School of Engineering Sciences and Technology

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Browsing School of Engineering Sciences and Technology by Author "Acharyya, Swati Ghosh"
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    A Study on Corrosion Resistance and Mechanical Performance of 6061 Aluminium Alloy: Galvanized Mild Steel Electron Beam Welds at Varying Welding Parameters
    ( 2020-04-01) Sravanthi, S. S. ; Acharyya, Swati Ghosh ; Joardar, Joydip ; Chaitanya, V. N.S.K.
    Dissimilar welds of steel and aluminium alloys have an inherent problem of the vast difference in solid solubility which questions their integrity. The present study elaborates on the mechanical failure and corrosion degradation of 6061 Al—galvanized mild steel lap joints fabricated by electron beam welding as a function of varying parameters such as processing speed, voltage and current. The interfaces of two weld specimens were examined using scanning electron microscopy, phase analysis by micro-area X-ray diffraction and hardness testing by Vickers micro-hardness tester. Results showed the generation of the intermetallic layer at the weld seam–mild steel interface in the specimens. The composition of the Al–Fe intermetallics in the layer was confirmed by micro-XRD analysis. The layer width increased with increased heat input and average width varied between 11 and 16 µm in the specimens. The micro-hardness of the layer was found to increase with a decrease in processing speed during welding. The corrosion resistance and mechanical strength of welds were evaluated as per ASTM G 67-04 and D 1002, respectively. The microstructures at weld interfaces have shown intergranular corrosion after nitric acid exposure for 24 h according to ASTM G 67-04. Weight loss analysis was done after the corrosion test. It was identified that welds fabricated at higher voltage exhibited greater weight loss of 55.9 mg and specimen joined at lower voltage was found to exhibit a weight loss of 41.1 mg, respectively. High intermetallic layer thickness in the welds resulted in failure at the weld seam region during lap shear testing.
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    Area-elficient interlayer signal propagation in 3D IC by introducing electron spin
    ( 2017-10-31) Debroy, Sanghamitra ; Acharyya, Amit ; Singh, Shiv Govind ; Acharyya, Swati Ghosh
    Through Silicon Via (TSV) is the major technology in order to transmit data among various devices in 3D IC. Therefore higher concentration of TSV is required for higher packing density in 3D IC. In order to obtain high density of TSV, the dimensions of TSV needs to be reduced. This may be achieved by increasing the surface area per layer which will benefit in packing of more components for any operation including logic implementation. In this paper we introduce electron spin rather than charge for the first time for interlayer signal transmission in 3D IC resulting in area efficiency. Ansys electromagnetic simulator (Maxwell 2D and 3D) and OOMMF simulation supported by theoretical analysis specifies an average of 90% area reduction per layer of 3D IC as compared to state-of-the art TSV.
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    Development of stress corrosion cracking resistant welds of 321 stainless steel by simple surface engineering
    ( 2017-12-31) Mankari, Kamal ; Acharyya, Swati Ghosh
    We hereby report a simple surface engineering technique to make AISI grade 321 stainless steel (SS) welds resistant to stress corrosion cracking (SCC) in chloride environment. Heat exchanger tubes of AISI 321 SS, welded either by (a) laser beam welding (LBW) or by (b) metal inert gas welding (MIG) were used for the study. The welds had high magnitude of tensile residual stresses and had undergone SCC in chloride environment while in service. The welds were characterized using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). Subsequently, the welded surfaces were subjected to buffing operation followed by determination of residual stress distribution and surface roughness by XRD and surface profilometer measurements respectively. The susceptibility of the welds to SCC was tested in buffed and un-buffed condition as per ASTM G-36 in boiling MgCl 2 for 5 h and 10 h, followed by microstructural characterization by using optical microscope and FESEM. The results showed that the buffed surfaces (both welds and base material) were resistant to SCC even after 10 h of exposure to boiling MgCl 2 whereas the un-buffed surfaces underwent severe SCC for the same exposure time. Buffing imparted high magnitude of compressive stresses on the surface of stainless steel together with reduction in its surface roughness and reduction in plastic strain on the surface which made the welded surface, resistant to chloride assisted SCC. Buffing being a very simple, portable and economic technique can be easily adapted by the designers as the last step of component fabrication to make 321 stainless steel welds resistant to chloride assisted SCC.
