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![Table 1.—Properties of Pyrolytic carbon [1].](profile/Vivek-Bajpai-2/publication/232974121/figure/tbl1/AS:393556486311948@1470842586938/Properties-of-Pyrolytic-carbon-1_Q320.jpg)
Pyrolytic carbon (PyC) has excellent biocompatibility, strength-to-weight ratio, and unique directional thermal properties. It finds application in biomedical implants like finger prosthesis, heart valves, and some thermonuclear components. Recently, engineered features have been demonstrated to improve the hemodynamics of heart valves. These featu...
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... Subsequently, Tang et al. [16] studied the pattern of graphite crack initiation and growth using electronic speckle pattern interferometry. Bajpai et al. [17] discussed the brittle fracture characteristics of the material based on the chip morphology produced by pyrolytic carbon during orthogonal micro-grooving. Wang et al. [18] carried out an atomic-level cutting study on graphite, on the basis of which the removal mechanism of the material at the atomic level was revealed using molecular dynamics. ...
Graphite is extensively used in the engineering field due to its unique properties, and the study of its cutting mechanism has become particularly important. However, the brittle fracture mechanism of graphite makes it rather easy for cracks with a unique pattern of initiation and growth to develop when processing. Herein, the ABAQUS was selected to establish a finite element model (FEM) of the graphite cutting process. The internal crystal structure of graphite was modelled by a Voronoi structure, and a cohesion unit was globally embedded into the solid unit to simulate crack initiation and growth. In addition, the complete process of chip formation and removal was demonstrated. The analysis of the simulation results showed that the graphite material underwent three periodic cycles of material removal during the cutting process, i.e., large, tiny, and small removal stages. Meanwhile, the simulation results indicated that when ac was large enough, the crack gradually grew inside the graphite and then turned to the upper surface of the graphite. However, when ac was tiny enough, the cracks hardly expanded towards the inside of the graphite but grew upwards for a short period. Then, orthogonal cutting experiments of graphite were conducted, and the FEM was verified based on the experimental chip morphology, machined surface morphology, and current geometric model of the graphite cutting process. The simulation and experimental results were consistent. The hereby-presented FEM was a complement to simulations of the processing of brittle materials.
... Design inspiration for this research taken from the On-X mitral valve, because the On-X mechanical heart valves provide good hemodynamics and made of pure Pyrolytic Carbon. 19 Its innovative design and progressive material increase the life span of prosthesis in human body without harming the surrounding tissue and blood cells. Surgeons prefer On-X heart valves because of its long life span with good hemocompatibility and patients with On-X heart valve require less warfarin and short-term anticoagulation therapy after implantation. ...
Heart valve problems affect more than 100 million people worldwide. According to statistics, around 55% of valvular diseases are treated by a mechanical prosthesis. The first heart valve replaced model was the caged-ball valve, more than 50 models of heart valves designed by different companies. Each design has different aspects such as valve geometry, leaflets design, materials used for model manufacturing, coating techniques, and coating materials. Depending on the patient's need and condition, the native heart valve either replaced by a biological or mechanical heart valve. Biological valves are made of living tissues whereas mechanical valves manufactured by the biomaterials, which are biocompatible and do not causes any reaction inside the body. The prototype discussed in this paper provides good hemocompatibility, because of the biomaterial used in this prototype manufacturing. It will reduce tissue ingrowth, due to the enhanced leaflet ear of the orifice ring. Moreover, it will cause less thrombotic effects into the host due to greater contact angel of graphite and smooth surface of graphite after pyrolytic coating. The significant evolution of mechanical valve designs consists of valve geometry, coating technique, and materials. In this research, the 3D-CAD model of Bileaflet Mechanical Mitral Heart Valve was designed using SOLID WORKS 2016 and fabricated by 5-axis Computer Numeric Control (CNC) machine. Graphite was used for the fabrication of prototype and Pyrolytic Carbon (PyC) coating was performed with Chemical Vapor deposition (CVD) technique. Scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) were used to determine the effects of CVD on surface topography and chemical structure of graphite model before and after coating. Furthermore, hemocompatibility of graphite and PyC analyzed through in-vitro hemolytic activity. The Characterization results showed that the Bileaflet Mechanical Mitral Heart valve prototype after PyC coating provides a smooth surface with improved hemocompatibility and less adhesion. Besides, the Mechanical Heart valves showed no hemolysis during the hemolytic activity. By virtue of its smooth and nonporous surface, it is antithrombotic and provides good hemodynamics. The advance long leaflet ear design reduces the tissue ingrowth around the orifice which will further limit the leaflets movement.
