scholarly journals Probabilistic Modeling of Slip System-Based Shear Stresses and Fatigue Behavior of Coarse-Grained Ni-Base Superalloy Considering Local Grain Anisotropy and Grain Orientation

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 813 ◽  
Author(s):  
Engel ◽  
Mäde ◽  
Lion ◽  
Moch ◽  
Gottschalk ◽  
...  
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Test Data ◽  
Grain Orientation ◽  
Fatigue Behavior ◽  
Coarse Grained ◽  
Shear Stresses ◽  
Grain Sizes ◽  
Crack Initiation Life ◽  
Base Superalloy

New probabilistic lifetime approaches for coarse grained Ni-base superalloys supplement current deterministic gas turbine component design philosophies; in order to reduce safety factors and push design limits. The models are based on statistical distributions of parameters, which determine the fatigue behavior under high temperature conditions. In the following paper, Low Cycle Fatigue (LCF) test data of several material batches of polycrystalline Ni-base superalloy René80 with different grain sizes and orientation distribution (random and textured) is presented and evaluated. The textured batch, i.e., with preferential grain orientation, showed higher LCF life. Three approaches to probabilistic crack initiation life modeling are presented. One is based on Weibull distributed crack initiation life while the other two approaches are based on probabilistic Schmid factors. In order to create a realistic Schmid factor distribution, polycrystalline finite element models of the specimens were generated using Voronoi tessellations and the local mechanical behavior investigated in dependence of different grain sizes and statistically distributed grain orientations. All models were first calibrated with test data of the material with random grain orientation and then used to predict the LCF life of the material with preferential grain orientation. By considering the local multiaxiality and resulting inhomogeneous shear stress distributions, as well as grain interaction through polycrystalline Finite Element Analysis (FEA) simulation, the best consistencies between predicted and observed crack initiation lives could be achieved.

Thermomechanical Fatigue Behavior of a Directionally Solidified Ni-Base Superalloy

2005 ◽  
Vol 127 (3) ◽  
pp. 325-336 ◽  
Author(s):  
M. M. Shenoy ◽  
A. P. Gordon ◽  
D. L. McDowell ◽  
R. W. Neu
Keyword(s):  
Crack Initiation ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Material Behavior ◽  
Directionally Solidified ◽  
Creep Tests ◽  
Physically Based ◽  
Estimation Scheme ◽  
Crack Initiation Life ◽  
Base Superalloy

A continuum crystal plasticity model is used to simulate the material behavior of a directionally solidified Ni-base superalloy, DS GTD-111, in the longitudinal and transverse orientations. Isothermal uniaxial fatigue tests with hold times and creep tests are conducted at temperatures ranging from room temperature (RT) to 1038°C to characterize the deformation response. The constitutive model is implemented as a User MATerial subroutine (UMAT) in ABAQUS (2003, Hibbitt, Karlsson, and Sorensen, Inc., Providence, RI, v6.3) and a parameter estimation scheme is developed to obtain the material constants. Both in-phase and out-of-phase thermo-mechanical fatigue tests are conducted. A physically based model is developed for correlating crack initiation life based on the experimental life data and predictions are made using the crack initiation model.

scholarly journals Effect of local anisotropy on fatigue crack initiation in a coarse grained nickel-base superalloy

2018 ◽  
Vol 165 ◽  
pp. 04004 ◽  
Author(s):  
Benedikt Engel ◽  
Tilmann Beck ◽  
Nadine Moch ◽  
Hanno Gottschalk ◽  
Sebastian Schmitz
Keyword(s):  
Shear Stress ◽  
Crack Initiation ◽  
Grain Orientation ◽  
Stress Amplitude ◽  
Fatigue Crack Initiation ◽  
Coarse Grained ◽  
Nickel Base Superalloy ◽  
Schmid Factor ◽  
Nickel Base ◽  
Base Superalloy

In the present work, theoretical approaches, based on grain orientation dependent Young’s modulus and Schmid factor are used to describe the influence of local grain orientation on crack initiation behaviour of the coarse grained nickel base superalloy René80. Especially for strongly anisotropic crystal structures with large grain size, such as the investigated material, the local elastic properties must be taken into account for assessment of fatigue crack initiation. With an extension of Schmid’s law, the resulting shear stress amplitude, which triggers local cyclic plastic deformation, can be calculated depending on local Young`s modulus and Schmid factor. A Monte Carlo simulation with 100,000 samples shows how random grain orientation affects these parameters. Furthermore, the product of Young`s modulus and Schmid factor (called E·m) is used as a parameter to determine how grain orientation influences resulting shear stress amplitude for given total strain amplitude. In addition to the theoretical work using that approach, this model is also validated using isothermal LCF experiments by determining local grain orientation influence on the crack initiation site using SEM-EBSD analyses.

