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Anand Krishna Kanjarla
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Anand Krishna Kanjarla
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Anand Krishna Kanjarla
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Kanjarla, A. K.
Kanjarla, Anand
Kanjarla, Anand K.
Kanjarla, Anand Krishna
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8 results
Now showing 1 - 8 of 8
- PublicationAn experimental and crystal plasticity investigation of anisotropic compression behaviour of Mg-Sn-Ca alloy(25-05-2023)
;Paramatmuni, Chaitanya ;Bandi, AnilThe 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. - PublicationA crystal plasticity FFT based study of deformation twinning, anisotropy and micromechanics in HCP materials: Application to AZ31 alloy(01-02-2019)
;Paramatmuni, ChaitanyaIn this paper, an infinitesimal-strain based FFT formulation is extended to account for deformation twinning in hexagonal close-packed (HCP) materials. A model called the Complex Voxel (CV) model is developed that includes twinning as pseudo-slip and accounts for interaction between parent grains and corresponding twin variants by assuming a Taylor-type approximation at the voxel level. The macroscopic deformation behavior of Magnesium alloy AZ31, a representative HCP material, is simulated in three different loading directions. Detailed analysis of twinning dominated deformation reveals that: (a) Global Schmid factors indicate twin variant selection and the rate of twin growth; (b) Basal slip is the dominant active slip system during the twin nucleation and twin growth stages; (c) A comparison of numerical results of the present study with the published experimental and numerical studies indicate that the evolution of local stress states in parent grains and corresponding twin variants depend on their orientation with respect to the loading direction and/or the neighbouring grains. Further, the need of immediate experimental evidence to assist assumptions made during modelling deformation twinning is discussed. - PublicationCrystal plasticity modelling of stability of residual stresses induced by shot peening(15-09-2022)
;Agaram, Sukumar ;Srinivasan, Sivakumar M.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. - PublicationNumerical study of the stress state of a deformation twin in magnesium(01-02-2015)
;Arul Kumar, M.; ;Niezgoda, S. R. ;Lebensohn, R. A.Tomé, C. N.We present here a numerical study of the distribution of the local stress state associated with deformation twinning in Mg, both inside the twinned domain and in its immediate neighborhood, due to the accommodation of the twinning transformation shear. A full-field elastoviscoplastic formulation based on fast Fourier transformation is modified to include the shear transformation strain associated with deformation twinning. We have performed two types of twinning transformation simulations with: (i) the twin completely embedded inside a single crystal and (ii) the twin front terminating at a grain boundary. We show that: (a) the resulting stress distribution is more strongly determined by the shear transformation than by the intragranular character of the twin or the orientation of the neighboring grain; (b) the resolved shear stress on the twin plane along the twin direction is inhomogeneous along the twin-parent interface; and (c) there are substantial differences in the average values of the shear stress in the twin and in the parent grain that contains the twin. We discuss the effect of these local stresses on twin propagation and growth, and the implications of our findings for the modeling of deformation twinning. - PublicationEffect of hydrogen on plasticity of α-Fe: A multi-scale assessment(01-06-2023)
;Kumar, Pranav ;Ludhwani, Mohit M. ;Das, Sambit ;Gavini, Vikram; 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. - PublicationBiaxial deformation behaviour of duplex stainless steels: Experiments and crystal plasticity based stress predictions(07-02-2023)
;Chalapathi, Darshan ;Bhaskar, Lalith Kumar ;Sivaprasad, P. V. ;Chai, Guocai ;Kumar, RaviBiaxial tensile tests are performed on two phase duplex stainless steel using a newly developed multiaxial testing rig integrated with a digital image correlation mapping facility. A cruciform-shaped specimen geometry is subjected to equibiaxial tensile (EBT) loading, and the load–strain response is captured. Unlike uniaxial tensile testing, a well-defined gauge area is absent in biaxial specimens; hence, stress cannot be estimated directly. Finite element analysis is used to calculate the stress state. The phenomenological finite element model failed to capture the inherent anisotropy of the material; hence, a crystal plasticity finite element based method is used to estimate the stresses. It is observed that the 0.2% proof stress increased, but the strain to failure remained constant in comparison with uniaxial tensile properties. The work hardening behaviour is isotropic similar to that observed during uniaxial testing. The goss and rotated goss orientations in austenite accommodated most of the strain along RD and TD, respectively. During EBT, the change in austenite and ferrite textures is minimal and similar to their single phase counterparts reported in the literature. The EBT test results indicate that the influence of micromechanical interactions between the phases on the work hardening behaviour and texture evolution is weak. - PublicationCrystal plasticity study of heterogeneous deformation behavior in γ matrix channels during high temperature low stress creep of single crystal superalloys(25-06-2019)
;Hariharan, AvinashSingle crystal nickel-based superalloys have high temperature creep resistance due to particle strengthening by high volume fraction of coherent γ 0 precipitates distributed within nickel-based solid solution γ matrix. In the high temperature low stress regime, published experimental studies reveal that the creep deformation mechanism during the secondary stage is predominantly by dislocation glide in the γ matrix only, and that there is a preferential motion of dislocations in the matrix, oriented in a direction perpendicular to the stress. In this work, the crystal plasticity finite element method is employed to perform creep simulations on a representative volume element in the high temperature and low stress regime. A sine-hyperbolic-based material creep model was used for the matrix, while the precipitates are assumed to be elastic. A softening model incorporating the evolution of mobile dislocation density was used to capture the transition from secondary to tertiary creep. The predicted creep curves agree well with the published experimental measurements on single crystal superalloy CMSX-4. The simulations predict a higher creep strain distribution in the horizontal channel of the matrix (perpendicular to the applied stress) as compared with the vertical channel (horizontal to the applied stress). Local creep strain distributions in the channels were found to be greater than twice their average creep strain. The results provide key insights into the distribution of macroscopic creep strain in the local channels of the γ matrix to further aid in the microstructural design of creep-resistant superalloys. - PublicationEffect of temperature on the selection of deformation modes in Zircaloy-4(12-09-2018)
;Bharat Reddy, G. ;Sarkar, Apu ;Kapoor, RajeevThe effect of deformation temperature (77, 298 and 573 K) on the evolution of slip and twinning modes in Zircaloy-4 was studied. Samples of Zircaloy-4 were uniaxially compressed to different strains at a nominal strain rate of 10−3 s−1. The compression direction was chosen so as to activate twinning. Microstructural examination was carried out using electron backscatter diffraction to relate the evolution of microstructure and texture to the micro-mechanics and work-hardening behaviour. In conjunction with experiments a visco-plastic self-consistent crystal plasticity model was used to determine the evolution of deformation modes. Extensive twinning was observed at all the test temperatures. Twinning activity at 298 and 573 K was comparable, but was lower than that at 77 K. A strong basal texture parallel to the compressive direction was found at 298 and 573 K. The VPSC model predicted well the texture evolution at 298 and 573 K. The basal texture developed at 77 K was found to have partially reoriented back to the initial texture due to secondary twinning. Prism slip was the dominant deformation mode with secondary slip becoming more active at higher temperatures.