Now showing 1 - 10 of 22
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    Dissipative Particle Dynamics Study of Strain Distribution in Capsules Deformed by Microfluidic Constrictions
    (01-01-2021)
    Rajkamal, Nishanthi
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    We present a dissipative particle dynamics (DPD) study of the deformation of capsules in microchannels. The strain in the membrane during this deformation causes the formation of temporary pores, which is termed mechanoporation. Mechanoporation is being considered as a means by which intracellular delivery of a broad range of cargo can be facilitated. In this work, we examine the strain distribution on the capsule membrane during transport of the capsule in converging-diverging microchannels of different constriction widths. The pore density is correlated to the strain in the membrane. We find that the highest strains and, consequently, the highest pore densities occur at intermediate channel widths. This occurs due to a competition of the bending of the membrane and fluid shear stresses in the flow.
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    Micromechanics based analytical model for estimation of stress distribution and failure initiation in constituents of UDFRP composites subjected to transverse loading
    (01-01-2020)
    Verma, Akash
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    Akella, Kiran
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    Sivakumar, Srinivasan M.
    When a Unidirectional fiber reinforced polymer (UDFRP) composite is subjected to transverse loading, there is spatial variation of stresses in the constituents. The failure in matrix initiates at the location of maximum stress. Stress distribution and failure initiation in constituents of UDFRP composites is usually studied through finite element (FE) analysis of representative volume element (RVE) which is computationally expensive and time consuming. The present study proposes an analytical model through which stress variation and failure initiation in the constituents of UDFRP composite can be obtained in simple and reliable way and it can be readily used in designing. For this model, RVE is idealized in the form of springs arranged in parallel and series. These springs represent the stiffness of constituents (fiber and matrix). The results of analytical model are compared with FE simulations and good agreement is observed. Influence of fiber volume fraction on failure initiation of UDFRP composites is also studied through FE analysis of RVE and analytical model.
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    Ballistic Impact Behaviour of Glass/Epoxy Composite Laminates Embedded with Shape Memory Alloy (SMA) Wires
    (01-01-2021)
    Verma, Luv
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    Andrew, Jefferson
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    Sivakumar, Srinivasan M.
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    Balaganesan, Gurusamy
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    Dhakal, Hom N.
    This paper aims to estimate the enhancement in the energy absorption characteristics of the glass fiber reinforced composites (GFRP) by embedding prestrained pseudo-elastic shape memory alloy (SMA) that was used as a secondary reinforcement. The pseudo-elastic SMA (PESMA) embedded were in the form of wires and have an equiatomic composition (i.e., 50%–50%) of nickel (Ni) and titanium (Ti). These specimens are fabricated using a vacuum-assisted resin infusion process. The estimation is done for the GFRP and SMA/GFRP specimens at four different impact velocities (65, 75, 85, and 103 m/s) using a gas-gun impact set-up. At all different impact velocities, the failure modes change as we switch from GFRP to SMA/GFRP specimen. In the SMA/GFRP specimen, the failure mode changed from delamination in the primary region to SMA-pull out and SMA deformation. This leads to an increase in the ballistic limit. It is observed that energy absorbed by SMA/GFRP specimens is higher than the GFRP specimens subjected to the same levels of impact energy. To understand the damping capabilities of SMA embedment, vibration signals are captured, and the damping ratio is calculated. SMA dampens the vibrations imparted by the projectile to the specimen. The damping ratio of the SMA/GFRP specimens is higher than the GFRP specimens. The damping effect is more prominent below the ballistic limit when the projectile got rebounded (65 m/s).
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    Characterization of unidirectional fiber reinforced polymer composites manufactured through resin film infusion process using micromechanical modeling
    (01-01-2020)
    Verma, Akash
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    Akella, Kiran
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    Sivakumar, Srinivasan M.
    Resin Film Infusion (RFI) process is used for manufacturing large and thick unidirectional fiber reinforced polymer (UD FRP) composite structures for load bearing applications. Designing these load bearing structures requires the knowledge of effective elastic and strength characteristics of these composites. In this study, strength and stiffness properties of UD FRP manufactured through RFI process are predicted using a micromechanical modeling approach. A 3D representative volume element (3DRVE) with hexagonal array of fibers is used and all nine elastic constants of UD FRP composite are predicted. Failure models for fiber and resin are used to predict longitudinal tension/compression, transverse tension/compression and longitudinal shear strengths. Experiments were conducted on UD FRP composite manufactured through RFI process to obtain strength and stiffness properties. Results of experiment and simulations are compared and results validated.
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    Modeling stress–strain response of shape memory alloys during reorientation of self-accommodated martensites with different morphologies
    (01-01-2022)
    Uchimali, Mahendaran
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    The shape memory effect observed in many alloys arises due to stress induced transformation between variants of the martensitic phase. It is difficult to study this process in detail using continuum approaches and particle based methods are eminently more suitable. In this work, we study detwinning, which is the transformation between martensite variants due to applied stress using a novel discrete particle model. The approach uses a novel multibody interparticle interaction defined directly using a non-convex free energy potential pertinent to such material behavior. This model is able to describe simultaneously occurring multiple microscale events during the detwinning process: nucleation and propagation of ledges along twin boundary. Due to these underlying microscale events the plateau region of stress–strain response shows a jerky nature. The effect of temperature and morphology on the stress–strain behavior of the self-accommodated martensite microstructure is studied in detail. From the simulations, we identify the morphological features affecting the transformation stress for detwinning. The critical parameters are found to be the length and number of twin and macro-twin boundaries and the number of mobile ledges.
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    Mechanical Characterization of Near-Isotropic Inconel 718 Fabricated by Laser Powder-Bed Fusion
    (01-01-2023)
    Sharma, Sunny
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    Palaniappan, Karthik
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    Mishra, Vagish D.
