Browsing by Author "Vakil Singh"

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Biomechanical analysis of distal femoral fracture fixation: dynamic condylar screw versus locked compression plate
(Springer Tokyo, 2014) Nidhi Narsaria; Ashutosh K. Singh; Amit Rastogi; Vakil Singh
Background: This human cadaveric study introduces a laboratory model to establish and compare the fixation stability of the distal femoral locking plate (DFLP) and dynamic condylar screw (DCS) in distal femoral fracture fixation.; Materials and methods: The study was conducted on 16 fresh cadaveric femoral specimens, 8 implanted with the DCS and the other 8 with the DFLP. The construct was made unstable by removing a standard-sized medial wedge with a 1-cm base (gap osteotomy) beginning 6 cm proximal to the lateral joint line in the distal metaphyseal region with loss of the medial buttress. Each specimen underwent axial and torsional stiffness testing along with cyclic axial loading to failure. The mean DEXA value for the DFLP group was 0.82 g/cm2 and in the DCS group was 0.79 g/cm2.; Results: Axial stiffness in the DFLP group was significantly higher than in the DCS group, but no significant difference was found in torsional stiffness between the groups. A significant difference was found in the load-to-failure results between the groups. Plastic and total deformation was significantly higher in constructs in the DCS group than in those in the DFLP group. Total energy absorbed before construct failure was also significantly higher in the DFLP group than in the DCS group.; Conclusions: The DFLP construct proved stronger than the DCS in both axial stiffness and cyclic loading, but similar in torsional stiffness in biomechanical testing in a simulated A3 distal femoral fracture. © 2014, The Japanese Orthopaedic Association.
Blistering observed in Mylar due to H+-ion bombardment
(1983) V. Shrinet; U.K. Chaturvedi; S.K. Agrawal; Vakil Singh; A.K. Nigam
So far the blistering phenomenon due to ion implantation has been observed in metals and alloys, but no blistering has been reported in polymers like Mylar etc. A severe blistering in Mylar (polyethylene teraphthalate) has been observed by us, due to 250 keV H+-ion bombardment up to a dose level of 7×1015 ions/cm2, at ambient temperature. In metals and alloys the blistering is due to the pressure built up by the coalescence of the implanted gaseous species. However, in Mylar the cause is entirely different. In fact, it is attributed to the hydrogen gas released on account of the breakage of aliphatic C-H bonds of monomer, due to ion implantation. Very interesting features, like uniform unexfoliated circular blisters, circular rings (Karnavalayas) and black dots of different sizes along with their development sequence, have been observed. The observed features are explained on the basis of the aliphatic CH bond breakage theory due to ion bombardment. © 1983.
Comparison of cutout resistance of dynamic condylar screw and proximal femoral nail in reverse oblique trochanteric fractures: A biomechanical study
(2012) Gursimrat Singh Cheema; Amit Rastogi; Vakil Singh; Satish Chandra Goel; Diwakar Mishra; Sumit Arora
Background: Reverse oblique trochanteric fracture of femur is a distinct fracture pattern. 95° Dynamic condylar screw (DCS) and proximal femoral nail (PFN) are currently the most commonly used implants for its fixation. This study aims to biomechanically compare the cutout resistance as well as modes of failure of DCS and PFN in reverse oblique trochanteric fractures. Materials and Methods: Sixteen freshly harvested cadaveric proximal femoral specimens were randomly assigned to three mean bone mineral density matched groups, eight of which were implanted with 95 DCS and the other eight with PFN. The constructs were made unstable to resemble a reverse oblique trochanteric fracture by removing a standard size posteromedial wedge. These constructs were subjected to computer controlled cyclic compressive loading with 200 kg at a frequency of 1 cycle/second (1 Hz) and end points of both the groups were analyzed. Results: The bending moment of the PFN group was approximately 50% less than that of the DCS group (P<0.0001). The PFN group resisted more number of cycles than the DCS group (P=0.03) and showed lesser number of component failures as compared with the DCS group (P=0.003). Conclusions: The PFN is biomechanically superior to DCS for the fixation of reverse oblique trochanteric fractures of femur.
