Influence of Extremum Temperatures on TMF of a Ni-Base Superalloy

2014 ◽  
Vol 891-892 ◽  
pp. 1314-1319 ◽  
Author(s):  
Michael M. Kirka ◽  
Sachin R. Shinde ◽  
Phillip W. Gravett ◽  
Richard W. Neu
Keyword(s):  
Elastic Modulus ◽  
Minimum Temperature ◽  
Mechanical Strain ◽  
Strain Range ◽  
Inelastic Strain ◽  
Thermomechanical Fatigue ◽  
Maximum Temperature ◽  
Cycle Temperature ◽  
Base Superalloy

Significantly reducing the minimum temperature while maintaining maximum temperature of thermomechanical fatigue (TMF) cycles can reduce the life even when mechanical strain ranges are similar. This applies to in-phase (IP) and out-of-phase (OP) TMF cycles. This reduction in life has generally been attributed to a combination of changes in microstructure arising from aging and increases in the cyclic inelastic strain promoted by increases in the elastic modulus as the minimum cycle temperature is reduced. TMF cycles under both IP and OP conditions were conducted with maximum cycle temperatures within the 750-950C range and with minimum cycle temperatures of either 100 or 500C. A reduction in minimum temperature was observed to promote a decrease in TMF life by as much as a factor of ten for all TMF experiments. The reduction in TMF life is primarily controlled by increases in the inelastic strain range associated with increases in the elastic modulus that arise when the minimum temperature is reduced.

scholarly journals Thermo-Mechanical Fatigue of the Nickel–Base Superalloy Nimonic 90

2007 ◽  
Vol 345-346 ◽  
pp. 347-350 ◽  
Author(s):  
M. Marchionni ◽  
Hellmuth Klingelhöffer ◽  
Hans Joachim Kühn ◽  
T. Ranucci ◽  
Kathrin Matzak
Keyword(s):  
Cooling System ◽  
Mechanical Strain ◽  
Hysteresis Loops ◽  
Strain Ratio ◽  
Maximum Temperature ◽  
Nickel Base Superalloy ◽  
Fatigue Striations ◽  
Mechanical Fatigue ◽  
Nickel Base ◽  
Base Superalloy

The thermo-mechanical fatigue (TMF) behaviour of the Nimonic 90 Nickel base superalloy has been investigated within two laboratories. In-phase-tests (IP) where the maximum mechanical strain occurs at the maximum temperature (850°C), and 180°-out-of-phase-tests (180° OP) where the maximum mechanical strain coincides with the minimum temperature (400°C) have been applied. All tests were carried out at varying mechanical strain ranges with a constant strain ratio of Rε = - 1. A temperature rate of 5 K/s was used throughout the whole cycle without any additional cooling system during decreasing temperature. The fatigue life of 180° OP tests is longer compared to identical IP tests. The stress / mechanical strain hysteresis loops are completely different and some characteristic values are compared to each other. The fracture surfaces observed show that fatigue crack (or cracks) starts on the external surface and propagates inwards. The fractures of 180° OP tests are transgranular showing the presence of fatigue striations, while the fractures of IP tests are mixed transgranular and intergranular with no fatigue striations.

Thermomechanical Fatigue of Mar-M247: Extension of a Unified Constitutive and Life Model to Higher Temperatures

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
K. A. Brindley ◽  
M. M. Kirka ◽  
P. Fernandez-Zelaia ◽  
R. W. Neu
Keyword(s):  
Kinematic Hardening ◽  
Thermomechanical Fatigue ◽  
Coarse Grained ◽  
Elastic Response ◽  
Maximum Temperature ◽  
Environmental Damage ◽  
Flow Rule ◽  
Life Model ◽  
Creep And Stress Relaxation ◽  
Base Superalloy

The predictive capability of the Sehitoglu–Boismier unified constitutive and life model for Mar-M247 Ni-base superalloy is extended from a maximum temperature of 871 °C to 1038 °C. The unified constitutive model suitable for thermomechanical loading is adapted and calibrated using the response from isothermal cyclic experiments conducted at temperatures from 500 °C to 1038 °C at different strain rates with and without dwells. The flow rule function and parameters as well as the temperature dependence of the evolution equation for kinematic hardening are established. Creep and stress relaxation are critical to capture in this elevated temperature regime. The coarse-grained polycrystalline microstructure exhibits a high variability in the predicted cyclic response due to the variation in the elastic response associated with the orientation of the crystallographic grains. The life model accounts for fatigue, creep, and environmental damage under both isothermal and thermomechanical fatigue (TMF).

