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Foster, DanielMechanical and Thermal Characterization of Ultrasonic Additive Manufacturing
Doctor of Philosophy, The Ohio State University, 2014, Welding Engineering
Additive manufacturing is an emerging production technology used to create net shaped 3-D objects from a digital model. Ultrasonic Additive Manufacturing (UAM) is a relatively new type of additive manufacturing that uses ultrasonic energy to sequentially bond layers of metal foils at temperatures much lower than the melting temperature of the material. Constructing metal structures without melting allows UAM to have distinct advantages over beam based additive manufacturing and other traditional manufacturing processes. This is because solidification defects can be avoided, structures can be composed of dissimilar material and secondary materials (both metallic and non-metallic) can be successfully embedded into the metal matrix. These advantages allow UAM to have tremendous potential to create metal matrix composite structures that cannot be built using any other manufacturing technique. Although UAM has tremendous engineering potential, the effect of interfacial bonding defects on the mechanical and thermal properties have not be characterized. Incomplete interfacial bonding at the laminar surfaces due to insufficient welding energy can result in interfacial voids. Voids create discontinuities in the structure which change the mechanical and thermal properties of the component, resulting in a structure that has different properties than the monolithic material used to create it. In-situ thermal experiments and thermal modeling demonstrates that voids at partially bonded interfaces significantly affected heat generation and thermal conductivity in UAM parts during consolidation as well as in the final components. Using ultrasonic testing, elastic properties of UAM structures were found to be significantly reduced due to the presence of voids, with the reduction being the most severe in the transverse (foil staking) direction. Elastic constants in all three material directions decreased linearly with a reduction in the interfacial bonded area. The linear trend permits the ability to predict bonded interfacial area in the manufacturing environment without the need for destructive mechanical or metallurgical tests. The feasibility of two process monitoring techniques for UAM were also evaluated. A method to test resonance frequency using a Photonic Doppler Velocimeter to detect vibrational motion was developed and tested. Preliminary testing revealed that resonance testing could be used to determine average interfacial bonded area in a UAM sample. In-situ vibration velocity of the sonotrode, welding foil and substrate were measured using the Photonic Doppler Velocimeter system. Analysis of the velocity data revealed that by analyzing absolute velocity, relative velocity and phase angles of the three structures a bonding vs. non-bonding conditions could be determined in-situ using the Photonic Doppler Velocimeter system.

Committee:

Wei Zhang, PhD (Advisor); Sudarsanam Suresh Babu, PhD (Committee Member); Glenn Daehn, PhD (Committee Member); Stanislav Rokhlin, PhD (Committee Member)

Subjects:

Aerospace Materials; Materials Science; Mechanical Engineering

Keywords:

Welding, Additive Manufacturing, Ultrasonic Additive Manufacturing, Photonic Doppler Velocimeter

Prabhu, Avinash WImproving Fatigue Life of LENS Deposited Ti-6Al-4V through Microstructure and Process Control
Master of Science, The Ohio State University, 2014, Welding Engineering
Laser Engineered Net Shaping (LENS) is a solid freeform fabrication process capable of producing net shape, custom parts through a layer-by-layer deposition of material using a laser energy source. LENS based Ti-6Al-4V parts are currently being explored for applications to aerospace and biomedical implant applications. To achieve satisfactory mechanical performance in the components, homogeneity of the microstructure and the physical structure is important. This study explores methods of improving the fatigue life of Ti-6Al-4V LENS deposits through the creation of defect free components with appropriate microstructure. The work focuses on the impact of beta grain refinement and the elimination of lack of fusion porosity defects on the fatigue life of the alloy. Further, a model is developed to predict the epitaxial grain growth in LENS builds of Ti-64. This model is used to augment the prediction capability of a simultaneous transformation kinetics (STK theory) based model developed previously. The beta grain refinement in the fatigue properties of Ti-64 is achieved through addition of boron in amounts < 3 wt%. The addition of boron is found to refine the columnar beta structure typically observed in LENS deposited Ti-64. However, at high concentrations of boron, it was difficult to discern the prior beta grain size to visualize the extent of grain refinement. The boron alloying further causes a significant change in the structure of alpha laths, leading the shorter and thicker individual laths. Grain boundary alpha is not observed in the microstructure on addition of boron above a certain threshold. The addition of boron is observed to improve the fatigue properties of deposited Ti-64 samples. The Ti-64 LENS builds are observed to contain lack-of-fusion porosity in the lower regions of the deposit close to the substrate. The effect of process parameters namely the power, travel speed, hatch width, pre-heating, powder flow rate, substrate surface quality, and the hatch path on the amount of porosity is analyzed through trial experiments followed by a more detailed design of experiments approach. At a fixed power setting of 400W, the hatch width and powder flow rate are observed to have a significant influence on the extent of porosity present in the deposit. The hatch width has been further optimized through a CFD based simulation based approach leading to an increased material efficiency and reduced time of building. These builds are observed to show a columnar beta grain structure growing epitaxially from the base of the deposit and consist of primarily basketweave alpha. The fatigue properties are analyzed at the combination of parameters determined through experiments and are found to show an improvement over previously reported values by 3 times. The epitaxial grain growth seen in the LENS deposits is modeled using the classical grain growth equation. The prediction is observed to be sensitive to the atomic mobility, starting grain size, activation energy for grain growth and alpha dissolution temperatures. This grain growth information is incorporated into simultaneous transformation kinetics (STK theory) based microstructure model to improve the predictions of microstructure fraction in Ti-6Al-4V LENS builds.

