The spinal cord may be injured through various spinal column injury patterns (e.g., burst fracture, fracture dislocation); however, the relationship between column injury pattern and cord damage is not well understood. A three-dimensional finite element model of a human cervical spine and spinal cord segment was developed, verified using published experimental data, and used to investigate differences in cord strain distributions during various column injury patterns. For a transverse contusion injury, as would occur in a burst fracture, a 33% canal occlusion resulted in two peaks of strain between the indentor and opposing vertebral body and intermediate peak strain values. For a distraction injury, relevant to column distortion injuries, a 2.6 mm axial displacement to the cord resulted in more uniform strains throughout the cord and low peak strain values. For a dislocation injury, as would occur in a fracture dislocation, an anterior displacement of C5 corresponding to 30% of the sagittal dimension of the vertebral body resulted in high peak strain values adjacent to the shearing vertebrae and increased strains in the lateral columns compared to contusion. This model includes more anatomical details compared to previous studies and provides a baseline for mechanical comparisons in spinal cord injury.

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Multilayer piezoelectric actuators are used in fuel injectors due to their quick response, high efficiency, accuracy, low power consumption, and excellent repeatability. Experimental results for soft lead zirconate titanate (PZT) stack actuators have shown that a significant amount of heat is generated when they are driven under high frequency and/or high electric-field magnitudes, both of which occur in fuel injectors. Self-heat generation in these actuators, mainly caused by losses, can significantly affect their reliability and piezoelectric properties, and may also limit their application. Other studies have demonstrated that at large unipolar electric-field magnitudes, displacement–electric-field loss (displacement hysteresis) shows a direct relation with polarization–electric-field loss (dielectric hysteresis). In this paper, a simplified analytical self-heating model is presented. The model directly relates self-heating in multilayer piezoelectric actuators to displacement–electric-field loss (displacement hysteresis). The model developed is based on the first law of thermodynamics, and accounts for different parameters such as geometry, magnitude and frequency of applied electric field, duty cycle percentage, fuel type, and environmental properties. The model shows reasonable agreement with experimental results at low and high electric-field magnitudes.

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In high speed machining of hard materials, tools with chamfered edge and materials resistant to diffusion wear are commonly used. In this paper, the influence of cutting edge geometry on the chip removal process is studied through numerical simulation of cutting with sharp, chamfered or blunt edges and with carbide and CBN tools. The analysis is based on the use of ALE finite element method for continuous chip formation process. Simulations include cutting with tools of different chamfer angles and cutting speeds. The study shows that a region of trapped material zone is formed under the chamfer and acts as the effective cutting edge of the tool, in accordance with experimental observations. While the chip formation process is not significantly affected by the presence of the chamfer, the cutting forces are increased. The effect of cutting speed on the process is also studied.

This study focuses on the development of a scheme for self-adapting the Particle Swarm Optimization (PSO) method to solve constrained optimization problems. PSO is a powerful natureinspired metaheuristic optimization method. Compared to other methods, PSO has the ability to determine the optimal solution in fewer evaluations and in general performs in a more efficient and effective manner. However, researches show that the PSO method suffers from premature convergence and a dependence on the initial control settings. Due to these flaws, the application of PSO could lead to a failure in obtaining the global optimal solution. An extensive parametric sensitivity analysis was conducted to understand the impact of the individual control parameters and their respective influence on the performance of PSO. Results of the sensitivity analysis revealed that PSO was most sensitive to the inertia weight, cognitive component and social component. Modifications were performed on the original PSO algorithm to adapt the control parameters with respect to the circumstances of the particles at a specific moment. The modified PSO variant is called the Unique Adaptive Particle Swarm Optimization (UAPSO). Unique control parameters were established for each particle through using a novel term known as the evolutionary state. In the developed approach, constraints were handled by forcing the particles to learn from their personal feasible solutions only. Therefore, in the proposed method, the constraint handling technique worked in accord with the adapting scheme to ensure that the particles were adapting to the environment by directing itself to the feasible regions. Furthermore, particles were reinitialized whenever they stagnated in the design space. Verification of the performance of the proposed method was done by means of a comparative study with other well-known algorithms. The comparative study demonstrated that UAPSO proved to be effective and efficient in solving the considered problems and especially in terms of the speed of convergence. Furthermore, design of a three-bar truss was investigated through the application of UAPSO along with multiple variants of PSO. The numerical results showed the superiority of UAPSO compared to the other variants, its ability in avoiding premature convergence and its consistency and efficiency. iv Lay Summary Particle Swarm Optimization (PSO) is an optimization method that uses the concept of animal foraging in birds and fishes to determine the optimal properties of a design or system. Despite of all its advantages over other methods, PSO suffers from a condition that causes it to fail in obtaining the best possible solution to a given problem. In this thesis, an initial study was performed to determine the causes of failure within the algorithm and based on the findings, modifications were applied to PSO. A novel approach was proposed to allow the PSO algorithm to adapt itself based on the conditions of the problem-solving environment. By allowing the algorithm to direct itself automatical...

Piezoelectric actuators are increasingly used in fuel injectors due to their quick response, high efficiency, accuracy, and excellent repeatability. Current understanding of their thermo-electro-mechanical performance under dynamic driving conditions appropriate for fuel injection is, however, limited. In this paper, the thermo-electro-mechanical performance of soft Lead Zirconate Titanate (PZT) stack actuators is experimentally investigated over a temperature range of -30°C to 80°C, under driving electric fields of up to 2.0 kV/mm (using an AC drive method and a biased DC offset), different frequencies, and a constant preload of about 5 MPa. Experimental results show that the dynamic stroke of the actuators increases with the magnitude and frequency of the applied electric field, as well as ambient temperature. The dynamic stroke was also found to increase with decreased driving field rise time, which is equivalent to increasing the driving field frequency. At driving frequencies lower than the resonance frequency of the test apparatus (~500 Hz), the strain-electric field behavior under different temperatures agreed well with previously obtained quasi-static results. The duty cycle was found to have a minimal effect on dynamic stroke but significantly affected the amount of heat generated under high electric field magnitudes and/or frequencies. The temperature increase due to self-heat generation under a continuous AC driving field (100% duty cycle) was very high, and limited the maximum driving field magnitude and/or frequency. Reducing the duty cycle significantly decreased the amount of heat generation.