... We further increased the temperature of the resistive heater to 850 o C at an increment of 50 o C, it was observed we had a CBM at both laser incident and non-incident regions and the D, G, and 2D peaks were around the same ballpark of Raman shifts reported above. 41 This means at 20sccm, we generated sufficient mass diffusion and flux from the gas phase and the substrate surface to initiate the reaction. Also, the photons from the pulsed laser effectively raised the local temperature of the bombarded region and heat was sufficiently conducted to the non-laser bombarded regions to promote the growth of our CBM by breaking the carbonhydrogen bonds at its dehydrogenation energy to produce sp2 hybridized carbon. ...
Carbon-based materials (CBMs) including graphene, carbon nanotubes (CNT), highly ordered pyrolytic graphite (HOPG), and pyrolytic carbon (PyC) have gained so much attention in research in recent years because of their unique electronic, optical, thermal, and mechanical properties. CBMs are relatively very stable and have minimal environmental footprint. Various techniques such as mechanical exfoliation, pulsed laser deposition, and chemical vapor deposition (CVD) have been used to grow CBMs and among them thermal CVD is the most common. This study aims to explore ways of reducing the energy requirement to produce CBMs, and for that, a novel pulsed laser-assisted CVD technique had been developed in our laboratory. The growth pattern was monitored by altering various growth parameters like gas flow rate, temperature, laser energy, and deposition time. CBMs were grown both on Si and Cu substrates, and better quality CBM films were found on Cu as it acts as a catalytic agent for two-dimensional growth. Raman spectroscopy confirms the presence of high quality PyC which was grown with optimum parameters (temperature of 750oC, CH4 gas flow rate of 20sccm, a laser frequency of 10Hz, energy density of 0.116J/cm2 per pulse). It is found that the local pulsed-laser bombardment helps in breaking the carbon-hydrogen bonds of CH4 at much lower temperature than its thermal decomposition temperature (1000oC-1200oC). With the further increase of temperature there was no significant change in the 2D peak intensity in Raman spectrum which is the indicator of the number of graphene layer. The intertwined graphene flakes of the PyC cause some surface roughness which is responsible for quenching the Raman 2D signal. Further development is needed to achieve a single layer of graphene and other 2D materials using the laser-assisted CVD technique.
... [77], descriptive research enables an in depth study of phenomena or characteristic associated with the subject population such as to who, what, when, where and how of the subject. [78], objectives of a descriptive research are identifying present conditions, needs, studying immediate status of a phenomenon, finding out facts about a problem and explaining the relationships of traits and characteristics. ...
... Experimental design methods [20], artificial neural networks [21], and the gray relational analysis method [22] were used to optimize the machining parameters for highpurity graphite in the end milling process. Additionally, Bajpai and Singh investigated the orthogonal micro-grooving of anisotropic pyrolytic carbon [23] and established a finite element model to understand the mechanics of material removal in the plane of transverse isotropy of pyrolytic carbon [24]. ...
Graphite and its composites have been widely used in various industrial fields. It has been generally accepted that, for positive rake angles, there is a significant increase in tension stress at the cutting zone during the machining of brittle materials, and cracks occur and spread easily, degrading the quality of the machined surface quality. However, it is found in this study that positive rake angles can improve the machined surface finish during the orthogonal cutting of graphite/polymer composites. Better machined surface finish is obtained for a larger rake angle. A finite element model is developed to reveal the mechanism of influence of the positive rake angle on the machined surface. Based on the effective stress field obtained from finite element analysis, it can be predicted that the crack initiates at the tool tip, subsequently propagates downward and forward, and later spreads gradually toward the free surface of the workpiece. A larger rake angle can promote crack propagation far from the machined surface. The crack initiation and propagation laws are validated by the edge-indentation experiments. In addition, the cutting force at various rake angles is investigated.
