The Experts below are selected from a list of 3207 Experts worldwide ranked by ideXlab platform
F P E Dunne - One of the best experts on this subject based on the ideXlab platform.
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competing mechanisms of particle fracture decohesion and slip driven Fatigue Crack Nucleation in a pm nickel superalloy
International Journal of Fatigue, 2020Co-Authors: Alexander Bergsmo, F P E DunneAbstract:Abstract Fatigue Cracks may initiate around non-metallic inclusions via particle fracture, particle decohesion and slip-driven Nucleation. Cohesive zone techniques within microstructurally faithful crystal plasticity modelling validated by micromechanical experiments (HR-DIC and HR-EBSD) are employed to investigate these Nucleation phenomena. Particle fracture and decohesion lead to stress redistribution which influences subsequent energy storage driving slip-driven Fatigue Crack Nucleation. Particle fracture and decohesion strengths were determined and using a stored energy criterion, the number of cycles to initiation of the Fatigue microCrack was predicted. A threshold applied stress below which decohesion and fracture do not occur was obtained, thus modestly increasing Fatigue life.
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is stored energy density the primary meso scale mechanistic driver for Fatigue Crack Nucleation
International Journal of Plasticity, 2018Co-Authors: Bo Chen, Jun Jiang, F P E DunneAbstract:Abstract Fatigue Crack Nucleation in a powder metallurgy produced nickel alloy containing a non-metallic inclusion has been investigated through integrated small-scale bend testing, quantitative characterisation (HR-DIC and HR-EBSD) and computational crystal plasticity which replicated the polycrystal morphology, texture and loading. Multiple Crack Nucleations occurred at the nickel matrix-inclusion interface and both Nucleation and growth were found to be crystallographic with highest slip system activation driving Crack direction. Local slip accumulation was found to be a necessary condition for Crack Nucleation, and that in addition, local stress and density of geometrically necessary dislocations are involved. Fatemi-Socie and dissipated energy were also assessed against the experimental data, showing generally good, but not complete agreement. However, the local stored energy density (of a Griffith-Stroh kind) identified all the Crack Nucleation sites as those giving the highest magnitudes of stored energy.
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crystal plasticity modelling and hr dic measurement of slip activation and strain localization in single and oligo crystal ni alloys under Fatigue
International Journal of Plasticity, 2017Co-Authors: Yongjun Guan, Jun Jiang, Bo Chen, Ben T Britton, Jinwen Zou, F P E DunneAbstract:Abstract Single crystal (CMSX4) and oligocrystal (MAR002) nickel have been studied using three-point beam bending under conditions of cyclic loading. SEM images have enabled identification of slip activation, and high resolution digital image correlation has been utilized to quantify the developing strain fields and the strain localization in both single and oligocrystals in Fatigue. The single and oligocrystal microstructures have been replicated within crystal plasticity finite element models and the Fatigue loading analysed such that grain-by-grain comparisons of slip may be carried out. Single and multiple slip activation, slip localization and microstructure-sensitive stress evolution have been examined. Single crystal bend Fatigue gives rise to non-symmetric slip fields and localization depending on crystallographic orientation. Modelling correctly captures slip activation and the developing non-symmetric slip fields. Oligocrystal slip is markedly heterogeneous, with grain misorientations driving strong variations, also reasonably captured by the model. Microstructure behaviour is found to vary spatially and include elastic-plastic hysteresis which is stable, and which undergoes mean stress relaxation so that plastic shakedown occurs. Remarkable variations occur between locations either side of grain boundaries, providing appropriate opportunities for Fatigue Crack Nucleation.
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Crack Nucleation using combined crystal plasticity modelling high resolution digital image correlation and high resolution electron backscatter diffraction in a superalloy containing non metallic inclusions under Fatigue
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2016Co-Authors: Tiantian Zhang, Barbara A. Shollock, Ben Britton, Jun Jiang, F P E DunneAbstract:A crystal plasticity finite-element model, which explicitly and directly represents the complex microstructures of a non-metallic agglomerate inclusion within polycrystal nickel alloy, has been developed to study the mechanistic basis of Fatigue Crack Nucleation. The methodology is to use the crystal plasticity model in conjunction with direct measurement at the microscale using high (angular) resolution-electron backscatter diffraction (HR-EBSD) and high (spatial) resolution-digital image correlation (HR-DIC) strain measurement techniques. Experimentally, this sample has been subjected to heat treatment leading to the establishment of residual (elastic) strains local to the agglomerate and subsequently loaded under conditions of low cyclic Fatigue. The full thermal and mechanical loading history was reproduced within the model. HR-EBSD and HR-DIC elastic and total strain measurements demonstrate qualitative and quantitative agreement with crystal plasticity results. Crack Nucleation by interfacial decohesion at the nickel matrix/agglomerate inclusion boundaries is observed experimentally, and systematic modelling studies enable the mechanistic basis of the Nucleation to be established. A number of Fatigue Crack Nucleation indicators are also assessed against the experimental results. Decohesion was found to be driven by interface tensile normal stress alone, and the interfacial strength was determined to be in the range of 1270–1480 MPa.
