Creep-Fatigue Behaviors and Life Assessments in Two Nickel-Based Superalloys

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Run-Zi Wang ◽  
Ji Wang ◽  
Jian-Guo Gong ◽  
Xian-Cheng Zhang ◽  
Shan-Tung Tu ◽  
...  
Keyword(s):  
Maximum Likelihood ◽  
Bayesian Information Criterion ◽  
Dwell Time ◽  
Strain Range ◽  
Information Criterion ◽  
Strain Ratio ◽  
Fatigue Data ◽  
Creep Fatigue ◽  
Principle Of Parsimony ◽  
Damage Summation

The aim of this paper is to investigate different factors, including dwell time, strain range, and strain ratio on creep-fatigue endurances in nickel-based Inconel 718 and GH4169 superalloys. We also summarize classic approaches for life assessments based on the generalizations of Coffin–Manson equation, linear damage summation (LDS), and strain-range partitioning (SRP) method. Each approach does have some degree of success in dealing with a specific set of creep–fatigue data. In order to evaluate the prediction capabilities of the validated approaches, a Bayesian information criterion (BIC) allowing for maximum likelihood and principle of parsimony is used to select the best performing model.

Biaxial Thermomechanical-Fatigue Life Property of a Directionally Solidified Ni-Base Superalloy

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Takashi Ogata
Keyword(s):  
Fatigue Life ◽  
Shear Strain ◽  
Hold Time ◽  
Strain Range ◽  
Strain Ratio ◽  
Life Assessment ◽  
Wave Form ◽  
Creep Fatigue ◽  
High Temperature Components ◽  
Failure Life

High-temperature components in thermal power plants are subjected to creep-fatigue loading where creep cavities initiate and grow on grain boundaries. Development of life assessment methods of high-temperature components in gas turbine for maintenance and operating cost reduction is strongly demanded by Japanese utilities. Especially, first row blades are subjected to complicated thermomechanical-fatigue (TMF) loading during start, steady state, stop cycles. Therefore it is important to clarify the TMF life property of blade materials to develop a life assessment procedure. In this study, tension-torsion biaxial TMF tests have been performed between 450°C and 870°C on a Ni-base directional solidified superalloy. Strain ratio ϕ was defined as shear strain range, Δγ, to normal strain range, Δε, and ϕ varied from 0 to infinity. The “Blade wave form,” which simulated temperature and strain condition of the blade surface, was employed. The biaxial TMF tests were also carried out on coated specimens with CoCrAlY. Fatigue life under the biaxial TMF loading showed strain ratio dependency giving shorter life with increasing ϕ. Considering biaxial stress effect on the failure life, an equivalent shear strain range was derived based on the Γ-plane theory, and the biaxial TMF life was well correlated with the equivalent shear strain range. The biaxial TMF life was reduced by introducing strain hold duration at the maximum temperature. The maximum stress increased by introducing the hold time due to increasing mean stress level in the Blade wave form. It was concluded that creep damage gradually accumulated during cycles resulting in reduction in the TMF life. The nonlinear creep-fatigue damage accumulation model was applied to predict failure life of the hold time tests. As a result, the failure lives were predicted within a factor of 1.5 on the observed life. It was found that the fatigue life of CoCrAlY coated material reduced 1∕2 to 1∕3 from that of the substrate. From observation of the longitudinal section of the coated specimens, many cracks started from the coating surface and penetrated into the substrate. It was concluded that the CoCrAlY coating reduced the biaxial TMF life due to acceleration of crack initiation period in the substrate.

scholarly journals Word2vec Skip-Gram Dimensionality Selection via Sequential Normalized Maximum Likelihood

Entropy ◽  
2021 ◽  
Vol 23 (8) ◽  
pp. 997
Author(s):  
Pham Thuc Hung ◽  
Kenji Yamanishi
Keyword(s):  
Probability Theory ◽  
Maximum Likelihood ◽  
Bayesian Information Criterion ◽  
Minimum Description Length ◽  
Information Criterion ◽  
Information Criteria ◽  
Efficient Computation ◽  
Data Sequence ◽  
Word Similarity ◽  
Normalized Maximum Likelihood

In this paper, we propose a novel information criteria-based approach to select the dimensionality of the word2vec Skip-gram (SG). From the perspective of the probability theory, SG is considered as an implicit probability distribution estimation under the assumption that there exists a true contextual distribution among words. Therefore, we apply information criteria with the aim of selecting the best dimensionality so that the corresponding model can be as close as possible to the true distribution. We examine the following information criteria for the dimensionality selection problem: the Akaike’s Information Criterion (AIC), Bayesian Information Criterion (BIC), and Sequential Normalized Maximum Likelihood (SNML) criterion. SNML is the total codelength required for the sequential encoding of a data sequence on the basis of the minimum description length. The proposed approach is applied to both the original SG model and the SG Negative Sampling model to clarify the idea of using information criteria. Additionally, as the original SNML suffers from computational disadvantages, we introduce novel heuristics for its efficient computation. Moreover, we empirically demonstrate that SNML outperforms both BIC and AIC. In comparison with other evaluation methods for word embedding, the dimensionality selected by SNML is significantly closer to the optimal dimensionality obtained by word analogy or word similarity tasks.

scholarly journals Maximum Likelihood Analysis of Rare Binary Traits Under Different Modes of Inheritance

