Browsing by Author "Department of Mechanical Engineering, School of Engineering"
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Item A 3D microfluidic device fabrication method using thermopress bonding with multiple layers of polystyrene film(IOP, 2015-05) Cao, Yuanzhi; Bontrager-Singer, Jacob; Zhu, Likun; Department of Mechanical Engineering, School of EngineeringIn this article, we present a fabrication method that is capable of making (3D) microfluidic devices with multiple layers of homogeneous polystyrene (PS) film. PS film was chosen as the primary device material because of its advantageous features for microfluidics applications. Thermopress is used as a bonding method because it provides sufficient bonding strength while requiring no heterogeneous bonding materials. By aligning and sequentially stacking multiple layers (3 to 20) of patterned PS film that were achieved by a craft cutter, complicated 3D structured microfluidic devices can be fabricated by multiple steps of thermopress bonding. The smallest feature that can be achieved with this method is approximately 100 μm, which is limited by the resolution of the cutter (25 μm) as well as the thickness of the PS films. Bonding characteristics of PS films are provided in this article, including a PS film bonding strength test, bonding precision assessment, and PS surface wettability manipulation. To demonstrate the capability of this method, the design, fabrication, and testing results of a 3D interacting L-shaped passive mixer are presented.Item Adaptive Nonlinear Model-Based Fault Diagnosis of Li-ion Batteries(IEEE, 2015-02) Sidhu, Amardeep Singh; Izadian, Afshin; Anwar, Sohel; Department of Mechanical Engineering, School of EngineeringIn this paper, an adaptive fault diagnosis technique is used in Li-ion batteries. The diagnosis process consists of multiple nonlinear models representing signature faults, such as overcharge and overdischarge, causing significant model parameter variation. The impedance spectroscopy of a Li-ion LiFePO4 cell is used, along with the equivalent circuit methodology, to construct nonlinear battery signature-fault models. Extended Kalman filters are utilized to estimate the terminal voltage of each model and to generate residual signals. The residual signals are used in the multiple-model adaptive estimation technique to generate probabilities that determine the signature faults. It can be seen that, by using this method, signature faults can be detected accurately, thus providing an effective way of diagnosing Li-ion battery failure.Item Advanced Silicate-based Lubricant Additive Induced Diamond-like Carbon Structured Restoration Layer(Elsevier, 2015-10) Zhang, Jing; Gu, Yanhong; Liu, Jiajun; Department of Mechanical Engineering, School of EngineeringAn advanced silicate based lubricant additive has been employed in long-term pin-on-disk tribological experiments. The worn steel/steel surfaces were characterized using nano-indentation, SEM, XPS, and Raman spectroscopy for their physical, mechanical, and chemical properties. The average nano-hardness of the repaired layers on the disk and the pin is 10.2 GPa and 16.7 GPa respectively, which is substantially higher than that of the disk (HV 221, or 0.71 GPa) and the pin (HRC55, or 1.8 GPa) before tribological tests, forming super hard surfaces on the contact pair surfaces. Combined Raman spectroscopy and XPS studies suggest the formation of diamond-like carbon based restoration layers. A new formation mechanism of the restoration DLC layer contributing to hard and smooth contact surfaces is proposed.Item Design of Progressively Folding Thin-Walled Tubular Components Using Compliant Mechanism Synthesis(ScienceDirect, 2015-10) Bandi, Punit; Detwiler, Duane; Schmiedeler, James P.; Tovar, Andres; Department of Mechanical Engineering, School of EngineeringThis work introduces a design method for the progressive collapse of thin-walled tubular components under axial and oblique impacts. The proposed design method follows the principles of topometry optimization for compliant mechanism design in which the output port location and direction determine the folding (collapse) mode. In this work, the output ports are located near the impact end with a direction that is perpendicular to the component's longitudinal axis. The topometry optimization is achieved with the use of hybrid cellular automata for thin-wall structures. The result is a complex enforced buckle zone design that acts as a triggering mechanism to (a) initiate a specific collapse mode from the impact end, (b) stabilize the collapse process, and (c) reduce the peak force. The enforced buckle zone in the end portion of the tube also helps to avoid or delay the onset of global bending during an oblique impact with load angles higher than a critical value, which otherwise adversely affects the structure's capacity for load-carrying and energy absorption. The proposed design method has the potential to dramatically improve thin-walled component crashworthiness.Item An efficient 3D