Committee:

Wei Zhang (Advisor); Dave Farson (Committee Member); Sudarsanam Babu (Committee Member)

Subjects:

Materials Science

Keywords:

Ti-6Al-4V; LENS; Additive Manufacturing; Laser Additive Manufacturing; Grain growth modeling; Boron alloyed Ti-6Al-4V;

Ranjan, RajitDesign for Manufacturing and Topology Optimization in Additive Manufacturing
MS, University of Cincinnati, 2015, Engineering and Applied Science: Mechanical Engineering
Additive Manufacturing (AM) processes are used to fabricate complex geometries using a layer by layer material deposition technique. These processes are recognized for creating complex shapes which are difficult to manufacture otherwise and for enabling designers to be more creative with their designs. However, as AM is still in its developing stages, relevant literature with respect to design guidelines for AM is not readily available. This research proposes a novel design methodology which can assist designers in creating parts with high manufacturability. The research includes formulation of design guidelines by studying the relationship between input part geometry and AM process parameters. Two approaches are considered for application of the developed design guidelines. The first approach presents a feature graph based design improvement method in which the concept of Producibility Index (PI) is used to compare the designs. This method is useful for performing manufacturing validation of pre-existing designs and modifying it for better manufacturability. The second approach presents a DFAM constrained topology optimization based design advisory which can help designers in creating entirely new lightweight designs that are additive friendly. In this approach, the developed AM design guidelines are mathematically integrated with existing structural optimization techniques. Application of both the methods is presented in the form of case studies where design improvement and evolution is observed.

Committee:

Sundararaman Anand, Ph.D. (Committee Chair); Sundaram Murali Meenakshi, Ph.D. (Committee Member); David Thompson, Ph.D. (Committee Member); Kumar Vemaganti, Ph.D. (Committee Member)

Subjects:

Engineering

Keywords:

Design for Additive Manufacturing;Additive Manufacturing;Direct Metal Laser Sintering;Feature Graph;Topology Optimization;Producibility Index

Makiewicz, Kurt TimothyDevelopment of Simultaneous Transformation Kinetics Microstructure Model with Application to Laser Metal Deposited Ti-6Al-4V and Alloy 718
Master of Science, The Ohio State University, 2013, Materials Science and Engineering
Laser based additive manufacturing has become an enabling joining process for making one-of-a-kind parts, as well as, repairing of aerospace components. Although, the process has been established for more than a decade, optimization of the process is still performed by trial and error experimentation. At the same time, deployment of integrated process-microstructure models has remained as a challenge due to some of the reasons listed below: (1) lack of good process models to consider the laser-material interactions; (2) inability to capture all the heat transfer boundary conditions; (3) thermo-physical-mechanical properties; and (4) robust material model. This work pertains to the development of robust material model for predicting microstructure evolution as a function of arbitrary thermal cycles (multiple heating and cooling cycles) that can be integrated into a process model. This study focuses on the development of a material model for Ti-6Al-4V and Alloy 718. These two alloys are heavily used in turbine engines and undergo complex phase transformations, making them suited to developing a material model for laser metal deposition (LMD). The model uses simultaneous transformation kinetics (STK) theory to predict the transformation of one parent phase into several products. The model uses calculated thermodynamic properties of the alloys for portions of the respective transformation characteristics. Being a phenomenological model there are several user defined calibration parameters to fit the predicted output to experimental data. These parameters modify the nucleation and growth kinetics of the individual transformations. Analyses of experimental LMD builds are used to calibrate the material model. A Ti-6Al-4V build made on a room temperature substrate showed primarily colony alpha morphology in the bottom half of the build with a transition to basketweave alpha in the top half. An increase in hardness corresponding to the microstructural transition was observed. This sample had an average of 340 HV hardness. Analysis of the calculated thermal profiles at the location of the morphology transition showed a transition from cooling below the beta transus to cooling above the beta transus. The Ti-6Al-4V STK model was calibrated using the experimental data from this sample. The substrate of a second build was heated above the Ti-6Al-4V beta transus. This build showed predominantly basketweave alpha without a microstructural transition. Large prior beta grains (>1mm) were observed growing epitaxially from the substrate. These large grains promoted the basketweave formation. Hardness testing showed an average of 344 HV. Samples built in this way were also fatigue tested in the as built condition. Results show that they match previous builds that had been stress relieved. A third build was performed at room temperature on a substrate with large prior beta grains. This build showed basketweave morphology like the second build even though the substrate was not thermally controlled. The hardness for this build averaged 396 HV which is ~50 HV higher than the previous two. This build shows that it may be possible to produce better mechanical properties by controlling the beta grain size rather than heating the substrate. Eighteen Alloy 718 builds were made using proprietary processing conditions. All of these builds were analyzed for nano-scale γ’ and γ’’ precipitates. Two of the builds were similar but had different laser powers. The low laser power build did not show nano-scale precipitates. The higher power build did show small amounts (<3%) of nano-scale precipitates and a corresponding increase in hardness at their locations. The higher power build was used to develop the STK model for Alloy 718. Sixteen of these builds were part of a design of experiments and are referred to as DOE samples. Eight of them have a single layer while the other eight have multiple layers. They were examined for nano-scale precipitates. The amounts of precipitates were correlated to hardness values and thermal profiles.

Committee:

Sudarsanam Babu (Advisor); Wolfgang Windl (Committee Member)

Subjects:

Aerospace Materials; Materials Science; Metallurgy

Keywords:

Simultaneous Transformation Kinetics; STK; Microstructure Modeling; Laser Additive Manufacturing; Laser Metal Deposition; aerospace repair; Ti-6Al-4V; Inconel 718; Alloy 718; Additive Manufacturing; LAM; LMD;

Wolcott, Paul JosephToward Load Bearing Reconfigurable Radio Frequency Antenna Devices Using Ultrasonic Additive Manufacturing
Master of Science, The Ohio State University, 2012, Mechanical Engineering

Ultrasonic additive manufacturing (UAM) is a low temperature, solid-state manufacturing process that enables the creation of layered solid metal structures with designed anisotropies and embedded materials. As a low temperature process, UAM enables the creation of composites using smart materials or other components that would otherwise be destroyed in fusion-type processes. The process uses ultrasonic energy to bond metallic foils to one another under an applied load through a scrubbing action at the foil interface. This scrubbing action creates the nascent surfaces necessary for solid state bonding. To be able to take full advantage of the UAM process, the mechanical properties of composites made therein must be fully characterized. In this study, scanning electron microscopy is utilized to investigate the bonding behavior at the foil interface of samples tested in tension. Findings show a relationship between the amount of ductile fracture and the strength of UAM samples. In addition, fatigue testing was conducted on UAM Al samples to determine their lifetime under cyclic loading conditions. The results indicate a flat S-N behavior between the loading and number of cycles to failure. This indicates that lifetime prediction of UAM samples is difficult at this time due to the inconsistent bonding at the interface. It is theorized that the unbonded areas at the interfaces grow into one another and eventually lead to fast fracture.

