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B K Choudhary - One of the best experts on this subject based on the ideXlab platform.

  • Creep Properties of G Tu
    2020
    Co-Authors: B K Choudhary, M. D. Mathew
    Abstract:

    Creep-rupture properties of T91 steam generator (SG condition in the stress range 55-150 MPa. At all stres Creep rate in the transient Creep followed by a minim Tertiary Creep stage. A systematic decrease in Creep Tertiary Creep. Stress dependence of minimum Creep r and rupture life exhibited deviations in terms of lowe at high stresses. A decrease in Creep ductility was transgranular at all test conditions. Creep-rupture s reported in literature as well as specified in French Nu

  • Modeling Creep Deformation and Damage Behavior of Tempered Martensitic Steel in the Framework of Additive Creep Rate Formulation
    Journal of Pressure Vessel Technology-transactions of The Asme, 2018
    Co-Authors: J Christopher, B K Choudhary
    Abstract:

    Additive Creep rate model has been developed to predict Creep strain-time behavior of materials important to engineering Creep design of components for high temperature applications. The model has two additive formulations: the first one is related to sine hyperbolic rate equation describing primary and secondary Creep deformation based on the evolution of internal stress with strain/time, and the second defines the Tertiary Creep rate as a function of Tertiary Creep strain. In order to describe Creep data accurately, Tertiary Creep rate relation based on MPC-Omega methodology has been appropriately modified. The applicability of the model has been demonstrated for tempered martensitic plain 9Cr-1Mo steel for different applied stresses at 873 K. Based on the observations, a power law relationship between internal stress and applied stress has been established for the steel. Further, a higher Creep damage accumulation with increasing life fraction has been observed at low stresses than those obtained at high stresses.

  • Tertiary Creep behaviour of 9cr 1mo ferritic steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
    Co-Authors: B K Choudhary
    Abstract:

    Abstract The paper presents Tertiary Creep behaviour of thick section 9Cr–1Mo ferritic steel forging at 793 and 873 K. The stress dependence of rupture life obeyed power law. The steel exhibited distinct low and high stress regimes characterised by separate values of power law exponent and constant in the Creep rate–rupture life relationships of Monkman–Grant type. Extensive Tertiary Creep in terms of both the large time spent and the large Creep strain accumulation during Tertiary Creep has been observed. The prolonged Tertiary Creep was associated with the high and distinct values of Creep damage tolerance factors in the low and high stress regimes indicating dominance of microstructural degradation in the steel. Separate master Creep curves have been obtained for low and high stress regimes in the coupled relationship for Creep deformation and damage that depends only on Creep damage tolerance factor envisaged in the continuum damage mechanics approach.

  • Tertiary Creep behaviour of 9Cr–1Mo ferritic steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
    Co-Authors: B K Choudhary
    Abstract:

    Abstract The paper presents Tertiary Creep behaviour of thick section 9Cr–1Mo ferritic steel forging at 793 and 873 K. The stress dependence of rupture life obeyed power law. The steel exhibited distinct low and high stress regimes characterised by separate values of power law exponent and constant in the Creep rate–rupture life relationships of Monkman–Grant type. Extensive Tertiary Creep in terms of both the large time spent and the large Creep strain accumulation during Tertiary Creep has been observed. The prolonged Tertiary Creep was associated with the high and distinct values of Creep damage tolerance factors in the low and high stress regimes indicating dominance of microstructural degradation in the steel. Separate master Creep curves have been obtained for low and high stress regimes in the coupled relationship for Creep deformation and damage that depends only on Creep damage tolerance factor envisaged in the continuum damage mechanics approach.

  • Creep deformation behaviour and kinetic aspects of 9Cr-1Mo ferritic steel
    Isij International, 2001
    Co-Authors: B K Choudhary, C Phaniraj, S L Mannan
    Abstract:

    This paper presents the detailed investigations on Creep behaviour of 9Cr-1Mo ferritic steel with an emphasis to understand and unify the different stages of Creep deformation in the framework of first order kinetic approach. The different values of stress exponent and apparent activation energy observed for the two stress regimes have been rationalized by invoking the concept of resisting stress. The detailed analysis of results revealed that both transient and Tertiary Creep obeyed first order kinetics with separate values of transient and Tertiary Creep parameters in the respective stress regimes. The two stress regimes with different values of stress exponent are manifested as separate master Creep curves for transient and steady state Creep. Similarly, the analysis of Tertiary Creep also revealed distinct master Creep curves relating steady state and Tertiary Creep in the respective stress regimes. The paper also focuses attention on two important relationships, one obtained between transient and steady state Creep, and the other between steady state and Tertiary Creep. The useful implications of these relationships in understanding the existing Creep rate-rupture life relationships of Monkman-Grant type are also highlighted in this paper.

