Artykuły w czasopismach: „CREEP ESTIMATION”

1

Bloom, J. M. "Validation of Creep Crack Growth Life Estimation Methodology/Hot Reheat Steam Pipes". Journal of Pressure Vessel Technology 116, nr 3 (1.08.1994): 331–35. http://dx.doi.org/10.1115/1.2929597.

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This paper documents a validation study of a creep crack growth life estimation methodology developed by Riedel and Rice, Saxena, and Bassani which has been implemented into a Babcock & Wilcox computer code. This computer code called PCCREEP was developed for estimation of remaining lives of fossil power plant components with both postulated and in-service determined defects. The initial validation was performed through comparisons with other computer codes. However, these comparisons were limited to continuous operating conditions (steady-state creep) and bulk creep deformation properties for secondary creep only. Even with the independent comparison with other available life estimation codes, the question still remained of how well can the creep crack growth methodology estimate actual field lives? This paper presents the results of a study of a life estimation scheme for hot reheat steam pipes having defects found in service. The initial survey was conducted by the Electric Power Research Institute (EPRI) of U.S. electric utility problems with hot reheat steam pipes. The primary reason for that study was three catastrophic failures of hot reheat steam pipes in 1979, 1985, and 1986. These pipes were seam-welded 1-1/4 Cr-1/2 Mo and 2-1/4 Cr-1 Mo. All these ruptures initiated from flaws (near the weld fusion line) which grew by a creep mechanism. This EPRI data base consisted of twelve pipes with flaws found from inspection. While several assumptions relating to material properties and operating conditions were required (due to insufficient information), predictions demonstrated that life estimation is possible provided material property data representative of the material condition for the component in question is available. Discussion is given regarding the significance of the postulated flaw location, constraint (stress triaxiality) effects for buried flaws, and the importance of weld metal, heat-affected zone, and base metal properties to the accuracy of the life estimations.

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Katinić, Marko, Dorian Turk, Pejo Konjatić i Dražan Kozak. "Estimation of C* Integral for Mismatched Welded Compact Tension Specimen". Materials 14, nr 24 (7.12.2021): 7491. http://dx.doi.org/10.3390/ma14247491.

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The C* integral for the compact tension (CT) specimen is calculated using the estimation equation in ASTM E1457-15. This equation was developed based on the assumption of material homogeneity and is not applicable to a welded CT specimen. In this paper, a modified equation for estimating the C* integral for a welded compact tension (CT) specimen under creep conditions is proposed. The proposed equation is defined on the basis of systematically conducted extensive finite element (FE) analyses using the ABAQUS program. A crack in the welded CT specimen is located in the center of the heat-affected zone (HAZ), because the most severe type IV cracks are located in the HAZ. The results obtained by the analysis show that the equation for estimating the C* integral in ASTM E1457-15 can underestimate the value of the C* integral for creep-soft HAZ and overestimate for creep-hard HAZ. Therefore, the proposed modified equation is suitable for describing the creep crack growth (CCG) of welded specimens.

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3

Abe, Fujio. "Creep modeling and creep life estimation of Gr.91". International Journal of Materials Research 103, nr 6 (czerwiec 2012): 765–73. http://dx.doi.org/10.3139/146.110769.

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Han, Bing, i Qiang Fu. "Study on the Estimation of Rock Rheological Parameters under Multi-level Loading and Unloading Conditions". MATEC Web of Conferences 213 (2018): 02003. http://dx.doi.org/10.1051/matecconf/201821302003.

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Determining reasonable rheological constitutive models based on laboratory rock creep test data and estimating rheological parameters are important means of studying rheological mechanical property of rocks. Previous rock uniaxial or triaxial compression creep tests mostly adopted the method of multi-level loading. In order to study the influence of unloading stress on the estimation of rock rheological parameters, rock triaxial creep tester RLW-2000 was used in this paper to carry out triaxial compression creep tests for granites in a given area with two different stress paths of multi-level loading and stepwise unloading. Study results indicate that rock rheological parameters obtained vary with different stress paths. The instantaneous elastic modulus and viscosity coefficient obtained through loading show a stepwise increase, while the viscoelastic modulus shows a progressive decrease.

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Abdul Ghafir, Mohammad Fahmi, Yi Guang Li, A. A. Wahab, Siti Nur Mariani Mohd Yunos, M. F. Yaakub, Siti Juita Mastura Mohd Salleh, Qamarul Ezani Kamarudin i Mohd Fikri Mohd Masrom. "Impact of Operating and Health Conditions on a Helicopter Turbo-Shaft Hot Section Component Using Creep Factor". Applied Mechanics and Materials 225 (listopad 2012): 239–44. http://dx.doi.org/10.4028/www.scientific.net/amm.225.239.

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The paper investigates the effects of various gas turbine operating and health conditions on its hot section component’s creep life via a simple relative creep life parameter known as Creep Factor. Using the Creep Factor, the correlation between individual gas turbine operating and health parameter and component’s creep life was established and the weight of the impact was measured. Analytical-parametric-based creep life estimation model combined with the Creep Factor approach was developed and integrated with an existing engine performance model to allow the estimation of various hot section component creep lives and the computation of the Creep Factors. The impact analysis was carried out on the high pressure turbine blade of a model turbo-shaft helicopter engine. The results indicate that for a clean engine, the change in engine rotational speed was seen to provide the highest impact on changing the blade’s creep life consumption while for a degraded engine, the presence of compressor fouling has the highest threat in changing the blade’s creep life. The analysis also shows that the Creep Factor is a good indicator of creep life consumption and provides a good technique to rank the influencing factor according to the threat they imposed.