Along with the developments made in understanding UAM mechanical properties, the design and manufacture of reconfigurable antennas was conducted with an eventual goal of developing a structural reconfigurable antenna using UAM. The reconfigurable antenna design concept uses shape memory alloy switches to electrically connect to an antenna structure to create discrete shifts in the antenna natural frequency. Using this design concept, three sets of shape memory alloy switches were made to connect with three different antenna structures. The first switch proved the concept of reconfiguration with a monopole antenna, yielding a frequency shift of 85 MHz. The second switch design used smaller dimensions to work in conjunction with a microstrip line, an antenna-like device. With this switch, the transmission of a radio frequency signal was tested to confirm the operation of the switches in both the on and off positions. This setup showed that the metallization of the antenna could effectively change the natural frequency while maintaining significant signal strength. A final set of switches was made for implementation into a planar antenna structure. The planar antenna was designed and constructed with free segments within the structure where switches are connected create reconfiguration. This antenna provides tunable frequency shifts from 2.43 GHz with no switches connected to 2.25 GHz when both switches are connected while maintaining a high gain and repeatable radiation pattern.

Committee:

Marcelo Dapino, Ph.D. (Advisor); S. Suresh Babu, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Ultrasonic Additive Manufacturing; Ultrasonic consolidation; Metal matrix composites; Fatigue; Reconfigurable antennas; Smart materials

Uth, Nicholas PComputational Design and Optimization of Bone Tissue Engineering Scaffold Topology
Master of Science, Miami University, 2016, Chemical, Paper & Biomedical Engineering
Bone tissue engineering aims to help the body naturally regenerate critical sized defects (and non-unions) that would otherwise require bone grafts. Scaffolds are a vital tool in this field, as they act as temporary matrices for cellular adhesion and bear mechanical loads during patient recovery. However, there are many aspects to designing such scaffolds, and two of the most vital (compressive modulus and porosity) conflict. Commonly, studies that attempt to determine viable designs use "trial-and-error" methods, which are resource demanding and may not guarantee fully optimized results. In this study, we sought to generate a scaffold topology that satisfied the compressive modulus and porosity requirements for trabecular bone regeneration with COMSOL optimization software. To determine the validity of COMSOL’s optimized topology and predicted behavior, we constructed and tested 24 scaffolds via 3D bioplotting, an additive manufacturing technique, according to a physical I-optimal split-plot designed experiment. The results were used to generate response surface methodology models that could be used to optimize scaffold topology and predict the resultant compressive modulus and porosity.

Committee:

Azizeh-Mitra Yousefi (Advisor); Byran Smucker (Advisor); Jens Mueller (Committee Member); Andrew Paluch (Committee Member)

Subjects:

Biomedical Engineering

Keywords:

bone tissue engineering; 3D bioplotting; additive manufacturing; topology; optimization; simulation; COMSOL; designed experiment

Samant, RutujaSupport structure accessibility and removal in Additive Manufacturing using octree data structure
MS, University of Cincinnati, 2015, Engineering and Applied Science: Mechanical Engineering
Metal Additive Manufacturing (AM) has made it possible to manufacture complex parts by adopting a layer-by-layer approach. However, additional support structures are needed to support the overhanging surfaces in a part and to alleviate thermal distortion that may occur in these parts. This leads to, increased build time for part manufacturing and additional post processing efforts for removal of supports. Support structures also affect the surface finish of regions in which they come in contact with part and many a time, removal of these supports becomes difficult due to complicated part features. Thus, minimizing the need of support for a part and ensuring its maximum removal is very crucial for an efficient part build in Additive Manufacturing. The main parameter that influences the need for support structures to build a part is its build orientation. One of the objectives of this work is to identify the optimum build orientation of a part such that, overall part build time is minimized while ensuring maximum removal of support and minimizing contact area between part and support. A hierarchical octree data structure has been used to check the accessibility of support structures for removal and to calculate the amount of support in contact with part. The part build time is approximated based on the overall part build height. Incorporating the above parameters, a multi-objective optimization routine is developed to obtain the optimal build orientation for a part. Another area focused on in this research is the identification of optimal number/directions of part set-ups required to remove support structures from a part. A 2D setup map highlighting the feasible directions of setups for support removal has also been presented.

Committee:

Sundararaman Anand, Ph.D. (Committee Chair); Sundaram Murali Meenakshi, Ph.D. (Committee Member); David Thompson, Ph.D. (Committee Member)

Subjects:

Mechanics

Keywords:

Additive Manufacturing;Accessibility Analysis;Setup Analysis;Support Structures;Octree;Optimization

Kusuma, ChandrakanthThe Effect of Laser Power and Scan Speed on Melt Pool Characteristics of Pure Titanium and Ti-6Al-4V alloy for Selective Laser Melting
Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering
Selective Laser Melting (SLM) is an additive manufacturing (AM) technique that creates complex parts by selectively melting metal powder layer-by-layer. In SLM, the process parameters decide the quality of the fabricated component. In this study, single beads of commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy are melted on a substrate of the same material as powder using an in-house built SLM machine. Multiple combinations of laser power and scan speed are used for single bead fabrication while the laser beam diameter and powder layer thickness are kept constant. This experimental study investigates the influence of laser power, scan speed and laser energy density on the melt pool formation, surface morphology, geometry (width, depth, and height) and hardness of melt pools. The results show that the quality, geometry, and hardness of melt pool is significantly affected by laser power, scanning speed and laser energy density. In addition, the observed unfavorable effects such as inconsistent melt pool formation, balling, porosity are discussed in detail. At the end, suggestions are provided to use optimal parameters to avoid such unfavorable effects.