Genetics ◽  
1996 ◽  
Vol 143 (4) ◽  
pp. 1819-1829 ◽  
Author(s):  
G Thaller ◽  
L Dempfle ◽  
I Hoeschele
Keyword(s):  
Maximum Likelihood ◽  
Mixed Model ◽  
Major Gene ◽  
Likelihood Ratio Statistic ◽  
Information Criterion ◽  
Genetic Models ◽  
Parameter Estimates ◽  
Gene Effects ◽  
Binary Traits ◽  
Deterministic Algorithms

Abstract Maximum likelihood methodology was applied to determine the mode of inheritance of rare binary traits with data structures typical for swine populations. The genetic models considered included a monogenic, a digenic, a polygenic, and three mixed polygenic and major gene models. The main emphasis was on the detection of major genes acting on a polygenic background. Deterministic algorithms were employed to integrate and maximize likelihoods. A simulation study was conducted to evaluate model selection and parameter estimation. Three designs were simulated that differed in the number of sires/number of dams within sires (10/10, 30/30, 100/30). Major gene effects of at least one SD of the liability were detected with satisfactory power under the mixed model of inheritance, except for the smallest design. Parameter estimates were empirically unbiased with acceptable standard errors, except for the smallest design, and allowed to distinguish clearly between the genetic models. Distributions of the likelihood ratio statistic were evaluated empirically, because asymptotic theory did not hold. For each simulation model, the Average Information Criterion was computed for all models of analysis. The model with the smallest value was chosen as the best model and was equal to the true model in almost every case studied.

The influence of biaxial strain ratio and strain range on crack growth mode and crack shape

2010 ◽  
Vol 46 (1) ◽  
pp. 215-227 ◽  
Author(s):  
T. H. Topper ◽  
J. J. F. Bonnen ◽  
M. Khalil ◽  
A. Varvani-Farahani
Keyword(s):  
Crack Growth ◽  
Strain Range ◽  
Strain Ratio ◽  
Growth Mode ◽  
Biaxial Strain ◽  
Crack Shape

Solder Creep-Fatigue Interactions With Flexible Leaded Parts

1992 ◽  
Vol 114 (2) ◽  
pp. 185-192 ◽  
Author(s):  
R. G. Ross ◽  
L. C. Wen ◽  
G. R. Mon ◽  
E. Jetter
Keyword(s):  
Computer Program ◽  
Strain Rate ◽  
Thermal Cycle ◽  
Failure Process ◽  
Strain Range ◽  
Strain Rate Effects ◽  
Rate Effects ◽  
Creep Fatigue ◽  
Solder Fatigue

With flexible leaded parts, the solder-joint failure process involves a complex interplay of creep and fatigue mechanisms. To better understand the role of creep in typical multi-hour cyclic loading conditions, a specialized non-linear finite-element creep simulation computer program has been formulated. The numerical algorithm includes the complete part-lead-solder-PWB system, accounting for strain-rate dependence of creep on applied stress and temperature, and the role of the part-lead dimensions and flexibility that determine the total creep deflection (solder strain range) during stress relaxation. The computer program has been used to explore the effects of various solder creep-fatigue parameters such as lead height and stiffness, thermal-cycle test profile, and part/board differential thermal expansion properties. One of the most interesting findings is the strong presence of unidirectional creep-ratcheting that occurs during thermal cycling due to temperature dominated strain-rate effects. To corroborate the solder fatigue model predictions, a number of carefully controlled thermal-cycle tests have been conducted using special bimetallic test boards.

scholarly journals Model Selection Procedures in Bounds Test of Cointegration: Theoretical Comparison and Empirical Evidence

Economies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 49 ◽  
Author(s):  
Waqar Badshah ◽  
Mehmet Bulut
Keyword(s):  
Model Selection ◽  
Akaike Information Criterion ◽  
Bayesian Information Criterion ◽  
Selection Process ◽  
Information Criterion ◽  
Small Sample ◽  
Information Criteria ◽  
Path Model ◽  
Sample Sizes ◽  
Bounds Test

Only unstructured single-path model selection techniques, i.e., Information Criteria, are used by Bounds test of cointegration for model selection. The aim of this paper was twofold; one was to evaluate the performance of these five routinely used information criteria {Akaike Information Criterion (AIC), Akaike Information Criterion Corrected (AICC), Schwarz/Bayesian Information Criterion (SIC/BIC), Schwarz/Bayesian Information Criterion Corrected (SICC/BICC), and Hannan and Quinn Information Criterion (HQC)} and three structured approaches (Forward Selection, Backward Elimination, and Stepwise) by assessing their size and power properties at different sample sizes based on Monte Carlo simulations, and second was the assessment of the same based on real economic data. The second aim was achieved by the evaluation of the long-run relationship between three pairs of macroeconomic variables, i.e., Energy Consumption and GDP, Oil Price and GDP, and Broad Money and GDP for BRICS (Brazil, Russia, India, China and South Africa) countries using Bounds cointegration test. It was found that information criteria and structured procedures have the same powers for a sample size of 50 or greater. However, BICC and Stepwise are better at small sample sizes. In the light of simulation and real data results, a modified Bounds test with Stepwise model selection procedure may be used as it is strongly theoretically supported and avoids noise in the model selection process.

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