S L Mannan - One of the best experts on this subject based on the ideXlab platform.

  • evolution of damage in Tertiary Creep of type 316 n ss weld metal
    Acta Materialia, 2004
    Co-Authors: G Sasikala, S L Mannan
    Abstract:

    Abstract This paper reports analysis of the Tertiary Creep data for SS 316(N) weld metal considering strain (rather than exposure time) as the parameter “driving” Creep damage, e ˙ / e ˙ 0 ; e ˙ is the instantaneous true Creep rate, and e ˙ 0 its value for the undamaged material. The early part of Tertiary Creep, which is the dominant fraction of the Creep life, is well described by the relation, ln e ˙ = ln e ˙ 0 + k ( e - e 0 ) ν , e ⩾ e 0 ; k and ν are constants, and e 0 a threshold strain corresponding presumably to nucleation/growth of voids to stable sizes. The quantitative formulation did reflect the significant modulation of Creep damage kinetics by the in situ transformation of δ-ferrite in the weld metal to embrittling phases. As long as the extents of δ-ferrite transformation during Creep covers a relatively narrow range for a given temperature, the parameters k , ν and e 0 were independent of stress while e ˙ 0 varied as a power of stress. The rupture strength for t r  = 10 5 h at 823 K could be predicted satisfactorily using this formulation.

  • Creep deformation behaviour and kinetic aspects of 9Cr-1Mo ferritic steel
    Isij International, 2001
    Co-Authors: B K Choudhary, C Phaniraj, S L Mannan
    Abstract:

    This paper presents the detailed investigations on Creep behaviour of 9Cr-1Mo ferritic steel with an emphasis to understand and unify the different stages of Creep deformation in the framework of first order kinetic approach. The different values of stress exponent and apparent activation energy observed for the two stress regimes have been rationalized by invoking the concept of resisting stress. The detailed analysis of results revealed that both transient and Tertiary Creep obeyed first order kinetics with separate values of transient and Tertiary Creep parameters in the respective stress regimes. The two stress regimes with different values of stress exponent are manifested as separate master Creep curves for transient and steady state Creep. Similarly, the analysis of Tertiary Creep also revealed distinct master Creep curves relating steady state and Tertiary Creep in the respective stress regimes. The paper also focuses attention on two important relationships, one obtained between transient and steady state Creep, and the other between steady state and Tertiary Creep. The useful implications of these relationships in understanding the existing Creep rate-rupture life relationships of Monkman-Grant type are also highlighted in this paper.

  • analysis of first order kinetics for Tertiary Creep in aisi 304 stainless steel
    Acta Materialia, 1996
    Co-Authors: C Phaniraj, M Nandagopal, S L Mannan, P Rodriguez, B P Kashyap
    Abstract:

    Abstract The results of constant load Creep tests on AISI 304 stainless steel at 873 and 973 K for different test conditions were found to obey the first order kinetics for Tertiary Creep. Distinct master Creep curves were obtained at 873 and 973 K with a separate set of constant values of K′, ϵt, β′ and CMG. A relationship between steady-state Creep rate ϵs, time spent in Tertiary Creep tt and limiting Tertiary Creep strain ϵt is formulated as ϵs·tt/ϵt = constant and is found to be valid for all test conditions. Further, this relation is identical to the modified Monkman—Grant relation (MMGR) for the conditions satisfying f = 1/λ; it is postulated that the validity of MMGR is a consequence of first order kinetics. Another important outcome of this study is a generalised relation of the form ϵs·tr = (ϵ23·ϵf) 1 2 ; and this relation is compared with the relation proposed by Radhakrishnan, i.e. ϵs·tr = (ϵ223·ϵf) 1 3 . It is suggested that cavities act as vacancy sinks and accelerate dislocation climb controlled recovery process leading to Tertiary Creep.