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on the mechanistic basis of Fatigue Crack Nucleation in ni superalloy containing inclusions using high resolution electron backscatter diffraction
Acta Materialia, 2015Co-Authors: Jun Jiang, F P E Dunne, Tiantian Zhang, Jie Yang, Ben T BrittonAbstract:Abstract A series of interrupted three-point bend low-cycle Fatigue tests were carried out on a powder metallurgy FHG96 nickel superalloy sample containing non-metallic inclusions. High resolution electron backscatter diffraction (HR-EBSD) was used to characterise the distribution and evolution of geometrically necessary dislocation (GND) density, residual stress and total dislocation density near a non-metallic inclusion. A systematic study of room temperature cyclic deformation is presented in which slip localisation, cyclic hardening, ratcheting and stabilisation occur, through to Crack formation and microstructurally-sensitive propagation. Particular focus is brought to bear at the inclusion–matrix interface. Complex inhomogeneous deformation structures were directly observed from the first few loading cycles, and these structures were found not to vary significantly with increasing number of cycles. A clear link was observed between Crack Nucleation site and microstructurally-sensitive growth path and the spatially-resolved sites of extreme values of residual stress and GND density.
Somnath Ghosh - One of the best experts on this subject based on the ideXlab platform.
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experimentally validated dwell and cyclic Fatigue Crack Nucleation model for α titanium alloys
Scripta Materialia, 2017Co-Authors: Deniz Ozturk, A L Pilchak, Somnath GhoshAbstract:Abstract This paper develops an experimentally calibrated and validated crystal plasticity finite element model with a probabilistic Crack Nucleation model for predicting dwell and cyclic Fatigue Crack Nucleation in polycrystalline microstructures of titanium or Ti alloys. The Nucleation model accounts for load-shedding due to time-dependent plastic flow and variability in crystal strength. The predictions are corroborated with experimental observations of Nucleation times for dwell and cyclic loading. Experimental characterization of failed samples reveal that Crack initiation on (0001) planes are highly inclined away from the stress axis. The probability distribution of simulated facet orientations are in agreement with experimentally measured orientations.
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crystal plasticity fe study of the effect of thermo mechanical loading on Fatigue Crack Nucleation in titanium alloys
Fatigue & Fracture of Engineering Materials & Structures, 2016Co-Authors: Deniz Ozturk, Ahmad Shahba, Somnath GhoshAbstract:In this paper, crystal plasticity simulations are conducted with a stabilized finite deformation finite element model to study the effects of microstructure as well as thermal and mechanical loading conditions on Fatigue Crack Nucleation of Ti alloys. The crystal plasticity model includes a non-local Crack Nucleation model. Results of simulations are used to understand the effects of dwell loading periods and microtexture on Fatigue Nucleation life in polycrystalline microstructures in comparison with experiments. From the thermo-mechanical studies of these alloys, it is found that anisotropic thermal expansion under thermal loading can induce stresses normal to the basal plane, which can help opening up microCracks. Moreover, in agreement with experimental results, the simulations show diminished load shedding at elevated temperature because of weakening of plastic anisotropy.
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microstructure and load sensitive Fatigue Crack Nucleation in ti 6242 using accelerated crystal plasticity fem simulations
International Journal of Fatigue, 2013Co-Authors: Somnath Ghosh, Pritam ChakrabortyAbstract:Abstract This paper investigates microstructure and load sensitive Fatigue behavior of Ti-6242 using cyclic crystal plasticity finite element (CPFE) simulations of statistically equivalent image-based microstructures. A wavelet transformation induced multi-time scaling (WATMUS) method [1,2] is used to perform accelerated cyclic CPFE simulations till Crack Nucleation, otherwise infeasible using conventional time integration schemes. A physically motivated Crack Nucleation model in terms of crystal plasticity variables [3] is extended in this work to predict Nucleation. The Crack Nucleation model is based on dislocation pile-up and stress concentration at grain boundaries, caused by inhomogeneous plastic deformation in the polycrystalline microstructure. The model is calibrated and validated with experiments. The dependence of yield strength on the underlying grain orientations and sizes is developed through the introduction of an effective microstructural parameter Plastic Flow Index or PFI . To determine the effects of the microstructure on Crack Nucleation, a local microstructural variable is defined in terms of the surface area fraction of soft grains surrounding each hard grain or SAFSSG . Simulations with different cyclic load patterns suggest that Fatigue Crack Nucleation in Ti-6242 strongly depends on the dwell cycle hold time at maximum stress.