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    Murthy, H.
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    The characterization of Ni-based superalloy Inconel® 718 fabricated by powder-based laser fusion process was performed to study microstructural evolution and accompanying mechanical properties of as-deposited and post-heat-treated material. The current effort employs a low laser volumetric energy density during the deposition. X-ray diffraction, optical, and scanning electron microscopy were done for microstructural characterization. Examination of hardness values, tensile properties, and fractography based on sample orientation was also performed. X-ray diffraction studies facilitated qualitative confirmation of as-deposited samples possessing cube texture. The optical and scanning electron micrographs aided in examining the evolution of microscopic features after each post-processing stage. The as-deposited material possessed columnar grain morphology along with melt-pool marks, which on further magnification showed cellular-dendritic sub-grains along with Laves phases in the interdendritic grain boundaries. Solution heat treatment resulted in reducing these detrimental Laves phases and relief of thermal residual stresses caused by non-homogeneous recrystallization. Solution treatment also led to the formation of equiaxed grain clusters at various sample locations along with the existing columnar grains. The incoherent δ phase was formed at the grain boundaries along with coherent γ″ precipitates. The mechanical properties of as-deposited Inconel 718 alloy were near-isotropic in specimens oriented parallel and perpendicular to the build direction which is ascribed to low laser volumetric energy density. Micrographs of fractured surfaces taken for both directions of all sample conditions showed a ductile mode of fracture.
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    Modeling size and orientation effects on the morphology of microstructure formed in martensitic phase transformations using a novel discrete particle model
    (15-02-2021)
    Uchimali, Mahendaran
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    The morphology of fine microstructure arising from reversible martensitic transformations is known to depend on the sample size and orientation to applied thermal or mechanical loading. In this paper we study these effects using a novel discrete particle approach. Our new approach uses a multibody interparticle interaction for the discrete particles which is obtained directly from a polyconvex continuum free energy appropriate for such materials. In order to study the interfaces between the austenite and martensite phases, the material is subjected to a temperature gradient. A competition between self-accommodation which causes formation of twinned martensite and the requirement of compatibility of the phases on the interfaces results in very distinctive microstructures. We study the effect of the angle between the applied temperature gradient and the orientation of the parent phase on the phase boundary. In smaller samples, a phase boundary between austenite and a single variant of martensite forms due to the effect of the free surface and the resultant microstructure takes a banded form. Detwinning under applied mechanical loading is strongly dependent on the initial microstructure. The implicit kinetic relation for twin boundary propagation of this approach shows a classical stick-slip form.
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    INCREMENTAL MODELLING OF ALLOY EMBEDDED COMPOSITE
    (01-01-2022)
    Verma, Luv
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    Mishra, Vagish D.
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    Mishra, Ashish
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    Sivakumar, Srinivasan M.
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    Fibre-reinforced composite materials offer a number of distinct advantages such as higher specific strengths and stiffness over more conventional engineering materials such as aluminum or steel. When loaded in the fibre direction, these materials are the best choices in the modern world, but they do suffer severe limitations when undergoing impact loadings such as dropped tool or runway debris. To design a composite material that can offer solutions to the problems discussed above is important. Thus in this paper, our aim is to introduce a highly ductile, energy dissipating shape memory alloy (SMA) wire inside a composite material as a fibre that exhibits pseudoelastic response. To predict the behaviour of the SMA composite, as SMA is a non-linear hysteretic material, we have developed an incremental SMA composite model using the Voigt method.
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    Modeling the role of phase boundaries on the pullout response of shape memory wire reinforced composites
    (01-01-2023)
    Ananchaperumal, Venkatesh
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    Shape memory alloy (SMA) wire-reinforced composites are being widely adopted in several applications. The interactions of the SMA wires with the matrix are quite complex due to heterogeneous strain distributions arising from phase transformations in SMA wires. There have been few studies of the role of the phase boundaries and their effect on debonding of the SMA wire. In this work, a discrete particle approach is used to model the effect of microstructure on the debonding of SMA composites. The force versus displacement response is studied under pullout loading conditions and the microstructure is found to have a strong effect.
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    Evaluation of quasi-static indentation response of superelastic shape memory alloy embedded GFRP laminates using AE monitoring
    (01-01-2021)
    Verma, Luv
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    Andrew, J. Jefferson
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    Sivakumar, Srinivasan M.
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    Balaganesan, G.
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    Dhakal, Hom N.
    In this paper, the potential of superelastic shape memory alloy (SE-SMA) wire embedded architectures to increase the quasi-static indentation properties of a laminated glass/epoxy composite material was evaluated. Three types of SE-SMA configurations namely straight independent, meshed and anchored wires were embedded in the glass/epoxy composite laminates via a vacuum bag resin infusion technique. Throughout this investigation, the changes in the quasi-static indentation behavior and allied damage mechanisms due to these embedments were compared with the homogenous glass/epoxy laminates. Real time acoustic emission (AE) monitoring technique was employed to characterize the damage profile of the different glass/epoxy specimens during the quasi-static indentation tests. The experimental results showed that SE-SMA embedments play a vital role in increasing the penetration resistance by enhancing redistribution of the indentation load all across the laminates. In particular, the meshed specimens restricted penetration of an indenter and delayed the critical fiber fracture unlike homogeneous and straight wired ones, whereas the anchored specimens further restricted extensive SMA/matrix pull-out, unlike meshed ones and provided the most excellent balance among rigidity, rear face fiber breakage, and SMA/matrix pull-out. Straight, meshed and anchored SE-SMA wires increased the load-carrying capacity approximately by 31%, 79%, and 100%, respectively, in comparison to the homogeneous ones.