Characterization of the Creep Deformation and Rupture Behavior of DS GTD-111 Using the Kachanov–Rabotnov Constitutive Model

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon ◽  
Erik A. Hogan ◽  
Ashok Saxena
Keyword(s):  
Creep Deformation ◽  
Creep Damage ◽  
General Purpose ◽  
Secondary Creep ◽  
Directionally Solidified ◽  
Element Analysis ◽  
Optimization Routine ◽  
Base Superalloy ◽  
Rupture Behavior

Creep deformation and rupture experiments are conducted on samples of the Ni-base superalloy directionally solidified GTD-111 tested at temperatures between 649°C and 982°C and two orientations (longitudinally and transversely oriented). The secondary creep constants are analytically determined from creep deformation experiments. The classical Kachanov–Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. The simulated annealing optimization routine is utilized in conjunction with the FEA implementation to determine the creep damage constants. A comparison of FEA and creep deformation data demonstrates high accuracy. Using regression analysis, the creep constants are characterized for temperature dependence. A rupture prediction model derived from creep damage evolution is compared with rupture experiments.

Modeling the Temperature-Dependence of Tertiary Creep Damage of a Directionally Solidified Ni-Base Superalloy

2009 ◽  
Author(s):  
Calvin M. Stewart ◽  
Erik A. Hogan ◽  
Ali P. Gordon
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Creep Damage ◽  
Time Estimation ◽  
General Purpose ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Directionally Solidified ◽  
Estimation Model ◽  
Element Analysis

Directionally solidified (DS) Ni-base superalloys have become a commonly used material in gas turbine components. Controlled solidification during the material manufacturing process leads to a special alignment of the grain boundaries within the material. This alignment results in different material properties dependent on the orientation of the material. When used in gas turbine applications the direction of the first principle stress experienced by a component is aligned with the enhanced grain orientation leading to enhanced impact strength, high temperature creep and fatigue resistance, and improve corrosion resistance compared to off axis orientations. Of particular importance is the creep response of these DS materials. In the current study, the classical Kachanov-Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture experiments are conducted on samples from a representative DS Ni-base superalloys tested at temperatures between 649 and 982°C and two orientations (longitudinally- and transversely-oriented). The secondary creep constants are analytically determined from available experimental data in literature. The simulated annealing optimization routine is utilized to determine the tertiary creep constants. Using regression analysis the creep constants are characterized for temperature and stress-dependence. A rupture time estimation model derived from the Kachanov-Rabotnov model is then parametrically exercised and compared with available experimental data.

Temperature and Orientation Dependence of Creep Damage of Two Ni-Base Superalloys

2007 ◽  
Author(s):  
Ali P. Gordon ◽  
Sameer Khan ◽  
David W. Nicholson
Keyword(s):  
Gas Turbines ◽  
Damage Model ◽  
Creep Damage ◽  
General Purpose ◽  
Orientation Dependence ◽  
Tertiary Creep ◽  
Directionally Solidified ◽  
Element Analysis ◽  
Stress And Deformation ◽  
Marine Air

Both polycrystalline (PC) and directionally-solidified (DS) Ni-base superalloys are commonly applied as turbine materials to primarily withstand creep conditions manifested in either marine-, air- or land-based gas turbines components. The thrust for increased efficiency of these systems, however, translates into the need for these materials to exhibit considerable strength and temperature resistance. This is critical for engine parts that are subjected to high temperature and stress conditions sustained for long periods of time, such as blades, vanes, and combustion pieces. Accurate estimates of stress and deformation histories at notches, curves, and other critical locations of such components are crucial for life prediction and calculation of service intervals. In the current study, the classical Kachanov-Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture experiments on samples from two representative Ni-base superalloys (PC and DS) tested at temperatures between 649 and 982°C and two orientations (longitudinally- and transversely-oriented for the DS case only) are applied to extend this damage formulation. The damage model coefficients corresponding to secondary and tertiary creep constants are characterized for temperature and orientation dependence. This updated formulation can be implemented for modeling full-scale parts containing temperature distributions.

