Parametric Modeling of Biomimetic Sharkskin for Wire EDM for Drag Reduction and Hydrophobicity

This research sets out to demonstrate the viability of parametric modeling for biomimetic sharkskin in the effort to reduce drag and create a self-cleaning surface. Multiple designs were created to be machined by Wire EDM on stainless steel and titanium and were comparatively tested. Limitations of current manufacturing processes to economically produce naturally occurring structures such as sharkskin, emphasize the need to be able to calculate the most accurate design for a given manufacturing process. By designing a simplified but parametrically consistent model compared to an accurately depicted 3D model of sharkskin, the textured samples produced can be further tested for drag reduction and hydrophobicity (the tendency to repel water) based on five independent numerical values. Advisor: Kamlakar Rajurka

Development of Arrayed Structures Using Reverse EDM (R-EDM)

In recent years, reverse electric discharge machining (R-EDM) has been developed as a method for the fabrication of arrayed structures which find applications in the fabrication of fins and component assembly. In this study, the feasibility of R-EDM process in the fabrication of arrayed features of Ø 3 mm and height 2 mm on mild steel has been studied through response surface methodology (RSM) based experimentation. The influence of machining parameters i.e., peak current (Ip), pulse-on time (Ton) and flushing pressure (Fp) on some of the vital response characteristics like material removal rate (MRR), surface roughness (SR), taper, cylindricity error and micro hardness and surface morphology of the pillared structures has been investigated. Further, a hybrid optimization method i.e., principal component analysis (PCA) based grey relational analysis (GRA) technique, is utilized to obtain optimal parameter combination with an aim to improve machining conditions for fabrication of arrayed features during R-EDM process. Analysis of variance (ANOVA) results shows that Ip has significant effect followed by Ton on MRR and Ip has major contribution towards SR, taper and cylindricity error. Micro hardness has maximum value in heat affected zone (HAZ). The optimal parameter combination based on PCA based GRA is found to be Ip = 10 A, Ton = 100 µs and Fp = 0.3 kg/cm2 which was further ascertained using confirmatory tes

Metallic hydrophobic surface fabrication and wettability study

Hydrophobic surfaces can be designed to have useful properties such as self-cleaning, anti-icing, and flow drag reduction. Research interests in this area have been growing with rising demands from various industries. Hydrophobic surfaces can be fabricated by coating, micro or nano-scale texturing, or a combination of the two. For industrial applications, methods for mass production of hydrophobic surfaces are desired. This thesis investigated two hydrophobic surface fabrication methods, laser machining and sandblasting, and conducted wettability analysis of the fabricated surfaces. In the laser machining, four microscale surface structures including channel, pillar, varied channel and varied pillar, are designed and fabricated. The static contact angles of all laser-machined samples are close to 130° without any coating. In sandblasting fabrication, three standoff distances (10 mm, 20 mm and 30 mm) between the spray nozzle and target surfaces are tested. For stainless steel, lower standoff distance leads to increased water contact angle on the sandblasted surfaces. For carbon steel, sandblasting increases wettability of the carbon steel, with lower contact angle from lower standoff distance. A low energy coating (Aculon) is applied on the samples from both fabrication methods. In the analysis, samples are divided into two groups, one for coated samples, and the other for the uncoated ones. Overall, the coating increases static contact angle and decreases hysteresis in all laser-machined samples and sandblasted ones. The difference in wettability of the samples from the two fabrication methods is analyzed in details. Sandblasted samples can reach 113°±4° without any coating, compared with static contact angle of 128°±5° from the laser-machined sample with pillar. After coating, the water contact angle of sandblasted samples increases to 137°±3° compared with 142°±4° on laser machined samples with pillar. The results of contact angle hysteresis are nearly same for the two methods before coating. After coating, contact angle hysteresis on sandblasted samples is overall lower than that on laser-machined samples

The influence of metallic surface topography towards adhesion of gram-positive & gram-negative bacteria

