Thesis (M.Eng.)--Memorial University of Newfoundland, 2005. / Restricted until May 2006. Bibliography: leaves 114-122.

The tube hydroforming process has gained increasing attention in recent years. Coordination of the internal pressurization and axial feeding curves is critical in the tube hydroforming process to generate successful parts without fracture or wrinkling failure. The stress state at a given time and location varies with the process history and the design and control of the load paths. A new process parameter, counter-pressure, is introduced to achieve a favorable tri-axial stress state during the deformation process. The new process is referred to as dual hydroforming. The benefits offered by dual hydroforming will be characterized based upon the amount of wall thinning, plastic instability limit and final bulged configuration. An analytical model is developed to analyze the stress and strain state in the part (tube) during the dual hydroforming process. The stress-strain condition analyzed will be used to evaluate and compare thinning for tube hydroforming and dual hydroforming. The effect of applying counter-pressure on the plastic instability of thin-walled tubes with only internal pressure and combination of internal pressure and independent axial loading is considered. Finite element analysis is used to quantify the merits of dual hydroforming in terms of final bulged configuration. A parametric study has been conducted to investigate the effectiveness of dual hydroforming based on the various material properties and process conditions. Dual hydroforming results in different stress and strain states compared to tube hydroforming. The counter-pressure enabled favorable tri-axial stress state during deformation that resulted in different thickness and percentage thinning. Finite element analysis showed that for a particular amount of wall thinning there is an increase of around 8% in bulge height for dual hydroforming. Dual hydroforming delays the onset of plastic instability. This increase in the value of effective strain to failure results in an increase of around 12% in bulge height for dual hydroforming as shown by finite element simulations. Results of this study indicate that dual hydroforming can increase expansion i.e. more difficult parts can be designed and manufactured. Also, for a given part geometry, higher strength and less formable materials can be used.

In this study, Thermomechanical properties of Ti-50.8 and 50.7 at% Ni alloy severely deformed using Equal Channel Angular Extrusion (ECAE) are investigated. The aim of this study is to reveal the effects of severe plastic deformation on shape memory, pseudelasticity, interplay between plastic deformation via dislocation slip and twinning, and forward and reverse martensitic transformation. The samples are processed at room temperature, i.e. slightly above the austenite finish temperature, and at 450 °C, i.e. well-above the austenite finish temperature. Transformation temperatures, microstructural evolution, and thermomechanical properties of ECAE processed samples are studied before and after low temperature annealing heat treatment and compared with conventional cold drawn and precipitation hardened material. The unique findings are: 1) the observation of a mixture of heavily deformed B2 (austenite) and B19’ (martensite) phases in the samples processed at room temperature although martensite stabilization was expected, 2) the observation of highly organized, twin-related nanograins in B2 phase of the samples deformed at room temperature which was attributed to B2 to B19' via SIM, and B19' to B2 via SPD (SIM: Stress Induced Martensitic transformation, SPD: Severe Plastic Deformation) transformation sequence, 3) simultaneous observation of B2 austenite and strain induced B19’ martensite in the samples deformed at 450 °C, and 4) perfect pseudoelasticity, small pseudoelastic stress hysteresis and excellent cyclic response with no irrecoverable strain up to 1000 cycles for ECAE at 450 °C processed sample. Strain induced martensite in NiTi alloys was reported for the first time. The formation of well-organized twin-related nanograins via severe plastic deformation opens a new opportunity for twinning induced grain boundary engineering in NiTi alloys which significantly improves the matrix strength and the cyclic response against degradation of shape memory and pseudoelasticity.