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    Distinguishing effect of buffing vs. grinding, milling and turning operations on the chloride induced SCC susceptibility of 304L austenitic stainless steel
    ( 2017-02-27) Kumar, Pandu Sunil ; Acharyya, Swati Ghosh ; Rao, S. V.Ramana ; Kapoor, Komal
    The study compares the effect of different surface working operations like grinding, milling, turning and buffing on the Cl– induced stress corrosion cracking (SCC) susceptibility of austenitic 304L stainless steel (SS) in a chloride environment. SS 304L was subjected to four different surface working operations namely grinding, milling, turning and buffing. The residual stress distribution of the surface as a result of machining was measured by X-ray diffraction. The Cl– induced SCC susceptibility of the different surface worked samples were determined by testing in boiling magnesium chloride as per ASTM G36 for 3 h, 9 h and 72 h. The surface and cross section of the samples both pre and post exposure to the corrosive medium was characterized using optical microscopy, scanning electron microscopy (SEM). The study revealed that grinding, milling and turning operations resulted in high tensile residual stresses on the surface together with the high density of deformation bands making these surfaces highly susceptible to Cl– induced SCC. On the other hand buffing produces compressive residual stresses on the surface with minimal plastic strain, making it more resistance to Cl– induced SCC. The study highlights that the conventional machining operations on 304L SS surfaces should be invariably followed by buffing operation to make the surfaces more resistance to SCC.
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    Effect of alloying elements on the microstructure, coefficient of friction, in-vitro corrosion and antibacterial nature of selected Ti-Nb alloys
    ( 2019-03-01) Chapala, Praveen ; Sunil Kumar, Pandu ; Joardar, Joydip ; Bhandari, Vasundhra ; Acharyya, Swati Ghosh
    Ti-Nb alloys having compositions Ti-24Nb-4Zr-8Sn, Ti-29Nb-13Ta-7Zr and Ti-35Nb-4Sn were synthesized by vacuum arc melting followed by ageing at 1273 K for 6 h in Ar atmosphere. The alloys were characterized by field emmision scanning electron microscopy (FESEM), transmission electron microscopy (TEM), micro X-ray diffraction, friction coefficient and nanohardness tests. In-vitro corrosion of the alloys were studied by potentiodynamic polarisation in body simulated fluid at 37 ○ C. The alloy surfaces were exposed to staphylococcus aureus bacteria under controlled environment and the retention of the bacteria was examined by confocal laser scanning microscopy. The alloys had different ratios of α, β phases, different nature of inclusion, and dislocation pile-up resulting in high hardness. Alloys also had good resistance to in-vitro corrosion, low coefficient of friction and were resistant to bacterial growth as compared to commercially pure (CP) Ti. The coefficient of friction was lowest for Ti-24Nb-4Zr-8Sn and it increased with increasing Nb content. The resistance to bacterial growth on the surface increased with increasing volume fraction of β phase in the alloy.
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    Effect of GMAW-brazing and Cold Metal Transfer Welding Techniques on the corrosion behaviour of Aluminium-Steel lap joints
    ( 2019-01-01) Sravanthi, S. S. ; Acharyya, Swati Ghosh ; Chapala, Praveen
    Dissimilar metal welds of steel and aluminium find major application in automotive sector as it makes the vehicles fuel efficient. But a major concern in the Al-steel joints is the microstructural in-homogeneities in the weld zone due to the low solid solubility issues between steel and Aluminium alloy and large differences in their thermal and electrochemical properties. The durability of such welds in service environment is still an issue to be resolved. Hence the main aim of this study is to compare the corrosion behaviour of H32 5052 Aluminium-galvanized mild steel joints welded by Gas metal arc welding-brazing (GMAW-brazing) and Cold metal transfer (CMT) techniques as a function of welding parameters viz., weld speed and wire feed rate. Lap joints were fabricated using Al-5%Si filler wire, followed by the microstructural characterization using Scanning electron microscopy, hardness measurement by nano-indentor and phase analysis by X-ray diffraction technique. Corrosion testing was done on the joints following ASTM G 67-04. The results establish the effect of welding parameters on the microstructure and the corrosion behaviour of the welds. A thick Al-Fe-Si intermetallic compound (IMC) layer was formed at the weld beadmild steel interface with Zinc entrapping in the foot region of both welds. The composition of this layer was confirmed by EDAX and XRD results. In both the cases, it had shown a severe impact on the intergranular corrosion behaviour of the welds. The results have also shown an increase in the thickness of the intermetallic layer with increase in the heat input, enhancing the galvanic and intergranular corrosion rate.