The presence of bacteria on metals is considered a serious source of potential contamination for domestic and industrial environments. Possible contributing factors to the formation of biofilm are related to the surface properties of materials used such as surface topography and hydrophobicity. Surface topography and hydrophobicity will be the focus in this investigation towards Gram-positive and Gram-negative bacteria (S. aureus, E. coli and B. subtilis) adhesion. Modified surfaces of 316L stainless-steel and Ti6Al4V, titanium prepared by polishing, WEDM and laser-assisted technique and the as-received substrates were also considered in the study. The corresponding surface topography and contact angle measurement were assessed by Bruker Optical Profilometry and Kruss DSA, Germany. The number of adhered bacterial on metal surfaces was determined by O.D, CFU and Fluorescent Microscopy. Polished, WEDM and laser-assisted surfaces managed to mitigate bacteria adhesion as opposed to controlling surfaces but increased the adhesion of E. coli on both stainless steel and titanium. The introduction of laser-assisted technique using argon gas successfully combatted the adhesion of both Gram-positive and Gram-negative bacteria, revealing the lowest adhesion for S. aureus and E. coli, surpassing those on polished surface and WEDM. The success factor was presumably contributed by the ability to suppress oxidation, while contours and nanograin surface effects prevent entrapments of bacteria whilst inducing an antibacterial property through contact killing mode

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Department of Mehcanical EngineeringSurface qualities including topography, texture, mechanical, and chemical stabilities have become an essential requirement in manufacturing along with a new paradigm of industrial revolution. The electron beam irradiation is a special technique for surface modification. Especially, the energy transfer through electrons with rapid thermal gradient inducing phase transformation and re-solidification of materials is the unique characteristics of large pulsed electron beam (LPEB) irradiation, which makes it a potential candidate for surface manufacturing. Despite the previous studies have revealed that the LPEB irradiation could reduce surface roughness and modify surface properties, the application of LPEB in manufacturing processes is rather limited as the mechanisms of LPEB irradiation and corresponding surface modifications are yet to be explored. In order to expand the application area of the LPEB irradiation, the dissertation aims at (1) predictive modeling of the LPEB irradiation to firmly establish the irradiating mechanisms, (2) fundamental understandings on surface modification factors specifying the modification mechanisms, and (3) applying the LPEB irradiation for multiscale and hybrid manufacturing processes based on the modification mechanisms. The first part of the dissertation will be temperature prediction using a numerical model during the LPEB process. The absorptance of electron beam was estimated considering electron scattering, backscattering, and transmission to adopt the natural interactions of electrons with substrates. The model predicts temperature distributions and molten depths depending on the irradiation conditions. The effects of considerations of absorptance containing natural interactions such as scattering, backscattering, and transmission on prediction accuracy were explored by comparing the predictive results between constant and calculated absorptance versus depth. The estimation of absorptance and energy transfer mechanisms resulted in more accurate predictions of molten depths. The experimental investigations of LPEB irradiation were mainly performed on mold steels (KP1 and KP4) and biomedical alloys (Ti-6Al-7Nb) in the second part. The nano-hardness of mold steels increased by 316% (KP1), 144% (KP4), and 154% (Ti-6Al-7Nb), respectively under optimized experimental parameters, which is affected by the increased dislocations in the re-solidified layer and a decreased fraction of the pre-dominant slip plane. Contact angle variations and oxides formation in the re-solidified layer projected that the surface became stable. Corrosion resistance of the irradiated surface was increased, as evidenced from the improved corrosion