Corrosion inhibition in paper and pulp industry by some organic compounds
(2006) M.A. Quaraishi; B. Lal; Vakil Singh
Paper industries in India face serious problems due to corrosion of structural components and their high cost of replacement and maintenance. Amongst the wide spectrum of preventive measures available, addition of inhibitors is considered to be a reliable and cost effective means for dealing with corrosion problems. The present investigation aims at evaluation of a few organic compounds, namely lauric hydrazide, undecenoic hydrazide, aniline and para anisidine on corrosion behavior of mild steel in simulated corrosive environment, encountered in paper industries, using weight loss and potentiodynamic methods. © University of Manchester and the authors 2006.
Effect of Al content on microstructure and cyclic oxidation performance of Pt-aluminide coatings
(2002) D.K. Das; Vakil Singh; S.V. Joshi
The effect of Al content, i.e., the amount of Al picked up during aluminizing, on the microstructure and cyclic oxidation properties of Pt-aluminide coatings has been investigated. The cast Ni-base superalloy CM-247 was used as the substrate material and a single-step, high-activity pack aluminizing process was used to produce the Pt-aluminide coatings. The Al content of these coatings was varied by using packs with different compositions of the Al source. Pt-aluminide coatings having three different Al contents, namely 6.5, 16, and 21 mg cm-2, were evaluated for their cyclic oxidation resistance at 1200°C in air. It was found that the Pt-aluminide coatings, irrespective of their Al contents, evolve in the same manner during aluminizing and result in a three-layer structure with an outer PtAl2 + NiAl two-phase layer, an intermediate NiAl layer, and the inner interdiffusion layer. The stability of this three-layer coating structure over long periods of aluminizing, however, is dependent on the availability of Al from the pack during this period. Below a certain threshold Al availability, the two-phase outer layer transforms to a single-phase NiAl structure causing the coating to change from its three-layer structure to a two-layer one. Cyclic oxidation results indicate that, while a minimum Al content in Pt-aluminide coatings is essential for deriving the best oxidation performance, increasing the Al content beyond a certain level does not significantly enhance oxidation behavior. The effect of Al content on aspects, such as coating degradation and nature of coating-surface damage during cyclic oxidation, is also discussed.
Effect of anodization on corrosion behaviour and biocompatibility of Cp-titanium in simulated body fluid
(2013) Archana Singh; B.P. Singh; Mohan R. Wani; Dinesh Kumar; J.K. Singh; Vakil Singh
The objective of this investigation is to study the effectiveness of anodized surface of commercial purity titanium (Cp-Ti) on its corrosion behaviour in simulated body fluid (SBF) and proliferation of osteoblast cells on it, to assess its potentiality as a process of surface modification in enhancing corrosion resistance and osseointegration of dental implants. Highly ordered nano-porous oxide layer, with nano-sized pores, is developed on the surface of Cp- Ti through electrochemical anodization in the electrolyte of aqueous solution of 0.5% HF at 15 V for 30 min at 24 °C. The nano-porous feature of the anodized surface is characterized by field-emission scanning electron microscope (FESEM). Pores of some anodized samples are sealed by exposing the anodized surface in boiling water. Corrosion behaviour of the anodized specimen is studied in Ringer's solution at 30 ± 2 °C, using electrochemical impedance and cyclic polarization technique. Biocompatibility of the anodized surface is accessed using MG63 osteoblast cells. Both corrosion as well as pitting resistance of Cp-Ti in simulated body fluid are found to be highest in the anodized and sealed condition and followed in decreasing order by those of anodized and unanodized ones. Significantly higher MG63 osteoblast cell proliferations are found on the anodized surface than that on the unanodized one. Anodized Cp-Ti develops nano-size surface pores, like that of natural bone. It enhances corrosion and pitting resistance and also the process of osteoblast cell proliferation on Cp-Ti. © Indian Academy of Sciences.