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    Effect of High-Power Intensity on Corrosion Behaviour of Aluminium—Steel Dissimilar Joints Made by Electron Beam Welding
    ( 2020-01-01) Sai Sravanthi, S. ; Acharyya, Swati Ghosh
    The automotive sector is keen on using lightweight components with aluminium–steel joints since it leads to reduced fuel consumption and lowered CO2 emission. However, huge variations in the metallurgical properties of aluminium and steel and the use of high energy beam processes such as electron beam welding for fabrication challenge the durability of the resultant joints obtained. The present work establishes the effect of high heat input applied during electron beam welding on the corrosion resistance of 5052 Al–galvanized mild steel lap joints. The study includes microstructural characterization of the weld interfaces using scanning electron microscope (SEM), hardness measurement near the interfacial regions using Vickers’s hardness tester. Results indicated the generation of Al–Fe intermetallic layer at the weld bead–mild steel interface whose width ranged between 2.8 and 10.5 µm from head to foot regions. The composition of the layer was confirmed by the elemental analysis that was done on the layer by Energy Dispersion Spectroscopy which was attached to SEM. The layer had shown a severe impact on the corrosion resistance of the joints when exposed to nitric acid for 24 h following ASTM G 67-04. The joints experienced de-bonding at the interface and have undergone a huge weight loss of 38.9 mg.
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    Effect of homogenization cooling on the precipitation behavior of 6061 Al alloy
    ( 2017-05-19) Sathaiah, Sriram ; Acharyya, Swati Ghosh
    In the present study, effect of homogenization cooling on the precipitation behavior of 6061 Al alloy has been investigated. Homogenization cooling is essential for any homogenization process to improve the extrudability because a fully solutionized 6061 Al alloy is difficult to extrude due to solid solution strengthening. Homogenized 6061 Al alloy (580°C for 8 h) samples were cooled to room temperature with four different cooling rates i.e. 500, 250, 150 and 30°C h-1. With decreasing cooling rates, the lengths of the Mg2Si precipitates were increased. Electrical conductivity and hardness showed an inverse relationship as the cooling rate decreases. Fine Mg2Si precipitates were observed at 500°C h-1 cooling rate. Further decreasing the cooling rates, (i.e. 250, 150 and 30°C h-1) the size of Mg2Si precipitates became large which are difficult to re-dissolve during the extrusion process and leads to surface defects. Hence the present study confirmed that 500°C h-1 is the optimum homogenization cooling rate for 6061 Al alloy which results in homogeneous structure with fine Mg2Si precipitates and sufficient hardness to improve the extrudability of 6061 Al alloy.
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    Effect of varying weld speed on corrosion resistance and mechanical behavior of Aluminium - steel welds fabricated by cold metal transfer technique
    ( 2019-10-26) Sravanthi, S. S. ; Acharyya, Swati Ghosh ; Prabhakar, K. V.Phani ; Joardar, Joydip
    Lap welds of 19000 Al–Zinc layered mild steel were joined by Cold Metal Transfer technique using Al-12% Si filler wire as a function of varying weld speed (0.5–1 m.min−1). The weld cross-section was characterized by electron microscopy techniques. Micro XRD was used for the phase analysis of the intermetallic layer generated at welding bead–steel interface in the weld samples. The mechanical strength of joints was evaluated by lap shear testing and corrosion evaluation was done following ASTM G 67–04 and ASTM G 48–03, respectively. Results have shown that the IMC layer width decreased with an enhanced welding speed resulting in lower intergranular corrosion. The layer width ranged between 0.45 and 2.3 µm in both the weld samples. During weight loss evaluation, the sample with lower welding speed exhibited a weight loss of 41.8 mg and the sample welded with higher speed had shown a weight loss of 7.75 mg. At higher weld speeds, lower volume fraction of intermetallics was observed resulting in reduced corrosion. The welds have shown optimum mechanical strength during lap shear test and failed in the base material region of Aluminium alloy.
