Saudi Cultural Missions Theses & Dissertations
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Item Restricted Effects of Needle Injuries and Simulated Repetitive Lifting on Lumbar Spinal Segments Mechanics and Annulus Fibrosus Structure(Flinders University, 2024-11-11) Alsharari, Tirad Sulaiman; Costi, JohnDespite the intervertebral disc's ability to withstand considerable loading, its resilience is critical in the context of widespread back disorders, such as low back pain (LBP), which impose significant global health and economic challenges. These challenges are exacerbated by factors like repetitive lifting, further complicating the disc's vulnerability not only to occurrences like annular tears but also to artificial interventions, including clinical needle punctures used in diagnosing and treating spinal issues. Although prior in vitro studies have examined the mechanical impact of needle injuries on intervertebral discs, they have not considered simulated in vivo mechanical loading conditions reflective of repetitive lifting, which is closely associated with these injuries. Moreover, there has been a lack of investigation into the development and potential morphological changes in the annulus fibrosus due to needle-induced rupture under conditions that mimic repetitive lifting. Bridging this gap requires an examination of the individual mechanical effects of repetitive lifting on functional spinal units (FSUs), incorporating more realistic conditions that include inter-day disc recovery. Consequently, this thesis aims to assess the mechanical influence of simulated repetitive lifting on ovine FSUs immediately after lifting and following a recovery period, both independently and in conjunction with disc needle injuries. It also seeks to quantify the morphological changes in needle-induced ruptures within the annulus fibrosus after exposure to simulated repetitive lifting. To fulfill the aims of the research, the sole mechanical effects of repetitive lifting were first evaluated. Twenty ovine FSUs underwent six degrees of freedom (6DOF) testing at 0.1 Hz for five cycles, followed by simulated repetitive lifting to replicate a day of lifting. This simulation involved 1000 cycles combining compression (1.1 MPa)—equivalent to lifting an intermediate weight of 20 kg, within safe manual handling limits—and flexion (13°). Subsequently, two additional 6DOF tests were conducted: one immediately after the lifting session and the other after a recovery period, allowing the discs to reach fluid equilibrium similar to that during sleep. Once these FSUs were adapted to the recovery state, further investigation was performed on the combined effects of needle injuries and simulated repetitive lifting. The FSUs were divided into control and injury groups, each comprising 10 FSUs. The injury group received 25G needle injuries in the posterolateral regions of the discs before repeating the simulated repetitive lifting and testing protocol on both groups. Microtome sections were successfully collected from some of these injuries, perpendicular to the injury axis, where microscope images were obtained, and the morphologies of these injuries were quantified. The sole mechanical effects of repetitive lifting were found to cause significant biomechanical changes in flexion, a primary direction applied to the load. The changes appeared as a decrease in stiffness (77.2%, P<0.001) and an increase in the phase angle (89%, P<0.001) immediately following the simulated repetitive lifting. After a period applied for disc recovery to allow for fluid equilibrium, the observed changes in flexion persisted. Specifically, there was a continued reduction in stiffness (71.2%, P<0.001) and an increased phase angle (63.8%, P<0.001). These findings suggested that the recovery period was insufficient to fully moderate the biomechanical damage induced by repetitive lifting, likely in the disc’s microstructure. Assessments of FSU mechanics by combined needle injuries and repetitive lifting demonstrated an increase in stiffness in right lateral bending (27.27%, P=0.01) immediately following the lifting, suggesting a compensatory mechanism for a compromised left posterolateral side due to a needle injury. This increase in stiffness response might relate to a permanent reduction in flexion stiffness caused by the previous repetitive lifting prior to needle injury, considering that an intrinsic aspect of forward bending relates to lateral bending. Furthermore, the vulnerability of the left side annulus to needle injuries could be due to disruption likely in the inner annulus as a consequence of cumulative damage from repetitive lifting. The right side's increased stiffness during lateral bending, previously not present, suggested a distinctive biomechanical response of the disc to counteract the reduced flexion stiffness, thereby maintaining equilibrium in bending movements and potentially preventing further injury or stress to the injured left side. The increase in stiffness was temporary since it diminished after a recovery period. Exploration of how repetitive lifting impacts the morphology of needle injuries in the annulus was insufficient to draw definitive conclusions due to encountered variability in the measurements. This variability might be linked to the different forms of needle injury inherent when inflicted into the annulus. The present research emphasised this variability further by identifying, for the first time, a hybrid injury form—a combination of the known parallel and cross forms. These forms naturally occur and intrinsically manifest, aligning with or intersecting the oblique fibres of the annulus, respectively. Preliminary analysis, conducted by taking morphological measurements on limited data with consistent injury forms, may encourage future studies to investigate the potential for differential responses to repetitive lifting among needle injuries based on their form. The findings of this thesis on the biomechanical effects of repetitive lifting can contribute to the development of safety guidelines for workers engaged in repetitive lifting tasks. Furthermore, investigating the interplay between repetitive lifting and disc needle injuries sets a foundation for future research to improve diagnosis and treatment strategies for disc issues.26 0Item Restricted Heat-Assisted Additive Manufacturing and Post-Heat Treatment of Inconel Supper Alloy: Investigating the Microstructure and Mechanical Properties(Saudi Digital Library, 2023) Almotari, Abdalmageed; Qattawi, AlaRecently, additive manufacturing (AM) has gained attention in the global manufacturing industry. The advantages are derived from the fact that it is a powder-based manufacturing process. The AM process enables the fabrication of complex