The mechanical characterization of the interfacial shear strength (IFSS) of carbon nanotube (CNT) coated carbon fibers and the interlaminar fracture toughness of woven fabric carbon fiber/epoxy composites toughened with CNT/epoxy interleave films is presented. The deposition of multiwalled carbon nanotubes (MWCNT) onto the surface of carbon fibers through thermal chemical vapor deposition (CVD) was used in an effort to produce a graded, multifunctional interphase region used to improve the interfacial strength between the matrix and the reinforcing fiber. Characterization of the IFSS was performed using the single-fiber fragmentation test. It is shown that the application of a MWCNT coating improves the interfacial shear strength between the coated fiber and matrix when compared with uncoated fibers. The effect of CNT/epoxy thin interleave films on the Mode I interlaminar fracture toughness of woven fabric carbon/epoxy composites is examined using the double-cantilever beam (DCB) test. Initiation fracture toughness, represented by critical strain energy release rate (GIC), is shown to improve over standard un-toughened composites using amine-functionalized CNT/epoxy thin films. Propagation fracture toughness is shown to remain unaffected using amine-functionalized CNT/epoxy thin films with respect to standard un-toughened composites.

A novel room temperature bonding method is used to package the micro-component. The bonding method utilizes metal microcap to package the micro-component under room temperature status, which not only can provide micro-component mechanical support also can prevent micro-component from contamination. The bonding condition under room temperature is the most conventional method can not achieve, which characteristic is the most significant effect factor to drive the wafer-level packaging process to improve in today. Utilizing ASTM standard, which was used as a macroscopic standard to evaluate and analyze the bonding shear strength relationship between the ASTM standard specimen and the metal microcap. The carrier wafer has been oxidized before photolithography process; the diameter of cavity and the contact area between the metal microcap and glass substrate were controlled by the photomask design and the accuracy of the photoresist exposure. The passivation treatment was developed to separate the microcap from the carrier wafer more easily. In this thesis, the metal microcap was fabricated by using electroforming process, which can control the thickness of metal microcap. The advantages of microcap are superior to the thin film poly-silicon made by the surface micromachining technique on the quality and mechanical properties. A glass is used as substrate of the metal microcap, and its transparent characteristic is a feature how we perform UV curing process. The adhesive can be cured under room temperature and the results exhibit the adhesive has excellent bonding strength. SEM is used to analyze the passivation result, the increasing rate of electroforming thickness. The shear stress-strain relationship between the metal microcap and the ASTM standard specimen is also discussed and analyzed in this thesis.

Several recently built inverted-T bent caps in Texas have shown significant inclined cracking triggering concern about current design procedures for such structures. The repair of such structures is very costly and often requires lane closures. For these reasons TxDOT funded Project 0-6416 aimed at obtaining a better understanding of the structural behavior of inverted-T bent caps and developing new design criteria to minimize such cracking in the future. Several tasks of the aforementioned project are addressed in this dissertation with particular focus on developing design criteria for strength and serviceability of inverted-T bent caps. Literature review revealed a scarcity of experimental investigation of inverted-T specimens. As part of this dissertation, an inverted-T database was assembled with experimental results from the literature and the current project. An extensive experimental program was completed to accomplish the objectives of the project with thirty one full-scale tests conducted on inverted-T beams. Experimental parameters varied in the study were: ledge length, ledge depth, web reinforcement, number of point loads, web depth, and shear span-to-depth ratio. The dissertation focuses on the effects of ledge length, ledge depth, number of point loads, and developing design criteria for strength and serviceability of inverted-T beams. Most inverted-T bent caps in Texas are designed using the traditional empirical design procedures outlined in the TxDOT bridge design manual LRFD (2011 current version) that follows closely the AASHTO LRFD bridge design specifications (2012 current version). Given the observed cracking in inverted-T bent caps, the accuracy and conservatism of the traditional design methods were evaluated based on experimental results. The accuracy and conservatism of STM design provisions recently developed in a TxDOT study (TxDOT Project 0-5253, Strength and Serviceability Design of Reinforced Concrete Deep Beams) were also evaluated. / text