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    Effect of welding parameters on corrosion behavior of dissimilar weld joints of Al5052 and galvanized mild steel
    ( 2018-01-01) Shajahan, Shaik ; Acharyya, Swati Ghosh
    The current study investigated the effect of welding parameters such as wire feed rate and welding speed on the corrosion behavior of dissimilar alloy welds of Al 5052 and Galvanized mild steel. Al 5052 alloy and galvanized mild steel plates welded in the form of lap joint by Cold Metal Transfer (CMT) welding process and Pulsed Arc Metal Inert Gas (PAMIG) welding process using 4043 Aluminum alloy filler. Welding conducted at different welding parameters viz., welding speed (0.8 mm/min and 1.0 mm/min) and wire feed rate (5.8 mm/min and 6.5 mm/min). The microstructure and phase determination of the weld joints analyzed by Field Emission Scanning electron microscopy and X-Ray Diffraction respectively. Resistance of crevice and inter granular corrosion of the welds were studied as a function of different welding parameters as per ASTMG67-Al-alloys. The effect of welding parameters on the corrosion resistance of the joints and correlation of microstructural features such as formation of intermetallics at the interfaces etc. throughout specimens studied in detail.
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    Effect of Welding Parameters on the Corrosion Behavior of Dissimilar Alloy Welds of T6 AA6061 Al-Galvanized Mild Steel
    ( 2018-10-01) Sravanthi, S. S. ; Acharyya, Swati Ghosh ; Phani Prabhakar, K. V. ; Padmanabham, G.
    Partial replacement of steel by Aluminium (Al) alloys is a promising approach adopted by automotive sector to improve fuel efficiency without compromising on the strength. However, this results in the generation of dissimilar welds of Al alloys and steel. Understanding the corrosion behavior of Al alloys–steel welds as a function of welding parameters is critical in the successful application of such alloys. The present study reports the intergranular corrosion behavior of T6 heat-treated AA6061 Al alloy-galvanized mild steel lap joints, welded by metal inert gas welding–brazing technique as a function of different welding parameters, viz. weld speed (4-6 m/min) and wire feed rate (0.8-0.9 m/min), following ASTM G 67-04. Weld characterization was performed by field emission scanning electron microscopy (FESEM), x-ray diffraction and nano-hardness measurement. Results indicate heavy dissolution and metal loss at the interface. A high volume fraction of Al-Fe intermetallics was precipitated at the weld interfaces, resulting in high hardness and higher localized corrosion. The thickness of Al-Fe intermetallic layer increased with increasing wire feed rate and lower weld speed which enhanced the severity of galvanic and intergranular corrosion.
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    Failure analysis of AISI 321 stainless steel welded pipes in solar thermal power plants
    ( 2018-04-01) Mankari, Kamal ; Acharyya, Swati Ghosh
    AISI 321 stainless steels (SS) pipes are commonly used in solar thermal power plants for transport of thermic fluid containing chloride ions at ~ 400 °C. Several of these SS pipes have failed while in service after very short exposure to service conditions leading to leakage of the thermic fluid. The present study aims to understand the root cause of failure of these pipes which were seam welded together with spot welds on the surface. The seam welding had been done either by a) laser beam welding (LBW) or by metal inert gas welding (MIG). Dye penetrant tests were applied to the pipes followed by microstructural analysis of the pipes using optical microscopy, and field emission scanning electron microscopy (FESEM). Subsequently, phase determination was carried out by X-ray diffraction. Stress corrosion cracking (SCC) susceptibility of the laser beam welded, MIG welded and spot welded joints were tested as per ASTM G36 in boiling MgCl2. Detailed investigation revealed that leakage in each case occurred near spot welded joints due to chloride-induced SCC of AISI 321 SS. SCC susceptibility tests of the welds showed that both the seam welds and the spot welds had residual stresses beyond the threshold limit which resulted in early nucleation of cracks in presence of chloride ions. Improper post-weld heat treatment (for LBW, MIG and spot weld) was identified to be the root cause of failure of the pipes.