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dwell Fatigue Crack Nucleation model based on crystal plasticity finite element simulations of polycrystalline titanium alloys
Journal of The Mechanics and Physics of Solids, 2011Co-Authors: M Anahid, Mahendra K Samal, Somnath GhoshAbstract:Abstract In this paper a crystal plasticity-based Crack Nucleation model is developed for polycrystalline microstructures undergoing cyclic dwell loading. The Fatigue Crack Nucleation model is developed for dual-phase titanium alloys admitting room temperature creep phenomenon. It is a non-local model that accounts for the cumulative effect of slip on multiple slip systems, and involves evolving mixed-mode stresses in the grain along with dislocation pileups in contiguous grains. Rate dependent, highly anisotropic behavior causes significant localized stress concentration that increases with loading cycles. The crystal plasticity finite element (CPFE) model uses rate and size-dependent anisotropic elasto-crystal plasticity constitutive model to account for these effects. Stress rise in the hard grain is a consequence of time-dependent load shedding in adjacent soft grains, and is the main cause of Crack Nucleation in the polycrystalline titanium microstructure. CPFE simulation results are post-processed to provide inputs to the Crack Nucleation model. The Nucleation model is calibrated and satisfactorily validated using data available from acoustic microscopy experiments for monitoring Crack evolution in dwell Fatigue experiments.
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a cold dwell Fatigue Crack Nucleation criterion for polycrystalline ti 6242 using grain level crystal plasticity fe model
International Journal of Fatigue, 2008Co-Authors: Kedar Kirane, Somnath GhoshAbstract:A grain-level Fatigue Crack Nucleation criterion for cold dwell in Ti-6242 alloy is developed in this paper using a rate and size dependent anisotropic elasto-crystal plasticity constitutive model, and validated with experiments. Early Crack initiation in Ti-6242 under cold dwell Fatigue has been identified to be caused by stress concentrations in a hard grain, induced by load shedding from creep in adjacent soft grains. Accurate prediction of local stress and strain evolution during loading requires a robust representation of morphological and crystallographic features of the microstructure. These are accounted for in the FE model in a statistically equivalent sense. The proposed Crack Nucleation model is based on the observed similarities between Crack evolution at the tip of a Crack and a dislocation pileup. The Nucleation model is calibrated and validated using data available from acoustic microscopy though real time monitoring of Crack evolution in dwell Fatigue experiments.
Jun Jiang - One of the best experts on this subject based on the ideXlab platform.
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is stored energy density the primary meso scale mechanistic driver for Fatigue Crack Nucleation
International Journal of Plasticity, 2018Co-Authors: Bo Chen, Jun Jiang, F P E DunneAbstract:Abstract Fatigue Crack Nucleation in a powder metallurgy produced nickel alloy containing a non-metallic inclusion has been investigated through integrated small-scale bend testing, quantitative characterisation (HR-DIC and HR-EBSD) and computational crystal plasticity which replicated the polycrystal morphology, texture and loading. Multiple Crack Nucleations occurred at the nickel matrix-inclusion interface and both Nucleation and growth were found to be crystallographic with highest slip system activation driving Crack direction. Local slip accumulation was found to be a necessary condition for Crack Nucleation, and that in addition, local stress and density of geometrically necessary dislocations are involved. Fatemi-Socie and dissipated energy were also assessed against the experimental data, showing generally good, but not complete agreement. However, the local stored energy density (of a Griffith-Stroh kind) identified all the Crack Nucleation sites as those giving the highest magnitudes of stored energy.