Committee:

Ahsan Mian, Ph.D. (Advisor); Henry D. Young, Ph.D. (Committee Member); Ha-Rok Bae, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

additive manufacturing; selective laser melting; melt pool characteristics

Burwell, Edwin DudleyA MICROPLASMA-BASED SPUTTERING SYSTEM FOR DIRECT-WRITE, MICROSCALE FABRICATION OF THIN-FILM METAL STRUCTURES
Master of Sciences (Engineering), Case Western Reserve University, 2015, EECS - Electrical Engineering
This thesis reports the development of a direct write, microplasma-based sputtering instrument and associated process for the fabrication of metallic microstructures on rigid and flexible substrates. The process capitalizes on a physical vapor that is generated within a small capillary by Ar ion bombardment of a small diameter metal wire. Forced Ar flow ejects the sputtered vapor through the orifice and onto the substrate. Integration with an x-y-z stage enables the direct patterning of structures without the need for masks. As-deposited, 40 nm-thick Au structures fabricated on glass substrates exhibit a resistivity that is only 20% higher than that of bulk Au. Deposition has also been demonstrated on liquid crystal polymer and PDMS substrates. The process is performed at atmospheric pressure, thereby addressing one of the most significant limitations associated with conventional magnetron sputtering. The direct-write capability and room temperature deposition make this process a potential alternative to ink-jet printing.

Committee:

Christian Zorman, Dr. (Advisor); Mohan Sankaran, Dr. (Committee Member); Philip Feng, Dr. (Committee Member)

Subjects:

Electrical Engineering; Engineering; Materials Science; Plasma Physics

Keywords:

microplasma; sputtering; additive manufacturing

Blake, Aaron JosephFrom 2D to 3D: On the Development of Flexible and Conformal Li-ion Batteries via Additive Manufacturing
Doctor of Philosophy (PhD), Wright State University, 2016, Engineering PhD
The future of electronic devices, such as smart skins, embedded electronics, and wearable applications, requires a disruptive innovation to the design of conventional batteries. This research was thus aimed at leveraging additive manufacturing as a means to invigorate the design of next-generation Li-ion batteries to meet the emerging requirements of flexible electronics. First, a state-of-the art approach for achieving flexible Li-ion batteries, using a robust, multi-walled carbon nanotube mat as current collector was demonstrated. A unique mechanical device was constructed to experimentally observe the correlation between mechanical fatigue and electrochemical stability. Points of failure in the conventional architecture were evaluated for improvement. Further, ink formulations were developed for printing both electrode and electrolyte membranes. Upon optimization of electrode porosity and electrical conductivity, application constraints, such as internal resistance, cycle life, and mechanical integrity, were studied to ensure maintenance of battery performance throughout the additive manufacturing process. Under similar evaluation, an electrolyte membrane fabricated using a phase inversion method with the addition of ceramic filler was revealed to impart a number of desirable performance characteristics (e.g., thermal stability, dendrite suppression) immediately upon extrusion and drying. Finally, a sequentially 3D-printed, full battery stack using these ink formulations was demonstrated to achieve targeted capacity and energy density requirements of 1 mAh cm-2 and 1.8 mWh cm-2, respectively.

Committee:

Hong Huang, Ph.D. (Advisor); Sharmila Mukhopadhyay, Ph.D. (Committee Member); Henry Young, Ph.D. (Committee Member); Christopher Muratore, Ph.D. (Committee Member); Michael Durstock, Ph.D. (Committee Member)

Subjects:

Energy; Engineering; Materials Science

Keywords:

additive manufacturing; 3D-printing; Li-ion battery; bendable battery; carbon nanotube current collectors; creasable battery; in situ mechanical testing; composite electrolyte

Sunitha Radhakrishnan, Shiv ShailendarStudy of Localized Electrochemical Deposition Using Liquid Marbles
MS, University of Cincinnati, 2016, Engineering and Applied Science: Mechanical Engineering
A liquid marble is a droplet of liquid coated with micro or nano-particles. A novel method of localized electrochemical deposition (LECD) using liquid marbles and the feasibility of application of this method in micro-repair has been studied. Controllability of the transportation of liquid marbles to any desired location by pick and place technique has been demonstrated. A theoretical model to predict the deposition height using a liquid marbles has been developed in this work. The height of deposition is a critical output parameter as it determines the minimum layer height in electrochemical additive manufacturing (ECAM). A physics based mathematical model using Faraday’s law of electrolysis and the knowledge of geometry of the tool and metal powder has been developed. Experiments were carried out to validate the theoretical model. Experimental results follow the trend predicted by the model. Electro deposition experiments were performed at defective spots with liquid marbles to confirm the feasibility of micro-repair using this novel technique. The corrosive property of the deposit with respect to the metal substrate has been studied. An immersion corrosion test was performed on substrates having micro spots made using LECD using 5% NaCl for 240 hours. The results were compared with specimens of the same dimension, which underwent the same corrosion testing process. It was found that the micro deposits did not affect the corrosion rate significantly and therefore localized electro deposition using liquid marbles may be considered as a potential method for micro repair.

Committee:

Murali Sundaram, Ph.D. (Committee Chair); Thomas Richard Huston, Ph.D. (Committee Member); Kumar Vemaganti, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Liquid Marble;Localized Elecrochemical Deposition;Additive Manufacturing;Micro Repair;Modeling;Corrosion

Pelini, AngeloInfluence of Strain Rate Sensitivity (SRS) of Additive Manufactured Ti-6Al-4V on Nanoscale Wear Resistance
Master of Science in Engineering, Youngstown State University, 2017, Department of Mechanical and Industrial Engineering
The widespread use of titanium alloys such as Ti-6Al-4V and the expense of manufacturing it, leads to a need of new manufacturing processes such as the innovative additive manufacturing technology of today. Ti-6Al-4V was studied in a series of experiments to determine the strain rate sensitivity of the material that was manufactured by conventional, mill-annealing, and additive manufacturing processes of electron beam melting and selective laser melting. Due to the high thermal cycles required in the hatching processes involved in building each layer of the part, and the rapid cooling, the grain size of dual phase titanium becomes very fine. Grain structure of each manufacturing process was studied and compared with the results. Constant rate of loading tests were performed on all three samples. Then the samples were tested in a multiple loading test where it was loaded at increasing maximum peak loads four times. The application of run-in wear can cause high friction where single asperity contact causes wear. Because of this, progressive scratch tests were performed at different loading rates and sliding speeds to compare to the indentation tests. Results show that grain size and structure influence the strain rate sensitivity as well as the scratch loading rate sensitivity. The results also show that the strain rate was affected by the fatigue induced by the multiple peak loads involved in the second test.