Creep Damage Formation and Crack Initiation / Growth Behavior of Notched Specimen for Directionally Solidified Ni-Base Superalloy by Interrupted Observation

2016 ◽  
Author(s):  
Go Ozeki ◽  
A. Toshimitsu Yokobori ◽  
Takashi Matsuzaki
Keyword(s):  
Crack Growth ◽  
Turbine Blades ◽  
Creep Condition ◽  
Creep Damage ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Directionally Solidified ◽  
Element Analysis ◽  
Notched Specimen ◽  
Base Superalloy

Directionally solidified Ni-base superalloy is used for gas turbine blades for high efficiency thermal power plant. Since gas turbine blades are subject to high temperature creep condition due to the high speed rotation of rotor, it is important to evaluate the creep strength. There are many studies using the smooth specimen for directionally solidified Ni-base superalloy. However, these are not so many researches which concern the mechanical behavior of a notched specimen. Therefore, the researches of creep damage formation and the crack growth behavior around a notch tip have not yet been clarified. Recently, electron backscatter diffraction (EBSD) method has been conducted to evaluate the creep damage for Ni-base superalloy. However, most of the studies also use the smooth specimen. When the materials are practically used for the component of structures, creep damage or crack may be originated at the site of stress concentration of equipment such as cooling holes. Therefore, in order to evaluate the creep damage formation and the crack growth behavior, it is important to conduct the research using notched specimens from the view point of application to actual components. In this study, creep damage formation and crack growth behavior of a notched specimen for directionally solidified Ni-base superalloy CM247LC under high temperature creep condition were investigated by conducting experiment and mechanical analysis. The interrupted observational test of creep crack growth was conducted to investigate the damage formation and the crack growth behavior around notches. In addition, the In-situ observation and the metallographical investigations were conducted for creep damaged specimens using SEM / EBSD analysis. Furthermore, in order to clarify the mechanism of creep damage formation behavior, the designed two-dimensional elastic-plastic creep finite element analysis was conducted for the model with various distributed grains obtained by EBSD analysis. And this analytical results were compared with experimental results. As a result, the micro creep crack around a notch tip was found to be caused by accumulation of micro damage and voids. In addition, macro cracks were found to initiate just before final unstable fracture. However, it is necessary to take into account for the variety of mechanical properties of each crystal orientation, the designed two-dimensional elastic-plastic creep finite element analysis was found to well represent the creep damage formation observed in experiments.

An Improved Anisotropic Tertiary Creep Damage Formulation

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon ◽  
Young Wha Ma ◽  
Richard W. Neu
Keyword(s):  
Damage Model ◽  
Creep Damage ◽  
Cyclic Fatigue ◽  
Grain Structure ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Directionally Solidified ◽  
Stress Concentrations ◽  
Element Analysis ◽  
Damage Formulation

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.

Finite-Element Analysis of Waspaloy Using Sinh Creep-Damage Constitutive Model Under Triaxial Stress State

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Mohammad Shafinul Haque ◽  
Calvin Maurice Stewart
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Creep Deformation ◽  
Damage Evolution ◽  
Rupture Life ◽  
Creep Damage ◽  
Nickel Base Superalloy ◽  
Element Analysis ◽  
Stress Levels ◽  
Nickel Base

The creep deformation and damage evolution of nickel base superalloy (Waspaloy) at 700 °C are studied using the classic Kachanov–Rabotnov (KR) and a recently developed Sin-hyperbolic (Sinh) model. Uniaxial creep deformation and Bridgman rupture data collected from literature are used to determine the model constants and to compare the KR and the Sinh solutions. Finite-element (FE) simulations on a single eight-node element are conducted to validate the accuracy of the FE code. It is observed that KR cannot predict the creep deformation, damage, and rupture life of nickel base superalloys accurately using one set of constants for all the stress levels. The Sinh model exhibits a superior ability to predict the creep behavior using one set of constants for all the stress levels. Finite-element analysis (FEA) on 3D Bridgman notched Waspaloy specimen using the Sinh model is conducted. The results show that the Sinh model when combined with a representative stress equation and calibrated with experimental data can accurately predict the “notch effect” observed in the rupture life of notched specimen. Contour plots of damage evolution and stress redistribution are presented. It is demonstrated that the Sinh model is less stress sensitive, produces unconditional critical damage equal to unity at rupture, exhibits a more realistic damage distribution around the crack tip, and offers better crack growth analysis than KR.