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Ohashi, Kayo, Jun-ichi Arai i Toshiaki Mizobuchi. "Study on estimation of creep behaviour of concrete at early age considering temperature effect". MATEC Web of Conferences 289 (2019): 10010. http://dx.doi.org/10.1051/matecconf/201928910010.

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Clarifying the creep behaviour of concrete at early age not only improves the accuracy of temperature stress analysis but also contributes to prediction accuracy and control measures in cracks caused by thermal stress. However, most past researches on creep behaviour were investigated after 28 days. Currently, it is difficult to accurately perceive the creep behaviour of concrete at an early age in the test method of creep which is generally carried out. Therefore, it is necessary to evaluate the creep behaviour of concrete at early age and to establish a convenient test method to estimate the creep behaviour. Therefore, in this study, experiments were carried out for concrete at early age within one week. As the result of the experiments, it was shown that the creep strain is proportional to the load stress of concrete at an early age and the strain of specific creep decreases as the loaded age increases. In addition, based on the experimental results, an estimation equation for creep strain at early age was proposed. Within the scope of this experimental result, it was confirmed that the estimation equation proposed in this study accurately represented the creep behaviour of concrete at early age.

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N, Shivakumar, i Anbazhagan R. "Estimation of Inexpensive Creep Testing Machine". International Innovative Research Journal of Engineering and Technology 4, nr 3 (30.03.2019): 4–8. http://dx.doi.org/10.32595/iirjet.org/v4i3.2019.80.

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Abe, Fujio. "Creep life estimation of Gr.91 based on creep strain analysis". Materials at High Temperatures 28, nr 2 (czerwiec 2011): 75–84. http://dx.doi.org/10.3184/096034011x13058176494936.

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Niu, Yu Jing, Hong Sheng Cai, Jin Feng Geng, Dong Fang Ma, Guo Dong Ma, Yong Feng Zhao i Xu Yang. "Creep Properties and Life Estimation of P91 Steel with Low Hardness". Advanced Materials Research 842 (listopad 2013): 201–4. http://dx.doi.org/10.4028/www.scientific.net/amr.842.201.

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The creep properties and creep life estimation experiment was carried out on the P91 steel with low hardness (About 135HBHLD),and the creep life of P91 pipe was estimated.The result was that the ability for anti-plastic fracture, cracking and crack propagation of resistance to damage of high pressure steam conduit pipe with low hardness (About 135HBHLD) is very poor at 566°C and that the working life of low hardness zones (About 135HBHLD) from the creep crack propagation tests is about 5914 hours at 540°C.

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Holmström, S., Y. Li, P. Dymacek, E. Vacchieri, S. P. Jeffs, R. J. Lancaster, D. Omacht i in. "Creep strength and minimum strain rate estimation from Small Punch Creep tests". Materials Science and Engineering: A 731 (lipiec 2018): 161–72. http://dx.doi.org/10.1016/j.msea.2018.06.005.

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DOI, Tomomichi, Masayuki ARAI i Kiyohiro ITO. "Estimation of creep constitutive equation by creep indentation test using cylindrical indenter". Mechanical Engineering Journal 7, nr 4 (2020): 20–00232. http://dx.doi.org/10.1299/mej.20-00232.

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Springer, S., A. Röcklinger, M. Leitner, F. Grün, T. Gruber, M. Lasnik i B. Oberwinkler. "Implementation of a viscoplastic substrate creep model in the thermomechanical simulation of the WAAM process". Welding in the World 66, nr 3 (11.12.2021): 441–53. http://dx.doi.org/10.1007/s40194-021-01232-x.

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AbstractThis research work focusses on the implementation of a viscoplastic creep model in the thermomechanical simulation of the wire arc additive manufacturing (WAAM) process for Ti-6Al-4 V structures. Due to the characteristic layer by layer manufacturing within the WAAM process, viscoplastic material effects occur, which can be covered by implementing a creep model in the thermomechanical simulation. Experimental creep tests with a wide temperature, load and time range were carried out to examine short-term creep behaviour in particular. A Norton-Bailey creep law is used to accurately fit the experimental data and describe the base material’s creep behaviour. Subsequently, the fitted Norton-Bailey creep law was implemented in the thermomechanical simulation of the WAAM process. Finally, to determine the effect of creep on global distortion and local residual stress state in the substrate, simulations of a simplified linear, three-layer WAAM structure, with and without applying the implemented creep law, were carried out and compared to experimental data. The thermomechanical simulation with implemented creep model reveals a significant improvement in the numerical estimation of distortion and residual stress state in the substrate. The maximum distortion is reduced by about 13% and respectively the mean absolute percentage error between simulation and experiment decreases by about 34%. Additionally, the estimation accuracy with respect to the local residual stress state in the substrate improved by about 10%.

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Kaczmarek, Łukasz, i Paweł Dobak. "Contemporary overview of soil creep phenomenon". Contemporary Trends in Geoscience 6, nr 1 (1.06.2017): 28–40. http://dx.doi.org/10.1515/ctg-2017-0003.

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AbstractSoil creep deformation refers to phenomena which take place in many areas and research in this field of science is rich and constantly developing. The article presents an analysis of the literature on soil creep phenomena. In light of the complexity of the issues involved and the wide variety of perspectives taken, this attempt at systematization seeks to provide a reliable review of current theories and practical approaches concerning creep deformation. The paper deals with subjects such as definition of creep, creep genesis, basic description of soil creep dynamics deformation, estimation of creep capabilities, various fields of creep occurrence, and an introduction to creep modeling. Furthermore, based on this analysis, a new direction for research is proposed.