... However, in case of an upmilling operation, the burr height showed very little variation with milling angle. They also found that burr height is a function of crystallographic orientation, particularly for the (110) and (111) cases. When hardened tool steel was micromilled and sizes of burrs were noted, Bissaco et al. [70] found that the size effects caused larger top burrs in micromilling than in macromilling. ...
... In another work using the same tool and AISI 1045 steel as the workpiece, it was noticed that dimples were observed due to the dual phase structure of AISI 1045 steel and a quasishear-extrusion chip was formed [109]. A microgrooving operation on anisotropic pyrolytic carbon was performed by Bajpai and Singh [110] using TiAlN-coated tungsten carbide. A full factorial design of experiments was formulated to study the effect of rake angle, tool width, cutting speed, and DOC on cutting forces and surface roughness. ...
The concept of miniaturizing machine tools has received a strong interest in the research community due to their ability to fabricate intricate components. Lower power consumption, higher productivity rate, and smaller sizes of work stations have enabled microscale machining operations to acquire an edge over other fabrication techniques in various applications such as aerospace, instrumentation, automotive, biomedical, etc. The literature is filled with works done by researchers working in this domain. A significant contribution comes from the works which have been published during the period 1998–2014. The focus of these studies has primarily been on conventional and nonconventional micromachining techniques. Since nonconventional machining operations such as microelectrical discharge machining, laser machining, etc., are not compatible with traditional workpiece materials, conventional micromachining techniques such as micromilling and microdrilling are generally used. However, as of today, there has been no revision on the state of the-art in this field to serve as a reference for the experienced researcher and as a handbook for the newcomer. In this review, we have attempted to summarize the current state of understanding on this topic. A variety of issues which are representative of micromachining operations are critically analyzed and presented. Conventional micromachining operations have been compared with their nonconventional counterparts with respect to performance characteristics such as burr formation, surface integrity, etc., and their advantages and shortcomings have been listed. Meticulous efforts have been taken to address the key challenges faced in typical micromachining operations. Taking the convenience of the reader into consideration, we have presented a bird's-eye view of the various micromachining operations and simulation studies as performed in the last decade. In the last few years, diamond turning operations have gained more importance and are particularly used for machining composite materials and superalloys. This paper gives an insight into these operations apart from providing an outlook for future growth and development of micromachining technology.
... Vapor deposition technique is the method of manufacturing which gives, layered composition with the density at 2.2 g/cm 3 . Due to the layered structure, there are two mutually perpendicular planes of interest AB plane (parallel to the layers) and C Plane (normal to the layers) [1]. Orientation of the material and machining conditions are explained in the section of experiment. ...
Abstract:
Pyrolytic carbon (PyC) is extremely biocompatible with high directional strength and unique directional thermal conductivity. PyC is used in biomedical devices like cardiovascular implants and finger prosthesis. Micro features on PyC have been proven as performance driving agents in many cases. This work is focused on micro-EDM characterization of PyC to understand the effect of material/thermal anisotropy on the process response. An L9 Taguchi design of experiments has been performed to analyze the effect of gap voltage, capacitance and frequency on the MRR, surface quality and dimensional accuracy. MRR increases by 16% with vibration in AB plane machining. In C plane the effect of vibration on MRR is not favorable. MRR reduces by 56% if the machining plane changes from AB to C due to the lower thermal conductivity along C. Surface roughness decreases by an order of magnitude if machining plane changes from AB to C. 65 nm surface roughness has been achieved in C plane under certain conditions. The error in dimensional accuracy in C plane is 46% lower than AB plane. EDS shows non-contaminated machined surface. Finally, micro-EDM process has been used to create micro-features in PyC, which could potentially improve/alter the desired surface quality.
Keywords: electrode discharge machining, pyrolytic-graphite, micro-features, micro-machining
... It is found that the proposed method reduces hole circularity down to 0.25 mm. Pyrolytic carbon has various applications in medical implants, biomedical industries, heart valves, prosthesis, and nuclear equipments [15]. Bajpai and Singh [15] performed microgrooving on anisotropic paralytic material to determine its significant impact on thrust force, SR, and chip morphology. ...