Nirmal K Sinha - One of the best experts on this subject based on the ideXlab platform.

  • Tertiary Creep in nickel base single crystal superalloys a case of geometric effect
    Canadian Aeronautics and Space Journal, 2006
    Co-Authors: Nirmal K Sinha
    Abstract:

    The Tertiary Creep in nickel-base single-crystal superalloys observed in conventional "constant-load" tests, for conditions where rafting of γ´ precipitates does not play a dominant role, represents a dynamic steady-state condition. The accelerating strain rate corresponds primarily to the increasing stress with decreasing cross-sectional area as the strain increases. Experiments on [001]-oriented CMSX-10 at 900 °C for the initially applied stresses of 500–700 MPa revealed this geometrically induced effect for the most part of the Creep life. A power-law describes the stress dependence of Creep rate. It is shown that one Creep rupture test provides a stress-strain rate relationship for dislocation Creep over a stress range of about 100 MPa. Consequently, this suggests an economical, time-saving experimental scheme for determining stress exponent n from one test for a short stress range or the variations in n over a larger stress range using only a few specimens. A simple nonlinear elasto-viscous Creep mod...

  • constant load Tertiary Creep in nickel base single crystal superalloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006
    Co-Authors: Nirmal K Sinha
    Abstract:

    Abstract Accelerating or Tertiary Creep in nickel-base single crystal (SX) superalloys, for constant-load tensile tests represents a “dynamic steady state” between the engineering strain rate and the corresponding actual or true stress. Experiments on nominally [0 0 1]-oriented CMSX-10 at 900 °C revealed this for initial stresses of 500–700 MPa for conditions of non-rafting γ′ precipitates. Analysis of results obtained elsewhere on [0 0 1]-oriented CMSX-10, for conditions of γ′ rafting at temperatures up to 1100 °C also indicate this dynamic steady state. This state is described by a power-law between stress and strain rate and one test provides the stress exponent over a stress range of 100 MPa. This suggests an economical method for evaluating initial microstructure-property relationship. A time-based elasto-viscous (non-linear) Creep model with only three material parameters predicts Tertiary Creep as long as the deformation is homogeneous. The onset of inhomogeneous deformation can be predicted by comparing the model output with the experimental observations using a normalized strain-rate technique. For [0 0 1]-oriented CMSX-10 at 900 °C and 500–700 MPa, inhomogeneous deformation is predicted for strains greater than 12%. This was verified by conducting interrupted tests and measuring the profile of the cross-sectional shape along the entire originally uniform gauge length. However, fractured specimens revealed very significant non-uniform deformation in the form of necking at two regions. The elongation of pores and cracking at pores walls are recognized as Creep enhancement factors that lead to double necking and final fracture at one of them. A survey of constant-load Creep results obtained in different laboratories on different nickel-base SX alloys (CMSX-4, CMSX-10, TMS75) at different temperatures and stresses confirm the hypothesis of dynamic steady state (including true strain rate versus true stress), during Tertiary stage.

R C Reed - One of the best experts on this subject based on the ideXlab platform.

  • critical assessment 31 on the modelling of Tertiary Creep in single crystal superalloys
    Materials Science and Technology, 2018
    Co-Authors: Sabin Sulzer, R C Reed
    Abstract:

    ABSTRACTModelling of Tertiary Creep in single-crystal superalloys – operative over the majority of the temperature/stress regime of relevance – is assessed. Traditional, empirical approaches are us...

