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.

Modeling the Tertiary Creep Damage Behavior of a Transversely-Isotropic Material Under Multiaxial and Periodic Loading Conditions

2010 ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon
Keyword(s):  
Creep Strain ◽  
Turbine Blades ◽  
Strain Tensor ◽  
Creep Damage ◽  
Transversely Isotropic ◽  
Tertiary Creep ◽  
Loading Conditions ◽  
Directionally Solidified ◽  
Damage Behavior ◽  
Periodic Loading

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.

Development of a Corrosion Resistant Directionally Solidified Material for Land Based Turbine Blades

1997 ◽  
Author(s):  
N. S. Cheruvu
Keyword(s):  
Turbine Blades ◽  
Grain Structure ◽  
Tensile Creep ◽  
Screening Tests ◽  
Directionally Solidified ◽  
Corrosion Resistant ◽  
Cooling Flow ◽  
Property Evaluation ◽  
Temperature Capability ◽  
Operating Stress

Advanced turbines with improved efficiency require materials that can operate at higher temperatures. Availability of these materials would minimize cooling flow requirements and thus, improve the efficiency of a turbine. Advanced processing such as directional solidification (DS), can improve temperature capability of the majority of Ni based superalloys. However, results of earlier work on IN-738 reveal that the DS process does not significantly improve temperature capability of this alloy. A research program was initiated to develop a corrosion resistant Ni-based DS blade material for land-based turbines. In this program, eight heats with varied Cr, Al, Ti, Ta, and W contents were selected for evaluation. Screening tests performed on these heats in the DS condition include tensile, creep, and corrosion. The results of experimental heats were compared with those of IN-738 in the equiaxed condition. From these results, two chemistries offering approximately 100°F temperature advantage at typical row 1 turbine blade operating stress, were selected for castability and further mechanical property evaluation. Several row 1 solid and cored turbine blades were successfully cast. The blades were evaluated for grain structure and mechanical properties. Tests were also conducted to evaluate the effects of withdrawal rates on properties. These results are summarized in this paper.

scholarly journals Experience in Extending the Life of Gas Turbine Blades

1980 ◽  
Author(s):  
J. Liburdi ◽  
J. O. Stephens
Keyword(s):  
Gas Turbine ◽  
Turbine Blade ◽  
Turbine Blades ◽  
Hot Isostatic Pressing ◽  
Creep Damage ◽  
Complete Recovery ◽  
Gas Turbine Blades ◽  
Reheat Treatment ◽  
Service Exposure ◽  
Prolonged Service

This paper presents the effects of deterioration of gas turbine blade life with prolonged service exposure. This deterioration is primarily due to internal microstructural changes and the formation of creep voids or cavitation. Methods of evaluating residual blade life or life trend curves are presented along with a documentation of the creep damage observed. The extension of blade life by Hot isostatic pressing versus reheat treatment is discussed and data is presented to show that complete recovery of properties can be achieved even after the material has suffered extensive internal creep damage. As a result, the time between overhauls for blades can be significantly extended, and the need for replacement blades can be minimized.

Crystal Visco-Plastic Model for Directionally Solidified Ni-Base Superalloys Under Monotonic and Low Cycle Fatigue

2021 ◽  
Author(s):  
Navindra Wijeyeratne ◽  
Firat Irmak ◽  
Ali P. Gordon
Keyword(s):  
Grain Boundaries ◽  
Gas Turbines ◽  
Thermal Stresses ◽  
Low Cycle Fatigue ◽  
Turbine Blades ◽  
Material Behavior ◽  
Flow Rule ◽  
Cycle Fatigue ◽  
Directionally Solidified ◽  
Crystallographic Slip

Abstract Nickel-base superalloys (NBSAs) are extensively utilized as the design materials to develop turbine blades in gas turbines due to their excellent high-temperature properties. Gas turbine blades are exposed to extreme loading histories that combine high mechanical and thermal stresses. Both directionally solidified (DS) and single crystal NBSAs are used throughout the industry because of their superior tensile and creep strength, excellent low cycle fatigue (LCF), high cycle fatigue (HCF), and thermomechanical fatigue (TMF) capabilities. Directional solidification techniques facilitated the solidification structure of the materials to be composed of columnar grains in parallel to the <001> direction. Due to grains being the sites of failure initiation the elimination of grain boundaries compared to polycrystals and the alignment of grain boundaries in the normal to stress axis increases the strength of the material at high temperatures. To develop components with superior service capabilities while reducing the development cost, simulating the material’s performance at various loading conditions is extremely advantageous. To support the mechanical design process, a framework consisting of theoretical mechanics, numerical simulations, and experimental analysis is required. The absence of grain boundaries transverse to the loading direction and crystallographic special orientation cause the material to exhibit anisotropic behavior. A framework that can simulate the physical attributes of the material microstructure is crucial in developing an accurate constitutive model. The plastic flow acting on the crystallographic slip planes essentially controls the plastic deformation of the material. Crystal Visco-Plasticity (CVP) theory integrates this phenomenon to describe the effects of plasticity more accurately. CVP constitutive models can capture the orientation, temperature, and rate dependence of these materials under a variety of conditions. The CVP model is initially developed for SX material and then extended to DS material to account for the columnar grain structure. The formulation consists of a flow rule combined with an internal state variable to describe the shearing rate for each slip system. The model presented includes the inelastic mechanisms of kinematic and isotropic hardening, orientation, and temperature dependence. The crystallographic slip is accounted for by including the required octahedral, cubic, and cross slip systems. The CVP model is implemented through a general-purpose finite element analysis software (i.e., ANSYS) as a User-Defined Material (USERMAT). Uniaxial experiments were conducted in key orientations to evaluate the degree of elastic and inelastic anisotropy. The temperature-dependent modeling parameter is developed to perform non-isothermal simulations. A numerical optimization scheme is utilized to develop the modeling constant to improve the calibration of the model. The CVP model can simulate material behavior for DS and SX NBSAs for monotonic and cyclic loading for a range of material orientations and temperatures.

