Over the last decade, biodegradable screws and plates have received wide acceptance over metallic fasteners for orthopedic fracture fixation. A biodegradable fastener would gradually "disappear" during healing of a fractured bone or tissues, therefore avoiding a secondary operation to remove that fastener. When using a metal fastener, the current approach requires manual threading on a large bone fragment for fixation. This technique is difficult when it is required to fixate a small bone fragment. This study puts forth the development of a threadless, polymer based orthopedic fastener for small fragment fixation which would provide stability and interfragmental compression to the fracture site. The fastener was designed with ratchets on its surface, which deflect during insertion into the drilled hole in the bone and subsequently stiffen to hold the bone fragments in place due to interference. The head of the fastener was developed analogous to a Belleville washer which deflects during insertion of the fastener and subjects the bone fragments to interfragmental compression. Finite element analysis (FEA) was conducted to design the fastener profile and assess its performance. The push-in and pull-out forces predicted by FEA were comparable to the experimental results for the prototype of the microfasteners. The push-in force was found to increase with increasing insertion depth and radial interference. The force required to initiate pull-out was maximum and was reduced with reducing fastener bone contact. An analytical model was proposed to explain the fastener bone interaction. It was found to be in good agreement with the FEA and experimental results at low levels of interference.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references.

In this study, we examine strain localization and failure initiation in cylindrical aluminum tubes subjected to radial impulse loading. This thesis is divided into two parts: the first part explores strain localization in aluminum 6061-T6 tubes undergoing radial expansion. An electromagnetically induced body force is used to expand a total of six tube specimens with varying body force intensities. The experimental response of the tube specimen is obtained by capturing images at different times of the expansion via a high-speed camera and conical mirror. A time history of the tube radius and global hoop strain is acquired by fitting the images of the tube with best fit circles using an iterative least-squares approach. For one specimen digital image correlation is implemented in addition to the circle fitting as a means of tracking the local true strain with time. Postmortem observations of the tube specimens reveal a localization pattern different than those found in previous studies that examined aluminum 6061-O tubes. An argument is made that Joule heating and thermal softening contribute to the unique localization pattern. Two numerical models, with differing magnitudes of thermal softening, are constructed to understand the observed localization. At the end of the chapter, proposals for future investigations are presented. The second chapter is devoted to buckling and fracture of an aluminum 7075-T73 tube exposed to a compressive impulse. A numerical model is constructed to analyze the development of fracture nucleation and propagation. Element failure is modeled with the Johnson-Cook damage criterion. Fracture in the walls of buckled cylindrical tubes appears to be a topic not addressed in previous literature. Nodal data and contour plots of the model are used to construct a general case for the response mechanism leading to fracture. Numerical results are compared to previous experimental investigations. Finally, proposals for future experimental examinations of fracture in buckled cylindrical tubes are provided. / text

Introduction Mallet finger is a common injury involving either an extensor tendon rupture at its insertion or an avulsion fracture involving the insertion of the terminal extensor tendon. It is usually caused by a forceful blow to the tip of the finger causing sudden flexion or a hyperextension injury. Fracture at the dorsal aspect of the base of the distal phalanx is commonly associated with palmar subluxation of the distal phalanx. Most mallet finger injuries are recommended to be treated with immobilization of the distal interphalangeal joint in extension by splints. However, surgical fixation is still indicated in certain conditions such as open injuries, avulsion fracture involving at least one third of the articular surface with or without palmar subluxation of the distal phalanx and also failed splinting treatment. This study was designed to identify the strongest peak load resistance among four mallet finger fracture fixation methods, namely Kirschner wire fixation, pull-out wire fixation, tension-band wire fixation and the JuggerKnot? (Biomet) soft anchor fixation and to assess the role of the JuggerKnot? technique in mallet finger fixation. Materials and method Four different fixation techniques were assigned among twenty-four specimens (all fingers, no thumbs) from six cadaveric human hands in a randomized block fashion. Only one technique was performed on each finger. A downward load was applied to flex the distal phalanx and the maximum loading force was recorded. The load was tested at 30 degrees, 45 degrees and 60 degrees of flexion of the distal interphalangeal joint. Two separate data sets were performed for each finger before and after the osteotomy and fixation. The data underwent Shapiro-Wilk normality testing before analysis. The values of the mean peak load of the four groups were compared using the one-way analysis of variance test in SPSS version 19.0. Result All data points passed the Shapiro-Wilk test for normality. The mean peak load of the tension-band wiring group was 67.8N at 60 degrees of flexion which was significantly higher than the other three groups (p=0.008). The JuggerKnot? fixation had mean peak loads of 13.35N (30°), 22.51N (45°) and 32.96N (60°) which were all above the required load for mobilization. No complications of implant failure or fragmentation of the dorsal fragment was noted. Discussion The tension-band wire fixation was the strongest fixation method among the four. However it was cumbersome and it had the most soft tissue trauma among the four. No major difficulty was encountered during the testing. No fragmentation of the dorsal fragment was encountered during the procedures. The JuggerKnot? soft anchor fixation was a simple and easy technique and did not require trans-articular Kirschner wire fixation for protection. It could reduce and immobilize a grossly displaced dorsal fragment easily and allowed for safe immediate mobilization of the joint after operation as indicated by the peak load results. This fixation technique was a viable option for treating mallet finger injuries with a dorsal bony fragment size at least one-third of the articular surface with or without palmar subluxation of the distal phalanx. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Medical Sciences

