Now showing 1 - 10 of 31
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    Influence of organoclay on flexural fatigue behavior of polyamide 66/hectorite nanocomposites at laboratory condition
    (01-11-2010)
    Timmaraju, Mallina Venkata
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    Polyamide 66/hectorite nanocomposites exhibit superior mechanical properties compared with pure polymers and are promising for structural applications. X-ray diffraction results revealed reduced degree of exfoliation with increase in organoclay content. Flexural fatigue characteristics of polyamide 66/hectorite nanocomposites containing different quantities of clay content were investigated, under deflection control mode, using a custom built flexural fatigue test rig. Addition of organoclay improved the moduli of the material. An enhanced resistance to cyclic softening was noticed at high temperatures with the incorporation of organoclay. Nanocomposite samples exhibited a significant improvement in fatigue life compared with pure polymers; however, the degree of enhancement is governed by the nanostructure of organoclay in polymer matrix. The fatigue life of nanocomposite samples is strongly affected by specimen temperature and induced stress. Macroscopic fracture surfaces changed from flat featureless structure to a highly perturbed structure with increase in organoclay content. © 2010 Society of Plastics Engineers.
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    Fretting Wear Behavior of Laser Peened Ti-6Al-4V
    (01-09-2012)
    Kumar, S. Anand
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    Sundar, R.
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    Kumar, H.
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    Kaul, R.
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    Ranganathan, K.
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    Oak, S. M.
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    Kukreja, L. M.
    This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples. © 2012 Copyright Taylor and Francis Group, LLC.
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    Microstructural evolution and mechanical properties of oil jet peened aluminium alloy, AA6063-T6
    (01-10-2010)
    Arun Prakash, N.
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    Grain size refinement by severe surface plastic deformation is one way of improving the surface properties. This paper describes the microstructural evolution due to severe surface plastic deformation by oil jet peening in aluminium alloy, AA6063-T6. Detail characterization of the treated surfaces using X-ray diffraction analysis and transmission electron microscopy revealed the formation of submicron size grains at and near the surface. The nozzle-traveling velocity decides the peening intensity and coverage and affects the surface properties. The specimen peened at low nozzle-traveling velocity exhibited an ultrafine grain size (∼210. nm) with high surface hardness (∼0.88. GPa), compressive residual stress (-102 ± 7. MPa) and dislocation density. The hardness is high at the surface and the depth of hardened layer is ∼400μm. Formation of high-density dislocations and associated grain refinement resulted in increased surface hardness. Presence of surface modified layer will be beneficial in improving the fatigue and tribo behavior. © 2010 Elsevier Ltd.
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    The effect of nanoclay reinforcement on the rolling contact fatigue behaviour of polyamide
    (01-01-2013)
    Charles, D. Finney
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    Polymer nanocomposite has received great research interest in design of engineering components owing to its remarkable improvement in tribological characteristics. Rolling contact fatigue is a predominant failure mode of the many functional components like gears, bearings, cams, ball screw rods and rail wheels. Nanosize clay fillers were dispersed into the polymer using melt intercalation method to produce polymer nanocomposite material. Injection-molded disctype specimens were made to run against each other on twin-disc test rig designed in-house. To understand the behaviour of the materials, rolling contact fatigue behaviour against different contact loads under constant speed were studied. Rolling contact fatigue testing of polymer nanocomposite has revealed significant difference from the pristine PA6 behaviour in failure modality and temperature rise. Addition of nanoclay to polymer although improved the modulus and strength of the nanocomposite, deteriorated the rolling contact behaviour. Rolling contact fatigue performance of PA6 was better than that of the clay-reinforced polymer nanocomposite under all tested conditions. Polymer nanocomposite materials have shown poor wear resistance as the specific wear rate was calculated to be higher for PNC materials under rolling contact fatigue conditions. Difference in surface temperature rise in PA6 and polymer nanocomposite has led to the different failure mechanism and reduction in rolling contact fatigue life of polymer nanocomposite materials. © IMechE 2012.
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    Effect of humidity on the indentation hardness and flexural fatigue behavior of polyamide 6 nanocomposite
    (15-05-2010)
    Rajeesh, K. R.
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    Velmurugan, R.
    Humidity affects the mechanical properties of polymers and their composites. Understanding the influence of humidity on the strength, stiffness and fatigue characteristics will aid in better product design. The effect of relative humidity (RH) on indentation hardness and flexural fatigue behavior of polyamide 6 nanocomposites is reported. Indentation hardness and indentation modulus of the material reduces up to ∼50% in the samples conditioned in water due to the plasticization and associated increased polymer chain mobility. Cantilever bending fatigue tests conducted at different relative humidity levels at constant displacement amplitude revealed increased fatigue life for polyamide 6 nanocomposites at high humidity. Hysteresis heating and molecular reorientation lowers the modulus during fatigue process and causes a reduction in the force amplitude at high humidity levels. The failure mechanisms at different humidity levels are discussed. © 2010 Elsevier B.V. All rights reserved.
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    Impact force of low velocity liquid droplets measured using piezoelectric PVDF film
    (05-03-2010)
    Sahaya Grinspan, A.