Committee:

Jae Joong Ryu, PhD (Advisor); Hazel Marie, PhD (Committee Member); Jason Walker, PhD (Committee Member)

Subjects:

Materials Science; Mechanical Engineering

Keywords:

Strain rate sensitivity; Ti-6Al-4V; Nano wear; Additive manufacturing

Allavarapu, SantoshA New Additive Manufacturing (AM) File Format Using Bezier Patches
MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering
Additive Manufacturing (AM) process is used to fabricate parts with complex geometries in a layer by layer approach. Current AM machines use Stereolithography (STL) file format to manufacture parts. An STL file format is a discrete representation of a CAD model which uses planar triangular facets to approximate the surface of part. Due to this planar approximation, the STL format does not retain the complete geometric information of a CAD model which leads to approximation errors in the STL files. The higher the curvature of a design surface, the larger is the approximation error of the STL file. Currently, translation errors are minimized by using finer tessellations with smaller triangular facets which increases the size and memory of the STL file. Moreover, even with finer tessellations, it is not possible to exactly represent a CAD part with curved surfaces. This thesis presents a methodology for developing a new file format using curved bi-quadratic Bezier patches which can better approximate a CAD model compared to the STL file. Two new Bezier based formats are presented in this research: the first format uses curved Bezier patches with linear edges and the second format uses curved Bezier patches with curved edges. In the first format named as the linear edge format, the patches are modeled such that the edges remain coincident with those of the original STL facets. In the second format called the curved edge format, the Bezier patch edges are modeled as quadratic Bezier curves. The new file formats have been developed for a test surface as well as several solid parts including cylinders and spheres. The accuracies of the new formats have been compared to those of the existing STL format for these test parts. Further validation of the file formats has been performed by comparing the profile errors, volumetric errors, cylindricity and sphericity errors for the chosen examples by virtually simulating the manufactured parts using the new Bezier formats and the STL format.

Committee:

Sundararaman Anand, Ph.D. (Committee Chair); Sundaram Murali Meenakshi, Ph.D. (Committee Member); David Thompson, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Additive Manufacturing;NURBS surface and STL format;Bezier Surface Fitting;Non-Linear Optimization;Slice Thicknesses - Layering;Computational Geometry

Sojiphan, KittichaiEffects of Very High Power Ultrasonic Additive Manufacturing Process Parameters on Hardness, Microstructure, and Texture of Aluminum 3003-H18 Alloy
Doctor of Philosophy, The Ohio State University, 2015, Welding Engineering
Very High Power Ultrasonic Additive Manufacturing (VHP-UAM) was used to fabricate 10 layers and up to 80 layers samples from aluminum alloy 3003-H18 foil (Al3003-H18) of 150 µm thickness with varying vibration amplitude and normal force. This research was aimed at studying the change in hardness, microstructure, and texture in Al3003-H18 foil both in as-processed conditions and in heat-treated (343°C-2hr) condition compared to original foil, and to utilize neutron diffraction method to characterize the bulk texture analysis of the bulk VHP-UAM samples. Results from Vicker microhardness measurement, optical microscopy, scanning electron microscopy, electron backscattered diffraction (EBSD), and neutron diffraction were used to describe the changes in hardness, microstructure, and texture. The difference in microstructure and texture evolution in VHP-UAM samples processed at different process parameters can be related to the energy input during VHP-UAM and the post-processing heat-treatment.

Committee:

Avraham Benatar (Advisor); Sudarsanam Suresh Babu (Advisor); John Lippold (Committee Member); Wei Zhang (Committee Member)

Subjects:

Materials Science; Metallurgy

Keywords:

Ultrasonic additive manufacturing; aluminum alloys; plastic deformation; dynamic recrystallization; dynamic recovery; grain growth; hardness; microstructure; texture; neutron diffraction; electron backscatter diffraction

Sheridan, Luke CharlesAn Adapted Approach to Process Mapping Across Alloy Systems and Additive Manufacturing Processes
Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering
The continually growing market for metal components fabricated using additive manufacturing (AM) processes has called for a greater understanding of the effects of process variables on the melt pool geometry and microstructure in manufactured components for various alloy systems. Process Mapping is a general approach that traces the influence of process parameters to thermal behavior and feature development during AM processing. Previous work has focused mainly on Ti-6Al-4V (Ti64), but this work uses novel mathematical derivations and adapted process mapping methodologies to construct new geometric, thermal, and microstructural process maps for Ti64 and two nickel superalloy material systems. This work culminates in the production of process maps for both Inconel 718 (IN718) and Inconel 625 (IN625) that were developed via both experimental and analytical data, and the tools used in the established process mapping approach have been thoroughly explored. This has resulted in a non-dimensional template for solidification behavior in terms of material solidification parameters and AM process parameters. The optimized non-dimensional approach presented here will increase the efficiency of future process map development and will facilitate the comparison of process maps across alloy systems and AM processes, laying the ground work for integrated AM feature control and evaluation of current and future materials for AM application.

Committee:

Nathan Klingbeil, Ph.D. (Advisor); Joy Gockel, Ph.D. (Committee Member); Raghavan Srinivasan, Ph.D. (Committee Member)

Subjects:

Engineering; Materials Science; Mechanical Engineering

Keywords:

additive manufacturing; Inconel; Inconel 718; Inconel 625; Ti-6Al-4V; process mapping; microstructure; melt pool; finite elements; closed-form process maps; solidification maps