Effect of cold rolling on the Coffin-Manson relationship in low-cycle fatigue of superalloy IN718
(2008) K.V.U. Praveen; Vakil Singh
The age-hardenable Ni-Fe-based superalloy IN718 exhibits a dual-slope Coffin-Manson (C-M) relationship during low-cycle fatigue (LCF). Effort was made to eliminate the dual-slope C-M relationship by introducing prior deformation. Peak-aged (PA) material was subjected to different degrees of cold reduction, and its LCF behavior was examined. Cold rolling is found to be highly effective in eliminating the dual slope and enhancing the fatigue life at low strain amplitudes. Cold rolling coupled with stress relieving (SR) treatment is found to further improve the fatigue life. The role of texture on the observed LCF behavior is analyzed and found to have no significant effect. © The Minerals, Metals & Materials Society and ASM International 2007.
Effect of H+ ion irradiation on surface morphology of Fe40Ni40B20 metallic glass
(Springer India, 1986) A.J.K. Prasad; Vakil Singh
The effect of irradiation by H+ ions on surface modifications of metallic glass Fe40Ni40B20, in the as-quenched, structurally related and crystallized state, has been studied. Swollen regions develop on the surface of the as-quenched and structurally relaxed specimens, whereas blisters form on the surface of the crystallized specimen, under identical conditions of irradiation. The results are explained in terms of the distribution of hydrogen in the amorphous and crystallized conditions. © 1986 Indian Academy of Sciences.
EFFECT OF HEAT TREATMENT ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF TITANIUM ALLOY IMI685.
(Trans Tech Publ, 1985) Vakil Singh; C. Ramachandra
[No abstract available]
Effect of prealuminizing diffusion treatment on microstructural evolution of high-activity pt-aluminide coatings
(Minerals, Metals and Materials Society, 2000) D.K. Das; Vakil Singh; S.V. Joshi
The effect of prealuminizing (or prior) diffusion treatment on the evolution of Pt-aluminide coatings on the Ni-based superalloy CM-247 has been studied by using a single-step, high-activity aluminizing process. Coatings generated without any prior diffusion treatment, as well as those formed by adopting two extreme prior-diffusion schedules (at 850 °C for 0.5 hours and at 1034 °C for 5 hours), were investigated by analyzing the coating structures at various stages of aluminizing. When the dilution of the Pt layer, caused by its interdiffusion with the substrate during the prior diffusion treatment, is only marginal (as in the case of no prior diffusion and diffusion at 850 °C for 0.5 hours), the equilibrium Pt-aluminide coating structure evolves through the formation of two transient layers during the initial stages of aluminizing. In contrast, for diffusion at 1034 °C for 5 hours, which results in extensive dilution of the Pt layer, the two-phase equilibrium structure (PtAl2 in a matrix of NiAl) in the outer layer of the coating is found to develop during very early stages of aluminizing and remains unchanged, even over extended periods of aluminizing. Further, in the case of prior diffusion at 1034 °C for 5 hours, Pt is found to remain distributed to a greater extent over the entire thickness of the coating than in the cases of limited prior diffusion treatment. The present findings underline the significance of the nature of the prior-diffusion schedule on the microstructural evolution of Pt-aluminide coatings. It has also been found that a prealuminizing diffusion treatment is particularly important for Pt-aluminide coatings from the point of view of coating adhesion to the substrate.