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14

Ha, Je Chang, Joon Hyun Lee, Masaaki Tabuchi i A. Toshimitsu Yokobori Jr. "Estimation of Creep Crack Growth Properties Using Circumferential Notched Round Bar Specimen for 12CrWCoB Rotor Steel". Key Engineering Materials 297-300 (listopad 2005): 397–402. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.397.

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Most heat resisting materials in structural components are used under multi-axial stress conditions and under such conditions ductile materials often exhibit brittle manner and low creep ductility at elevated temperature. Creep crack initiation and growth properties are also affected by multi-axial stress and it is important to evaluate these effects when laboratory data are applied to structural components. Creep crack growth tests using circumferential notched round bar specimens are a simple method to investigate multi-axial stress effects without using complicated test facilities. Creep crack growth tests have been performed using a 12CrWCoB turbine rotor steel. In order to investigate the effects of multi-axial stress on creep crack growth properties, the tests were conducted for various notch depths at 650°C. The circumferential notched round bar specimen showed brittle crack growth behaviour under multi-axial stress conditions. Creep crack growth rate was characterized in terms of the C* parameter. A 12CrWCoB turbine rotor steel has been tested using circumferential notched round bar specimens with different multi-axiality. Circumferential notched round bar specimens show increased brittle creep crack growth behaviour due to the multi-axial stress condition. Creep crack growth properties could be predicted by allowing for the decrease of creep ductility under multi-axial conditions.

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15

Aliev, A. A. "Long-Term Strength Estimation of Zirconia Ceramics". Proceedings of Higher Educational Institutions. Маchine Building, nr 11 (728) (listopad 2020): 83–88. http://dx.doi.org/10.18698/0536-1044-2020-11-83-88.

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A standard experimental assessment of the service life of high-temperature zirconia ceramics (GOST 4070–2014) requires the use of complicated heating and measuring equipment and hundreds of expensive specimens. This necessitates the development of calculation methods for evaluating long-term strength depending on the thermomechanical loading conditions without carrying out a full range of laboratory tests. The existing experimental estimation models of the primary and secondary creep regimes of ceramics consider the temperature range up to 1600°C, which is lower than zirconia limiting operating temperatures (2000°C and higher). Based on the Norton – Bailey law, long-term strength estimation of fully stabilized zirconia ceramics is carried out. Using previously known experimental data of other authors for ceramics made of fully stabilized zirconia (0.1Y2O3 + 0.9ZrO2), the creep constants values were calculated at high-temperature (1600–1800 °C) loading levels ≤5 MPa. A power-law regression equation with a high degree of correlation that evaluates the creep of the test material under loads up to 20 MPa and temperatures up to 2100 °C is proposed.

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16

Wilshire, Brian, H. Burt i N. P. Lavery. "Prediction of Long Term Stress Rupture Data for 2124". Materials Science Forum 519-521 (lipiec 2006): 1041–46. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.1041.

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The standard power law approaches widely used to describe creep and creep fracture behavior have not led to theories capable of predicting long-term data. Similarly, traditional parametric methods for property rationalization also have limited predictive capabilities. In contrast, quantifying the shapes of short-term creep curves using the q methodology introduces several physically-meaningful procedures for creep data rationalization and prediction, which allow straightforward estimation of the 100,000 hour stress rupture values for the aluminum alloy, 2124.

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Miyazaki, Noriyuki, Toru Ikeda i Toshihiro Komura. "Estimation of Steady-State Creep Behavior of Al2O3/YAG Eutectic Composite by Image-Based Finite Element Analysis". Journal of Engineering Materials and Technology 125, nr 3 (1.07.2003): 277–82. http://dx.doi.org/10.1115/1.1555657.

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Al 2 O 3 / YAG eutectic composite has been developed for a structural material used in ultra high temperature environments over 1500°C such as a gasturbine. Creep behavior is one of the important material properties in ultra high temperature materials. In the present study, we propose an image-based finite element analysis for estimating the steady state creep behavior of the Al2O3/YAG eutectic composite. In the image-based finite element analysis, microstructure of the material taken by a SEM is modeled into a finite element mesh using a software for image process. Then finite element creep analyses are carried out to obtain the steady state creep behavior of the Al2O3/YAG eutectic composite by using steady state creep constitutive equations for both Al2O3 single crystal and YAG single crystal. The results of steady state creep behavior obtained from the image-based finite element analysis are compared with the experimental results. It is found that the steady state creep behavior of the Al2O3/YAG eutectic composite is accurately estimated by the image-based finite element analysis. Furthermore, we examine the effect of volume fractions of the constituents on the steady state creep behavior of the Al2O3/YAG eutectic composite.

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Guo, Jin Quan, Long Tian, Hui Chao Shi i Wu Zhou Meng. "Using Stress Relaxation Data to Predict Creep Behavior". Advanced Materials Research 842 (listopad 2013): 382–85. http://dx.doi.org/10.4028/www.scientific.net/amr.842.382.

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An estimation method to predict creep performances of high temperature structural materials has been proposed. A Stress relaxation equation is obtained by fitting stress relaxation testing curves and modifying Tanaka-Ohba reloading stress relaxation constitutive equation. Based on the relationship between stress relaxation and creep, a unified prediction equation of creep is deduced. The method is to use the unified equation to derive creep strain rates or creep strain vs. time curves from stress relaxation measurements through some specified time increments. In order to validate the approach, the predicted results are compared to the experimental results of uni-axial isothermal creep tests conducted on 1Cr10NiMoW2VNbN steel. Good agreement between results of creep tests and the predicted results indicates that the developed method can be recommended in the creep behavior evaluation of high temperature materials.