  • inverse method for parameter optimisation in superalloy Tertiary Creep equations
    Materials Science and Technology, 2002
    Co-Authors: M A Rist, R C Reed
    Abstract:

    A new methodology has been devised for the optimisation of material parameters in equations that govern the Tertiary Creep deformation of single crystal superalloys. Such information is ordinarily extracted by conducting a series of mechanical experiments over a range of appropriate environmental conditions, e.g. at various fixed stresses and temperatures. However, the current technique allows material behaviour to be characterised from a limited number of tests of short duration performed under non-uniform stress. A strategy is presented in which the time dependent strain response under a distributed stress gradient is measured using a novel testpiece geometry incorporating a concave gauge length profile. Spatial strain distribution is determined by accurate post-deformation measurement of specimen shape. Both spatial and temporal deformation are then simulated using a well founded mechanistic damage model, and the agreement between model results and experimental data is optimised by systematic perturbation of model parameters using the Nelder-Mead direct search method, i.e. an inverse modelling approach is applied. The overall strategy has been successfully, validated for SRR99 by direct comparison with a database of more conventional tensile Creep data, but it has the potential for broad application in cost effective and efficient prototyping of new materials generally.

  • characterization of superalloy Tertiary Creep by inverse modeling
    2001
    Co-Authors: R C Reed
    Abstract:

    The design of new alloys for high-temperature engineering applications frequently requires the rapid characterization of material mechanical behavior, particularly Creep resistance. Such information is ordinarily extracted by conducting a series of time-consuming and costly experiments under uniform load or stress. To expedite material prototyping we have developed a technique that allows estimation of the stress-dependence of material behavior from a single, short-duration, tensile test performed under non-uniform stress. The approach involves inverse modeling of experiments conducted using a novel tensile testpiece with a concave gauge-length profile. Temporal strain and post-deformation spatial strain distribution are simulated using a well-founded mechanistic Creep damage model, and agreement between model results and experimental data is optimized by systematic perturbation of model parameters. This inverse strategy has been validated by examining high temperature Tertiary Creep in three generations of nickel superalloy single-crystal materials, but has wider application to materials characterization generally.

Ali P. Gordon - One of the best experts on this subject based on the ideXlab platform.

  • A Modified Theta Projection Creep Model for a Nickel-Based Super-Alloy
    Volume 7A: Structures and Dynamics, 2013
    Co-Authors: Ali P. Gordon
    Abstract:

    Accurate prediction of Creep deformation is critical to assuring the mechanical integrity of heavy-duty, industrial gas turbine (IGT) hardware. The classical description of the Creep deformation curve consists of a brief primary, followed by a longer secondary, and then a brief Tertiary Creep phase. An examination of Creep tests at four temperatures for a proprietary, nickel-based, equiaxed, super-alloy revealed many occasions where there is no clear transition from secondary to Tertiary Creep. This paper presents a new Creep model for a Nickel-based super-alloy, with some similarities to the Theta Projection (TP) Creep model by Evans and all [1].The alternative Creep equation presented here was developed using meaningful parameters, or θ’s, such as: the primary Creep strain, time at primary Creep strain, minimum (or secondary) Creep rate, and time that Tertiary Creep begins. By plotting the first and second derivative of Creep, the authors were able to develop a Creep equation that accurately matches tests. This Creep equation is identical to the primary Creep portion of the theta projection model, but has a modified second term. An additional term is included to simulate Tertiary Creep. An overall scaling factor is used to satisfy physical constraints and ensure solution stability. The new model allows a constant Creep rate phase to be maintained, captures Tertiary Creep, and satisfies physical constraints.The coefficients of the Creep equations were developed using results from 27 Creep tests performed at 4 temperatures. An automated routine was developed to directly fit the θ coefficients for each phase, resulting in a close overall fit for the material. The resultant constitutive Creep model can be applied to components which are subjected to a wide range of temperatures and stresses. Useful information is provided to designers in the form of time to secondary and Tertiary Creep for a given stress and temperature. More accurate Creep predictions allow PSM to improve the structural integrity of its turbine blades and vanes.© 2013 ASME

  • an anisotropic Tertiary Creep damage constitutive model for anisotropic materials
    International Journal of Pressure Vessels and Piping, 2011
    Co-Authors: Calvin M. Stewart, Ali P. Gordon
    Abstract:

    Abstract When an anisotropic material is subject to Creep conditions and a complex state of stress, an anisotropic Creep damage behavior is observed. Previous research has focused on the anisotropic Creep damage behavior of isotropic materials but few constitutive models have been developed for anisotropic Creeping solids. This paper describes the development of a new anisotropic Tertiary Creep damage constitutive model for anisotropic materials. An advanced tensorial damage formulation is implemented which includes both material orientation relative to loading and the degree of Creep damage anisotropy in the model. A variation of the Norton-power law for secondary Creep is implemented which includes the Hill’s anisotropic analogy. Experiments are conducted on the directionally-solidified bucket material DS GTD-111. The constitutive model is implemented in a user programmable feature (UPF) in ANSYS FEA software. The ability of the constitutive model to regress to the Kachanov-Rabotnov isotropic Tertiary Creep damage model is demonstrated through comparison with uniaxial experiments. A parametric study of both material orientation and stress rotation are conducted. Results indicate that Creep deformation is modeled accurately; however an improved damage evolution law may be necessary.

