Now showing 1 - 10 of 19
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    An experimental and crystal plasticity investigation of anisotropic compression behaviour of Mg-Sn-Ca alloy
    (25-05-2023)
    Paramatmuni, Chaitanya
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    Bandi, Anil
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    The ductility of Magnesium alloys is often limited due to the strong basal texture. Initial attempts were made to reduce the intensity of the basal textures by adding rare earth(RE) elements. However, owing to the cost and scarcity of RE elements, alloys with calcium and tin were recently introduced. Among them, Mg-2Sn-2Ca alloys are the most promising, with high strength reported in the extruded condition. In this work, we report, for the first time, the mechanical properties of the alloy in the sheet form. In plane mechanical anisotropy in compressive behaviour is studied along with the detailed characterisation of texture, microstructure and the deformation twins in the material. Unlike strongly basal textured Mg alloys, deformation twinning was also observed in samples loaded along the normal direction. Crystal plasticity simulations were performed to confirm the slip and twin activity. Furthermore, a detailed analysis of deformation twins revealed that the so called Schmid twins accommodate strain by both twin growth and slip, whereas the non-Schmid twins accommodate the strain exclusively by crystallographic slip.
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    Effect of the structure and morphology of carbon nanotubes on the vibration damping characteristics of polymer-based composites
    (01-03-2020)
    Joy, Anand
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    S., Sankaran
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    The structure and morphology of the reinforcing material play an important role in the vibration damping characteristics of polymer composites. In this work, multiwalled carbon nanotubes (MWCNTs) with different structures and morphologies are incorporated into a polymer matrix. The vibration damping characteristics of the nanocomposites, in Oberst beam configuration, are studied using a free vibration test in cantilever mode. Inner tube oscillation is established as the vibration damping mechanism by correlating the extent of the loss factor obtained from the two nanocomposites with the dissimilarities in the structure and morphology of the two varieties of MWCNTs. Inner tube oscillation is simulated using molecular dynamics (MD). Since the open-ended double walled CNT (DWCNT) models used in earlier studies over predict the damping, we propose a capped DWCNT model. This can simulate the atomic interactions at the end caps of the tube. This study indicates that the contributions to the observed damping have their origins in the interaction between atoms that constitute the inner and outer tubes rather than the inter-tube frictional energy loss.
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    Reduced-Order Damage Assessment Model for Dual-Phase Steels
    (01-12-2022)
    Thakre, Sanket
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    We present a microstructure and work hardening sensitive reduced-order model using random forest regression for predicting damage initiation in dual-phase (DP) steels. The ductile damage behavior of banded and non-banded DP steels is evaluated for various degrees of ferrite hardening. The banded microstructures show a superior damage resistance which is further improved by ferrite hardening. A general framework to rank the severity of damage initiation in various classes using a statistical fitting procedure is introduced. The regression-based and statistical fitting-based models can successfully quantify the damage initiation and group the various classes into three major clusters. The proposed framework is a step toward developing more effective and invertible reduced-order structure–property correlations
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    Crystal plasticity modelling of stability of residual stresses induced by shot peening
    (15-09-2022)
    Agaram, Sukumar
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    Srinivasan, Sivakumar M.
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    Gas turbine components are often shot-peened to improve surface integrity and fatigue capability. Compressive Residual Stress (CRS) and increased surface hardness are the key outcomes of shot peening. But the CRS is observed to relax during the service life, and its stability depends on the amount of cold work during the shot peening process and the applied load during service life. This study develops a numerical framework capable of accurately estimating the amount of cold work using a dislocation density-based crystal plasticity model. The proposed framework captures the evolution of microstructure during the shot peening process, incorporating the effects of grain size, orientation, and strain rate. The simulation methodology is used to investigate the influence of loading conditions on work hardening and relaxation. The numerical predictions are shown to agree with available experimental observations. The proposed method demonstrates the capability to optimize microstructure and shot peening parameters to reduce the relaxation of CRS during service life.
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    Dislocation density based crystal plasticity model incorporating the effect of precipitates in IN718 under monotonic and cyclic deformation
    (01-06-2021)
    Agaram, Sukumar
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    Bhuvaraghan, Baskaran
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    Srinivasan, Sivakumar M.
    A dislocation density based crystal plasticity model is developed to account for the precipitate induced cyclic softening in IN718. The new model treats the interaction between the precipitates and the dislocations using a probabilistic approach. It is also capable of capturing the reduction in the effective size of the precipitates due to reversible dislocations shearing through them. Further, the phenomenological model accounts for the heterogeneous accumulation of dislocations in the microstructure (i) as a function of distance to the nearest grain boundary and (ii) the interparticle spacing within a grain. The developed model is used to simulate the macroscopic mechanical response of IN718 under a series of monotonic and cyclic loads at different strain rates and alternating strain levels, respectively. Model predictions of macroscopic behavior are shown to be in good agreement with experimental data. They can capture the initial hardening and subsequent softening during cyclic loading for several strain amplitudes. Sensitivity analyses have been performed to understand the influence of grain size, reversible dislocations, and the size of the precipitates.