Pursuit of unconventional gas and oil has prompted the development and adoption of innovative fracturing solutions. Energized fracturing is one promising technology that can be an effective alternative to mainstream slickwater or hybrid fracturing fluids in many applications. Yet, field use of energized fluids accounted for only 2-3% of 2011-2012 reported fracturing treatments in the U.S. compared to a markedly higher share of 42-46% in Canada. Recently, the superior performance and economics of foams were reported in the Montney Gas Formation in western Canada. In this thesis, we utilized field data and a compositional, 3D fracturing simulator to showcase the production performance of energized fluids in several areas of the Cardium and Bakken Light Oil Formations within the Western Canadian Sedimentary Basin. Average well data in the Cardium revealed better production results for foam compared to nitrified slickwater in the West Willesden Green and Buck Lake-Wilson Creek fields. Foams had a 110% higher initial peak production rate and 51% higher long term cumulative production in the West Willesden Green field with a similar initial production profile and a 16.2% higher long-term production in the Buck Lake-Wilson Creek fields. In contrast, the initial peak production rate of nitrified slickwater was 28% higher with 95% incremental oil production relative to foam in the West Pembina field. This shows that the effectiveness of foam fracturing fluids can vary significantly perhaps because of better fracture containment and lower rock water sensitivity in some fields. Across all the areas studied, foam completions on average were found to have 5-20% lower costs and lower water and proppant requirements by 72-87% and 7-38%, respectively. Fracture modeling, on the other hand, showed 53% higher well productivity increase using nitrified slickwater largely because of better contained fractures in the thin Cardium reservoir interval. Nitrified slickwater had twice the propped fracture length and conductivity of foam. With markedly improved fracture containment in depleted Cardium wells, foam is likely to outperform nitrified slickwater as fracturing fluid recovery is enhanced and permeability/relative permeability damage is reduced in water sensitive areas. In the Bakken Formation, field data showed an average of 15.8% higher long term cumulative production for foam compared to crosslinked gel despite the higher initial rate of crosslinked gel. Foam fractures were predicted to have 44% higher well productivity increase than crosslinked gel fractures based on simulations conducted. Foam had 50% longer propped fracture, 73% higher fracture conductivity, and twice the relative permeability to oil in the invaded zone compared to crosslinked gel. In our simulation, some factors were not accounted for such as formation heterogeneity, the effect of solution gas drive and associated water production, and the interaction between induced and natural fractures. Also, our modeling work was based on generic and synthesized data. For more accurate comparisons, we recommend performing simulation runs with detailed well-specific data. / text

In this report, we develop a computational procedure to investigate propagation of 3D cracks in isotropic linearly elastic media in a 2D framework. We reduce the 3D weakly singular, weak-form traction integral equation to its 2D analog by introducing a constraint on crack profile in out-of-plane direction. Symmetric Galerkin boundary element method based on the obtained 2D weak-form traction integral equation is adopted to model these fractures. In particular, we consider multiple interacting cracks in unbounded domain subject to internal pressure to model hydraulic fracture. / text

Not available / text

published_or_final_version / Surgery / Master / Master of Surgery

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy