In this study the role of passive mechanism for deformation of neutrophils, namely the effect of mechanical properties, was studied using microgels as model system. Both alginate-poly(N-isopropylacrylamide) interpenetrating polymer network (IPN) microgels and agarose microgels were synthesized in microfluidic device. The Young’s modulus and relaxation time of the IPN microgels were studied using atomic force microscopy equipped with a tipless cantilever. The lower limits of the elasticity found in this study were within the range of the elasticity reported for neutrophils. Agarose microgels were also prepared with a range of elastic shear modulus similar to neutrophils, and their flow under constrained geometries was studied. The flow profiles of four agarose microgel samples in a microchannel containing a constriction were analyzed. It was found that the stiffness of the microgels affected their velocity before, in and after the constriction.

Nano-grained nickel produced by electroforming technique was investigated for its microstructure evolution and mechanical properties upon annealing. It was found that during low temperature annealing (T<250 oC), electroformed nano-grained nickel showed scattered and isolated abnormal grain growth, followed by a major abnormal grain growth at 320 oC. A secondary abnormal grain growth, featuring faceted grain boundaries, was observed at a higher annealing temperature (T=528 oC). A semi-in-situ observation using optical microscopy was conducted to track the movement of the faceted grain boundaries, and it was found that these boundaries were mostly immobile. The mechanical properties under various annealing conditions were studies using hardness and tensile testing. The hardness was observed to decrease with increasing annealing temperature. The material became very brittle after annealing at 320 oC or higher temperatures. Fractography investigation showed that the brittleness is caused by intergranular fracture.

Nano-grained nickel produced by electroforming technique was investigated for its microstructure evolution and mechanical properties upon annealing. It was found that during low temperature annealing (T<250 oC), electroformed nano-grained nickel showed scattered and isolated abnormal grain growth, followed by a major abnormal grain growth at 320 oC. A secondary abnormal grain growth, featuring faceted grain boundaries, was observed at a higher annealing temperature (T=528 oC). A semi-in-situ observation using optical microscopy was conducted to track the movement of the faceted grain boundaries, and it was found that these boundaries were mostly immobile. The mechanical properties under various annealing conditions were studies using hardness and tensile testing. The hardness was observed to decrease with increasing annealing temperature. The material became very brittle after annealing at 320 oC or higher temperatures. Fractography investigation showed that the brittleness is caused by intergranular fracture.

In this study the role of passive mechanism for deformation of neutrophils, namely the effect of mechanical properties, was studied using microgels as model system. Both alginate-poly(N-isopropylacrylamide) interpenetrating polymer network (IPN) microgels and agarose microgels were synthesized in microfluidic device. The Young’s modulus and relaxation time of the IPN microgels were studied using atomic force microscopy equipped with a tipless cantilever. The lower limits of the elasticity found in this study were within the range of the elasticity reported for neutrophils. Agarose microgels were also prepared with a range of elastic shear modulus similar to neutrophils, and their flow under constrained geometries was studied. The flow profiles of four agarose microgel samples in a microchannel containing a constriction were analyzed. It was found that the stiffness of the microgels affected their velocity before, in and after the constriction.

This study determined the independent effects of various homogenization cycles and precipitation treatments on the elevated temperature workability and the final ambient temperature mechanical properties of AA2024 aluminum alloy and on the T3 tensile properties of 2014 aluminum alloy as well as T6 tensile properties of 2618 and 2618 (Curich) aluminum alloys. The elevated-temperature tensile and extrusion tests indicate that the workability of AA2024 alloy improves with elevated-temperature precipitation treatment as suggested by earlier investigations. The precipitation treatments do not appear to degrade the ambient-temperature T3 and T8 tensile properties. The time at the precipitation temperature appears to affect the T3 and T8 tensile properties in unextruded ingot, longer times especially providing both relatively high ambient-temperature strength and ductility of AA2024 alloy. The time at the standard homogenization temperature and the heat-up and cool-down rates do not dramatically affect the T3 tensile properties of unextruded ingot of AA2024 and 2014 alloys. However, long soak times at the homogenization temperature and more rapid cooling rates may improve the properties somewhat of AA2024 alloy and longer heat-up times and rapid cooling rates may slightly improve the properties of 2014 alloy. The higher standard solution temperature appears to increase both strength and ductility of 2014 alloy over lower temperatures. The homogenization temperature affects the T6 tensile properties of 2618 and 2618 (Cu-rich) alloys, a high homogenization temperature (compare to standard homogenization temperature) providing both high strength and ductility. Increased manganese and copper appears to increase the strength, but slightly decreases the ductility. The standard aging temperature and time produce higher strength but lower the ductility than lower temperatures at the same or shorter aging times in 2618 (Cu-rich) alloy. / Graduation date: 1993