... Pyrolytic carbon has various applications in medical implants, biomedical industries, heart valves, prosthesis, and nuclear equipments [15]. Bajpai and Singh [15] performed microgrooving on anisotropic paralytic material to determine its significant impact on thrust force, SR, and chip morphology. The profile is described in Fig. 6. ...
... -Typical profile of machined groove (Bajpai and Singh[15]).1294S. P. LEO KUMAR ET AL. ...
Technology development has led to the need of micro and miniaturized products in the field of automobile, aerospace, electronics, medical implants, biomedicine, robotics, and so on. Micromachining is the key technology to satisfy the need of the industry in terms of functionality and miniaturization in size. In this article, state-of-the-art review on tool-based micromachining processes such as microturning, microdrilling, micromilling, electric discharge micromachining (Micro-EDM), and electrochemical micromachining (Micro-ECM) has been carried out. The review begins with an overview of micromachining, classifications, and discussions about different aspects of tool-based micromachining processes. The research works carried out for the past 10 years are analyzed in terms of materials perspective, process parameters, size effects, performance characteristics, condition monitoring, product development, micro features generation, and fabrication of micro tools. A statistical analysis has been performed with respect to the previous review articles, numbers of publications in the related area, and their research gap. Finally, the possible future research direction is presented.
... Pyrolytic carbon (PyC) is a material known for its excellent biocompatibility, high strength-to-weight ratio and unique directional thermal properties which finds application in biomedical implants and thermal sinks. It has layers of brittle graphite-like material as shown in Figure 1 [1]. The layered AB plane is the plane of transverse isotropy and the C plane is anisotropic. ...
... Mechanical Micromachining can be used to create functional features in PyC. However, with notable exceptions of few experimental studies [1,2,3], most of the experimental and modeling work reported in the literature on mechanical micromachining (micromilling, microturning, etc.) is for isotropic, homogeneous, and plastically deforming metals [4][5][6][7]. Figure1. ...
... Figure1. Schematic and SEM image of PyC [1] To the best of authors' knowledge, no work has been reported on the modeling of micromachining deteriorates as a function of strain [8]. The chip formation mechanism uses traction separation law for interlaminar decohesion which captures the peeling, slipping and delamination in the layered chip. ...
... Pyrolytic carbon (PyC) is a material known for its excellent biocompatibility, high strength-to-weight ratio and unique directional thermal properties which finds application in biomedical implants and thermal sinks. It has layers of brittle graphite-like material as shown in Fig. 1 [1]. The layered AB plane is the plane of transverse isotropy and the C plane is anisotropic. ...
... Mechanical Micromachining can be used to create functional features in PyC. However, with notable exceptions of few experimental studies [1][2][3], most of the experimental and modeling work reported in the literature on mechanical micromachining (micromilling, microturning, etc.) is for isotropic, homogeneous, and plastically deforming metals [4][5][6][7]. ...
... The reaction does not change significantly with the tool width and, therefore, the thrust force also remains fairly constant. Similar behavior has been observed during micromachining experiments of PyC [1]. Fig. 16(c) shows the effect of the rake angle on the cutting forces. ...
Engineered features on pyrolytic carbon (PyC) have been reported to improve the functional performance of the cardiovascular implants. PyC also finds application in thermonuclear components due to its unique directional thermal properties. Note that PyC comprises of stacked layers of brittle graphite-like material and its machining characteristics differ from plastically deformable isotropic materials due to brittle damage and interlaminar decohesion. Consequently, this study is aimed at understanding the mechanics of material removal in the plane of transverse isotropy (horizontally stacked laminae) of PyC via a finite element model. A damaged plasticity material model has been used to capture the effect of material degradation of a brittle material under machining. Uniaxial tension/compression tests have been carried out to calibrate the damaged plasticity model. A surface based cohesive bonding has been used between the layers to simulate the interlaminar decohesion which results in peeling, slipping and delamination during machining. The model predicts the cutting force and thrust forces under different process conditions. The cutting force predictions from the finite element model have been validated against the experimental data for different cutting conditions. In addition, the model also predicts the chip morphology for different machining conditions. The prediction error in the model lies between 2% and 23%. Parametric studies have also been performed to understand the effect of the machining parameters, such as rake angle, uncut chip thickness on the process response. It is found that use of the positive rake angle decreases the cutting forces up to 72%.