Fatigue Behavior of Circumferentially Notched Round Bars of Austenitic Stainless Steel Under Torsional and Axial Loads

2010 ◽  
Author(s):  
Masao Itatani ◽  
Keisuke Tanaka ◽  
Isao Ohkawa ◽  
Takehisa Yamada ◽  
Toshiyuki Saito
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Static Tension ◽  
Cyclic Torsion ◽  
Cyclic Tension ◽  
Crack Initiation Life

Fatigue tests of smooth and notched round bars of austenitic stainless steels SUS316NG and SUS316L were conducted under cyclic tension and cyclic torsion with and without static tension. Fatigue strength under fully reversed (R=−1) cyclic tension once increased with increasing stress concentration factor up to Kt=1.5, but it decreased from Kt=1.5 to 2.5. Fatigue life increased with increasing stress concentration under pure cyclic torsion, while it decreased with increasing stress concentration under cyclic torsion with static tension. From the measurement of fatigue crack initiation and propagation lives using electric potential drop method, it was found that the crack initiation life decreased with increasing stress concentration and the crack propagation life increased with increasing stress concentration under pure cyclic torsion. Under cyclic torsion with static tension, the crack initiation life also decreased with increasing stress concentration but the crack propagation life decreased or not changed with increasing stress concentration then the total fatigue life of sharper notched specimen decreased. It was also found that the fatigue life of smooth specimen under cyclic torsion with static tension was longer than that under pure cyclic torsion. This behavior could be explained based on the cyclic strain hardening under non-proportional loading and the difference in crack path with and without static tension.

scholarly journals Experimental and Numerical Crack Initiation Analysis of the Compressor Blades Working in Resonance Conditions

2011 ◽  
Vol 2011 (3) ◽  
pp. 134-153
Author(s):  
Lucjan Witek
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Transverse Vibration ◽  
Numerical Models ◽  
Fatigue Behavior ◽  
Time History ◽  
Fatigue Properties ◽  
Compressor Blades ◽  
Blade Vibration ◽  
Number Of Cycles

Experimental and Numerical Crack Initiation Analysis of the Compressor Blades Working in Resonance ConditionsThis paper presents the results of a complex experimental and numerical crack initiation analysis of the helicopter turbo-engine compressor blades subjected to vibrations. A nonlinear finite element method was utilized to determine the stress state of the blade during the first mode of transverse vibration. In this analysis, the numerical models without defects as well as those with V-notches were defined. The quality of the numerical solution was checked by the convergence analysis. The obtained results were next used as an input data into crack initiation (ε-N) analyses performed for the load time history equivalent to one cycle of the transverse vibration. In the fatigue analysis, the different methods such as: Neuber elastic-plastic strain correction, linear damage summation and Palmgreen-Miner rule were utilized. As a result of ε-N analysis, the number of load cycles to the first fatigue crack appearing in the compressor blades was obtained. Moreover, the influence of the blade vibration amplitude on the number of cycles to the crack initiation was analyzed. Values of the fatigue properties of the blade material were calculated using the Baumel-Seeger and Muralidharan methods. The influence of both the notch radius and values of the UTS of the blade material on the fatigue behavior of the structure was also considered. In the last part of the work, the finite element results were compared with the results of experimental vibration HCF tests performed for the compressor blades.

Fatigue Analysis of Locking Parts in the Gauge-Adjustable Wheelsets System Considering the Variation of the Fatigue Strength

2008 ◽  
Vol 33-37 ◽  
pp. 217-222 ◽  
Author(s):  
Chul Su Kim ◽  
Cheon Soo Jang ◽  
Seung Ho Jang ◽  
Jung Kyu Kim
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Fatigue Strength ◽  
Crack Initiation ◽  
Fatigue Analysis ◽  
Railroad Network ◽  
Fatigue Data ◽  
Curved Track ◽  
Crack Initiation Life ◽  
The Cost

To reduce the cost and time of transport due to the different track gauges(narrow, standard, broad) in the Eurasian railroad network such as TKR(Trans-Korea Railway), TCR(Trans-China Railway) and TSR(Trans-Siberia Railway), it is very necessary to develop and adapt the gauge-adjustable wheelsets system. The freight trains’ with gauge-adjustable system could operate on the different track gauges in the transcontinental railway. Therefore, to assure the safety of the newly developed gauge-adjustment wheelsets system, it is essential to evaluate integrity of locking parts in the system by using fatigue analysis. In this study, it was performed that contact stress analysis of locking parts by using FEM(Finite Element Method) in the case both the gauge changeover operation and freight trains' service in the curved track, respectively. Besides, to consider the variation of fatigue data, the crack initiation life was statistically evaluated.