Repair of Advanced Gas Turbine Blades

2005 ◽  
Author(s):  
Julie McGraw ◽  
Reiner Anton ◽  
Christian Ba¨hr ◽  
Mary Chiozza
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
High Efficiency ◽  
High Reliability ◽  
Turbine Blades ◽  
Base Material ◽  
Operating Experience ◽  
Cost Effective ◽  
Directionally Solidified ◽  
Hot Gas

In order to promote high efficiency combined with high power output, reliability, and availability, Siemens advanced gas turbines are equipped with state-of-the-art turbine blades and hot gas path parts. These parts embody the latest developments in base materials (single crystal and directionally solidified), as well as complex cooling arrangements (round and shaped holes) and coating systems. A modern gas turbine blade (or other hot gas path part) is a duplex component consisting of base material and coating system. Planned recoating and repair intervals are established as part of the blade design. Advanced repair technologies are essential to allow cost-effective refurbishing while maintaining high reliability. This paper gives an overview of the operating experience and key technologies used to repair these parts.

Life Assessment of Gas Turbine Blades Under Creep Failure Mechanism Considering Humidity

2018 ◽  
Author(s):  
Bita Soltan Mohammad Lou ◽  
Mohammad Pourgol-Mohammad ◽  
Mojtaba Yazdani
Keyword(s):  
Gas Turbine ◽  
Failure Mechanism ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Prediction Models ◽  
Turbine Blades ◽  
Life Assessment ◽  
Creep Life ◽  
Creep Failure ◽  
Design Assessment

Gas turbines are the most important components in thermal power plants, and these components such as turbine has been studied carefully. Gas turbine components operate predominantly under elevated temperature and high stress, and consequently gradual deformation becomes temporally inevitable. In turbine blades, creep is common failure mechanism, and it is an important factor for design assessment. The gas turbine blade is a component operating at high elevated temperatures, requiring a cooling systems to reduce the temperature. Common power enhancement approach is to spray water into compressor, and it is how humidity becomes an important factor in creep failure mechanism. The humidity variability results in temperature level change during the turbine operation, potentially affecting the blades creep life. In this paper, first different creep life prediction models were classified, and then a new model is proposed for creep life considering humidity based on Arrhenius equation. In our study, failure criterion is rupture. As a case study, the creep life of Nimonic-90 alloy turbine blade was predicted using proposed method and compared with FEA results which collected by literature surveys. Proposed model is capable of predicting creep life with only knowing dry temperature (WAR = 0), and there is no need to measure blade temperature variation during operation. The influence of humidity (%WAR) were studied on turbine blades creep life, and results show that creep life of turbine blade increase with increasing humidity percentage.

scholarly journals Recent Development in Turbine Blade Film Cooling

2001 ◽  
Vol 7 (1) ◽  
pp. 21-40 ◽  
Author(s):  
Je-Chin Han ◽  
Srinath Ekkad
Keyword(s):  
Turbine Blade ◽  
Film Cooling ◽  
Gas Turbines ◽  
High Performance ◽  
Pressure Ratio ◽  
Turbine Blades ◽  
Protective Layer ◽  
Turbine Rotor ◽  
Industrial Applications ◽  
Inlet Temperature

Gas turbines are extensively used for aircraft propulsion, land-based power generation, and industrial applications. Thermal efficiency and power output of gas turbines increase with increasing turbine rotor inlet temperature (RIT). The current RIT level in advanced gas turbines is far above the .melting point of the blade material. Therefore, along with high temperature material development, a sophisticated cooling scheme must be developed for continuous safe operation of gas turbines with high performance. Gas turbine blades are cooled internally and externally. This paper focuses on external blade cooling or so-called film cooling. In film cooling, relatively cool air is injected from the inside of the blade to the outside surface which forms a protective layer between the blade surface and hot gas streams. Performance of film cooling primarily depends on the coolant to mainstream pressure ratio, temperature ratio, and film hole location and geometry under representative engine flow conditions. In the past number of years there has been considerable progress in turbine film cooling research and this paper is limited to review a few selected publications to reflect recent development in turbine blade film cooling.

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.

A Multistage Creep Damage Constitutive Model for Isotropic and Transversely-Isotropic Materials With Elastic Damage

2011 ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon
Keyword(s):  
Constitutive Model ◽  
Creep Deformation ◽  
Constitutive Models ◽  
Creep Damage ◽  
Transversely Isotropic ◽  
Common Source ◽  
Isotropic Materials ◽  
Damage Constitutive Model ◽  
Transversely Isotropic Materials ◽  
Elastic Damage

In the pressure vessel and piping and power industries, creep deformation has continued to be an important design consideration. Directionally-solidified components have become commonplace. Creep deformation and damage is a common source of component failure. A considerable effort has gone into the study and development of constitutive models to account for such behavior. Creep deformation can be separated into three distinct regimes: primary, secondary, and tertiary. Most creep damage constitutive models are designed to model only one or two of these regimes. In this paper, a multistage creep damage constitutive model is developed and designed to model all three regimes of creep for isotropic materials. A rupture and critical damage prediction method follows. This constitutive model is then extended for transversely-isotropic materials. In all cases, the influence of creep damage on general elasticity (elastic damage) is included. Methods to determine material constants from experimental data are detailed. Finally, the isotropic material model is exercised on tough pitch copper tube and the anisotropic model on a Ni-base superalloy.

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