parts that can be manufactured at a lower cost. This approach allows on-demand production, minimal structural limitations, and custom design. Many industries are concerned about the reliability and durability of AM metallic parts. The properties of the materials are not entirely known, and imperfections resulting from the production process are frequently detected, which lowers the performance of the material. Consequently, many studies have been conducted on the microstructures and mechanical properties of materials produced by AM. With recent advances in AM over the past decade and the introduction of high lasers and higher-quality raw materials, AM can produce functioning components with high mechanical performance. The manufacturing and post-fabrication processing conditions, in addition to post-heat treatments, strongly influence the microstructure and mechanical characteristics of additively manufactured components. Metal components are affected by the manufacturing orientation, such as the laser power, laser scanning speed, and powder layer thickness. Anisotropic mechanical behaviors, such as tensile strength and stiffness in additively manufactured components, are caused by the directed fabrication method and thermal history, which provide a microstructure different from that anticipated in traditional production. In addition, additively manufactured components are unpredictable because of imperfections generated by the unmelted powder or entrapped gases during manufacturing. This dissertation investigates the influence of various processing factors on the microstructure and mechanical behavior of additively manufactured components. In addition, a better understanding of how modified heat treatment and building process parameters affect the mechanical behavior and microstructure and how to account for them when designing products may lead to more durable and reliable components. The layer-by-layer manufacturing approach intrinsic to AM permits a heat input. Therefore, the thermal gradient and solidification rates vary throughout the process, resulting in changing solidification conditions and thus various solidification microstructures. The processing parameters used during fabrication and post-processing significantly affect the microstructure and mechanical performance of the additively manufactured parts. The first objective of this investigation was to study the influence of different processing variables using heat-assisted AM on the microstructure and mechanical performance of IN718 additively manufactured components. The second objective of this study was to optimize the post-heat treatments for IN 718 materials fabricated by AM. The third objective is to model the combined effect of heat-assisted AM and post-heat treatments on the precipitates δ, γ', and γ'' using Neural Network.30 0Item Restricted The Effects of Combined Heat-Assisted Additive Manufacturing and Laser Re-melting on Martensitic Stainless Steel(OhioLINK Electronic Theses and Dissertations Center, 2023-12) Ali, Majed Saleh; Qattawi, AlaLaser powder bed fusion (LPBF) has become an attractive manufacturing method due to its ability to fabricate metals with complex designs. LPBF can build accurate parts with geometries that are not possible in traditional manufacturing processes. Many applications of LPBF such as dental implants, replacement prosthetic joints, and gas turbine engines have demonstrated significant improvement in mechanical properties and microstructure. However, to qualify the LPBF process as an industry standard, more research and testing are necessary using different parameters to understand the influencing factors of the material properties. In LPBF, the produced parts require post-processing. In most cases, the fabricated part needs heat treatment to enhance the microstructure and mechanical properties and achieve better homogenous material. Some applications need post- processing to reduce surface roughness. These needs have motivated many research studies on how to improve material strength and obtain the desired surface roughness for LPBF materials in general. In addition, the quality and mechanical properties of the materials must be considered. The disadvantage of LPBF is the formation of internal stresses. When the laser fuses a layer, the rapid cooling results in residual stress as the laser moves across its path. Laser remelting with a heat-assisted additive manufacturing process can improve the surface quality and relieve residual stresses; however, if the laser power and laser speed are not suitable, it can reduce the strength and hardness of the material which was within the range of typical wrought properties. There is a lack of understanding of the effect of laser remelting and its parameters on the resultant material properties and any improvement that can be achieved for LPBF for metals such as steel. The integration of laser re-melting and heat-assisted additive manufacturing is also not fully understood in terms of its contribution to improving materials' microstructure and reduction in the high residual stresses usually formed during LPBF. The first objective of this dissertation is to investigate the effects of laser re-melting on stainless steel material fabricated by heat-assisted additive manufacturing in terms of mechanical properties. The second objective focuses on identifying the effects of laser re- melting on stainless steel fabricated by heat-assisted additive manufacturing to study the phase transformation and the formation of martensite in the stainless-steel material as the phase transformation is affected by the cooling rate. The retained austenite results in anisotropy of the mechanical properties. It was found the heat-treated samples have a reduction in the amount of retained austenite, homogeneous grain structure, and better mechanical properties. The transformation of the martensite-austenite phase was observed between 533 °C and 928 °C for austenite in heating, and between 175 °C and 74 °C for martensite in cooling. The martensite changes into reverted austenite if the heating is below the austenite phase starting temperature. The third objective is to predict the phase transformation in additively manufactured martensitic steel through a neural network with experimental validation. Retained austenite in martensitic steel is influenced by various temperature and time parameters. An increase in retained austenite tends to reduce the strength of the material. Neural networks are among the most dominant machine learning approaches used for their ability to fit into various classification or regression problems. In this context, the neural network is employed to predict the retained austenite based on post-processing heat treatment process parameters.72 0