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Sujatanond, Supamard, Yoshiharu Mutoh, Yukio Miyashita i Yuichi Otsuka. "Tensile and Compressive Creep Behavior of Magnesium Alloy AZ91D". Applied Mechanics and Materials 313-314 (marzec 2013): 98–102. http://dx.doi.org/10.4028/www.scientific.net/amm.313-314.98.

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Tensile and compressive creep tests of the extruded magnesium alloy AZ91D were carried out in vacuum at 150°C under constant engineering stresses ranged from 60 to 150 MPa. From the test results, the secondary creep rate in tension was found to be significantly higher than that in compression. Moreover, the estimation method of creep curve under a constant true stress was proposed by considering the reduction of cross sectional area during tensile loading where the specimen cross-sectional area and length were measured periodically until the end of creep test. The creep curve under a constant true stress obtained in the present study was still different between tensile and compressive loadings. Therefore, it should be noted that the different creep curves and creep exponents should be used in the creep deformation analysis of structures.

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Guo, Jin Quan, Hui Chao Shi i Wu Zhou Meng. "Prediction Methodology of Creep Performance from Stress Relaxation Measurements". Applied Mechanics and Materials 401-403 (wrzesień 2013): 920–23. http://dx.doi.org/10.4028/www.scientific.net/amm.401-403.920.

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An estimation method to predict creep performances of high temperature structural materials has been proposed. The method is to use a simplified and normalized model of stress relaxation to derive creep strain rates and creep strain vs. time curves from stress relaxation measurements through an integrated analytical procedure according to the relationship between stress relaxation and creep. In order to validate the approach, the predicted results are compared to the experimental results of uni-axial isothermal creep tests conducted on 1Cr10NiMoW2VNbN steel with the same temperature of stress relaxation tests. Good agreement between results of relaxation tests and the predicted results indicates that the developed method can be recommended in the creep behavior evaluation of high temperature materials.

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Kaji, Y., I. Ioka, I. Nishiguchi i Y. Miyamoto. "Estimation of Creep Buckling Deformation Under External Pressure at Elevated Temperature". Journal of Pressure Vessel Technology 118, nr 2 (1.05.1996): 194–97. http://dx.doi.org/10.1115/1.2842180.

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The effect of the initial ovality, wall thickness, and pressure level on the collapse time of a heat transfer tube subjected to both constant and cycled external pressure at elevated temperature was examined experimentally and analytically. The creep deformation of the tube obtained by FEM code and the simplified method was a good approximation. The simplified method proposed by Nishiguchi et al. is an effectual method in the estimation of the creep buckling deformation and the collapse time of the tube under external pressure at elevated temperature as compared with the experimental results and the FEM. Though many cracks initiated by creep collapse were observed on the outer surface of a few test tubes, the cracks did not pass through the tube thickness, and leak tightness was maintained despite a collapse for all tubes tested.

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Park, Jong-Bum, Jung-Il Park, Sung-Pil Chang i Jae-Yeol Cho. "Estimation Method of Creep Coefficient in Concrete Structures". Journal of the Korea Concrete Institute 21, nr 5 (31.10.2009): 619–28. http://dx.doi.org/10.4334/jkci.2009.21.5.619.

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Liu, Hui, i Fu-Zhen Xuan. "A new model for life estimation of creep". Nuclear Engineering and Design 240, nr 10 (październik 2010): 2528–31. http://dx.doi.org/10.1016/j.nucengdes.2010.04.038.

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Gokhale, A. M. "Estimation of creep strain due to intergranular cavitation". Scripta Metallurgica 23, nr 8 (sierpień 1989): 1269–71. http://dx.doi.org/10.1016/0036-9748(89)90042-2.

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MUNAKATA, Yoshiyuki, i Tetsuya SENDA. "Life Estimation Method Based on Creep-fatigue Interaction". Bulletin of JSME 29, nr 258 (1986): 3986–92. http://dx.doi.org/10.1299/jsme1958.29.3986.

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Ewald, J., K. H. Keienburg i K. Maile. "Estimation of manufacturing defects in the creep range". Nuclear Engineering and Design 87 (lipiec 1985): 389–98. http://dx.doi.org/10.1016/0029-5493(85)90128-1.

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To¨nu¨k, Ergin, i M. Barbara Silver-Thorn. "Nonlinear Viscoelastic Material Property Estimation of Lower Extremity Residual Limb Tissues". Journal of Biomechanical Engineering 126, nr 2 (1.04.2004): 289–300. http://dx.doi.org/10.1115/1.1695575.

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Axisymmetric nonlinear finite-element analysis was used to simulate force-relaxation and creep data obtained during in vivo indentation of the residual limb soft tissues of six individuals with trans-tibial amputation [1]. The finite-element models facilitated estimation of an appropriate set of nonlinear viscoelastic material coefficients of extended James-Green-Simpson material formulation for bulk soft tissue at discrete, clinically relevant test locations. The results indicate that over 90% of the experimental data can be simulated using the two-term viscoelastic Prony series extension of James-Green-Simpson material formulation. This phenomenological material formulation could not, however, predict the creep response from relaxation experiments, nor the relaxation response from creep experiments [2–5]. The estimated material coefficients varied with test location and subject indicating that these coefficients cannot be readily extrapolated to other sites or individuals.