In the life of a well, the cement sheath not only provides zonal isolation but also supports casing and increases casing-collapse resistance. Due to the high-pressure, high-temperature (HPHT) conditions, the cement sheath plays an important role in maintaining wellbore integrity. During the production process in HPHT wells, the pressure differential inside the casing and the surrounding formation is larger than the conventional wells. The stress induced by fluid withdrawal in highly compact reservoirs can cause the cement and the casing failure in these wells. These present a greater challenge to the wellbore integrity than the conventional wells. To have reliable data, extensive experimental work on Class G cement was carried out to measure the principal parameters for mechanical structural calculations. The experiment was also set up to simulate conditions under which cement low-cycle fatigue failure could occur. Zero-based cyclic pressure was applied to the casing in the cement low-cycle fatigue test. Three types of cement (72-lbm/ft3, 101-lbm/ft3 and 118-lbm/ft3) were cured and tested at 300ºF to study the cement mechanical properties under high-temperature conditions over the long term. The tests included a 1-year mechanical properties measurement such as compressive strength development; i.e., Young’s modulus and Poisson’s ratio. Finite element methods (FEM) were used to study the casing buckling deformation characteristics of reservoir compaction in some south Texas wells. The 2D and 3D FEM models were built to study the effects of mechanical properties and reservoir compaction on HPHT well integrity. As the confining pressure increases, the cement shows more plasticity and can withstand more pressure cycles. The cement with a higher Poisson’s ratio and lower Young’s modulus showed better low-cycle fatigue behavior. Casing collapse resistance is very sensitive to void location, cement Poisson’s ratio, cement Young’s modulus, and pore pressure. Casing eccentricity and voids shape have minor effect on the casing-collapse resistance. Casing shear failure, tension failure, and buckling failure are the most likely failure modes in reservoir compaction. For different casing wall thickness, the critical buckling strain is almost identical. This study presents a better understanding of casing failure and cement failure in HPHT wells. The results of the study will help improve cement and casing design to maintain wellbore integrity that can in turn be expected to extend throughout the life of the well.

Composites are multiphasic materials with individual constituent parts that work cooperatively to produce some desired result. For the common case of structural composites, the use of nanoscale additives does not always yield a predictable outcome due to the complex interactions that occur in the interfacial region where a reinforcing filler meets the supporting matrix. It stands to reason, however, that the thoughtful and deliberate exploitation of unusual effects in this region could lead to the development of nanocomposite materials with extraordinary properties. In this thesis work, I will introduce two such responses in a compliant nanocomposite consisting of highly-aligned carbon nanotubes (CNTs) encased within a poly(dimethylsiloxane) (PDMS) matrix. It is first demonstrated that the material exhibits extremely anisotropic dynamic mechanical behavior. The composite will behave in a way that is evocative of the neat polymer when deformed orthogonal to the CNT alignment direction, yet will exhibit strain softening when cyclically compressed along their axis due to the collective buckling of the nanotube struts. Next, it is shown that this nanocomposite material has the ability to respond and adapt to applied loads. Independent, yet complimentary tests reveal that the structure of the polymer in the presence of nanoscale interstitials will evolve during dynamic stressing, an effect that was predicted nearly 50 years ago. With support from both recent and established literature, an updated mechanism is proposed. Collectively, these results provide insight into the complicated mechanics between polymer matrices and embedded nanoparticles, and assist in the design of advanced synthetic materials with unique physical properties.