Application of the Monkman-Grant Relationship for Ultrafine-Grained Metallic Materials

2013 ◽  
Vol 577-578 ◽  
pp. 137-140
Author(s):  
Marie Kvapilová ◽  
Jiří Dvořák ◽  
Petr Král ◽  
Milan Svoboda ◽  
Vàclav Sklenička
Keyword(s):  
Creep Deformation ◽  
Damage Tolerance ◽  
Creep Damage ◽  
Tolerance Factor ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Metallic Materials ◽  
Ultrafine Grained ◽  
Ultrafine Grained Materials ◽  
The Relationship

The applicability of the Monkman-Grant relationship was analyzed and validated for ultrafine-grained metallic materials under investigation. A special attention has been given to the creep damage tolerance factor which is defined as the ratio of the strain to fracture to the Monkman-Grant ductility and which describes the coupling between creep deformation and damage based on continuum creep damage approach. It was found, that ultrafine-grained materials generally obey the Monkman-Grant relationship, however, the relationship is especially suitable for materials exhibiting short secondary creep and long tertiary creep stages when dislocation-controlled creep is dominant.

Modeling Creep Deformation and Damage Behavior of Tempered Martensitic Steel in the Framework of Additive Creep Rate Formulation

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
J. Christopher ◽  
B. K. Choudhary
Keyword(s):  
Creep Rate ◽  
Internal Stress ◽  
Creep Strain ◽  
Creep Deformation ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Time Behavior ◽  
Secondary Creep ◽  
Modeling Creep ◽  
Applied Stresses

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.

Strain and Damage-Based Analytical Methods to Determine the Kachanov–Rabotnov Tertiary Creep-Damage Constants

2011 ◽  
Vol 21 (8) ◽  
pp. 1186-1201 ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon
Keyword(s):  
Creep Behavior ◽  
Creep Deformation ◽  
Analytical Methods ◽  
Numerical Optimization ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Nickel Base Superalloy ◽  
Trial And Error ◽  
Nickel Base ◽  
Base Superalloy

In the power generation industry, the goal of increased gas turbine efficiency has led to increased operating temperatures and pressures necessitating nickel-base superalloy components. Under these conditions, the tertiary creep regime can become the dominant form of creep deformation. In response, the classical Kachanov–Rabotnov coupled creep-damage constitutive model is often used to predict the creep deformation and damage of Ni-base superalloys. In this model, the secondary creep behavior can be determined through analytical methods while the tertiary creep behavior is often found using trial and error or numerical optimization. Trial and error may produce no constants. Numerical optimization can be computationally expensive. In this study, a strain-based and damage-based approach to determine the tertiary creep behavior of nickel-base superalloys has been developed. Analytically determined constants are found for a given nickel-base superalloy. Creep deformation and damage evolution curves are compared. Methods to deal with stress dependence are introduced and studied.

Identification of Stress Multiaxiallity Effect on Creep Damage by a Combination of Experiments and Numerical Analyses

2009 ◽  
Author(s):  
Yukio Takahashi
Keyword(s):  
Finite Element ◽  
Synergetic Effect ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Compact Tension ◽  
Simple Expression ◽  
Creep Rupture ◽  
Creep Tests ◽  
Element Analysis ◽  
Rupture Behavior

Structural materials experience various stress states and their integrity under a wide variety of stress multiaxility needs to be evaluated in design and life management for various components. Especially creep rupture behavior is known to be quite sensitive to the stress multiaxiality. To systematically evaluate the multiaxial effect on creep rupture behavior of modified 9Cr-1Mo steel, a number of creep tests were conducted on round-bar specimens with circumferential notches. Strong effects of temperature and deformation rate on the reduction of area were observed and their synergetic effect was modeled by a simple expression. Then crack growth in compact tension specimens was simulated by finite element analysis to derive ductility under higher stress triaxiality. Finally, true rupture strain was expressed as a function of temperature, inelastic strain rate and triaxiality factor and its validity was demonstrated through finite element analyses on notched bar and compact tension specimens employing it as a local fracture criterion.

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