scholarly journals Cyclic Creep Behavior and Modified Life Prediction of Bainite 2.25Cr-1Mo Steel at 455 °C

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1486
Author(s):  
Hao Jiang ◽  
Oluwadamilola Ogunmola ◽  
Zizhen Zhao ◽  
Bingbing Li ◽  
Xu Chen
Keyword(s):  
Life Prediction ◽  
Accumulation Rate ◽  
Prediction Method ◽  
Strain Curve ◽  
Cyclic Creep ◽  
Strain Component ◽  
Creep Tests ◽  
Systematic Classification ◽  
Static Creep ◽  
Unloading Rate

Uniaxial static and cyclic creep tests were carried out on bainite 2.25Cr-1Mo steel at 455 °C. Effects of the unloading rate from 0.6 to 39 MPa/s and valley stress duration from 0 to 30 min on the cyclic creep deformation behavior were discussed. The results indicated that the fracture behavior under static and cyclic creep conditions showed a consistent ductile mode. The strain accumulation rate under cyclic creep was significantly retarded as compared with static creep due to the presence of anelastic recovery which was apparently influenced by the unloading conditions. For cyclic creep tests, the unrecoverable strain component determined by a systematic classification of the stress–strain curve was the true damage. A modified life prediction method proposed based on the unrecoverable strain component presented a good life prediction for cyclic creep.

Damage Evolution and Life Prediction of a P91 Longitudinal Welded Tube Under Internal Pressure Creep

2008 ◽  
Author(s):  
Takashi Ogata ◽  
Takayuki Sakai ◽  
Masatsugu Yaguchi
Keyword(s):  
Internal Pressure ◽  
Heat Affected Zone ◽  
Void Growth ◽  
Damage Evolution ◽  
Life Prediction ◽  
Prediction Method ◽  
Creep Damage ◽  
Creep Tests ◽  
Creep Analysis ◽  
Welded Tube

Clarification of creep damage mechanism and establishment of remaining life prediction methods of longitudinal welded piping of P91 steel are important subjects to maintain reliable operation of boilers in thermal power plants. Internal pressure creep tests were conducted on P91 steel longitudinal welded tubes to characterize the evolution of creep damage with time and to evaluate a life prediction method. Interrupted creep tests were utilized for damage observation in addition to rupture tests. Three dimensional FE creep analysis of the creep tested specimens were conducted to identify stress and creep strain distribution within the specimen during creep. Failure occurred at a heat affected zone without significant macroscopic deformation. It was found that initiation of creep voids had concentrated at mid-thickness region rather than surface. The creep analysis results indicated that triaxial tensile stress yielded at the mid-thickness region of the heat affected zone due to difference of creep deformation property between the base metal, heat affected zone and weld metal. It was suggested that the triaxial stress state caused acceleration of the creep damage evolution in the heat affected zone resulting in internal failure of the tube specimens. A rupture time prediction method of the welded tube is proposed based on the maximum principal stress and the triaxial stress factor. Void growth behavior in the heat affected zone was well predicted by the previously proposed void growth simulation method by introducing void initiation function to the method.

Investigation of Cyclic Creep Behavior and Life Prediction Method of Notch Specimen During High Temperature Fatigue

2008 ◽  
Author(s):  
Zhichao Fan ◽  
Xuedong Chen ◽  
Heng Jiang ◽  
Jie Dong
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Creep Behavior ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Prediction Method ◽  
Creep Damage ◽  
Cyclic Creep ◽  
High Temperature Stress ◽  
The Mean

Cyclic creeps can bring to additional damage, resulting in shorter fatigue lives, so the effects of fatigue damage and cyclic creep damage should be taken into account in the life prediction. In this case, the mean strain rate model based on ductility exhaustion theory can be adopted. An engineering structure inevitably has some stress concentration area. As to this situation, by high temperature low cycle fatigue tests with different notch sizes, cyclic creep behavior is investigated and compared with that of smooth specimens in this paper. The results indicate that, due to existence of notch, the cyclic creep deformation is restricted within a little range around notch and cannot spread widely, so the fatigue strength of notch specimens increases. Based on the ductility dissipation theory and effective stress concept of continuum damage mechanism (CDM), the mean displacement rate at half life is acted as control parameter, and a high temperature multi-axial fatigue life prediction method is proposed in this paper. The prediction results show that all test data are within ±2.0 error factor, which is better than that of axial maximum stress method. This method has simple form and fewer constants, can be used to predict high temperature stress-controlled fatigue life whatever smooth or notch specimens.

High Temperature Behavior of Polysilicon

2002 ◽  
Vol 741 ◽  
Author(s):  
Chung-Seog Oh ◽  
George Coles ◽  
William N. Sharpe
Keyword(s):  
Intelligent Design ◽  
Life Prediction ◽  
Permanent Deformation ◽  
Strain Curve ◽  
Laser Interferometry ◽  
Stress Strain Curve ◽  
Creep Tests ◽  
Thermal Actuators ◽  
Fundamental Understanding ◽  
Initial Results

ABSTRACTThe polysilicon elements of thermal actuators can reach temperatures high enough to cause permanent deformation. A fundamental understanding of the constitutive behavior is necessary for intelligent design and life prediction, but mechanical testing at high temperatures is especially challenging at the micron level.This paper describes techniques for testing freestanding thin-film polysilicon specimens in tension at temperatures up to 700°C. Strain is measured directly on the specimens by laser interferometry from platinum markers. The complete stress-strain curve can be obtained as well as strain versus time for creep tests. Initial results show that polysilicon is ductile at temperatures above 500°C and can have a high creep rate.

A New Empirical Life Prediction Equation for Stress-Controlled Fatigue-Creep Interaction

2008 ◽  
Author(s):  
Huifeng Jiang ◽  
Xuedong Chen ◽  
Zhichao Fan ◽  
Jie Dong
Keyword(s):  
Life Prediction ◽  
Equivalent Stress ◽  
Cavity Growth ◽  
Cyclic Creep ◽  
Control Mode ◽  
Creep Process ◽  
Mean Stress ◽  
Equivalent Radius ◽  
Static Creep ◽  
The Mean

A new empirical life prediction method is developed. The equivalent radius of cavities at grain boundary is adopted as the damage parameter. Similar with Nam’s model, in this paper, it is also assumed that cavities only nucleate during fatigue cycles and further grow with the development of creep. