Browsing by Author "Department of Mechanical Engineering, School of Engineering and Technology"

Now showing 1 - 10 of 35
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    3D Printed ABS and Carbon Fiber Reinforced Polymer Specimens for Engineering Education
    (Springer, 2016) Golub, Michael; Guo, Xingye; Jung, Mingyo; Zhang, Jing; Department of Mechanical Engineering, School of Engineering and Technology
    Three 3D printed plastic materials, ABS, ABS plus, and CFRP, have been studied for their potential applications in engineering education. Using tensile test, the stress strain curves of the materials have been measured. The Young’s modulus, ultimate strength, and fracture toughness of the materials are calculated from the stress strain curve. The results show that CFRP has the highest stiffness or Young’s modulus. ABS plus has strongest mechanical properties, with highest ultimate strength and fracture toughness. With the measured properties, the 3D printed samples are a viable solution for engineering students to learn mechanical properties of materials.
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    Ab initio study of anisotropic mechanical properties of LiCoO2 during lithium intercalation and deintercalation process
    (AIP, 2015-12) Wu, Linmin; Zhang, Jing; Department of Mechanical Engineering, School of Engineering and Technology
    The mechanical properties of LixCoO2 under various Li concentrations and associated anisotropy have been systematically studied using the first principles method. During the lithium intercalation process, the Young's modulus,bulk modulus,shear modulus, and ultimate strength increase with increasing lithium concentration. Strong anisotropy of mechanical properties between a-axis and c-axis in LixCoO2 is identified at low lithium concentrations, and the anisotropy decreases with increasing lithium concentration. The observed lithium concentration dependence and anisotropy are explained by analyzing the charge transfer using Bader charge analysis, bond order analysis, and bond strength by investigating partial density of states and charge density difference. With the decrease of Li concentration, the charge depletion in the bonding regions increases, indicating a weaker Co-O bond strength. Additionally, the Young's modulus,bulk modulus,shear modulus, and toughness are obtained by simulating ab initio tensile tests. From the simulated stress-strain curves, LixCoO2 shows the highest toughness, which is in contraction with Pugh criterion prediction based on elastic properties only.
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    Active Disturbance Rejection Control based on Generalized Proportional Integral Observer to Control a Bipedal Robot with Five Degrees of Freedom
    (IEEE, 2016-07) Arcos-Legarda, Jaime; Cortes-Romero, John; Tovar, Andres; Department of Mechanical Engineering, School of Engineering and Technology
    An Active Disturbance Rejection Control based on Generalized Proportional Integral observer (ADRC with GPI observer) was developed to control the gait of a bipedal robot with five degrees of freedom. The bipedal robot used is a passive point feet which produces an underactuated dynamic walking. A virtual holonomic constraint is imposed to generate online smooth trajectories which were used as references of the control system. The proposed control strategy is tested through numerical simulation on a task of forward walking with the robot exposed to external disturbances. The performance of ADRC with GPI observer strategy is compared with a feedback linearization with proportional-derivative control. A stability test consisting on analyzing the existence of limit cycles using the Poincaré's method revealed that asymptotically stable walking was achieved. The proposed control strategy effectively rejects the external disturbances and keeps the robot in a stable dynamic walking.
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    Bis(aryl) Tetrasulfides as Cathode Materials for Rechargeable Lithium Batteries
    (Wiley, 2017) Guo, Wei; Wawrzyniakowski, Zachary D.; Cerda, Matthew M.; Bhargav, Amruth; Pluth, Michael D.; Ma, Ying; Fu, Yongzhu; Department of Mechanical Engineering, School of Engineering and Technology
    An organotetrasulfide consists of a linear chain of four sulfur atoms that could accept up to 6 e− in reduction reactions, thus providing a promising high-capacity electrode material. Herein, we study three bis(aryl) tetrasulfides as cathode materials in lithium batteries. Each tetrasulfide exhibits two major voltage regions in the discharge. The high voltage slope region is governed by the formation of persulfides and thiolates, and the low voltage plateau region is due to the formation of Li2S2/Li2S. Based on theoretical calculations and spectroscopic analysis, three reduction reaction processes are revealed, and the discharge products are identified. Lithium half cells with tetrasulfide catholytes deliver high specific capacities over 200 cycles. The effects of the functional groups on the electrochemical characteristics of tetrasulfides are investigated, which provides guidance for developing optimum aryl polysulfides as cathode materials for high energy lithium batteries.