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crystal plasticity modelling and hr dic measurement of slip activation and strain localization in single and oligo crystal ni alloys under Fatigue
International Journal of Plasticity, 2017Co-Authors: Yongjun Guan, Jun Jiang, Bo Chen, Ben T Britton, Jinwen Zou, F P E DunneAbstract:Abstract Single crystal (CMSX4) and oligocrystal (MAR002) nickel have been studied using three-point beam bending under conditions of cyclic loading. SEM images have enabled identification of slip activation, and high resolution digital image correlation has been utilized to quantify the developing strain fields and the strain localization in both single and oligocrystals in Fatigue. The single and oligocrystal microstructures have been replicated within crystal plasticity finite element models and the Fatigue loading analysed such that grain-by-grain comparisons of slip may be carried out. Single and multiple slip activation, slip localization and microstructure-sensitive stress evolution have been examined. Single crystal bend Fatigue gives rise to non-symmetric slip fields and localization depending on crystallographic orientation. Modelling correctly captures slip activation and the developing non-symmetric slip fields. Oligocrystal slip is markedly heterogeneous, with grain misorientations driving strong variations, also reasonably captured by the model. Microstructure behaviour is found to vary spatially and include elastic-plastic hysteresis which is stable, and which undergoes mean stress relaxation so that plastic shakedown occurs. Remarkable variations occur between locations either side of grain boundaries, providing appropriate opportunities for Fatigue Crack Nucleation.
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Crack Nucleation using combined crystal plasticity modelling high resolution digital image correlation and high resolution electron backscatter diffraction in a superalloy containing non metallic inclusions under Fatigue
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2016Co-Authors: Tiantian Zhang, Barbara A. Shollock, Ben Britton, Jun Jiang, F P E DunneAbstract:A crystal plasticity finite-element model, which explicitly and directly represents the complex microstructures of a non-metallic agglomerate inclusion within polycrystal nickel alloy, has been developed to study the mechanistic basis of Fatigue Crack Nucleation. The methodology is to use the crystal plasticity model in conjunction with direct measurement at the microscale using high (angular) resolution-electron backscatter diffraction (HR-EBSD) and high (spatial) resolution-digital image correlation (HR-DIC) strain measurement techniques. Experimentally, this sample has been subjected to heat treatment leading to the establishment of residual (elastic) strains local to the agglomerate and subsequently loaded under conditions of low cyclic Fatigue. The full thermal and mechanical loading history was reproduced within the model. HR-EBSD and HR-DIC elastic and total strain measurements demonstrate qualitative and quantitative agreement with crystal plasticity results. Crack Nucleation by interfacial decohesion at the nickel matrix/agglomerate inclusion boundaries is observed experimentally, and systematic modelling studies enable the mechanistic basis of the Nucleation to be established. A number of Fatigue Crack Nucleation indicators are also assessed against the experimental results. Decohesion was found to be driven by interface tensile normal stress alone, and the interfacial strength was determined to be in the range of 1270–1480 MPa.
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on the mechanistic basis of Fatigue Crack Nucleation in ni superalloy containing inclusions using high resolution electron backscatter diffraction
Acta Materialia, 2015Co-Authors: Jun Jiang, F P E Dunne, Tiantian Zhang, Jie Yang, Ben T BrittonAbstract:Abstract A series of interrupted three-point bend low-cycle Fatigue tests were carried out on a powder metallurgy FHG96 nickel superalloy sample containing non-metallic inclusions. High resolution electron backscatter diffraction (HR-EBSD) was used to characterise the distribution and evolution of geometrically necessary dislocation (GND) density, residual stress and total dislocation density near a non-metallic inclusion. A systematic study of room temperature cyclic deformation is presented in which slip localisation, cyclic hardening, ratcheting and stabilisation occur, through to Crack formation and microstructurally-sensitive propagation. Particular focus is brought to bear at the inclusion–matrix interface. Complex inhomogeneous deformation structures were directly observed from the first few loading cycles, and these structures were found not to vary significantly with increasing number of cycles. A clear link was observed between Crack Nucleation site and microstructurally-sensitive growth path and the spatially-resolved sites of extreme values of residual stress and GND density.
Ben T Britton - One of the best experts on this subject based on the ideXlab platform.
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crystal plasticity modelling and hr dic measurement of slip activation and strain localization in single and oligo crystal ni alloys under Fatigue
International Journal of Plasticity, 2017Co-Authors: Yongjun Guan, Jun Jiang, Bo Chen, Ben T Britton, Jinwen Zou, F P E DunneAbstract:Abstract Single crystal (CMSX4) and oligocrystal (MAR002) nickel have been studied using three-point beam bending under conditions of cyclic loading. SEM images have enabled identification of slip activation, and high resolution digital image correlation has been utilized to quantify the developing strain fields and the strain localization in both single and oligocrystals in Fatigue. The single and oligocrystal microstructures have been replicated within crystal plasticity finite element models and the Fatigue loading analysed such that grain-by-grain comparisons of slip may be carried out. Single and multiple slip activation, slip localization and microstructure-sensitive stress evolution have been examined. Single crystal bend Fatigue gives rise to non-symmetric slip fields and localization depending on crystallographic orientation. Modelling correctly captures slip activation and the developing non-symmetric slip fields. Oligocrystal slip is markedly heterogeneous, with grain misorientations driving strong variations, also reasonably captured by the model. Microstructure behaviour is found to vary spatially and include elastic-plastic hysteresis which is stable, and which undergoes mean stress relaxation so that plastic shakedown occurs. Remarkable variations occur between locations either side of grain boundaries, providing appropriate opportunities for Fatigue Crack Nucleation.