Effect of prior treatment on the low cycle fatigue behaviour of aluminium alloy RR58 at 423K
(1980) Vakil Singh; M.S.N. Rao; P.Rama Rao
The effect of the quenching medium and of varying the microstructure on low cycle fatigue behaviour of aluminium alloy RR58 has been investigated at 423K. It is observed that fatigue resistance is significantly impaired if, following solutionizing, the alloy is quenched in water instead of in oil. Thermal as well as thermomechanical treatments were employed to produce different microstructures. The overaged microstructure displayed the highest fatigue life. It is shown with the help of fractographic observations that differences in fatigue resistance due to differences in severity in quenching or in microstructure arise mainly due to the influence of these variables on crack initiation and early crack propagation. It has also been demonstrated that as the rate of hardening or softening is increased, cyclic strength coefficient K′ and fatigue hardening exponent n′ increase; the fatigue ductility coefficient ε{lunate}′f decreases as a result of varying microstructures, and the fatigue resistance at 423K of the alloy is lowered. When compared with the behaviour at ambient temperature, the test temperature of 423K has been found to have no significant effect on the fatigue life/strain plot. © 1980.
Effect of simvastatin on fracture healing-an experimental study
(2007) S.K. Saraf; Ajit Singh; R.S. Garbyal; Vakil Singh
Left femur was osteotomized and fixed with K wire in 21 rabbits. One group was fed simvastatin (120 mg/kg body wt/day) orally, whereas another group without medication served as control. Both groups were assessed radiologically, morphologically, histologically and biomechanically at 4, 8 and 12 weeks. An analysis of various parameters of study showed that simvastatin treated group had improved bone healing at 4 and 8 weeks of follow up, however, the difference was not significant statistically at 12 weeks. So it is concluded that Simvastatin favourably hastened the process of fracture healing in the rabbits at earlier phases.
Effect of ultraviolet irradiation on the osseointegration of a titanium alloy with bone
(Medknow Publications, 2017) Ashish Yadav; Ranjana Yadav; Aratee Gupta; Akash Baranwal; Atul Bhatnagar; Vakil Singh
Introduction: Attempt has been made to analyze the potential of titanium (Ti) alloy for osteointegration by the effect of surface photo functionalization in different aspects as follows: in Ringer's solution, in vitro cell growth, and in vivo study on rabbit. The present study was aimed to investigate the influence of ultraviolet (UV) light on surface topography, corrosion behavior, and bioactivity of indigenously manufactured samples of Ti alloy mini-implant. Materials and Methods: The study includes surface modification of Ti samples by UV treatment, corrosion testing of the specimens using Potentiostat (GAMRY System), qualitative examination of modified surface topography using scanning electron microscope, and cellular viability test on Ti alloy surface (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide ASSAY). To find the effect of UV light on implant bone integration, biochemical test was performed on the femur of rabbits. Results and Discussion: Corrosion resistance of untreated Ti alloy in Ringer's solution was found to be less, whereas corrosion rate was more. Corrosion resistance of UV-Treated samples was found to increase significantly, thereby lowering the corrosion rate. Cell growth in UV-Treated specimen was observed to be higher than that in untreated samples. It is important to mention that cell growth was significantly enhanced on samples which were UV treated for longer duration of time. Conclusions: There was a marked improvement in cell growth on UV-Treated Ti alloy samples. Hence, it is expected that it would enhance the process of osseointegration of Ti with bone. Another important finding obtained was that the removal torque values of UV-Treated implants were higher than that of untreated implants. The overall result reveals that UV treatment of implants does help us in speeding up the osseointegration process. © 2017 Medknow Publications. All rights reserved.
Effects of hydrogen bombardment on Ni40Fe6Co20Cr12Mo6B16 amorphous alloy
(1981) R.D.S. Yadava; N.I. Singh; A.K. Nigam; Vakil Singh
The effect of H+ ion implantation at the energy level of 250 keV on the surface behaviour of an amorphous alloy, Ni40Fe6Co20Cr12Mo6B16, in three different conditions, namely the amorphous, crystallized by annealing at 460°C for 20 min and for 60 min, has been studied. It is observed that the material in the amorphous state is highly resistant to blistering in the fluence range 0.72 × 108 to 1.5 × 1019 ions/cm2; however, under identical conditions of irradiation, the material annealed for 20 min is relatively less resistant and the one annealed for 60 min is the least resistant to blistering. A typical surface feature consisting of fine nodules and pinholes is observed to develop due to irradiation, depending on the initial condition of the material and the dose level of implantation. The high resistance of the material against blistering in the amorphous state is explained in terms of a large solubility and low diffusivity of hydrogen, low probability of irradiation-induced disordering, and high strength combined with adequate ductility in the amorphous condition. © 1981.