This thesis explores the analysis and fabrication of plastic hypodermic needles. The hypotheses for this work are that replacing metal hypodermic needles with plastic ones will reduce or eliminate the possibility of the second-hand infections from needle sticks and unsterlized reuse and will be more cost and time efficient to recycle. The most critical structural failure mode for plastic needles is buckling due to their shape (thin walled hollow column). The consideration of buckling is critical to avoid structural failure and to ensure reliability for medical applications. The buckling strength of a cannula is analyzed by analytic (Euler buckling theory) and finite element analysis (FEA) methods. A 22 gage needle model (OD 0.7mm, ID 0.4mm, Length 12.7mm) was analyzed. Euler buckling theory was used to calculate the critical buckling load. Numerical approaches using finite element analyses showed very similar results with analytic results. A skin model was introduced to simulate boundary conditions in the numerical approaches. To verify the results of the analyses, cannulas with the same cross-sectional dimensions were fabricated using a micro injection molding technique. To make the parts hollow, a core assembly of straightened wire was used. Using the tip of a 22 gage needle, cannulas with the inverse shape of an actual hypodermic needle were made. The structural (buckling) characteristics of cannulas were measured by a force-displacement testing machine. When buckling occurred, an arch shape was visible and there was an abrupt change in the load plot. Test results showed the relation between the needles length and the buckling load, which was similar to that predicted by Euler buckling theory. However, test values were 60% of the theoretical or analytical results. Several reasons to explain these discrepancies can be found. The first is that an unexpected bending moment resulted from an eccentric loading due to installation off-center to the center of the testing machine or to the oblique insertion. A cannula that was initially bent during ejection from the mold can add an unexpected bending moment. The quality control of cannulas can be another reason. Bent or misaligned core wires produce eccentric cannulas, and the thinner wall section can buckle or initiate fracture more easily. The last reason may be that Euler buckling theory is not fully valid in short cannula, because the axial stress reaches yield stress before buckling occurs. Inelastic deformation occurs (i.e., the modulus is reduced) during compression in short cannula. The Johnson column formula is introduced to explain this situation. Especially for the nylon nanocomposite material tested, a loss in modulus due to moisture absorption may be another explanation for the discrepancies.