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    Graphene coating on mild steel by spin coating method
    ( 2020-01-01) Srinivasa Vadayar, K. ; Jhansee, J. ; Acharyya, Swati Ghosh
    Mild steel is one of the main construction resources used in the industries as it consists of light weight. It has a young modulus of 200GNm-2. Mild steel consist of low content of carbon approximately 0.05% to 0.25% carbon. It consists of low quantity of carbon percentage it is corroded easily by exposing corroding atmosphere. In this work graphene derived products were produced after synthesizing graphene oxide via modified Hummers method by using natural graphite. The obtained graphene after reduction (RGO) was dispersed in DMF (di-methyl formaldehyde) to get a coating solution sometimes solutions with binders for good adherent film onto the substrate surface. In this study I use the binder like polyvinyl alcohol (PVA) coated solution for coating the substrate. The substrate material properties remain the same as coatings of grapheme. They are extremely thin whether they form mono or multi layers on it. The inertness of graphene in various atmospheres makes it strong and is a good barrier to movement of gases through it. Hence graphene films inhibit corrosion. In the present investigation the mild steel substrates were coated with graphene using spin coating techniques. Prepared graphene oxide and reduced graphene oxide is characterized by using X-ray diffraction and Raman spectroscopy and FESEM analysis .The coated mild steel is analysed by SEM analysis.
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    Integrity of 5052 Al-mild steel dissimilar welds fabricated using MIG-brazing and cold metal transfer in nitric acid medium
    ( 2019-06-01) Sravanthi, S. S. ; Acharyya, Swati Ghosh ; Phani, Phani Prabhakar ; Padmanabham, G.
    Comparitive analysis of the corrosion resistance of H32 5052 Al alloy and galvanized mild steel lap joints fabricated by a) Metal Inert Gas (MIG) Welding-brazing and b) Cold metal transfer (CMT) was done by keeping wire feed rate and welding speed constant. The weld interfaces of 5052 Al and mild steel were characterized using Field emission scanning electron microscopy, X-ray diffraction and nano-indentation measurements. Weight loss tests were done as per ASTM G 67-04 on the lap joints. Results indicated formation of Al-Fe-Si layer at the weld bead-mild steel interface in both the techniques. The layer was found to be Aluminium rich in MIG –braze sample whereas it was iron rich in the CMT sample. The layer thickness was found to be higher in the toe region than the head region in both samples. The Al-Fe-Si layer preferentially dissolved during the weight loss test of the welds. The thickness of Al-Fe-Si layer for MIG-braze welds was greater resulting in higher intergranular corrosion.
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    Microstructural and electrochemical behaviour of aluminium alloy composites produced using different sintering techniques
    ( 2018-01-01) Muthuchamy, A. ; Annamalai, A. Raja ; Acharyya, Swati Ghosh ; Nagaraju, Nidhi ; Agrawal, Dinesh K.
    Present research work analyses the effect of heating modes on the densification, microstructure and mechanical properties of aluminum alloys [65Al-20Cu-15Mn] fabricated through powder metallurgy route. Sintering of compacts using conventional, microwave and spark plasma sintering methods has been carried out at 525°C. From the results, it has been observed that the spark plasma sintering method produced the samples with better mechanical properties than the other two methods, followed by microwave and conventionally sintered counterparts. Microstructural analysis using optical microscopy revealed that spark plasma sintered sample has finest microstructure due to faster rate of heating than microwave and conventional methods.
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    Nanomagnetic computing for next generation interconnects and logic design
    ( 2019-01-01) Debroy, Sanghamitra ; Sivasubramani, Santhosh ; Acharyya, Swati Ghosh ; Acharyya, Amit
    In this chapter a holistic approach towards the design of energy-efficient circuitry has been discussed. The novel material graphene with extraordinary mechanical, electrical, thermal and magnetic properties has been shown to have a huge potential in replacing copper for clocking the nanomagnetic-based circuits so that the huge current required for generating external magnetic field can be reduced. Through simulation results the above mentioned has also been established. This chapter on the other hand also provides an insight on nanomagnetic computing for next generation interconnects and logic design. The role of MQCA-based digital arithmetic circuits and their impact has also been well demonstrated in this chapter.