scholarly journals Interactions between geometrical defects and microstructure during high cycle fatigue of polycrystalline aluminium with different grain sizes

2018 ◽  
Vol 165 ◽  
pp. 14004
Author(s):  
Benoît Bracquart ◽  
Charles Mareau ◽  
Nicolas Saintier ◽  
Franck Morel
Keyword(s):  
Grain Size ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Cycle Fatigue ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Geometrical Defects

In this work, the influence of the geometrical defect size on the high cycle fatigue behavior of polycrystalline aluminium with different grain sizes is investigated, to better understand the role of internal length scales. Two sizes of grains and defect are used: 100 μm and 1000 μm, the grain size being controlled with thermomechanical treatments. Fully reversed stress-controlled fatigue tests are then carried out. According to fatigue test results, surface crack initiation is delayed when the grain size is reduced, while an approximation of the fatigue limit shows that it is not much influenced by the average grain size. The relative defect diameter (compared to the grain size) seems to be the leading parameter influencing fatigue crack initiation from a defect. Finally, Electron BackScattered Diffraction (EBSD) maps are collected for specimens with large grains and small defects. Fatigue crack initiation from a defect is found to be strongly impacted by the crystallographic orientation of the surrounding grain, crack initiation preferably occurring in crystals being favorably oriented for plastic slip.

Subsurface Stress Fields in Face-Centered-Cubic Single-Crystal Anisotropic Contacts

2005 ◽  
Vol 128 (4) ◽  
pp. 879-888 ◽  
Author(s):  
Nagaraj K. Arakere ◽  
Erik Knudsen ◽  
Gregory R. Swanson ◽  
Gregory Duke ◽  
Gilda Ham-Battista
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Single Crystal ◽  
Turbine Blades ◽  
Stress Fields ◽  
Shear Stresses ◽  
Face Centered Cubic ◽  
Subsurface Stress

Single-crystal superalloy turbine blades used in high-pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high-cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single-crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two- and three-dimensional (3D) subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single-crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii (1963, Theory of Elasticity of an Anisotropic Elastic Body, Holden-Day, Inc., San Francisco, pp. 1–40). Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis. Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single-crystal contact problems require extremely refined 3D finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses on the principal slip planes also involves considerable postprocessing work. For these reasons, it is very advantageous to develop analytical solution schemes for subsurface stresses, whenever possible.

Effect of Recrystallization on Low-Cycle Fatigue Behavior of DZ4 Directionally-Solidified Superalloy

2006 ◽  
Vol 306-308 ◽  
pp. 175-180 ◽  
Author(s):  
Hui Ji Shi ◽  
Hai Feng Zhang ◽  
Yan Qing Wu
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Grain Boundaries ◽  
Shot Peening ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Nickel Base Superalloy ◽  
Directionally Solidified ◽  
Crack Initiation Life

Effect of recrystallization on DZ4 directionally-solidified nickel-base superalloy was investigated both at room temperature and high temperature of 673K. In-situ SEM surface observation were performed. Experimental results reveal that the material performance is strongly influenced by surface recrystallization layer. All specimens were prepared under conditions of shot peening and 4h 1220°C high temperature annealing. Different shot peening pressure specimens have different recrystallization states. High shot penning pressure specimens have clear and straight grain boundaries and the grain size appears to be a little bit larger. Recrystallization state seems not only affect the fatigue life, but also the crack initiation pattern and crack initiation life. Low shot peening pressure specimens have much lower fatigue life which is around 8-10% of virgin one, and SEM Real-time observation reveals that channeling cracks initiated at the early stage of fatigue life. High shot peening pressure specimens have higher fatigue life comparing to low shot peening pressure specimens, although it’s almost half lower than the virgin one, and cracks initiated not until middle or latter stage of fatigue life. Crack initiation life is also much longer than those of low shot peening pressure. Low shot peening pressure specimens seems not fully recrystallized, and its grain boundaries are much fragile which is responsible for high density microcracks initiation, and finally leads to the failure. Further nano-indention experiments on surface recrystallized layers show that higher shot peening recrystallized layers have much lower elastic module, which may explain the longer crack initiation life.

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