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    Cellular Helmet Liner Design through Bio-inspired Structures and Topology Optimization of Compliant Mechanism Lattices
    (SAE International, 2018-12-28) Najmon, Joel; DeHart, Jacob; Wood, Zebulun; Tovar, Andres; Department of Mechanical Engineering, School of Engineering and Technology
    The continuous development of sport technologies constantly demands advancements in protective headgear to reduce the risk of head injuries. This article introduces new cellular helmet liner designs through two approaches. The first approach is the study of energy-absorbing biological materials. The second approach is the study of lattices comprised of force-diverting compliant mechanisms. On the one hand, bio-inspired liners are generated through the study of biological, hierarchical materials. An emphasis is given on structures in nature that serve similar concussion-reducing functions as a helmet liner. Inspiration is drawn from organic and skeletal structures. On the other hand, compliant mechanism lattice (CML)-based liners use topology optimization to synthesize rubber cellular unit cells with effective positive and negative Poisson's ratios. Three lattices are designed using different cellular unit cell arrangements, namely, all positive, all negative, and alternating effective Poisson's ratios. The proposed cellular (bio-inspired and CML-based) liners are embedded between two polycarbonate shells, thereby, replacing the traditional expanded polypropylene foam liner used in standard sport helmets. The cellular liners are analyzed through a series of 2D extruded ballistic impact simulations to determine the best performing liner topology and its corresponding rubber hardness. The cellular design with the best performance is compared against an expanded polypropylene foam liner in a 3D simulation to appraise its protection capabilities and verify that the 2D extruded design simulations scale to an effective 3D design.
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    Characterization of Microstructure and Mechanical Properties of Direct Metal Laser Sintered 15–5 PH1 Stainless Steel Powders and Components
    (Springer, 2016) Zhang, Jing; Zhang, Yi; Guo, Xingye; Lee, Weng Hoh; Hu, Bin; Lu, Zhe; Jung, Yeon-Gil; Lee, Je-Hyun; Department of Mechanical Engineering, School of Engineering and Technology
    15–5 PH1 stainless steel powder is one of the common materials used for the DMLS process. In this study, both the powder and parts fabricated via DMLS have been characterized. The microstructure and elemental composition have been examined. The microhardness and surface roughness have also been measured. The results show that most powder particle are in spherical with a particle size of 5 ~ 60 μm. Chemical compositions of the powder compare well with the literature data. The thickness of rough surface is about 1 μm. The measured Rockwell hardness is HRC 42.9±0.3, which is also in good agreement with literature.
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    Deformability of Human Mesenchymal Stem Cells Is Dependent on Vimentin Intermediate Filaments
    (Springer, 2017-05) Sharma, Poonam; Bolten, Zachary T.; Wagner, Diane R.; Hsieh, Adam H.; Department of Mechanical Engineering, School of Engineering and Technology
    Mesenchymal stem cells (MSCs) are being studied extensively due to their potential as a therapeutic cell source for many load-bearing tissues. Compression of tissues and the subsequent deformation of cells are just one type physical strain MSCs will need to withstand in vivo. Mechanotransduction by MSCs and their mechanical properties are partially controlled by the cytoskeleton, including vimentin intermediate filaments (IFs). Vimentin IF deficiency has been tied to changes in mechanosensing and mechanical properties of cells in some cell types. However, how vimentin IFs contribute to MSC deformability has not been comprehensively studied. Investigating the role of vimentin IFs in MSC mechanosensing and mechanical properties will assist in functional understanding and development of MSC therapies. In this study, we examined vimentin IFs’ contribution to MSCs’ ability to deform under external deformation using RNA interference. Our results indicate that a deficient vimentin IF network decreases the deformability of MSCs, and that this may be caused by the remaining cytoskeletal network compensating for the vimentin IF network alteration. Our observations introduce another piece of information regarding how vimentin IFs are involved in the complex role the cytoskeleton plays in the mechanical properties of cells.