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    When a liquid droplet impacts on a solid surface, a transient impact force is developed at the interface between the liquid and the solid surface. Impact velocity, surface tension and density of the liquid are the important parameters that influence the impact force. In the present study, impact forces of two different oils' droplet (hydraulic oil ISO VG 68 and lubrication oil SAE 30) are compared with the impact force of water droplet. The impact velocity is varied from about 1.38 to 2.96 m/s. The impact force is determined experimentally using polyvinylidene difluoride (PVDF) piezoelectric film attached on the solid surface. The dynamic response of the PVDF piezoelectric film is acquired using data acquisition system with personal computer. The film is dynamically calibrated using bead drop impact method. A linear relationship between voltage output of the PVDF piezoelectric film and impact force is established. The droplet impact force is determined by measuring the voltage output delivered by the PVDF piezoelectric film and converted it into the impact force. Impact forces developed by both the oils' droplets are lesser than the impact force of water droplet. The impact duration observed is about 600 μs. © 2010 Elsevier B.V. All rights reserved.
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    Friction and wear behavior of surface nanocrystallized aluminium alloy under dry sliding condition
    (15-04-2010)
    Prakash, N. Arun
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    One way of improving the surface properties of engineering material is by reducing the grain size at the surface. Controlled ball impact process is developed for producing surface nanocrystallization and improves the surface mechanical properties by inducing compressive residual stress on the metallic materials. Improvement in the surface mechanical properties will affect the tribological properties. This paper reports the influence of the surface nanocrystallization on the tribological properties of aluminium alloy. Tribological properties were evaluated under dry sliding conditions using a reciprocating wear test facility. The friction coefficient of the treated surface is lower than that of the untreated samples and treatment improves the wear resistance of aluminium alloys. The improvement in the friction and wear properties is due to enhancement of surface strength, due to grain refinement and induction of compressive residual stress. The worn surfaces observed using scanning electron microscope reveal the dominant adhesive nature of wear and mild abrasive wear. © 2009 Elsevier B.V. All rights reserved.
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    Effects of laser peening on fretting wear behaviour of alloy 718 fretted against two different counterbody materials
    (01-10-2017)
    Anand Kumar, S.
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    Sundar, R.
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    Kaul, R.
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    Ranganathan, K.
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    Bindra, K. S.
    This paper deals with the effects of laser peening on fretting wear behaviour of a nickel-based superalloy, alloy 718, fretted against two different counterbody materials (alumina and SAE 52100 steel). Laser peening was carried out on alloy 718. Microstructural characterization of laser peened surface was done by electron back-scattered diffraction and transmission electron microscopy. Surface roughness, nanoindentation hardness, and residual stress of both laser peened and unpeened samples were determined. Fretting wear tests were conducted on unpeened and laser peened samples using two different counterbody materials (alumina and SAE 52100 steel balls). The results show that nanocrystallites formed in the surface and near-surface regions and compressive residual stress were induced after laser peening. Hardness increased due to grain refinement at the surface and near-surface regions. There was no significant change in the surface roughness. The laser peened sample exhibited lower tangential force coefficient values compared to unpeened samples at all loads, which may be attributed to higher hardness. Samples fretted against alumina counterbody exhibited higher tangential force coefficient compared to samples fretted against steel counterbody. Owing to increased surface hardness and higher compressive residual stress, laser peened samples exhibited lower fretting wear damage compared to unpeened samples. Due to tribochemical reactions, the wear volume of unpeened and laser peened samples fretted against alumina counterbody was higher than that of the samples fretted against steel counterbody.
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    Dry sliding wear behaviour of oil jet peened aluminium alloy, AA6063-T6
    (01-11-2010)
    Arun Prakash, N.
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    Oil jet peening makes use of high-pressure oil jet to impart compressive residual stresses on the surface of metallic materials in order to improve the surface properties. This article reports the dry sliding wear characteristics of oil jet peened aluminium alloy, AA6063-T6. The presence of compressive residual stress and high hardness improves the wear resistance of oil jet peened surfaces. Changes in the hardness, surface morphology, and residual stress distribution due to peening affect the tribological behaviour. The initial and steady-state coefficient of friction are less in the treated samples compared to untreated samples. The scanning electron microscope images of the worn surfaces reveal the dominant adhesive and mild abrasive form of wear.
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    Monotonic and cyclic behavior of polyamide 66/hectorite nanocomposites in marine environment
    (01-10-2019)
    Venkata Timmaraju, Mallina
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    Product design for safe performance and operation in harsh environments triggers the importance of understanding property degradation due to prolonged exposure of advanced composite materials to such environments. The effect of seawater immersion on monotonic tensile, stress relaxation, and cyclic bending fatigue response of polyamide 66 nanocomposites containing 0%, 1%, and 5% hectorite organoclay were investigated. Seawater equilibrated nanocomposites demonstrated less moisture absorption compared to their pure counterparts. The imbibed seawater significantly increased the ductility, and reduced the tensile modulus and strength of nanocomposites. A nine-parameter Prony series viscoelastic constitutive model was used to estimate the influence of seawater on the viscoelastic behavior based on stress relaxation data. The phenomenological model evaluated a drop of 82% in the instantaneous and the residual elastic moduli indicating a significant plasticizing effect of seawater. However, the amount of increase in the rubbery nature of polyamide is observed from the reduction in stress relaxation time of first Maxwell element by about 40%. Nanocomposites exhibited improved fatigue life with an increase in organoclay content even after equilibration in seawater. The fracture surface observation of seawater equilibrated bending fatigue specimen revealed rubbery behavior indicating the positive difference between cyclic steady-state temperature and material glass transition temperature.