  • An Improved Anisotropic Tertiary Creep Damage Formulation
    Journal of Pressure Vessel Technology-transactions of The Asme, 2011
    Co-Authors: Calvin M. Stewart, Ali P. Gordon
    Abstract:

    Directionally solidified (DS) Ni-base superalloys are commonly used as gas turbine materials to primarily extend the operational lives of components under high load and temperature. The nature of DS superalloy grain structure facilitates an elongated grain orientation, which exhibits enhanced impact strength, high temperature Creep and fatigue resistance, and improved corrosion resistance compared with off-axis orientations. Of concern to turbine designers are the effects of cyclic fatigue, thermal gradients, and potential stress concentrations when dealing with orientation-dependent materials. When coupled with a Creep environment, accurate prediction of crack initiation and propagation becomes highly dependent on the quality of the constitutive damage model implemented. This paper describes the development of an improved anisotropic Tertiary Creep damage model implemented in a general-purpose finite element analysis software. The Creep damage formulation is a tensorial extension of a variation in the Kachanov–Rabotnov isotropic Tertiary Creep damage formulation. The net/effective stress arises from the use of the Rabotnov second-rank symmetric damage tensor. The Hill anisotropic behavior analogy is used to model secondary Creep and Tertiary Creep damage behaviors. Using available experimental data for a directionally solidified Ni-base superalloy, the improved formulation is found to accurately model intermediate oriented specimen.

  • analytical method to determine the Tertiary Creep damage constants of the kachanov rabotnov constitutive model
    ASME 2010 International Mechanical Engineering Congress and Exposition IMECE 2010, 2010
    Co-Authors: Calvin M. Stewart, Ali P. Gordon
    Abstract:

    The classic Kachanov-Rabotnov isotropic Creep damage constitutive model has been used in many situations to predict the Creep deformation of high temperature components. Typically, the secondary Creep behavior is determined by analytical methods; however, the Tertiary Creep damage constants are found using a mixture of trial and error and numerical optimization. These methods require substantial hand calculations and computational time to determine the Tertiary Creep damage constants. In this paper, a novel analytical method is developed to determine the Tertiary Creep damage constants. Comparisons between numerical optimized constants and those found using the analytical method are given for a Ni-based superalloy. Creep deformation, damage evolution, and rupture time predictions are compared. A detailed discussion of the analytical method is given.Copyright © 2010 by ASME

  • modeling the Tertiary Creep damage behavior of a transversely isotropic material under multiaxial and periodic loading conditions
    ASME 2010 Pressure Vessels and Piping Division K-PVP Conference PVP2010, 2010
    Co-Authors: Calvin M. Stewart, Ali P. Gordon
    Abstract:

    Despite the advent of single crystal turbine blades, the aerospace and industrial gas turbine industries have continued to use directionally-solidified turbine blades due to higher manufacturing yields. These transversely-isotropic turbine blades are subjected to high temperature multiaxial cyclic loading conditions which lead to complex Creep strain histories. Few tensor-based constitutive models have been developed that accurately model Creep-damage behavior. This paper describes an anisotropic Tertiary Creep damage model for transversely-isotropic materials. The model is a tensorial expansion of the Kachanov-Rabotnov isotropic Creep damage formulation. The analytical techniques required to determine the associated material constants are derived and demonstrated. The model is shown to accurately model a directionally-solidified Ni-base superalloy. A parametric study under biaxial and hydrostatic loading is conducted and the resulting Creep strain tensor is evaluated. A series of periodic loading simulations are conducted to examine the stress-strain behavior and damage evolution during ratcheting.Copyright © 2010 by ASME