Recent interests on the plastic deformation of strontium titanate (SrTiO3) are derived from its unusual ductile-to-brittle-to-ductile transition (DBDT). The transition is divided into three regimes (A, B and C) corresponding to the temperature range of 113 K to 1053 K (-160oC to 780oC), 1053 K to ~ 1503 K (780oC to ~ 1230oC) and ~ 1503 K to 1873 K (~ 1230oC to 1600oC), discovered by Sigle and colleagues in the MPI-Stuttgart. We report the dislocation substructures in (001) single crystal SrTiO3 deformed by Vickers indentation at room temperature, studied by scanning and transmission electron microscopy (SEM and TEM). Dislocation dipoles of screw and edge character are observed and confirmed by inside-outside contrast using g-vector by weak-beam dark field imaging. They are formed by edge trapping, jog dragging and cross slip-pinching off. Similar to dipole breaking off in deformed sapphire (£\-Al2O3) at 1200oC and £^-TiAl intermetallic at room temperature, the dipoles pinch off at one end, and emit a string of loops at trail. Two sets of slip systems {110}<-11 0> and {100}<011> are activated under both 100 g and 1 kg load. The suggestion is that plastic deformation has reached the stage II work hardening, which is characterized by multiplication of dislocations through cross slip, interactions between dislocations, and operating of multiple slip systems. In nanoindentation experiments, it is generally believed that the shear stress at the onset of plasticity can approach the theoretical shear strength of an ideal. Here we report direct evidence that plasticity in a single crystal SrTiO3 can begin at very small forces, remarkably. However, the shear stresses associated with these very small forces is excess the theoretical shear strength of SrTiO3 (16.1 GPa). Our observations entail correlating quantitative load¡Vdisplacement measurements with individual stage microstructure during nanoindentation experiments in a transmission electron microscope. We also report direct evidence that with the prevalent notion that the first obvious displacement excursion in a nanoindentation test is indicative of the onset of plastic deformation. The SrTiO3 deforms elastically before the pop-in depth, but exhibits a plastic-elastic behavior after that. TEM observations reveal that the slip band is the predominant deformation mechanism in SrTiO3 during indentation. The cracks usually initiate at the intersection of slip bands to produce the sessile dislocations with Burger vectors [1-10] (or [110]) along the (110) (or (1-10)) crack plane. In addition, theoretical analysis confirms that the pop-in event is associated with the onset plasticity of SrTiO3. The plastic deformation of (001) single crystal SrTiO3 is investigated using compression along [001] at room temperature. A total plastic strain of ~19+2% is consistently obtained. The stress-strain curve exhibiting four work-hardening stages are describable using the stage 0 of axis rotation, the stage I ¡§easy glide¡¨, the stage II multiple slip and the wall-and-cell structure, and the stage III work softening and dynamic recovery before sample fracture takes place. It is revealed by analyzing the microstructure for each work-hardening stage that the plastic deformation of single crystal SrTiO3 closely resembles that of metals. The primary slip systems of [011](0-11) and [01-1](011) predominate in stage I where plastic deformation occurs by the migration of kink pairs in collinear partial dislocations. The activation of multiple slips including [101](-101) and [10-1](101), and [011](0-11) and [0-11](011) in stage II produces the cell-and-wall structure which is also characteristic of plastically deformed metals. In stage III with decreasing work-hardening rate, the bow-out dislocation interaction from opposite walls results in annihilation. The reaction between dislocations from adjacent walls produces the resultant dislocations with b = [-110] parallel to the load axis [001]. These dislocations are sessile, which eventually leads to sample fracture. We have analyzed the microstructure of <001> SrTiO3 single crystal deformed using compression at room temperature using transmission electron microscopy. A representative stress-strain (£m-£`) curve is established, similar to that for metals it consists of three hardening stages before failure occurs at a strain £` = 19+2%. Dislocation analysis suggests that the primary slip systems in [011](0-11) and [0-11](011) are activated in the £m-£` curve stress plateau region usually addressed as easy glide. Three characteristic features are identified from samples deformed to stage I hardening by easy glide: (a) rectangular glide loops, (b) collinear partials, and (c) kink pairs. Dislocations have predominantly pure edge character. Kink pairs are observed only on the edge segments suggesting that screw dislocations have higher mobility. In easy glide, the migration and annihilation of kink pairs occurring on both the trailing and leading partials lends support to a previous report by Castillo-Rodriguez and Sigle (2011) that dislocation glide is controlled by the long-segment limit of a kink-pair model. Pure edge dislocations are dissociated into collinear partials with b = 1/2[011] (or 1/2[0-11]) by glide in (0-11) (or(011)), and kink pairs are formed on both leading and trailing partials. The suggestion is that in the low-stress regime hardening by dislocation pile-up in stage I is compensated for by kink pair nucleation and migration. The overall hardening rate thus remains unchanged at approximately zero, resembling easy glide in the deformation of metals, over an increasing strain of £` ? 4% before reaching stage II hardening. Microcrack nucleation and propagation behavior in the crack tip was investigated by using transmission electron microscopy (TEM) through compressive test and Vickers indenter. Observation results showed that fracture process was completed in this <001> SrTiO3 single crystal material by connecting dislocations. The crack were nucleated and developed in the dislocation free zone (DFZ) or super thinned area ahead of crack tip under local high stress concentration. The cracks were linked with each other by mutual dislocation emission which expedites the propagation of crack tips effectively. We suggested a dislocation based the Hirsch et al. model of plastic-zone evolution in which dislocations emitted from the crack tip glide away to form a crack-tip plastic zone. Each emitted dislocation reduces the crack tip stress intensity via elastic interactions (the ¡¥¡¥shielding¡¨ effect).

People to feel more and more attention to health, the pursuit of high quality of life, biomedical sensing is one of the development of technology, person to understand the current state of health, currently known as blood sugar and blood pressure monitors, to track health status of the instrument is obvious too inadequate, usually go to the hospital for examination, but it is quite time-consuming, ranging from a waste of time, so the immediate biomedical optical fiber sensor to do direction. Evanescent wave ways to do research for my use of the sensing material-specific dye, sensing agent in different situations will be absorbed to change the situation, the use of sol-gel method (Sol-Gel) to coated with the specific dye, to make our fiber clothes (cladding), when the light in optical fibers, through the specific dye to change the energy of light in optical fibers.