Elimination of dual slope from the Coffin-Manson relationship of low-cycle fatigue in the titanium alloy timetal 834, by cold rolling
(2007) K.V. Sai Srinadh; Vakil Singh
Cold rolling of the titanium alloy Timetal 834 was found to cause marked enhancement in low-cycle fatigue (LCF) life at low strain amplitude and to eliminate bilinear behavior from the Coffin-Manson (C-M) relationship. It was due to work hardening of surface grains of soft orientation and consequent increase in resistance of the material against crack initiation. The observed effect was not associated with texture. © The Minerals, Metal & Materials Society and ASM International 2007.
Enhanced osteoblast proliferation and corrosion resistance of commercially pure titanium through surface nanostructuring by ultrasonic shot peening and stress relieving
(Allen Press Inc., 2014) Shitu Jindal; Rajesh Bansal; Bijay P. Singh; Rajiv Pandey; T. S. N. Shankar Narayanan; Mohan R. Wani; Vakil Singh
This investigation was carried out to study the effect of a novel process of surface modification, surface nanostructuring by ultrasonic shot peening, on osteoblast proliferation and corrosion behavior of commercially pure titanium (c p-Ti) in simulated body fluid. A mechanically polished disc of c p-Ti was subjected to ultrasonic shot peening with stainless steel balls to create nanostructure at the surface. A nanostructure (<20 nm) with inhomogeneous distribution was revealed by atomic force and scanning electron microscopy. There was an increase of approximately 10% in cell proliferation, but there was drastic fall in corrosion resistance. Corrosion rate was increased by 327% in the shot peened condition. In order to examine the role of residual stresses associated with the shot peened surface on these aspects, a part of the shot peened specimen was annealed at 400°C for 1 hour. A marked influence of annealing treatment was observed on surface structure, cell proliferation, and corrosion resistance. Surface nanostructure was much more prominent, with increased number density and sharper grain boundaries; cell proliferation was enhanced to approximately 50% and corrosion rate was reduced by 86.2% and 41% as compared with that of the shot peened and the as received conditions, respectively. The highly significant improvement in cell proliferation, resulting from annealing of the shot peened specimen, was attributed to increased volume fraction of stabilized nanostructure, stress recovery, and crystallization of the oxide film. Increase in corrosion resistance from annealing of shot peened material was related to more effective passivation. Thus, the surface of c p-Ti, modified by this novel process, possessed a unique quality of enhancing cell proliferation as well as the corrosion resistance and could be highly effective in reducing treatment time of patients adopting dental and orthopedic implants of titanium and its alloys.
Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process
(Minerals, Metals and Materials Society, 1998) O.K. Das; Vakil Singh; S.V. Joshi
This study deals with the aluminizing of a directionally cast Ni-base superalloy, namely CM-247, by a single-step process using a high-activity pack. It is observed that significant incorporation of Al into the substrate surface during aluminizing continues over a period of about 1 hour and is not restricted merely to the first few minutes, as reported in the literature. Based on the microstructural details of the coatings formed at various stages of aluminizing, it is concluded that the coating growth in the above process takes place primarily by inward Al diffusion initially, followed by an intermediate stage when the growth involves both inward Al and outward Ni diffusion. In the final stages, the outward diffusion of Ni dominates the coating formation process. The above mechanism of coating formation is different from the one that prevails in the conventional two-step high-activity coating process in that the reaction front for the formation of NiAl remains spatially stationary despite the outward diffusion of nickel during the intermediate stage. It is also shown in the present study that the content of the Al source in the pack affects the coating structure significantly. It is further demonstrated that the microstructure of the aluminide coatings depends not only on the amount of Al incorporated in the sample during aluminizing but also on the time over which the uptake of this Al takes place.