Increasing regulatory pressure to reduce fuel consumption of new vehicles has prompted the automotive industry to seek ways to reduce the weight of their automobiles. The use of steel tailor welded blanks has been successful in reducing vehicle weight while simultaneously reducing manufacturing costs; however, further weight reductions are possible if steel alloys are substituted with aluminum alloys. This has created a need to identify and develop welding techniques that would enable the production of high-quality welds between aluminum sheets of different thicknesses at rates compatible with the demands of the automotive industry. A relatively new welding technique that has been shown to have potential for joining aluminum sheet for tailor welded blank applications is the double-sided arc welding (DSAW) process. In DSAW, an arc is struck between two welding torches situated on either side of the sheets to be welded allowing the aluminum surface oxide to be electrically cleaned simultaneously from both sides of the joint. The demonstrated potential for welding aluminum sheet and the low capital cost compared to conventional laser welding systems typically used for fabricating TWBs makes DSAW an excellent candidate for welding aluminum TWBs. The objective of the research described in this thesis was to assess the feasibility and merits of using a DSAW system to manufacture aluminum TWBs. In this study, a DSAW system comprised of a plasma arc welding (PAW) torch above the work piece and a gas tungsten arc welding (GTAW) torch below the work piece was applied to the high speed welding of 1.0 to 1.5 mm thick AA5182-O aluminum alloy sheets in the butt-joint configuration. A series of conduction-mode DSAW welds were made in the horizontal position to identify the welding conditions that produced good quality welds using visual acceptance criteria and with minimal geometric discontinuity across the weld. Further studies were conducted to determine the influence of the welding process parameters on the hardness, strength, ductility, formability and internal flaws of DSAW welds. DSAW welds were made using a series of welding torch-to-work piece distances, between 1.5 and 6.0 mm, to investigate the influence of varying the relative arc forces acting on the top and bottom of the weld pool on the resulting weld bead dimensions including weld metal drop through. It was found that increasing the torch-to-work piece distance decreased the process efficiency when a constant welding power was used resulting in narrower welds being produced. Weld metal sag or drop through was not observed to be affected by varying the welding torch-to-work piece distance; however, decreasing the PAW torch-to-work piece distance to 1.5 mm was found to produce a pronounced surface ripple pattern on the top surface of the weld. A series of DSAW welds were made to investigate the range of welding speeds and powers that produced visually acceptable welds on 1.0 to 1.5 mm thick AA5182 aluminum sheets. Welding powers ranging from 1.4 to 4.6 kW were found to produce acceptable welds at travel speeds between 10 and 70 mm/s when the net heat input per unit distance was between 60 and 110 J/mm. Above these speeds, unacceptable weld bead quality and lack of fusion defects were observed due to incomplete cathodic etching of the oxide from the surfaces and inconsistent coupling between the welding arcs the sheets. It was found that the visual appearance of the weld was improved and travel speeds could be increased for a given welding power when welding specimens were stainless steel wire brushed prior to welding to break-up and remove most of the pre-existing hydrated aluminum surface oxide. Significant reductions in hydrogen gas porosity were also observed when stainless steel wire brushing was used. The strength, ductility and formability of DSAW welds were found to vary significantly depending on the welding parameters used and the occurrence of porosity defects in the welds. Welds made using welding speeds greater than 30 mm/s were found to exhibit solidification shrinkage micro-porosity and a corresponding degradation in mechanical properties, especially ductility and formability. As the welding speed was further increased, degradation of the material properties continued to increase due to an increase in the quantity of micro-porosity defects in the weld. These defects caused significant strain localization resulting in a marked decrease in ductility and formability. The severity of solidification shrinkage micro-porosity present in the weld metal was found to correspond to the relative length-to-width ratio of the weld pool for all the welding conditions examined. Welds produced at high welding speeds resulted in large length-to-width ratios, a relatively large distance between the liquidus and non-equilibrium solidus and low thermal gradients in the mushy zone at the tail of the weld. These conditions are known to promote micro-porosity in alloys with a wide freezing range. Visually acceptable DSAW welds produced using welding speeds below 25 mm/s were found to have excellent material properties that were nearly indistinguishable from the base metal with excellent ductility and formability. These welds had relatively small length-to-width ratios and little or no evidence of solidification micro-porosity, because the length of the mushy zone at the tail of the weld was much smaller and the thermal gradients were much higher. These conditions are known to prevent solidification micro-porosity during solidification of alloys with a wide freezing range. They also provide more time and opportunity for any hydrogen bubbles that may form during solidification to float up and escape through the top surface of the weld pool thereby further reducing the propensity for hydrogen porosity. The DSAW process has been shown to be capable of successfully producing tailor-welded blanks in 5182 aluminum alloy sheets with excellent ductility and formability provided that all sources of porosity are eliminated. This includes careful cleaning and removal of preexisting hydrated oxides using stainless steel wire brushing prior to welding to minimize hydrogen porosity and welding at slow enough speeds to prevent the formation of solidification micro-porosity at the tail of the weld pool.