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SUJATANOND, Supamard, Yukio MIYASHITA, Yoshiharu MUTOH i Yuichi OTSUKA. "PS56 Estimation of Creep Curve at a Constant True Stress in AZ91D Magnesium Alloy". Proceedings of the Materials and Mechanics Conference 2010 (2010): 174–76. http://dx.doi.org/10.1299/jsmemm.2010.174.

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He, Xiao Cong. "Sensitivity Study on Parameters for Fatigue-Creep Modeling of Stainless Steel Materials". Advanced Materials Research 628 (grudzień 2012): 217–20. http://dx.doi.org/10.4028/www.scientific.net/amr.628.217.

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In present paper, sensitivity study on parameters for fatigue-creep model of stainless steel materials has been carried out. An analytical model has been established to predict fatigue-creep life of AISI347 stainless steel. Manson’s Universal Slopes equation has been used as an empirical correlation which relates fatigue endurance to tensile properties. Different creep prediction models have been studied in order to correlate the results of shout-time elevated temperature tests with long-term service performance at more moderate temperatures. Comparison between the different creep prediction models and experimental results were carried out for a range of stresses and temperatures. A linear damage summation method has been used to combined fatigue and creep. The results of sensitivity analysis indicate that strain range and temperature have very significant influence on creep-fatigue life estimation.

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Guo, Long, i Xing Zhong Zhang. "Positive Effects of High-Temperature Steel Creep Behavior on Continuous Casting Slab". Key Engineering Materials 723 (grudzień 2016): 103–10. http://dx.doi.org/10.4028/www.scientific.net/kem.723.103.

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Mechanical properties and creep behavior of continuous casting slab subjected to uniaxial tensile tests at 1100 and 1150 °C were considered in this paper. All of specimens was given a typical in-situ melting thermal history and interrupted cooling cycle before testing. An increase in load and temperature accelerates the creep rate thereby decreasing the steady state range. A new creep equation whose parameters are calculated by inverse-estimation using the regression analysis was proposed based on Norton-Bailey creep law. Primary and secondary creep stages could be described accurately by the new equation. Positive creep effects on straightening technology in continuous casting slab were presented in this paper. Involute continuous straightening technology could give full play to the role of steel creep deformation at high temperature. This research is helpful for the design of the new casting machine and improvement of old casting machine in using depended on high temperature creep behavior.

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Mandziej, Stan T. "Simulative Accelerated Creep Test on Gleeble". Materials Science Forum 638-642 (styczeń 2010): 2646–51. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.2646.

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The simulative accelerated creep test (ACT) on Gleeble thermal-mechanical simulator was developed as a response to an overall need of gaining in a short time useful physical data for estimation of long-term behaviour of materials exposed to operation at elevated temperatures. While most of the design of components and estimation of power plants lifetime is based on long-term creep data, which are generally available for the plate and pipe creep resisting steels, in case of the welded joints on these components such data are not always easily found and e.g. for the repair welds are very often not available. Next to its short duration, demanded from the accelerated creep testing procedure are the following conditions: - The basic temperature and applied strains in the ACT must prevent odd transformations like secondary dissolution of carbides or intensive formation of non-equilibrium phases. - The final deformation at fracture must be like at real creep – just a few pct in total. - The depletion of weld metal or steel matrix in alloying elements must be achieved similar to that of crept steels and the carbide phases at onset of cracks must not be different. To meet these requirements a low-cycle thermal-mechanical deformation-relaxation test was developed, during which the sub-structural processes characteristic of creep occurred much faster, transforming the initial microstructure of the creep resisting steels and welds to the near-to-equilibrium one in less than 30hours. The formation of dislocation configurations and the sequence of carbide precipitation and coagulation, as confirmed by TEM investigations, well resembled these of the conventional creep, so the testing procedure, hence called the simulative accelerated creep test – ACT, has been verified this way.

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Lim, Byeong Soo, C. S. Jeong, Si Yon Bae, Seog Hyeon Ryu, Jeong Tae Kim i Y. T. Keum. "Inspection of Creep Defects and Degraded Zone Using Ultrasound". Materials Science Forum 475-479 (styczeń 2005): 4141–44. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.4141.

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The initiation and growth of internal defects usually cause the failure of long term operated structural components at high temperature. Therefore, by investigating the internal defects of material, the integrity of the system can be maintained and the unexpected failure can be prevented. The main purpose of this study is to investigate the possibility of the application of ultrasound to the measurement and estimation of the creep damage. In this study, the phased array ultrasound and backward ultrasound were employed to detect the internal defects caused by creep. Using the newly developed P92 steel, both creep and NDE ultrasound tests were performed. The results of defect inspection were checked by microstructure examination. Reliable information on the size and position of crack were obtained and successful estimation of the amount of micro-voids and their distribution proved to be obtainable by the ultrasound inspection technique. The width of the creep degraded zone was confirmed by the width of ultrasonic signal, and the severity of degradation was confirmed by ultrasonic amplitude.

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Duda, Piotr, Łukasz Felkowski i Andrzej Duda. "An Analysis of Creep Phenomena in the Power Boiler Superheaters". Metals 8, nr 11 (1.11.2018): 892. http://dx.doi.org/10.3390/met8110892.