Tire bales have become an innovative and cost effective fill material that can be used for the construction of geotechnical structures, like embankments for highway projects. The mechanical and physical properties they present allow them to be suitable for this type of structures, as long as they are provided with an appropriate drainage system. Stability of these structures is controlled by the interface shear strength existing in the contact surfaces between the bales. However, the tire bale has a jagged, uneven and highly variable surface and it presents a number of irregular tire ridges with random dimensions that are difficult to quantify. Due to the flexibility of these ridges, deformation of the interface occurs when a horizontal shear load is applied, and following this deformation the actual displacement of the interface takes place. Freilich (2009) performed large scale tests in the field and in the laboratory to observe the behavior of the whole tire bale structure, which is composed of the tire bale mass and the tire bale interface. Due to the irregular and highly variable surface of the tire bale, the deformations that occur on the ridges along the interface cannot be directly measured and quantified. Following similar concepts of some rock mechanic models, Freilich characterized the tire ridge interface using three parameters and came up with a model. Using these parameters, an ideal interface was constructed where the variability was reduced by incorporating a known geometry, and it can still be characterized in the same manner as that for the tire bale interface. Loads, deformations and displacements occurring along the interface were measured and recorded. From this data, shear strength parameters are defined and incorporated into Freilich’s tire ridge interface model that is used to predict the geometric and mechanical behavior of the irregular ridges controlling the interface shear strength. The behavior predicted from the model is then compared to the recorded data representing the actual geometric and mechanical behavior of the interface with known geometry, where the deformations on the asperities are approximated. This comparison verifies that the consideration of the flexibility from the tire ridges is not entirely described by the tire ridge interface model. Therefore a possible modification, based on the observations recorded, could be found. / text

published_or_final_version / abstract / toc / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil and Structural Engineering / Doctoral / Doctor of Philosophy

The objective of this research was to further understand the behavior of the soil under the action of a tillage tool, with the purpose of finding a relation between the tool geometry and the resultant soil seed bed. Thus the problem consisted of understanding the mechanics of producing soil break up and to find a logical method of analyzing it. / The problem was solved using fundamental principles of soil mechanics and force equilibrium analyzis. As a result, a mathematical model was developed which describes three failure zones within the cut soil volume. The model can be programmed into a computer to generate maps of normal and shear stresses to visualize the three failure zones. / The failure zones are the shear failure zone, the tensile fracturing zone and the no failure zone. The tensile fracturing zone is delimited by the tensile stress reaching the tensile strength of the soil at the given soil moisture content and soil density. The tensile strength of the soil was measured using an apparatus and method designed in this research. / The mathematical model gives an explanation of the mechanics of crumbling and the shape of the failed volume, but it does not give information concerning soil aggregate quality and arrangement within the soil furrow. Then, a method of analyzing the formed aggregates was developed which considers some soil physical properties of aggregates. / The study concluded that the smaller tool width and the smaller tool rake angle, among the ones used in this research, produced the most efficient geometry in producing the largest amount of soil break up, the most uniform aggregate formation and the most stable aggregate arrangement. The same tool geometry requires less energy per unit volume of soil disturbed. The best performance is produced at the lowest soil water content among those tested.

No description available.

Timber beams with end splits were investigated in this study to determine their shear strength. Two conditions were considered: a) Group 1 had supports located near the ends with the portion of the beam extending beyond the support, and b) Group 2 had supports located right at the end of the beam subjected to a horizontal split at approximately mid height. In Group 1, seventeen beams were tested under static loading and four were tested in fatigue. In Group 2, nineteen beams were tested under static loading and four under fatigue. In Group 1, eight beams under static loading failed in shear. In Group 2, all beams under static loading failed in shear. Group 1 and Group 2 beams under static load produced average shear strength values of 4.93 MPa and 4.49 MPa, respectively. During fatigue tests, Group 1 sustained more cycles than beams in Group 2.

No description available.