parameters. Based on the mechanisms of surface hardening, the nitriding process of Ti-6Al-7Nb using the LPEB irradiation was also explored. The atomic concentration of nitrogen atoms at the re-solidified layer could be achieved up to ~18% by LPEB nitriding. Nano-hardness in the re-solidified layer was improved further by ~75% following the LPEB nitriding process, as a result of the formation of TiN. The nitrided layer induced by the LPEB nitriding, consisted of TiN, TiO2, and TiOxNy, which modified the corrosion resistance as evidenced from the improved electrochemical parameters. An increase in the fraction of TiN at the re-solidified layer was considered responsible for the remarkable improvement of surface properties embedding uniformly noble and stable characteristics at the top surface. Based on the fundamental mechanisms of LPEB irradiations specified in the first and second parts, multiscale and hybrid manufacturing processes using the LPEB will be discussed in the last part. The patterned metal masks fabricated by a laser and drilled CFRP composites were selected as a microscale application of the LPEB irradiation as a deburring process based on the melting mechanism. The generated burrs were tried to be eliminated by a LPEB-assisted hybrid deburring process on metal masks. The size of burrs after the process was decreased about 81% from 38.01 ??m to 7.2 ??m comparing to the results of abrasive deburring alone. The distribution of burr size also decreased about 85% and surface roughness (Ra) was modified from 640 nm to 121 nm, indicating the formation of a uniform surface texture. The optimized irradiation also improved the accuracy of the shapes of the holes, and reduced the sizes of the burrs by 97% on drilled CFRP composites. This modified the deviations of hole accuracy by 93%. The unique deburring mechanisms started with evaporation of the resin that coats the carbon fibers was revealed through experimental observations. Moreover, superhydrophobic transformation of patterned metal surfaces was also investigated as one of the microscale applications of LPEB based on the surface modification. The Wenzel-to-Cassie transition occurred at 140?? with a groove depth of 250 ??m after the WEDM fabrication which indicated the development of a hydrophobic surface. However, the contact angle increased to 166.7?? with the Cassie state after the LPEB irradiation at a lower depth of groove (200 ??m). The modification of surface roughness following the LPEB irradiation on the patterns resulted in a decreased the critical angle for Wenzel-to-Cassie transition. FT-IR spectroscopy acquired at the ATR mode specified the elimination of hydrophilic functional groups on the surface following LPEB irradiation. Finally, silver nanowires (AgNWs) were selected as a nanoscale application of LPEB irradiation based on the energy transfer mechanism. The welding of silver nanowires to form percolation networks using the LPEB irradiation was investigated. The welded AgNWs showed modified electrical and mechanical characteristics with a low contact resistance at junctions. Therefore, the LPEB-welded AgNW electrode exhibited modified sheet resistance of 12.63 ??/sq and higher transmittance of 93% (at 550 nm). Furthermore, the outstanding mechanical flexibility was obtained than other AgNW electrodes prepared by thermal annealing. The feasibility of LPEB-welded AgNW electrodes were proved by the fabrication of polymer light-emitting diodes (PLEDs). The result supported that the LPEB-welded AgNWs could become an alternative to indium tin oxide (ITO). The dissertation will explore a comprehensive approach on the LPEB irradiation encompassing materials selection, understanding of the underlying multi-physical phenomena, surface modification mechanisms, surface qualities, and applications of LPEB irradiation for multiscale and hybrid manufacturing processes. This unique research approach will overcome the limitations of conventional finishing processes, incorporate subdivided finishing processes into a single step, and bring a new paradigm of finishing systems. It should be anticipated that the outcome of the dissertation will expand the application areas of the LPEB irradiation in the overall manufacturing industries including automotive, aerospace, biomedical, and semi-conductors in multiscale from macro- to nano-levels.clos