Microstructure and Thermomechanical Fatigue Behavior of Directionally Solidified Ni-Based Superalloys in OP Condition

2018 ◽  
Author(s):  
Dongyi Seo ◽  
Seong-Moon Seo ◽  
Young-Soo Yoo ◽  
Daejin Kim
Keyword(s):  
Numerical Simulation ◽  
Loading Condition ◽  
Fatigue Behavior ◽  
Mechanical Strain ◽  
Strain Range ◽  
Damage Mechanism ◽  
Longitudinal Section ◽  
Thermomechanical Fatigue ◽  
The Other ◽  
Directionally Solidified

Two directionally solidified (DS) Ni-base superalloys, one with the GTD-111 composition and the other with a modified composition derived by numerical simulation, were produced using the Bridgman method. Solution and aging heat treatments were applied to the DS alloys to produce the desired microstructures. Thermomechanical fatigue (TMF) tests were conducted under fully reversed mechanical strain (R = −1) in the temperature range of 538–927°C in laboratory air. The tests were performed under the out-of-phase (OP) loading condition at the mechanical strain range of 0.8–1.5% with multiple specimens tested at each test condition to confirm the trend in fatigue lives. In general, the OP-TMF lives of the DS alloys depended on the applied mechanical strain range as well as the microstructural features of the alloys. By analyzing the fracture surface and longitudinal section of the tested specimens, the TMF lives of the DS alloys tested at mechanical strain ranges lower than 1.5% were found to be primarily affected by the coarse carbides formed in the interdendritic regions. In this study, the main damage mechanism of each alloy under the OP-TMF condition was elucidated in terms of its microstructural features, and recommendations were made to control the microstructures of the DS alloys to achieve enhanced TMF resistance.

scholarly journals Spatiotemporal Evolution of Fractional Vegetation Cover and Its Response to Climate Change Based on MODIS Data in the Subtropical Region of China

2021 ◽  
Vol 13 (5) ◽  
pp. 913
Author(s):  
Hua Liu ◽  
Xuejian Li ◽  
Fangjie Mao ◽  
Meng Zhang ◽  
Di’en Zhu ◽  
...  
Keyword(s):  
Vegetation Cover ◽  
Minimum Temperature ◽  
Maximum Temperature ◽  
Distribution Area ◽  
Spatiotemporal Pattern ◽  
Climate Factors ◽  
Important Indicator ◽  
Fractional Vegetation Cover ◽  
Annual Minimum Temperature ◽  
Total Study Area

The subtropical vegetation plays an important role in maintaining the structure and function of global ecosystems, and its contribution to the global carbon balance are receiving increasing attention. The fractional vegetation cover (FVC) as an important indicator for monitoring environment change, is widely used to analyze the spatiotemporal pattern of regional and even global vegetation. China is an important distribution area of subtropical vegetation. Therefore, we first used the dimidiate pixel model to extract the subtropical FVC of China during 2001–2018 based on MODIS land surface reflectance data, and then used the linear regression analysis and the variation coefficient to explore its spatiotemporal variations characteristics. Finally, the partial correlation analysis and the partial derivative model were used to analyze the influences and contributions of climate factors on FVC, respectively. The results showed that (1) the subtropical FVC had obvious spatiotemporal heterogeneity; the FVC high-coverage and medium-coverage zones were concentratedly and their combined area accounted for more than 70% of the total study area. (2) The interannual variation in the average subtropical FVC from 2001 to 2018 showed a significant growth trend. (3) In 76.28% of the study area, the regional FVC showed an increasing trend, and the remaining regional FVC showed a decreasing trend. However, the overall fluctuations in the FVC (increasing or decreasing) in the region were relatively stable. (4) The influences of climate factors to the FVC exhibited obvious spatial differences. More than half of all pixels exhibited the influence of the average annual minimum temperature and the annual precipitation had positive on FVC, while the average annual maximum temperature had negative on FVC. (5) The contributions of climate changes to FVC had obvious heterogeneity, and the average annual minimum temperature was the main contribution factor affecting the dynamic variations of FVC.

