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.

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.

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.

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 Ni-Based Alloy

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon
Keyword(s):  
Temperature Dependence ◽  
Creep Deformation ◽  
Mechanical Response ◽  
Axial Stress ◽  
Nauk Sssr ◽  
Damage Model ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Continuum Damage ◽  
Over Time

To capture the mechanical response of Ni-based materials, creep deformation and rupture experiments are typically performed. Long term tests, mimicking service conditions at 10,000 h or more, are generally avoided due to expense. Phenomenological models such as the classical Kachanov–Rabotnov (Rabotnov, 1969, Creep Problems in Structural Members, North-Holland, Amsterdam; Kachanov, 1958, “Time to Rupture Process Under Creep Conditions,” Izv. Akad. Nauk SSSR, Otd. Tekh. Nauk, Mekh. Mashin., 8, pp. 26–31) model can accurately estimate tertiary creep damage over extended histories. Creep deformation and rupture experiments are conducted on IN617 a polycrystalline Ni-based alloy over a range of temperatures and applied stresses. The continuum damage model is extended to account for temperature dependence. This allows the modeling of creep deformation at temperatures between available creep rupture data and the design of full-scale parts containing temperature distributions. Implementation of the Hayhurst (1983, “On the Role of Continuum Damage on Structural Mechanics,” in Engineering Approaches to High Temperature Design, Pineridge, Swansea, pp. 85–176) (tri-axial) stress formulation introduces tensile/compressive asymmetry to the model. This allows compressive loading to be considered for compression loaded gas turbine components such as transition pieces. A new dominant deformation approach is provided to predict the dominant creep mode over time. This leads to development of a new methodology for determining the creep stage and strain of parametric stress and temperature simulations over time.

Anisotropic Creep Damage and Elastic Damage of Notched Directionally Solidified Materials

2011 ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon
Keyword(s):  
Crack Initiation ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Transversely Isotropic ◽  
Grain Structure ◽  
Directionally Solidified ◽  
Elastic Damage

Drives to improve gas turbines efficiency have lead to an increase in firing temperatures. This increase in exhaust temperature has a negative impact upon turbine blade life. Both engineers and material scientists have produced methods to improve turbine blade life under these conditions. Cooling holes have become commonplace and use relatively cool gas to create a lower temperature barrier around a turbine blade. These cooling holes creating internal and external surfaces; a common sight of crack initiation. Directionally-solidified (DS) turbine blades have also become commonplace. These turbine blades exhibit a transversely-isotropic grain structure that improves creep strength in a desired direction. To model a component under such conditions, anisotropic constitutive models are required. In this paper, an anisotropic tertiary creep damage constitutive model for transversely-isotropic materials is given. The influence of creep-damage on general linear elasticity (elastic damage) is described by a modified Hooke’s compliance tensor. Finite element simulations of a V-notched tensile specimen are conducted to replicate a crack initiation site. A discussion on stress triaxiality, stress redistribution, and damage distribution due to anisotropy is provided.

A Novel and Simple Approach for Predicting Creep Life Based on Tertiary Creep Behavior

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Khosrow Zarrabi ◽  
Lawrence Ng
Keyword(s):  
Gas Turbines ◽  
Damage Model ◽  
Creep Damage ◽  
Life Assessment ◽  
Advanced Technology ◽  
Creep Life ◽  
Practical Applications ◽  
Damage Models ◽  
Multiaxial Creep ◽  
Creep Damage Model

The creep of materials is a research topic of major significance in the life assessment and design of many modern engineering components of advanced technology such as power generation plant, chemical plant, gas turbines, jet engines, spacecrafts, and components made of plastics and polymers. To predict the creep life of such components, one necessary ingredient is a creep damage model. The current creep damage models are either too cumbersome to be readily employed and/or not sufficiently accurate for practical applications. This paper describes a new multiaxial creep damage model that alleviates the major shortcomings of the existing models. Yet it is relatively simple and accurate and is readily applicable to industrial cases.

Three-Dimensional Modeling of Creep Damage in Airfoils for Advanced Turbine Systems

2008 ◽  
Author(s):  
Ventzislav G. Karaivanov ◽  
Danny W. Mazzotta ◽  
Minking K. Chyu ◽  
William S. Slaughter ◽  
Mary Anne Alvin
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Gas Turbines ◽  
Damage Mechanics ◽  
Thermal Loading ◽  
Three Dimensional ◽  
Creep Damage ◽  
Creep Model ◽  
Working Fluid ◽  
Element Analysis