Investigation into vibration assisted micro milling: theory, modelling and applications

PhD ThesisPrecision micro components are increasingly in demand for various engineering industries, such as biomedical engineering, MEMS, electro-optics, aerospace and communications. The proposed requirements of these components are not only in high accuracy, but also in good surface performance, such as drag reduction, wear resistance and noise reduction, which has become one of the main bottlenecks in the development of these industries. However, processing these difficult-to-machine materials efficiently and economically is always a challenging task, which stimulates the development and subsequent application of vibration assisted machining (VAM) over the past few decades. Vibration assisted machining employs additional external energy sources to generate high frequency vibration in the conventional machining process, changing the machining (cutting) mechanism, thus reducing cutting force and cutting heat and improving machining quality. The current awareness on VAM technology is incomplete and effective implementation of the VAM process depends on a wide range of technical issues, including vibration device design and setup, process parameters optimization and performance evaluation. In this research, a 2D non-resonant vibration assisted system is developed and evaluated. Cutting mechanism and relevant applications, such as functional surface generation and microfluidic chips manufacturing is studies through both experimental and finite element analysis (FEA) method. A new two-dimensional piezoelectric actuator driven vibration stage is proposed and prototyped. A double parallel four-bar linkage structure with double layer flexible hinges is designed to guide the motion and reduce the displacement coupling effect between the two directions. The compliance modelling and dynamic analysis are carried out based on the matrix method and lagrangian principle, and the results are verified by finite element analysis. A closed loop control system is developed and proposed based on LabVIEW program consisting of data acquisition (DAQ) devices and capacitive sensors. Machining experiments have been carried out to evaluate the performance of the vibration stage and the results show a good agreement with the tool tip trajectory simulation results, which demonstrates the feasibility and effectiveness of the vibration stage for vibration assisted micro milling. The textured surface generation mechanism is investigated through both modelling and experimental methods. A surface generation model based on homogenous matrices transformation is proposed by considering micro cutter geometry and kinematics of vibration assisted milling. On this basis, series of simulations are performed to provide insights into the effects of various vibration parameters (frequency, amplitude and phase difference) on the generation mechanism of typical textured surfaces in 1D and 2D vibration-assisted micro milling. Furthermore, the wettability tests are performed on the machined surfaces with various surface texture topographies. A new contact model, which considers both liquid infiltration effects and air trapped in the microstructure, is proposed for predicting the wettability of the fish scales surface texture. The following surface textures are used for T-shaped and Y-shaped microchannels manufacturing to achieve liquid one-way flow and micro mixer applications, respectively. The liquid flow experiments have been carried out and the results indicate that liquid flow can be controlled effectively in the proposed microchannels at proper inlet flow rates. Burr formation and tool wear suppression mechanisms are studied by using both finite element simulation and experiment methods. A finite element model of vibration assisted micro milling using ABAQUS is developed based on the Johnson-Cook material and damage models. The tool-workpiece separation conditions are studied by considering the tool tip trajectories. The machining experiments are carried out on Ti-6Al-4V with coated micro milling tool (fine-grain tungsten carbides substrate with ZrO2-BaCrO4 (ZB) coating) under different vibration frequencies (high, medium and low) and cutting states (tool-workpiece separation or nonseparation). The results show that tool wear can be reduced effectively in vibration assisted micro milling due to different wear suppression mechanisms. The relationship between tool wear and cutting performance is studied, and the results indicate that besides tool wear reduction, better surface finish, lower burrs and smaller chips can also be obtained as vibration assistance is added

Laser surface texturing of biomaterials: from conceptualization to implementation

Laser surface modification and more specifically laser surface functionalization is widely being considered as a way to efficiently give the surfaces of innovative high value products added or enhanced surface properties. The technology offers a number of desired advantages over competing technologies, of which: selectivity, relatively high processing speeds and the absence of waste or harmful by-products. Nevertheless, the full range of potential applications and suitable target materials is not yet explored, and some feasibility and implementation challenges remain open-ended concerns. With the limited literature available on laser surface texturing of cobalt chrome alloys, a prevalent implant material, the research presented in this thesis aims to address the suitability of this technology in that context and compare it with the current state-of-the-art in the orthopaedics industry. Furthermore, the transferability of the laser surface texturing process from 2D planar test samples to actual 3D parts will be assessed and the effects of 3D laser processing disturbances on the surface functionality evaluated. Finally, a method for laser processing complex surfaces productively is presented and validated on additively manufactured spherical parts

Metal Surfaces

This collection covers the physical and chemical phenomena of metal surfaces, including surface modifications and treatments. It is targeted at researchers working in materials science and also at newcomers to the research field of metal surfaces and surface analysis

Proceeding Of Mechanical Engineering Research Day 2016 (MERD’16)

This Open Access e-Proceeding contains a compilation of 105 selected papers from the Mechanical Engineering Research Day 2016 (MERD’16) event, which is held in Kampus Teknologi, Universiti Teknikal Malaysia Melaka (UTeM) - Melaka, Malaysia, on 31 March 2016. The theme chosen for this event is ‘IDEA. INSPIRE. INNOVATE’. It was gratifying to all of us when the response for MERD’16 is overwhelming as the technical committees received more than 200 submissions from various areas of mechanical engineering. After a peer-review process, the editors have accepted 105 papers for the e-proceeding that cover 7 main themes. This open access e-Proceeding can be viewed or downloaded at www3.utem.edu.my/care/proceedings. We hope that these proceeding will serve as a valuable reference for researchers. With the large number of submissions from the researchers in other faculties, the event has achieved its main objective which is to bring together educators, researchers and practitioners to share their findings and perhaps sustaining the research culture in the university. The topics of MERD’16 are based on a combination of fundamental researches, advanced research methodologies and application technologies. As the editor-in-chief, we would like to express our gratitude to the editorial board and fellow review members for their tireless effort in compiling and reviewing the selected papers for this proceeding. We would also like to extend our great appreciation to the members of the Publication Committee and Secretariat for their excellent cooperation in preparing the proceeding of MERD’16