scholarly journals Strong controls of daily minimum temperature on the autumn photosynthetic phenology of subtropical vegetation in China

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Peixin Ren ◽  
Zelin Liu ◽  
Xiaolu Zhou ◽  
Changhui Peng ◽  
Jingfeng Xiao ◽  
...  
Keyword(s):  
Climate Change ◽  
Minimum Temperature ◽  
Vegetation Index ◽  
Climatic Factors ◽  
Time Lag ◽  
Evergreen Forest ◽  
Maximum Temperature ◽  
Daily Minimum Temperature ◽  
Study Region ◽  
Cumulative Precipitation

Abstract Background Vegetation phenology research has largely focused on temperate deciduous forests, thus limiting our understanding of the response of evergreen vegetation to climate change in tropical and subtropical regions. Results Using satellite solar-induced chlorophyll fluorescence (SIF) and MODIS enhanced vegetation index (EVI) data, we applied two methods to evaluate temporal and spatial patterns of the end of the growing season (EGS) in subtropical vegetation in China, and analyze the dependence of EGS on preseason maximum and minimum temperatures as well as cumulative precipitation. Our results indicated that the averaged EGS derived from the SIF and EVI based on the two methods (dynamic threshold method and derivative method) was later than that derived from gross primary productivity (GPP) based on the eddy covariance technique, and the time-lag for EGSsif and EGSevi was approximately 2 weeks and 4 weeks, respectively. We found that EGS was positively correlated with preseason minimum temperature and cumulative precipitation (accounting for more than 73% and 62% of the study areas, respectively), but negatively correlated with preseason maximum temperature (accounting for more than 59% of the study areas). In addition, EGS was more sensitive to the changes in the preseason minimum temperature than to other climatic factors, and an increase in the preseason minimum temperature significantly delayed the EGS in evergreen forests, shrub and grassland. Conclusions Our results indicated that the SIF outperformed traditional vegetation indices in capturing the autumn photosynthetic phenology of evergreen forest in the subtropical region of China. We found that minimum temperature plays a significant role in determining autumn photosynthetic phenology in the study region. These findings contribute to improving our understanding of the response of the EGS to climate change in subtropical vegetation of China, and provide a new perspective for accurately evaluating the role played by evergreen vegetation in the regional carbon budget.

scholarly journals The effect of average temperature on suicide rates in five urban California counties, 1999–⁠2019: an ecological time series analysis

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Sierra Cheng ◽  
Rebecca Plouffe ◽  
Stephanie M. Nanos ◽  
Mavra Qamar ◽  
David N. Fisman ◽  
...  
Keyword(s):  
Public Health ◽  
Suicide Rate ◽  
Minimum Temperature ◽  
The United States ◽  
Additive Models ◽  
Maximum Temperature ◽  
Mortality Data ◽  
Average Temperature ◽  
Suicide Rates ◽  
Average Maximum