Abstract A new technique for bonding of polymer micro-fluidic devices has been developed. This method can easily bond biochips with complex flow patterns and metal layer. Above all, using a patterned glass, the micro-channel structures on Poly-Methyl Meth-Acrylate (PMMA) substrates were generated by one-step hot embossing procedure. In contrast with the traditional thermal bonding, this paper presents low-temperature and low-pressure packaging for polymer micro-fluidic platforms. Furthermore, the disposable plastic biochip has successfully been tested by the measurement of tensile strength and surface roughness. This paper also reports details of the passive and active micro-mixers. According to experimental and numerical investigations, the mixing performance of passive micro-mixers is expectably to be found. In addition, to quantify the mixing concentration distribution in the micro-channel, it has been demonstrated by launching the image analysis programs. The bonding efficiency of the solvent is twenty four times as strong as thermal bonding efficiency.

Abstract Recently, a-Si:H TFT based liquid-crystal display has encroached on the territory of the cathode ray tubes. There is a tendency to fabricate the active matrix LCD on the plastic or flexible substrates. Instead of glass, flexible substrates will make the application of TFT-LCD extensive due to the several advantages: i.e. ultra-slim, light-weight and unbreakable, etc. Nevertheless, the limitation of process temperature for the low-melting substrates is an important issue. In this thesis, the feasibility of a-Si TFT devices fabricated on flexible substrates by using two different technologies have been evaluated. First, a-Si TFT devices were fabricated on glass at 150¢Jsuccessfully and the characteristics of films deposited at lowtemperature have been studied sequentially. For improving the adhesion between organic and inorganic layers and protecting substrate against water or gas during processes, several hot coating layers were investigated. With hot coating layer be introduced, glass was substituted by plastic substrates. We chose PES as the flexible substrate from several candidates due to better optical transmittance and good thermal stability below 200¢J. After direct fabrication on flexible substrate, the stability of electronic characteristics were been investigated with bending examination. In addition, TFT devices were successfully separated from glass and transferred to flexible substrates such as PES or metal foil. Using this technology, temperature limitation has been circumvented and TFT devices still exhibit good electronic characteristic. Furthermore, the bending measurements have been also applied to devices.

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In this study, Thermomechanical properties of Ti-50.8 and 50.7 at% Ni alloy severely deformed using Equal Channel Angular Extrusion (ECAE) are investigated. The aim of this study is to reveal the effects of severe plastic deformation on shape memory, pseudelasticity, interplay between plastic deformation via dislocation slip and twinning, and forward and reverse martensitic transformation. The samples are processed at room temperature, i.e. slightly above the austenite finish temperature, and at 450 °C, i.e. well-above the austenite finish temperature. Transformation temperatures, microstructural evolution, and thermomechanical properties of ECAE processed samples are studied before and after low temperature annealing heat treatment and compared with conventional cold drawn and precipitation hardened material. The unique findings are: 1) the observation of a mixture of heavily deformed B2 (austenite) and B19’ (martensite) phases in the samples processed at room temperature although martensite stabilization was expected, 2) the observation of highly organized, twin-related nanograins in B2 phase of the samples deformed at room temperature which was attributed to B2 to B19' via SIM, and B19' to B2 via SPD (SIM: Stress Induced Martensitic transformation, SPD: Severe Plastic Deformation) transformation sequence, 3) simultaneous observation of B2 austenite and strain induced B19’ martensite in the samples deformed at 450 °C, and 4) perfect pseudoelasticity, small pseudoelastic stress hysteresis and excellent cyclic response with no irrecoverable strain up to 1000 cycles for ECAE at 450 °C processed sample. Strain induced martensite in NiTi alloys was reported for the first time. The formation of well-organized twin-related nanograins via severe plastic deformation opens a new opportunity for twinning induced grain boundary engineering in NiTi alloys which significantly improves the matrix strength and the cyclic response against degradation of shape memory and pseudoelasticity.