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    Design of Self-Supported 3D Printed Parts for Fused Deposition Modeling
    (ASME, 2016-08) Lischke, Fabian; Tovar, Andres; Department of Mechanical Engineering, School of Engineering and Technology
    One of the primary challenges faced in Additive Manufacturing (AM) is reducing the overall cost and printing time. A critical factor in cost and time reduction is post-processing of 3D printed (3DP) parts, of which removing support structures is one of the most time consuming steps. Support is needed to prevent the collapse of the part or certain areas under its own weight during the 3D printing process. Currently, the design of self-supported 3DP parts follows a set of empirical guide lines. A trial and error process is needed to produce high quality parts by Fused Depositing Modeling (FDM). The usage of chamfer angle with a max 45° angle form the horizontal for FDM is a common example. Inclined surfaces with a smaller angle are prone to defects, however no theoretical basis has been fully defined, therefore a numerical model is needed. The model can predict the problematic areas at a print, reducing the experimental prints and providing a higher number of usable parts. Physical-based models have not been established due to the generally unknown properties of the material during the AM process. With simulations it is possible to simulate the part at different temperatures with a variety of other parameters that have influence on the behavior of the model. In this research, analytic calculations and physical tests are carried out to determine the material properties of the thermoplastic polymer Acrylonitrile - Butadiene - Styrene (ABS) f or FDM at the time of extrusion. This means that the ABS is going to be extruded at 200°C to 245°C and is a viscous material during part construction. Using the results from the physical and analytical models, i.e., Timoshenko’s modified beam theory for micro-structures, a numerical material model is established to simulate the filament deformation once it is deposited onto the part. Experiments were also used to find the threshold for different geometric specifications, which could then be applied to the numerical model to improve the accuracy of the simulation. The result of the finite element analysis is compared to experiments to show the correlation between the prediction of deflection in simulation and the actual deflection measured in physical experiments. A case study was conducted using an application that optimizes topology of complex geometries. After modeling and simulating the optimized part, areas of defect and errors were determined in the simulation, then verified and and measured with actual 3D prints.
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    Discrete element modeling of powder flow and laser heating in direct metal laser sintering process
    (Elsevier, 2017-06) Lee, Weng-Hoh; Zhang, Yi; Zhang, Jing; Department of Mechanical Engineering, School of Engineering and Technology
    A novel particle-based discrete element model (DEM) is developed to simulate the whole Direct Metal Laser Sintering (DMLS) process, which includes simplified powder deposition, recoating, laser heating, and holding stages. This model is first validated through the simulation of particle flow and heat conduction in the powder bed, and the simulated results are in good agreement with either experiment in the literature or finite element method. Then the validated model is employed to the DMLS process. The effects of laser power, laser scan speed, and hatch spacing on the temperature distributions in the powder bed are investigated. The results demonstrate that the powder bed temperature rises as the laser power is increased. Increasing laser scan speed and laser hatch spacing will not affect the average temperature increase in the powder bed since energy input is kept same. However, a large hatch spacing may cause non-uniform temperature distribution and microstructure inhomogeneity. The model developed in this study can be used as a design and optimization tool for DMLS process.
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    Effect of Printing Orientation on Strength of 3D Printed ABS Plastics
    (Springer, 2016) Cai, Linlin; Byrd, Philip; Zhang, Hanyin; Schlarman, Kate; Zhang, Yi; Golub, Michael; Zhang, Jing; Department of Mechanical Engineering, School of Engineering and Technology
    The mechanical strengths of ABS (Acrylonitrile Butadiene Styrene) components fabricated by fused deposition modeling (FDM) technique have been studied, with the focus on the effect of printing orientations on the strength. Using the properties derived from stress-strain curves of the samples, the 0-degree printed sample has the strongest mechanical properties, which is likely due to preferred orientations in individual slice.