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    Novel Ti-Nb alloys with improved wear resistance for biomedical implant application
    ( 2016-10-13) Chapala, Praveen ; Acharyya, Swati Ghosh ; Shariff, S. M. ; Naik, Ganesh
    The present study involved fabrication of titanium niobium based alloys having elastic modulus close to that of human bone and subsequently determining the wear resistance of these alloys for biomedical application. In the present study three beta stabilized titanium niobium alloys having composition Ti-24Nb-4Zr-8Sn, Ti-35Nb-4Sn and Ti-29Nb-13Ta-7Zr were made by vacuum arc melting. The alloys were then aged at 1000 C for 6 hours in an argon atmosphere. Detailed microstructural characterization and phase identification was carried out using scanning electron microscopy and x-ray diffraction respectively. The hardness of the samples were measured by micro hardness measurements. The wear resistance and the friction coefficient of the samples were measured by testing in Ringer's solution (simulated body fluid). The results showed improved wear resistance of the fabricated alloys.
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    Self healing nature of bilayer graphene
    ( 2016-08-01) Debroy, Sanghamitra ; Pavan Kumar Miriyala, V. ; Vijaya Sekhar, K. ; Acharyya, Swati Ghosh ; Acharyya, Amit
    The phenomenon of self healing of cracks in bilayer graphene sheet has been studied using molecular dynamics simulations. The bilayer graphene sheet was subjected to uniaxial tensile load resulting in initiation and propagation of cracks on exceeding the ultimate tensile strength. Subsequently, all forces acting on the sheet were removed and sheet was relaxed. The cracks formed in the graphene sheet healed without any external aid within 0.4 ps The phenomenon of self healing of the cracks in graphene sheet was found to be independent of the length of the crack, but occurred for critical crack opening distance less than 5 Å for AA stacked sheet and 13 Å for AB stacked bilayer graphene sheet. Self healing was observed for both AB (mixed stacking of armchair and zigzag graphene sheet) and AA (both sheets of similar orientation i.e. either armchair-armchair or zigzag-zigzag) stacking of bilayer graphene sheet.
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    Self-healing phenomena of graphene: Potential and applications
    ( 2016-01-01) Vijayasekhar, K. ; Acharyya, Swati Ghosh ; Debroy, Sanghamitra ; Miriyala, V. Pavan Kumar ; Acharyya, Amit
    The present study investigates the self healing behavior of both pristine and defected single layer graphene using a molecular dynamic simulation. Single layer graphene containing various defects such as preexisting vacancies and differently oriented pre-existing cracks were subjected to uniaxial tensile loading till fracture occurred. Once the load was relaxed, the graphene was found to undergo self healing. It was observed that this self healing behaviour of cracks holds irrespective of the nature of pre-existing defects in the graphene sheet. Cracks of any length were found to heal provided the critical crack opening distance lies within 0.3-0.5 nm for a pristine sheet and also for a sheet with pre-existing defects. Detailed bond length analysis of the graphene sheet was done to understand the mechanism of self healing of graphene. The paper also discusses the immense potential of the self healing phenomena of graphene in the field of graphene based sub-nano sensors for crack sensing.
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    Shape memory alloy smart knee spacer to enhance knee functionality: Model design and finite element analysis
    ( 2016-10-13) Gautam, Arvind ; Rani, A. Bhargavi ; Callejas, Miguel A. ; Acharyya, Swati Ghosh ; Acharyya, Amit ; Biswas, Dwaipayan ; Bhandari, Vasundhra ; Sharma, Paresh ; Naik, Ganesh R.
    In this paper we introduce Shape Memory Alloy (SMA) for designing the tibial part of Total Knee Arthroplasty (TKA) by exploiting the shape-memory and pseudo-elasticity property of the SMA (e.g. NiTi). This would eliminate the drawbacks of the state-of-the art PMMA based knee-spacer including fracture, sustainability, dislocation, tilting, translation and subluxation for tackling the Osteoarthritis especially for the aged people of 45-plus or the athletes. In this paper a Computer Aided Design (CAD) model using SolidWorks for the knee-spacer is presented based on the proposed SMA adopting the state-of-the art industry-standard geometry that is used in the PMMA based spacer design. Subsequently Ansys based Finite Element Analysis is carried out to measure and compare the performance between the proposed SMA based model with the state-of-the art PMMA ones. 81% more bending is noticed in the PMMA based spacer compared to the proposed SMA that would eventually cause fracture and tilting or translation of spacer. Permanent shape deformation of approximately 58.75% in PMMA based spacer is observed compared to recoverable 11% deformation in SMA when same load is applied on both separately.