FAILURE ANALYSIS OF FRACTURED DENTAL IMPLANTS
(Association of Metallurgical Engineers of Serbia, 2022) Rajesh Bansal; Amit Raj Sharma; Vakil Singh
The success and predictability of titanium implants over long periods of time are well established, and there has been a tremendous increase in implant popularity among patients and clinicians over the last four decades. However, complications can occur, resulting in the loss of both the implant and the prosthesis. Dental implant fracture is uncommon; however, implants or abutment screws can fracture and cause significant problems for both the clinician and the patient. Improper design, overload, fatigue, and corrosion are all potential causes of implant fracture. Six retrieved fractured dental implants of varying diameter and thread design were collected on a regular basis to characterize their fracture behavior by SEM and assess the fracture mechanism. The majority of the implants were fractured as a result of fatigue crack initiation and propagation from the thread roots. © 2022, Association of Metallurgical Engineers of Serbia. All rights reserved.
High temperature oxidation behaviour of directionally solidified nickel base superalloy CM - 247LC
(2003) D.K. Das; Vakil Singh; S.V. Joshi
The present paper describes the isothermal and cyclic oxidation behaviour of the technologically important nickel base directionally solidified superalloy CM - 247LC in air in the temperature range 1000 - 1200°C. This superalloy behaves as a transition nickel base alloy under isothermal oxidation conditions and exhibits a fairly long transient oxidation period (∼20 h at 1100°C). Irrespective of the temperature of exposure and nature of oxidation (isothermal or cyclic), a composite oxide scale develops on CM - 247LC. While the outer portion of the oxide scale consists of either spinel (NiAl2O4) or a mixture of spinel and NiO, depending on oxidation temperature, the inner portion is always constituted of alumina. Beyond the transient period, the alloy is found to follow parabolic oxidation kinetics. The oxide layer that forms is invariably very non-uniform in thickness, and is dispersed with two types of oxide particles. While tantalum rich oxide particles are found scattered in the outer zone of the oxide layer, hafnium rich oxide particles lie close to the oxidelmetal interface. Results also reveal that the nature of oxidation associated with the CM - 247LC superalloy causes entrapment of metal islands in the oxide layer.
High-manganese and nitrogen stabilized austenitic stainless steel (Fe-18Cr-22Mn-0.65N): A material with a bright future for orthopedic implant devices
(IOP Publishing Ltd, 2021) Chandra Shekhar Kumar; Gaurav Singh; Suruchi Poddar; Neelima Varshney; Sanjeev Kumar Mahto; Arijit Saha Podder; Kausik Chattopadhyay; Amit Rastogi; Vakil Singh; Girija Shankar Mahobia
The rationale behind the success of nickel free or with extremely low nickel austenitic high manganese and nitrogen stabilized stainless steels is adverse influences of nickel ion on human body. Replacement of nickel by nitrogen and manganese provides a stable microstructure and facilitates better biocompatibility in respect of the conventional 316L austenitic stainless steel (316L SS). In this investigation, biocompatibility of the high-manganese and nitrogen stabilized (Fe-18Cr-22Mn-0.65N) austenitic stainless steel was studied and found highly promising. In vitro cell culture and cell proliferation (MTT) assays were performed on this stainless steel and assessed in respect of the 316L SS. Both the steels exhibited similar cell growth behavior. Furthermore, an enhancement was observed in cell proliferation on the Fe-18Cr-22Mn-0.65N SS after surface modification by ultrasonic shot peening (USP). The mean percent proliferation of the MG-63 cells increased from ≈88% for Un-USP to 98% and 105% for USP 3-2 and USP 2-2 samples, respectively for 5 d of incubation. Interestingly, in vivo animal study performed in rabbits for 3 and 6 weeks showed callus formation and sign of union without any allergic reaction. © 2021 IOP Publishing Ltd.