Future oxy-fuel and hydrogen-fired turbines promise increased efficiency and low emissions. However, this comes at the expense of increased thermal load from higher inlet temperatures and a change in the working fluid in the gas path, leading to aero-thermal characteristics that are significantly different than those in traditional gas turbines. A computational methodology, based on three-dimensional finite element analysis (FEA) and damage mechanics is presented for predicting the evolution of creep in airfoils in these advanced turbine systems. Information revealed from three-dimensional computational fluid dynamics (CFD) simulations of external heat transfer and thermal loading over a generic airfoil provides detailed local distributions of pressure, surface temperature, and heat flux penetrating through the thermal barrier coated layer. There is an additional mechanical loading due to the centrifugal acceleration of the airfoil. Finite element analysis is then used to predict temperature and stress fields over the domain of the airfoil. The damage mechanics-based creep model uses a scalar damage parameter. This creep model is coupled with finite element analysis to predict the evolution of stress and creep damage over the entire airfoil. Visualization of the creep damage evolution over the airfoil shows the regions that are most susceptible to failure by creep.

Crack FEA of the First Stage Blade of Gas Turbines

2010 ◽  
Vol 450 ◽  
pp. 429-432
Author(s):  
Ping Zhao ◽  
Wei Li ◽  
Qing Hua He
Keyword(s):  
Gas Turbines ◽  
Life Prediction ◽  
Crack Nucleation ◽  
Creep Damage ◽  
Nucleation And Growth ◽  
Prediction System ◽  
Edge Region ◽  
Element Analysis ◽  
Fatigue Crack Nucleation ◽  
Crack Nucleation And Growth

To investigate the physical cause of premature blade cracking during the acceleration mission test (AMT) in a test cell environment, an in-depth finite element analysis (FEA) of the blade was conducted using a life prediction system. The results obtained showed that the blades had suffered excessive airfoil creep damage, leading to excessive blade lengthening and airfoil untwisting particularly in the trailing edge region. It is predicted that the uneven rubbing action might have contributed to the fatigue crack nucleation and growth process just below the platform in the shank region of the blade under AMT fatigue cycling conditions, and the excessive creep deformation made a significant effect on the overall crack nucleation process.

Modeling Coupled Flow-Stress-Damage during Creep Deformation

2012 ◽  
Vol 204-208 ◽  
pp. 3294-3298
Author(s):  
Ru Bin Wang ◽  
Wei Ya Xu ◽  
Jiu Chang Zhang
Keyword(s):  
Creep Deformation ◽  
Failure Process ◽  
Damage Model ◽  
High Stress ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Coupled Flow ◽  
Creep Failure ◽  
Plastic Model ◽  
Elastic Plastic

In order to reflect the tertiary rheological characteristics of hard rocks at the high stress states, a new nonlinear visco-elastic-plastic model is proposed on the basis of linear visco-elastic-plastic model and nonlinear visco-elastic-plasticity. And then the corresponding constitutive model are deduced, which can be used for describing rocks’ long-term strength characteristics and their creep deformational behavior and time-dependent damage under interaction of coupled seepage-stress field in rock engineering. At last, considering the time effect of rock damage in the process of tertiary creep, a coupled seepage -stress creep damage model for investigating the whole creep deformation behavior, including tertiary creep failure process is established, and the related equations governing the evolution of stress, creep damage and rock permeability along with the creep deformation of rock is introduced.

scholarly journals Modeling and Verification of Creep Strain and Exhaustion in a Welded Steam Mixer

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Stefan Holmström ◽  
Juhani Rantala ◽  
Anssi Laukkanen ◽  
Kari Kolari ◽  
Heikki Keinänen ◽  
...  
Keyword(s):  
Creep Strain ◽  
Three Dimensional ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Dimensional Structure ◽  
Rigid Plastic ◽  
Element Analysis ◽  
Filtering Technique ◽  
Long Term Behavior ◽  
Creep Regime

Structures operating in the creep regime will consume their creep life at a greater rate in locations where the stress state is aggravated by triaxiality constraints. Many structures, such as the welded steam mixer studied here, also have multiple material zones differing in microstructure and material properties. The three-dimensional structure as such, in addition to interacting material zones, is a great challenge for finite element analysis (FEA), even to accurately pinpoint the critical locations where damage will be found. The studied steam mixer, made of 10CrMo 9-10 steel (P22), has after 100,000 h of service developed severe creep damage in several saddle point positions adjacent to nozzle welds. FE-simulation of long term behavior of this structure has been performed taking developing triaxiality constraints, material zones, and primary to tertiary creep regimes into account. The creep strain rate formulation is based on the logistic creep strain prediction model implemented to ABAQUS, including primary, secondary, and tertiary creep. The results are presented using a filtering technique utilizing the formulation of rigid plastic deformation for describing and quantifying the developing “creep exhaustion.”

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