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on the mechanistic basis of Fatigue Crack Nucleation in ni superalloy containing inclusions using high resolution electron backscatter diffraction
Acta Materialia, 2015Co-Authors: Jun Jiang, F P E Dunne, Tiantian Zhang, Jie Yang, Ben T BrittonAbstract:Abstract A series of interrupted three-point bend low-cycle Fatigue tests were carried out on a powder metallurgy FHG96 nickel superalloy sample containing non-metallic inclusions. High resolution electron backscatter diffraction (HR-EBSD) was used to characterise the distribution and evolution of geometrically necessary dislocation (GND) density, residual stress and total dislocation density near a non-metallic inclusion. A systematic study of room temperature cyclic deformation is presented in which slip localisation, cyclic hardening, ratcheting and stabilisation occur, through to Crack formation and microstructurally-sensitive propagation. Particular focus is brought to bear at the inclusion–matrix interface. Complex inhomogeneous deformation structures were directly observed from the first few loading cycles, and these structures were found not to vary significantly with increasing number of cycles. A clear link was observed between Crack Nucleation site and microstructurally-sensitive growth path and the spatially-resolved sites of extreme values of residual stress and GND density.
Tiantian Zhang - One of the best experts on this subject based on the ideXlab platform.
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Crack Nucleation using combined crystal plasticity modelling high resolution digital image correlation and high resolution electron backscatter diffraction in a superalloy containing non metallic inclusions under Fatigue
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2016Co-Authors: Tiantian Zhang, Barbara A. Shollock, Ben Britton, Jun Jiang, F P E DunneAbstract:A crystal plasticity finite-element model, which explicitly and directly represents the complex microstructures of a non-metallic agglomerate inclusion within polycrystal nickel alloy, has been developed to study the mechanistic basis of Fatigue Crack Nucleation. The methodology is to use the crystal plasticity model in conjunction with direct measurement at the microscale using high (angular) resolution-electron backscatter diffraction (HR-EBSD) and high (spatial) resolution-digital image correlation (HR-DIC) strain measurement techniques. Experimentally, this sample has been subjected to heat treatment leading to the establishment of residual (elastic) strains local to the agglomerate and subsequently loaded under conditions of low cyclic Fatigue. The full thermal and mechanical loading history was reproduced within the model. HR-EBSD and HR-DIC elastic and total strain measurements demonstrate qualitative and quantitative agreement with crystal plasticity results. Crack Nucleation by interfacial decohesion at the nickel matrix/agglomerate inclusion boundaries is observed experimentally, and systematic modelling studies enable the mechanistic basis of the Nucleation to be established. A number of Fatigue Crack Nucleation indicators are also assessed against the experimental results. Decohesion was found to be driven by interface tensile normal stress alone, and the interfacial strength was determined to be in the range of 1270–1480 MPa.
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on the mechanistic basis of Fatigue Crack Nucleation in ni superalloy containing inclusions using high resolution electron backscatter diffraction
Acta Materialia, 2015Co-Authors: Jun Jiang, F P E Dunne, Tiantian Zhang, Jie Yang, Ben T BrittonAbstract:Abstract A series of interrupted three-point bend low-cycle Fatigue tests were carried out on a powder metallurgy FHG96 nickel superalloy sample containing non-metallic inclusions. High resolution electron backscatter diffraction (HR-EBSD) was used to characterise the distribution and evolution of geometrically necessary dislocation (GND) density, residual stress and total dislocation density near a non-metallic inclusion. A systematic study of room temperature cyclic deformation is presented in which slip localisation, cyclic hardening, ratcheting and stabilisation occur, through to Crack formation and microstructurally-sensitive propagation. Particular focus is brought to bear at the inclusion–matrix interface. Complex inhomogeneous deformation structures were directly observed from the first few loading cycles, and these structures were found not to vary significantly with increasing number of cycles. A clear link was observed between Crack Nucleation site and microstructurally-sensitive growth path and the spatially-resolved sites of extreme values of residual stress and GND density.