Brant, AnneAn Explorative Study of Electrochemical Additive Manufacturing
MS, University of Cincinnati, 2016, Engineering and Applied Science: Mechanical Engineering
A multi-faceted explorative study was carried out on electrochemical additive manufacturing, a viable candidate as a nontraditional commercial additive manufacturing process. First, a feasibility study was carried out on the process to show that the process can work experimentally to create various geometries using a current feedback system. Second, a finite element simulation study was carried out on the effect of variation of process parameters and changing boundary conditions during the deposition process on the output geometry was observed. Next, a case study of support structure-less, voxel-by-voxel electrochemical deposition of a 3D part was introduced. This method allows for the creation of overhanging parts without reliance on support structures, which are difficult if not impossible to remove. Then, preliminary work was done to test the cloud-based application of an in-house micro metal additive manufacturing by electrochemical deposition process. Additive manufacturing, being a computer-based system that can save point-by-point data of parts to be manufactured, can be easily integrated into the cloud. Finally, the effects of the deposition parameters on the residual stress of output parts were investigated. In the feasibility study, it was seen that mostly-vertical parts can be deposited, but more complex geometries with horizontal layers remain a challenge. In the finite element simulation, trends were found between specific process parameters and output geometries in the simulations; trends varied between linear and nonlinear, and certain process parameters such as voltage and interelectrode gap were found to have a greater influence on the output than others. The simulations were able to predict the output width of deposition of experiments in an error of 8-30%. Next, standard values and procedures were established in order to create design rules for the electrochemical deposition process. The voxel size, tool clearance values, raster path generation, approach and retract paths, and part segmentation rules were established. The algorithm was then executed on a sample part and successful performance was verified. Then, the system was linked to commercial cloud and email access for constant real-time communication from any user with a phone, tablet, or personal computer. The process could be started, stopped, altered, and queried remotely via the cloud. Input parameters were specified and plots of output performance, time, and current information were communicated back to the user on-demand, as well as stored on the cloud long-term. The cloud could then link input parameters to the history of system performance on such input parameters in a cloud-stored database. An experiment was executed to optimize horizontal deposition parameters based on deposition resolution, and save these values into the cloud for future use. Finally, there were trends seen in the tensile and compressive output stresses corresponding to the input voltage, pulse period, and duty cycle. Overall, the information gained from this research allows for greater understanding of electrochemical additive manufacturing output and its enormous potential as a commercial additive manufacturing process of complex 3D parts. This lays the foundation for future commercial adoption of this manufacturing process.

Committee:

Sundaram Murali Meenakshi, Ph.D. (Committee Chair); Woo Kyun Kim, Ph.D. (Committee Member); Sundararaman Anand, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering; Mechanics

Keywords:

additive manufacturing;localized electrochemical depositon;maskless;3d printing;support structure-less;residual stress

Gullapalli, Ram AA Study of Mixed Manufacturing Methods in Sand Casting Using 3D Sand Printing and FDM Pattern-making Based on Cost and Time
Master of Science in Engineering, Youngstown State University, 2016, Department of Mechanical and Industrial Engineering
Sand casting has long been known to be an effective manufacturing method for metal casting and especially for parts of large dimensions and low production volume. But, for increasing complexity, the conventional sand casting process does have its limitations; one of them mainly being the high cost of tooling to create molds and cores. With the advent of additive manufacturing (AM), these limitations can be overcome by the use of a 3D sand printer which offers the unique advantage of geometric freedom. Previous research shows the cost benefits of 3D sand printing molds and cores when compared to traditional mold and core making methods. The line of research presented in this thesis introduces the idea of additive manufacturing at different stages of the sand casting process and investigates the decision-making process as well as the cost-based effects. This will enable foundries and manufacturers to integrate the use of AM machines more smoothly into their production process without the need for completely re-engineering the existing production system. A critical part of this thesis is the tooling cost estimation using a casting cost model that is significantly accurate to industry standard quotes. Based on these considerations, this thesis outlines three approaches for achieving this goal apart from traditional mold and core making methods. The first approach integrates 3D Printing at the pattern making level where the patterns and core-boxes are “printed” on an FDM printer. This eliminates the tooling costs associated with a traditional sand casting method. The second approach integrates 3D Printing at the core-making level by “mixing” traditional mold-making process and 3D sand printing process for core-making. The third approach, the 3D sand printer is used to create both the molds and the cores, thereby eliminating the need for traditional methods. An initial hypothesis is created which states that, for a given production volume, with increased complexity of the casting, additively manufacturing only the cores and conventionally manufacturing the molds is cost-feasible when compared to traditional manufacturing or 3D sand printing. It is finally concluded that the initial hypothesis is valid when part geometries are highly complex and production volumes range between medium to high. It is also concluded that a decision making tool based on the methodology provided can help determine a specific mixed manufacturing method for the manufacturer.

Committee:

Brett Conner, PhD (Advisor); Darrell Wallace, PhD (Committee Member); Eric MacDonald, PhD (Committee Member)

Subjects:

Economics; Engineering; Mechanical Engineering

Keywords:

3D Printing; Additive Manufacturing; Manufacturing; Sand Casting; Casting; Molds; Cores; Patterns; Pattern-making; 3D printed parts;

Lenner, LukasEngine Redesign Utilizing 3D Sand Printing Techniques Resulting in Weight and Fuel Savings
Master of Science in Engineering, Youngstown State University, 2016, Department of Mechanical and Industrial Engineering
Lightweighting is an important part of the automotive industry. As US manufacturers push the boundaries for lightweighting further every year, application of 3D sand printed molds for casting engine blocks and cylinder heads can play an expanding role. This masters thesis describes redesign of 350 Chevy engine with implementation of 3D sand printing featured into new design. Weight savings of more than 8lb. were achieved. A reverse engineering process was used to obtain the parametric data from the original engine castings. This was accomplished by using a 3D-scanner. Castings that have been redesigned include two cylinder heads, intake manifold and connecting rod. Castings were modified in CAD software SolidWorks. Weight savings were achieved by merging the intake manifold with two cylinder heads. This step allowed eliminating unvented bolt joints while creating highly complex part castable exclusively through molds fabricated by 3D sand printing. The implementation of lattice structure in connecting rod design provided weight savings of almost 2 lb. Seven different designs were proposed until the final design shape was obtained. New design of connecting rod was then verified through FEA. After the total weight saving were determined the fuel savings were calculated and extrapolated per fleet of the vehicles using similar engine. Annual fuel savings were provided and environmental impact of these fuel saving was found. Combination of intake manifold and cylinder heads into one casting eliminated the need for three gating systems. This modification saved more than 28lb of metal which would be considered as scrap if casting each part separately.