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Higher temperatures of the power boiler superheater operation may lead to high strains caused by the creep phenomenon. This paper presents a determination of the maximum allowable operating temperature limited by the creep phenomenon for steam superheater SH3. The calculations are carried out first on the basis of applicable European standards. Then, calculations are performed based on conducted creep tests, a proposed creep model, and a finite element method (FEM) model. A detailed creep phenomenon analysis based on the conducted creep tests shows that stresses that determine the creep process are mainly caused by pressure. Normal stresses resulting from bending are mainly the effect of thermal expansion. These stresses undergo significant relaxation because of creep. The creep phenomenon analysis explains the equations of the European standards. The presented calculations enable estimation of a safe value of the operating temperature which is constant over time. The estimated time of safe operation does not take account of temperature spikes. For this reason, pressure elements working at high temperatures must be inspected regularly to assess their wear state.

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Gooch, D. J., i S. T. Kimmins. "C∗ correlations for creep crack growth in weld metals". Journal of Strain Analysis for Engineering Design 21, nr 4 (1.10.1986): 231–42. http://dx.doi.org/10.1243/03093247v214231.

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Creep crack growth tests have been performed on compact tension specimens of 2 1/4CrlMo, C—Mn, and AISI 316 weld metals at 565°C, at 360 and 390°C, and at 600°C, respectively. The data have been analysed in terms of the C∗ creep parameter obtained directly from experimental measurements and by use of estimation formulae which depend on uniaxial creep data and evaluation of a reference stress. When expressed in the form d a/d t = D C∗ q the two approaches result in correlations which differ both in the constant, D, and in the exponent, q. The differences in the constant may be largely rationalized in terms of the constraint on deformation appropriate to the test conditions and the effects of this on the reference stress. The exponent, q, was generally lower when the estimation formulae were used than when C∗ was calculated from measured displacement rates. This was attributed to the lower stress dependence of the load-line displacement rates of the compact tension specimens compared with that of the uniaxial minimum creep rate at similar stress levels. This arises because primary creep strains may dominate the overall deformation behaviour of a compact tension specimen for many practical circumstances.

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Zgheib, E., i W. Raphael. "Study of the Admixtures Effect on Concrete Creep Using Bayesian Linear Regression". Archives of Civil Engineering 65, nr 3 (1.09.2019): 127–40. http://dx.doi.org/10.2478/ace-2019-0039.

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AbstractAdmixtures are commonly used nowadays in the mix composition of concrete. These additions affect concrete properties and performance especially creep deformations. This paper shows the effect of admixtures on creep of concrete. In fact, creep deformations have prejudicial consequences on concrete behaviour; an incorrect or inaccurate prediction leads to undesirable consequences in structures. Therefore, an accurate estimation of these deformations is mandatory. Moreover, design codes do not consider admixtures’ effect while predicting creep deformations, thus it is necessary to develop models that predict accurately creep deformations and consider the effect of admixtures. Using a large experimental database coming from international laboratories and research centres, this study aims to update the Eurocode 2 creep model by considering the type and percentage of admixtures using Bayesian Linear Regression method. The effect of two types of admixtures is presented in this paper; the water reducer and silica fume.

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Unterreiter, Guenter, Daniel R. Kreuzer, Bernd Lorenzoni, Hans U. Marschall, Christoph Wagner, Robert Machhammer i Gernot Hackl. "Compressive Creep Measurements of Fired Magnesia Bricks at Elevated Temperatures Including Creep Law Parameter Identification and Evaluation by Finite Element Analysis". Ceramics 3, nr 2 (22.04.2020): 210–22. http://dx.doi.org/10.3390/ceramics3020019.

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Creep behavior is very important for the selection of refractory materials. This paper presents a methodology to measure the compressive creep behavior of fired magnesia materials at elevated temperatures. The measurements were carried out at 1150–1500 °C and under compression loads from 1–8 MPa. Creep strain was calculated from the measured total strain data. The obtained creep deformations of the experimental investigations were subjected to detailed analysis to identify the Norton-Bailey creep law parameters. The modulus of elasticity was determined in advance to simplify the inverse estimation process for finding the Norton-Bailey creep parameters. In the next step; an extended material model including creep was used in a finite element analysis (FEA) and the creep testing procedure was reproduced numerically. Within the investigated temperature and load range; the creep deformations calculated by FEA demonstrated a good agreement with the results of the experimental investigations. Finally; a finite element unit cell model of a quarter brick representing a section of the lining of a ferrochrome (FeCr) electric arc furnace (direct current) was used to assess the thermo-mechanical stresses and strains including creep during a heat-up procedure. The implementation of the creep behavior into the design process led to an improved prediction of strains and stresses.

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Chatzidakis, Stylianos, Miltiadis Alamaniotis i Lefteri H. Tsoukalas. "Creep Rupture Forecasting". International Journal of Monitoring and Surveillance Technologies Research 2, nr 2 (kwiecień 2014): 1–25. http://dx.doi.org/10.4018/ijmstr.2014040101.

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Creep rupture is becoming increasingly one of the most important problems affecting behavior and performance of power production systems operating in high temperature environments and potentially under irradiation as is the case of nuclear reactors. Creep rupture forecasting and estimation of the useful life is required to avoid unanticipated component failure and cost ineffective operation. Despite the rigorous investigations of creep mechanisms and their effect on component lifetime, experimental data are sparse rendering the time to rupture prediction a rather difficult problem. An approach for performing creep rupture forecasting that exploits the unique characteristics of machine learning algorithms is proposed herein. The approach seeks to introduce a mechanism that will synergistically exploit recent findings in creep rupture with the state-of-the-art computational paradigm of machine learning. In this study, three machine learning algorithms, namely General Regression Neural Networks, Artificial Neural Networks and Gaussian Processes, were employed to capture the underlying trends and provide creep rupture forecasting. The current implementation is demonstrated and evaluated on actual experimental creep rupture data. Results show that the Gaussian process model based on the Matérn kernel achieved the best overall prediction performance (56.38%). Significant dependencies exist on the number of training data, neural network size, kernel selection and whether interpolation or extrapolation is performed.

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Guo, Long, i Xingzhong Zhang. "High-Temperature Creep Behaviour and Positive Effect on Straightening Deformation of Q345c Continuous Casting Slab". High Temperature Materials and Processes 37, nr 3 (26.03.2018): 253–60. http://dx.doi.org/10.1515/htmp-2016-0190.

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AbstractMechanical and creep properties of Q345c continuous casting slab subjected to uniaxial tensile tests at high temperature were considered in this paper. The minimum creep strain rate and creep rupture life equations whose parameters are calculated by inverse-estimation using the regression analysis were derived based on experimental data. The minimum creep strain rate under constant stress increases with the increase of the temperature from 1000 °C to 1200 °C. A new casting machine curve with the aim of fully using high-temperature creep behaviour is proposed in this paper. The basic arc segment is cancelled in the new curve so that length of the straightening area can be extended and time of creep behaviour can be increased significantly. For the new casting machine curve, the maximum straightening strain rate at the slab surface is less than the minimum creep strain rate. So slab straightening deformation based on the steel creep behaviour at high temperature can be carried out in the process of Q345c steel continuous casting. The effect of creep property at high temperature on slab straightening deformation is positive. It is helpful for the design of new casting machine and improvement of old casting machine.

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Reggiani, Barbara, Lorenzo Donati i Luca Tomesani. "Constitutive Laws for the Deformation Estimation of Extrusion Die in the Creep-Fatigue Regime". Key Engineering Materials 491 (wrzesień 2011): 233–40. http://dx.doi.org/10.4028/www.scientific.net/kem.491.233.

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Tools are exposed to severe working conditions during the hot extrusion process. In particular, dies and mandrels can be subjected to an excessive amount of deformation as a result of the developed high cyclic loads and temperatures. In this scenario, a physical experiment reproducing the thermo-mechanical conditions of a mandrel in a porthole die was performed with the Gleeble machine on the AISI H11 tool steel with the aim to investigate the mechanisms that influence the die deformation. The design of experiment consisted of 4 levels of temperature, 3 levels of stress and 3 types of load, i.e. pure creep, pure fatigue and creep-fatigue. In all the testing conditions, a comparable pattern of the mandrel displacement-time curve was found reproducing the 3 stages of softening typical of the strain evolution in a standard creep test but with a marked primary phase. Thus, with the aim to identify an easy-applicable equation to estimate the die deformation, the time hardening creep law was chosen. Coefficients of the time-hardening law were optimized, for each testing condition, on the basis of experimental data starting from values for similar alloys taken from the literature. Results in terms of mandrel displacement were then compared to experimental data for the creep-fatigue condition at different stress and temperature levels. The values found were validated against additional experimental data performed with different specimen geometries. A good average agreement was found between experimental and numerical results. The developed procedure was then applied to an industrial die.

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Moradi, Ali, i Nasser Soltani. "Response Surface Methodology for the Remaining Creep Life Estimation by the Small Punch Creep Test". Journal of Testing and Evaluation 46, nr 6 (19.03.2018): 20170198. http://dx.doi.org/10.1520/jte20170198.

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Okazaki, M., M. Hashimoto i T. Mochizuki. "Creep-Fatigue Strength of Long-Term Post-Service 2 · 1/4 Cr-1 · Mo Steel and Remaining Life Estimation". Journal of Pressure Vessel Technology 113, nr 4 (1.11.1991): 549–55. http://dx.doi.org/10.1115/1.2928794.

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Creep-fatigue strength of post-service 2 · 1/4 Cr-1 · Mo steel used for about one hundred-thousand hours in a fossil fuel power plant was studied. The creep-fatigue strength of the post-service material was lower than that of the virgin material, whereas it was comparable to that of thermally aged material, which was artificially exposed at high temperature for a long time so that it had an equivalent value of the Larson-Miller parameter to the post-service material. The nondestructive detection of the long-term degradation damage due to long-term thermal aging, as well as due to creep-fatigue, was also investigated by applying an ultrasonic technique. It was found that the energy attenuation coefficient, α, which is defined by the ratio of input to output energies of a longitudinal ultrasonic wave, had a good correlation with creep-fatigue damage in the virgin, aged and post-service materials; and hence, α was a successful parameter to detect creep-fatigue damage. Based on the results thus obtained, a new remaining life estimation method for creep-fatigue of in-service high-temperature materials was proposed. The application of the method to the post-service material tested gave good predicted results.

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Monfared, Vahid. "Neural Network Based Simulation of Micro Creeping Fibrous Composites SiC/Al6061 for Plastic Behaviour". Journal of Theoretical and Applied Mechanics 47, nr 1 (1.03.2017): 36–48. http://dx.doi.org/10.1515/jtam-2017-0003.

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Abstract The present work presents a new approach based on neural network prediction for simple and fast estimation of the creep plastic behaviour of the short fiber composites. Also, this approach is proposed to reduce the solution procedure. Moreover, as a significant application of the method, shuttles and spaceships, turbine blades and discs are generally subjected to the creep effects. Consequently, analysis of the creep phenomenon is required and vital in different industries. Analysis of the creep behaviour is required for failure, fracture, fatigue, and creep resistance of the optoelectronic/photonic composites, and sensors. One of the main applications of the present work is in designing the composites with optical fibers and devices. At last, a good agreement is seen among the present prediction by neural network approach, finite element method (FEM), and the experimental results.

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Pagadala, Srivyshnavi, Sony Bathala i B. Uma. "An Efficient Predictive Paradigm for Software Reliability". Asian Journal of Computer Science and Technology 8, S3 (5.06.2019): 114–16. http://dx.doi.org/10.51983/ajcst-2019.8.s3.2051.

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Software Estimation gives solution for complex problems in the software industry which gives estimates for cost and schedule. Software Estimation provides a comprehensive set of tips and heuristics that Software Developers, Technical Leads, and Project Managers can apply to create more accurate estimates. It presents key estimation strategies and addresses particular estimation challenges. In the planning of a software development project, a major challenge faced by project managers is to predict the defects and effort. The Software defect plays critical role in software product development. The estimation of defects can be determined in the product development using many advanced statistical modelling techniques based on the empirical data obtained by the testing phases. The proposed estimation technique in this paper is a model which was developed using Rayleigh function for estimating effect of defects in Software Project Management. The present study offers to decide how many defects creep in to production and determine the effort spent in months. The estimation model was used on Software Testing Life Cycle (STLC) to complete product. The accuracy of the model explains the variation in spent efforts in months associated with number of defects. The model helps the senior management in estimating the defects, schedule, cost and effort.

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Radhakrishnan, V. M., M. Kamaraj i V. V. Balasubramaniam. "Life Estimation of Cracked Stainless Steel Components Under Creep Conditions". Journal of Engineering Materials and Technology 113, nr 3 (1.07.1991): 303–6. http://dx.doi.org/10.1115/1.2903410.

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Experimental investigations have been carried out to study the creep crack growth in types 316, 308 Cb, and 304 L stainless steel in the temperature range of 873–1073 K under plane stress condition. Testings have been carried out with both the base metal and the welded composite joints, because such joints are commonly used in nuclear power industries. Among the various parameters tried to correlate the creep crack growth, the energy rate line integral has been found to give the best description of the crack growth rate. The steady-state energy rate line integral has been found to correlate well with the rupture time. Based on this observation, life estimations are presented for thin components containing various initial defect sizes.

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Dai, Yanwei, Fei Qin, Yinghua Liu, Weizhe Feng i Guian Qian. "Estimation of C∗-Integral for Central Cracked Plate Under Biaxial Loading". International Journal of Applied Mechanics 12, nr 07 (sierpień 2020): 2050079. http://dx.doi.org/10.1142/s1758825120500799.

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The reference stress method (RSM) is a classical method to estimate [Formula: see text]-integral of creep crack. An extended reference stress method (ERSM) is given for the central cracked plate (CCP) under biaxial loading in this paper. The applicability and verification for the proposed ERSM is given. The study finds that the solutions with the proposed ERSM agree better than those of RSM under biaxial loading condition. A theoretical form to predict the relationship of [Formula: see text]-integral between biaxial loading and uniaxial loading is discussed. Relation between [Formula: see text]-integral and creep time under biaxial loading is validated and discussed.

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Mukai, M., T. Kawakami, Y. Hiruta, K. Takahashi, K. Kishimoto i T. Shibuya. "Fatigue Life Estimation of Solder Joints in SMT-PGA Packages". Journal of Electronic Packaging 120, nr 2 (1.06.1998): 207–12. http://dx.doi.org/10.1115/1.2792623.

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The fatigue life estimation of solder joints is one of the most critical requirements in the development of reliable electronic components. In this study, we first examined a constitutive model for Sn63-Pb37 solder based on the results of material tests. It was confirmed that the behavior of the solder material can be expressed by the elastic-creep constitutive equations when the strain rate was low. Secondly, elastic-creep stress analysis was carried out for the solder joints of a SMT-PGA (surface mount technology pin grid array) package. The location of the failure predicted by the analytical results agreed well with those of the thermal cycle tests (TCT). It was shown that the fatigue life estimation of solder joints based on the present method is satisfactory for engineering purposes.

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Contesti, E., G. Cailletaud i C. Levaillant. "Creep Damage in 17–12 SPH Stainless Steel Notched Specimens: Metallographical Study and Numerical Modeling". Journal of Pressure Vessel Technology 109, nr 2 (1.05.1987): 228–35. http://dx.doi.org/10.1115/1.3264901.

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Creep-rupture tests on notched specimens of 17–12 SPH stainless steel are performed at elevated temperature (600°C). Metallographic examination allows the quantitative estimation of the intergranular cracking damage occurring during creep tests. Numerical computations based on currently used rupture criteria are performed and compared to both intergranular damage profile and creep life. With regards to the intergranular damage profile measured by interrupting tests on the 1-mm notch radius specimen, Von Mises stress criterion does not predict the experimental location of the maximum damage, because of the influence of stress-triaxiality on the rupture process.

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MORISHITA, Tomohiro, Masahiko HIRAO i Hidekazu FUKUOKA. "Creep damage estimation in pure copper using ultrasonic waves." Journal of the Society of Materials Science, Japan 39, nr 437 (1990): 208–13. http://dx.doi.org/10.2472/jsms.39.208.

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Chandel, Chaman, P. K. Srivastava i Agraj Upadhyay. "Estimation of Rheological Properties of Snow Subjected to Creep". Defence Science Journal 57, nr 4 (20.07.2007): 393–401. http://dx.doi.org/10.14429/dsj.57.1786.

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Sorvari, Joonas, i Matti Malinen. "On the direct estimation of creep and relaxation functions". Mechanics of Time-Dependent Materials 11, nr 2 (17.10.2007): 143–57. http://dx.doi.org/10.1007/s11043-007-9038-1.

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