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    Statistical analyses of the relationship between inclination angle and twin growth in uniaxial compression of Mg alloys
    (26-07-2023)
    Paramatmuni, Chaitanya
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    Zeng, Xun
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    Guan, Dikai
    Inclination angle (IA), which is that between the c-axis of a twin and the global loading direction, satisfactorily captures trends observed in area fractions of both Schmid and non-Schmid twins. The detailed analyses also show that the non-Schmid twins form preferentially in smaller grains compared to that of Schmid ones.
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    Surface reconstruction in core@shell nanoalloys: Interplay between size and strain
    (01-08-2022)
    Settem, Manoj
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    Kumar, Pranav
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    Shell structure in core@shell nanoalloys is studied where the core comprises of smaller atoms and covered by a thin shell with larger atoms. Mismatch strain, due to the size difference between core and shell atoms, plays a key role in determining the shell arrangement. Binary alloy systems having a wide range of lattice mismatch are considered which include Ni-Ag, Co-Ag, Cu-Ag, Co-Pt, Ni-Pd, Rh-Au, and Ni-Cu. Beginning from very small sizes, transformations in the shell structure are sketched out up to large sizes of ∼ 12 nm. These changes are accompanied by reconstruction of {100} facets in the shell to pseudo hexagonal (p-Hex) surfaces. Results show that p-Hex reconstruction occurs in specific size windows. The stability regime and the fraction of p-Hex surfaces is strongly dependent on the lattice mismatch. Comparison of p-Hex and {111} surfaces reveal significant atomic pressure differences. Finally, shells that are thicker than a monolayer are considered and it is found that p-Hex reconstruction is favored in thicker shells as well.
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    Hot Deformation Studies on β 0 Stabilized TiAl Alloy Made Through Ingot Metallurgy Route
    (01-12-2021)
    Gupta, R. K.
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    Kumar, V. Anil
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    Raj, J. Nitesh
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    Singh, Bhavanish Kumar
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    Hot deformation studies of a newly designed γ + α2 based TiAl alloy of composition Ti–42Al–6Nb–3Cr–0.1B at.% (nominal) realized through ingot metallurgy route using double vacuum arc remelting were carried out. Hot isothermal compression testing was performed in Gleeble™ 3500 at different temperatures ranging from 1123 to 1373 K at 50 K intervals and strain rates of 0.001–1 s−1. Processing maps were developed using an approach of dynamic material modeling of the flow curves to establish the safe hot working regime. Strain rate sensitivity and Zener–Holloman parameters were calculated and constitutive equation was derived. Microstructural investigation revealed dynamic recrystallization and activation of multiple twin systems as the main softening mechanisms operating at optimum hot working conditions. Safe hot working temperature and strain rate regime for the alloy was found to be in the temperature range of 1323–1373 K and strain rate range of 0.001–0.01 s−1.
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    Bain variant dependent plastic anisotropy and formability in duplex stainless steels
    (15-01-2022)
    Tirumalasetty, Deepika
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    Chalapathi, Darshan
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    Veeramusti, Veerabhadra
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    Crystallographic texture is known to have significant effect on the plastic anisotropy and formability in materials. In single phase materials, the texture is often a function of prior thermomechanical processing. However in materials with multiple phases such as duplex stainless steels (DSS), the texture is also influenced by the orientation relationship (OR) maintained during the phase transformations. In the present work, we study the role of OR and their Bain variant classifications on the plastic anisotropy and, in turn, on the formability of DSS. Crystal plasticity modelling is used to calculate the in-plane anisotropy of the r-values for DSS with different initial austenite textures. Further, finite element simulations of the deep drawing process are presented to obtain the earing profiles and show the Bain variant dependency on the formability.
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    Effect of hydrogen on plasticity of α-Fe: A multi-scale assessment
    (01-06-2023)
    Kumar, Pranav
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    Ludhwani, Mohit M.
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    Das, Sambit
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    Gavini, Vikram
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    A multi-scale study was carried out to quantify the effect of interstitial hydrogen concentration on plasticity in α-Fe. In this work, the influence of hydrogen on the screw dislocation glide behavior was examined across several length-scales. The insights obtained were integrated to provide an accurate continuum description for the effect of hydrogen on the dislocation based plasticity in polycrystalline α-Fe. At the outset of this work, a new Fe[sbnd]H interatomic potential was formulated that enhanced the atomistic estimation of the variation in dislocation glide behavior in presence of hydrogen. Next, the dislocation core reconstruction observed due to the addition of hydrogen using atomistic simulations was validated with the help of large-scale DFT calculations based on the DFT-FE framework. Several atomistic simulations were carried out to comprehensively quantify the effect of hydrogen on the non-Schmid behavior exhibited during the dislocation glide in α-Fe. Finally, crystal plasticity simulations were carried out to understand the effect of hydrogen on the meso-scale deformation behavior of polycrystalline α-Fe.