Committee:

Brett Conner, PhD (Advisor); Kerry Meyers, PhD (Committee Member); Jae Joong Ryu, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Engine Redesign;additive manufacturing;3D sand printing

Jeong, Kyoung HoDesign, Fabrication and Measurement of Millimeter Fresnel Lens and Helical Antenna using Additive Manufacturing
Master of Science, The Ohio State University, 2017, Electrical and Computer Engineering
Design, simulation, fabrication and measurement results of 3D-printed Fresnel lens and helical antenna are presented. Because the real and imaginary permittivity of the 3D-printed material (Polylactic Acid) at the frequencies of interest were unknown, we have measured these properties using time-domain spectroscopy as well as impedance/material analyzer. Full-wave simulation was used to design and optimize the realized gain of the lens and helical antenna. These devices were later on fabricated using fused deposition modeling and stereolithography, respectively. The gain pattern measurements were then performed in the anechoic chamber. Measurement results showed that the lens could achieve a gain improvement of 8-9 dB at 30 GHz. Furthermore, a 3D-printed helical antenna with suspended microstrip was shown to achieve a gain of 14 dB and half-power beam width of 30°, which closely agreed with the simulated data. By designing, fabricating and characterizing the two aforementioned examples, the limitation and challenges associated with additive manufacturing for antenna applications were studied. Moreover, our study will advance realization of antenna structures, specifically in the millimeter wave band.

Committee:

Nima Ghalichechian (Advisor); Wladimiro Villarroel (Committee Member)

Subjects:

Electrical Engineering; Engineering

Keywords:

Additive manufacturing, 3D printing, Helical antenna, Fresnel lens

Schomer, John JEmbedding fiber Bragg grating sensors through ultrasonic additive manufacturing
Master of Science, The Ohio State University, 2017, Mechanical Engineering
Fiber Bragg Grating (FBG) sensorsare optical fibers that detect in-situ strain through deviation of a reflected wavelength of light to detect in-situ strain. These sensors are immune to electromagnetic interference, and the inclusion of multiple FBGs on the same fiber allows for a seamlessly integrated sensing network. FBGs are attractive for embedded sensing in aerospace applications due to their small noninvasive size and prospect of constant, real-time nondestructive evaluation. FBGs are typically used in composite laminate type applications due to difficulties in building them into metallic structures. Additive manufacturing, also referred to as 3D printing, can allow for the inclusion of sensors inside of structural entities by the building of material around the sensor to be embedded. In this study, FBG sensors are embedded into aluminum 6061 via ultrasonic additive manufacturing (UAM), a rapid prototyping process that uses high power ultrasonic vibrations to weld similar and dissimilar metal foils together. UAM was chosen due to the desire to embed FBG sensors at low temperatures, a requirement that excludes other additive processes such as selective laser sintering or fusion deposition modeling. This study demonstrated the feasibility of embedding FBGs in aluminum 6061 via UAM. Further, the sensors were characterized in terms of birefringence losses, post embedding strain shifts, consolidation quality, and strain sensing performance. Sensors embedded into an ASTM test piece were compared against an exterior surface mounted foil strain gage at both room and elevated temperatures using cyclic tensile tests. The effects of metal embedment at temperatures above the melting point of the protective coating (160 degrees Celsius) of the FBG sensors were explored, and the hermetic sealing of the fiber within the metal matrix was used to eplain the coating survival. In-situ FBG sensors were also used to monitor the UAM process itself. Lastly, an example application was both modeled using finite element analysis to identify areas where FBG sensors could be placed, and then built with an embedded FBG sensor.

Committee:

Marcelo Dapino (Advisor); Mo-How Shen (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Fiber Bragg Grating, Ultrasonic Additive Manufacturing, Structural Health Monitoring, 3D Printing, Fiber Optic

Vincent, Timothy JohnComputational Modeling and Simulation of Thermal-Fluid Flow and Topology Formation in Laser Metal Additive Manufacturing
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Engineering
The field of metal additive manufacturing holds great promise in several industries for its potential to reduce cost and open the doors to new design paradigms as well as agile and efficient logistical systems. However, the complex, multi-faceted physics of additive metals processing has proved to be a significant barrier to quickly deploying and utilizing this technology. The connection between processing parameters and build quality remains an active field of research, further complicated by the particular intricacies of each process implemented by various equipment manufacturers. As direct experimentation remains relatively costly in this field, a clear opportunity exists for developing accurate and cost efficient simulation tools to aid in untangling the relationships between process specifics and build outcomes. In this work, the salient physical phenomena were analyzed for a blown powder and a powder bed process. Models were then formulated based on this analysis to capture the effects of build parameters on micro-scale topology and temperature distributions. These models were then implemented using the OpenFOAM Finite Volume software library. A steady-state model and simulation code was developed for the blown powder process and the topology predictions were validated quantitatively using experimental data from the literature. A time-dependent model and simulation code was developed for the powder bed process with an emphasis on capturing the complex interaction of thermally induced fluid flow with deformation of the gas-liquid interface of the melt pool. The salient aspects of this code were verified using simplified application cases and the code was demonstrated using a representative test case, which showed qualitative agreement with previous work. These two new codes enhance the field of additive metals processing by potentially reducing the effort necessary to produce parts by minimizing defects and maximizing microstructure quality.

Committee:

Markus Rumpfkeil, Ph.D. (Advisor); John Petrykowski, Ph.D. (Committee Member); Christopher Muratore, Ph.D. (Committee Member); Anil Chaudhary, Sci.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

multiphysics modeling, multiphase flow, CFD, additive manufacturing, SLM, DDM

Mokasdar, Abhiram S.A Quantitative Study of the Impact of Additive Manufacturing in the Aircraft Spare Parts Supply Chain
MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering
Additive manufacturing is a promising manufacturing technology which is finding its way into mainstream manufacturing industry. As compared to conventional manufacturing it has a number of advantages in terms of better energy efficiency, cutback in emissions, better design handling and lower manufacturing lead time. This work focuses on these aspects of additive manufacturing by evaluating its impact on the aircraft spare parts supply chain. An aircraft supply chain is very critical because even a small shortage of spare part leads to heavy financial losses. This makes it mandatory for the aircraft companies and operators to keep large stock of all the spare parts throughout the year and thus invest a lot of money in the inventory. The peculiarity of the aircraft spare parts is that they require several months for manufacturing using conventional manufacturing processes like casting, drilling, electrical discharge machining and welding. Conversely the manufacturing lead time of additive manufacturing is small as compared to these conventional processes and hence this work tries to advocate this feature of additive manufacturing to demonstrate how the total inventory of spare parts held in an aircraft spare parts supply chain can be significantly reduced using additive manufacturing.