Increasing regulatory pressure to reduce fuel consumption of new vehicles has prompted the automotive industry to seek ways to reduce the weight of their automobiles. The use of steel tailor welded blanks has been successful in reducing vehicle weight while simultaneously reducing manufacturing costs; however, further weight reductions are possible if steel alloys are substituted with aluminum alloys. This has created a need to identify and develop welding techniques that would enable the production of high-quality welds between aluminum sheets of different thicknesses at rates compatible with the demands of the automotive industry. A relatively new welding technique that has been shown to have potential for joining aluminum sheet for tailor welded blank applications is the double-sided arc welding (DSAW) process. In DSAW, an arc is struck between two welding torches situated on either side of the sheets to be welded allowing the aluminum surface oxide to be electrically cleaned simultaneously from both sides of the joint. The demonstrated potential for welding aluminum sheet and the low capital cost compared to conventional laser welding systems typically used for fabricating TWBs makes DSAW an excellent candidate for welding aluminum TWBs. The objective of the research described in this thesis was to assess the feasibility and merits of using a DSAW system to manufacture aluminum TWBs. In this study, a DSAW system comprised of a plasma arc welding (PAW) torch above the work piece and a gas tungsten arc welding (GTAW) torch below the work piece was applied to the high speed welding of 1.0 to 1.5 mm thick AA5182-O aluminum alloy sheets in the butt-joint configuration. A series of conduction-mode DSAW welds were made in the horizontal position to identify the welding conditions that produced good quality welds using visual acceptance criteria and with minimal geometric discontinuity across the weld. Further studies were conducted to determine the influence of the welding process parameters on the hardness, strength, ductility, formability and internal flaws of DSAW welds. DSAW welds were made using a series of welding torch-to-work piece distances, between 1.5 and 6.0 mm, to investigate the influence of varying the relative arc forces acting on the top and bottom of the weld pool on the resulting weld bead dimensions including weld metal drop through. It was found that increasing the torch-to-work piece distance decreased the process efficiency when a constant welding power was used resulting in narrower welds being produced. Weld metal sag or drop through was not observed to be affected by varying the welding torch-to-work piece distance; however, decreasing the PAW torch-to-work piece distance to 1.5 mm was found to produce a pronounced surface ripple pattern on the top surface of the weld. A series of DSAW welds were made to investigate the range of welding speeds and powers that produced visually acceptable welds on 1.0 to 1.5 mm thick AA5182 aluminum sheets. Welding powers ranging from 1.4 to 4.6 kW were found to produce acceptable welds at travel speeds between 10 and 70 mm/s when the net heat input per unit distance was between 60 and 110 J/mm. Above these speeds, unacceptable weld bead quality and lack of fusion defects were observed due to incomplete cathodic etching of the oxide from the surfaces and inconsistent coupling between the welding arcs the sheets. It was found that the visual appearance of the weld was improved and travel speeds could be increased for a given welding power when welding specimens were stainless steel wire brushed prior to welding to break-up and remove most of the pre-existing hydrated aluminum surface oxide. Significant reductions in hydrogen gas porosity were also observed when stainless steel wire brushing was used. The strength, ductility and formability of DSAW welds were found to vary significantly depending on the welding parameters used and the occurrence of porosity defects in the welds. Welds made using welding speeds greater than 30 mm/s were found to exhibit solidification shrinkage micro-porosity and a corresponding degradation in mechanical properties, especially ductility and formability. As the welding speed was further increased, degradation of the material properties continued to increase due to an increase in the quantity of micro-porosity defects in the weld. These defects caused significant strain localization resulting in a marked decrease in ductility and formability. The severity of solidification shrinkage micro-porosity present in the weld metal was found to correspond to the relative length-to-width ratio of the weld pool for all the welding conditions examined. Welds produced at high welding speeds resulted in large length-to-width ratios, a relatively large distance between the liquidus and non-equilibrium solidus and low thermal gradients in the mushy zone at the tail of the weld. These conditions are known to promote micro-porosity in alloys with a wide freezing range. Visually acceptable DSAW welds produced using welding speeds below 25 mm/s were found to have excellent material properties that were nearly indistinguishable from the base metal with excellent ductility and formability. These welds had relatively small length-to-width ratios and little or no evidence of solidification micro-porosity, because the length of the mushy zone at the tail of the weld was much smaller and the thermal gradients were much higher. These conditions are known to prevent solidification micro-porosity during solidification of alloys with a wide freezing range. They also provide more time and opportunity for any hydrogen bubbles that may form during solidification to float up and escape through the top surface of the weld pool thereby further reducing the propensity for hydrogen porosity. The DSAW process has been shown to be capable of successfully producing tailor-welded blanks in 5182 aluminum alloy sheets with excellent ductility and formability provided that all sources of porosity are eliminated. This includes careful cleaning and removal of preexisting hydrated oxides using stainless steel wire brushing prior to welding to minimize hydrogen porosity and welding at slow enough speeds to prevent the formation of solidification micro-porosity at the tail of the weld pool.

No description available.