topology optimization code written in Matlab(Springer, 2015-06) Liu, Kai; Tovar, Andres; Department of Mechanical Engineering, School of EngineeringThis paper presents an efficient and compact Matlab code to solve three-dimensional topology optimization problems. The 169 lines comprising this code include finite element analysis, sensitivity analysis, density filter, optimality criterion optimizer, and display of results. The basic code solves minimum compliance problems. A systematic approach is presented to easily modify the definition of supports and external loads. The paper also includes instructions to define multiple load cases, active and passive elements, continuation strategy, synthesis of compliant mechanisms, and heat conduction problems, as well as the theoretical and numerical elements to implement general non-linear programming strategies such as SQP and MMA. The code is intended for students and newcomers in the topology optimization. The complete code is provided in Appendix C and it can be downloaded from http://top3dapp.com.Item Modeling of a Hydraulic Wind Power Transfer Utilizing a Proportional Valve(IEEE, 2015-03) Deldar, Majid; Izadian, Afshin; Vaezi, Masoud; Anwar, Sohel; Department of Mechanical Engineering, School of EngineeringHydraulic circuits can transfer remarkable amounts of energy in the desired direction without taking large space. To implement this technology for harvesting the energy of wind appropriately, models of the system are required. Hydraulic wind power technology has the benefits of eliminating expensive and bulky variable ratio gearbox and its costly maintenance, while enabling the integration of multiple wind turbines in a single generation unit. In this paper, the dynamics of different hydraulic elements are studied, nonlinearities are taken into account, pressure dynamics in different parts of the system are studied, and the motor load effects are considered. Based on these considerations, a novel nonlinear state-space representation of the system is introduced. Results of the mathematical model and the experimental data are compared to verify the proposed model. The comparison demonstrated that the mathematical model captures all major characteristics of the hydraulic circuit and can model the system behavior under different operating conditions.Item Statistical analysis of the influence of tooth geometry in the performance of a harmonic drive(Springer, 2015-03) León, Dennis; Arzola, Nelson; Tovar, Andres; Department of Mechanical Engineering, School of EngineeringThe objective of this research is to determine the influence of gear tooth geometrical variations in the performance of a double wave harmonic drive through statistical analysis. This work incorporates state of the art analytical and numerical models to evaluate kinematic error, load capacity, bending fatigue strength, and pitting. The geometric variables considered in this study include gear modulus, pressure angle, and tooth correction factor. The statistical analysis follows a three-level full-factorial design of experiments. Nonlinear dynamic simulation is accompanied by finite element analysis to estimate contact and bending stresses. Largest bending fatigue strength is also determined. Results demonstrate that gear modulus is the geometric parameter with prevalent influence on the kinematic error, and pitting life is rather high for all geometric variables considered.Item Three-Dimensional Phase Field Based Finite Element Study on Li Intercalation-Induced Stress in Polycrystalline LiCoO2(Elsevier, 2015-12) Wu, Linmin; Zhang, Yi; Jung, Yeon-Gil; Zhang, Jing; Department of Mechanical Engineering, School of EngineeringIn this study, the stress generation of LiCoO2 with realistic 3D microstructures has been studied systematically. Phase field method was employed to generate the 3D microstructures with different grain sizes. The effects of grain size, grain crystallographic orientation, and grain boundary diffusivity on chemical diffusion coefficient and stress generation were studied using finite element method. The calculated chemical diffusion coefficient is about in the range of 8.5 × 10−10 cm2/s–3.6 × 10−9 cm2/s. Stresses increase with the increase of grain size, due to more accumulation of Li ion near the grain boundary regions in larger grain size systems, which causes a larger concentration gradient. Failure is more likely to occur in large grain systems. The chemical diffusion coefficients increase with increasing grain orientation angle irrespective of grain boundary diffusivity, due to alignment of global Li ion diffusion path with high grain orientations. Grain boundary diffusivity has opposite effect on the hydrostatic stress. As small grain boundary diffusivity, the stress increases with increasing grain orientation angle, due to grain boundary blockage of Li ion diffusion. In contrast, with large grain boundary diffusivity, the stress decreases with increasing grain orientation angle due to reduced concentration gradients in grain boundary regions.