Committee:

Hongdao Huang, PhD (Committee Chair); Sundaram Murali Meenakshi, PhD (Committee Member); David Thompson, PhD (Committee Member)

Subjects:

Mechanics

Keywords:

Additive Manufacturing; Supply Chain; Safety Inventory; Inventory Holding Cost; Lead Time

Bhatia, ShaleenEffect of Machine Positional Errors on Geometric Tolerances in Additive Manufacturing
MS, University of Cincinnati, 2014, Engineering and Applied Science: Mechanical Engineering
Additive Manufacturing (AM) is the process of producing 3D parts from a digital model in a layer by layer manner without the need for part specific tooling. Part material is typically a liquid that is photocured as in Stereolithography (SLA) or a powder that is sintered, as in Selective Laser Sintering (SLS) or Direct Metal Laser Sintering (DMLS). In this research a mathematical model of a typical DMLS machine is created to evaluate errors during additive manufacturing. This model incorporates machine error parameters to account for imperfections in machine linkages that cause these errors. The total machine error is modelled as two independent systems: the laser positioning error on the bed and the platform movement error along the z direction. The AM process is then simulated using a Virtual Manufacturing (VM) scheme to compute the actual geometry of the manufactured part for given AM process parameters. Part build orientation and location on manufacturing platform are the two process parameters that were considered in this VM process. Then cylindricity and flatness errors on this part are measured. The virtual manufacturing process is repeated for different values of layer thickness and different part location on the AM machine’s platform. These results are used to identify part orientations and part locations on the manufacturing platform that meet cylindricity and flatness tolerance requirement specified on the part.

Committee:

Sundararaman Anand, Ph.D. (Committee Chair); Sundaram Murali Meenakshi, Ph.D. (Committee Member); David Thompson, Ph.D. (Committee Member)

Subjects:

Mechanics

Keywords:

Additive Manufacturing;Virtual Simulation;Form Errors;Machine Positional Errors

Zha, WentaoGeometric Approaches to Input File (STL) Modification for Part Quality Improvement in Additive Manufacturing
MS, University of Cincinnati, 2015, Engineering and Applied Science: Mechanical Engineering
Additive manufacturing (AM) machines use the Stereolithography (STL) file as standard input file format to build parts. STL model is a triangular faceted approximation of a CAD model which represents a part with less accuracy than the CAD model. Commercial softwares have the ability to convert a CAD file into an STL file based on a user defined threshold value to uniformly convert the entire part body into triangular facets. Increasing the geometric accuracy of STL models is typically accomplished by decreasing the user defined threshold value, which results in an increase in STL file size. In this research, a Surface-based Modification Algorithm (SMA) that adaptively and locally increases the facet density of an STL model is presented. The Surface-based Modification Algorithm is an error minimization approach to modify the STL facets locally based on chordal error, cusp height and cylindricity error for cylindrical features and is typically able to achieve a smaller file size compared to uniform export option. A novel bounding box based algorithm is developed to calculate cusp height error from the point cloud generated from the part by slicing the STL facets or from the CAD surface. Final results show a distinct improvement in the part error of the STL model using Surface-based Modification Algorithm (SMA) when compared to the original STL file.

Committee:

Sundararaman Anand, Ph.D. (Committee Chair); Thomas Richard Huston, Ph.D. (Committee Member); David Thompson, Ph.D. (Committee Member)

Subjects:

Engineering

Keywords:

Additive Manufacturing;STL File;Cusp Height;Virtual Manufacturing;Chordal Error

Taheri Andani, MohsenModeling, Simulation, Additive Manufacturing, and Experimental Evaluation of Solid and Porous NiTi
Master of Science, University of Toledo, 2015, Mechanical Engineering
In recent years, shape memory alloys (SMAs) have entered a wide range of engineering applications in fields such as aerospace and medical applications. Nickel-titanium (NiTi) is the most commonly used SMAs due to its excellent functional characteristics (shape memory effect and superelasticity behavior). These properties are based on a solid-solid phase transformation between martensite and austenite. Beside these two characteristics, low stiffness, biocompatibility and corrosion properties of NiTi make it an attractive candidate for biomedical applications (e.g., bone plates, bone screws, and vascular stents). It is well know that manufacturing and processing of NiTi is very challenging. The functional properties of NiTi are significantly affected by the impurity level and due to the high titanium content, NiTi are highly reactive. Therefore, high temperature processed parts through methods such as melting and casting which result in increased impurity levels have inadequate structural and functional properties. Furthermore, high ductility and elasticity of NiTi, adhesion, work hardening and spring back effects make machining quite challenging. These unfavorable effects for machining cause significant tool wear along with decreasing the quality of work piece. Recently, additive manufacturing (AM) has gained significant attention for manufacturing NiTi. Since AM can create a part directly from CAD data, it is predicted that AM can overcome most of the manufacturing difficulties. This technique provides the possibility of fabricating highly complex parts, which cannot be processed by any other methods. Curved holes, designed porosity, and lattice like structures are some examples of mentioned complex parts. This work investigates manufacturing superelastic NiTi by selective laser melting (SLM) technique (using PXM by Phenix/3D Systems). An extended experimental study is conducted on the effect of subsequent heat treatments with different aging conditions on phase transformation temperatures of the manufactured parts. To this end both phase transformation and mechanical behavior of the AM parts are studied. Moreover, the application of additive manufacturing to develop NiTi components with desired stiffness by introducing engineered porosity is studied. To this end, a unit cell made of two interconnecting struts is used to generate the CAD files for a series of porous structures with six different levels of porosity in the range of 20% to 82%. Finite element analyses are conducted to examine the stress-strain behavior of the fabricated structures under loading. To validate the simulations, uniaxial compression tests are performed on three NiTi samples with three different levels of porosity (32%, 45%, and 58%). The experimental data closely match with the analytical results. The findings of this study indicate that introducing porosity to a NiTi structure results in a significant drop in the stiffness of the component. These results pave the way for designing porous NiTi structures with the desired level of stiffness.

Committee:

Mohammad Elahinia (Advisor); Mehdi Pourazady (Committee Member); Matthew Franchetti (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Shape Memory Alloy, NiTi, Nitinol, Porous NiTi, Implant, Porosity, Stress Shielding, Selective laser melting, additive manufacturing, Heat Treatment, Aging NiTi

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