD) is one of the main life limiting factors for aeroengine fan blades. The FOD impacts during takeoff and landing cause severe damage to aerofoils, resulting in reduced air safety and life time with an estimated annual cost of $4 billion for the aeroengine industry. Advanced surface treatments, such as Laser Shock Peening (LSP) have significantly improved the fatigue strength and crack growth resistance of critical components under FOD. However, it is not yet possible to predict the protective residual stresses and utilise their full potential for enhancing fatigue resistance and damage tolerance capacity in service. This research programme aims to utilise some of the established methods for fatigue tolerance assessment of critical components, based on fracture mechanics principles, to address the effects of complex residual stresses due to LSP and FOD on fatigue crack growth in aerofoils under simulated service loading conditions. The experimental study involved fatigue testing of LSPed and FODed specimens with a geometry representative of fan blades made from Ti-6Al-4V alloy. A four point bend fatigue test setup was designed and calibrated. A real-time computer-controlled crack growth monitoring system and optical crack monitoring techniques were developed. Scanning Electron Microscopy (SEM) and Back-Scatter Electron (BSE) were used to conduct metallographic and fractographic studies, including crack initiation, early fatigue crack growth and FOD damage characterisation. The fracture mechanics analyses used the weight function method and the finite element method to obtain a modified stress intensity factor considering residual stresses due to LSP and FOD. Fatigue crack growth data under low cycle fatigue(LCF), high cycle fatigue (HCF) and combined LCF and HCF loading conditions were correlated using a standard and the modified stress intensity factors. The influence of impact angles and loading conditions on fatigue crack growth behaviour was assessed, and the results were compared with those from untreated FODed specimens.