Abstract Background Suicide is among the top 10 leading causes of premature morality in the United States and its rates continue to increase. Thus, its prevention has become a salient public health responsibility. Risk factors of suicide transcend the individual and societal level as risk can increase based on climatic variables. The purpose of the present study is to evaluate the association between average temperature and suicide rates in the five most populous counties in California using mortality data from 1999 to 2019. Methods Monthly counts of death by suicide for the five counties of interest were obtained from CDC WONDER. Monthly average, maximum, and minimum temperature were obtained from nCLIMDIV for the same time period. We modelled the association of each temperature variable with suicide rate using negative binomial generalized additive models accounting for the county-specific annual trend and monthly seasonality. Results There were over 38,000 deaths by suicide in California’s five most populous counties between 1999 and 2019. An increase in average temperature of 1 °C corresponded to a 0.82% increase in suicide rate (IRR = 1.0082 per °C; 95% CI = 1.0025–1.0140). Estimated coefficients for maximum temperature (IRR = 1.0069 per °C; 95% CI = 1.0021–1.0117) and minimum temperature (IRR = 1.0088 per °C; 95% CI = 1.0023–1.0153) were similar. Conclusion This study adds to a growing body of evidence supporting a causal effect of elevated temperature on suicide. Further investigation into environmental causes of suicide, as well as the biological and societal contexts mediating these relationships, is critical for the development and implementation of new public health interventions to reduce the incidence of suicide, particularly in the face increasing temperatures due to climate change.

scholarly journals Effects of Cropland Expansion on Temperature Extremes in Western India from 1982 to 2015

Land ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 489
Author(s):  
Jinxiu Liu ◽  
Weihao Shen ◽  
Yaqian He
Keyword(s):  
Land Use ◽  
Heat Flux ◽  
Land Cover ◽  
Minimum Temperature ◽  
Negative Impact ◽  
Maximum Temperature ◽  
Daily Minimum Temperature ◽  
Daily Maximum ◽  
Temperature Extremes ◽  
Western India

India has experienced extensive land cover and land use change (LCLUC). However, there is still limited empirical research regarding the impact of LCLUC on climate extremes in India. Here, we applied statistical methods to assess how cropland expansion has influenced temperature extremes in India from 1982 to 2015 using a new land cover and land use dataset and ECMWF Reanalysis V5 (ERA5) climate data. Our results show that during the last 34 years, croplands in western India increased by ~33.7 percentage points. This cropland expansion shows a significantly negative impact on the maxima of daily maximum temperature (TXx), while its impacts on the maxima of daily minimum temperature and the minima of daily maximum and minimum temperature are limited. It is estimated that if cropland expansion had not taken place in western India over the 1982 to 2015 period, TXx would likely have increased by 0.74 (±0.64) °C. The negative impact of croplands on reducing the TXx extreme is likely due to evaporative cooling from intensified evapotranspiration associated with croplands, resulting in increased latent heat flux and decreased sensible heat flux. This study underscores the important influences of cropland expansion on temperature extremes and can be applicable to other geographic regions experiencing LCLUC.

Observations on 287 thunder-storms made at highfield house, near Nottingham, during the last nine years

1851 ◽  
Vol 5 ◽  
pp. 957-957
Keyword(s):  
Minimum Temperature ◽  
Maximum Temperature ◽  
Tabular Form ◽  
The Hours ◽  
The Mean ◽  
Atmospheric Phenomena ◽  
Rotatory Motion

The thunder-storms referred to in this communication are recorded in a tabular form., arranged according to their dates. In this table are given the date; the hour of the commencement of the storm; the mean height of the barometer to tenths of an inch; whether it is rising, stationary, or falling; the direction of the wind before the storm, during its continuance, and after its cessation; the maximum temperature on the day of the storm and on the day after; the minimum temperature on the night before and on the night after; and general remarks on the storms. This table is followed by remarks on particular storms recorded in it. In conclusion the author gives the results of his observations with reference to the number of storms in each year; the number in each month, with the hours at which they mostly occur in particular months; the number that have occurred with a rising, stationary, or falling barometer; the number in respect to the direction of the wind and of the current in which the storms moved; the number of storms that have occurred at the various heights of the maximum, and also of the minimum thermometer; the number in which the peculiar breeze that suddenly springs up on the commencement of thunder-storms has been well marked; the change in the direction of some of these storms, and indications of rotatory motion; and finally, the different atmospheric phenomena which have accompanied these storms.

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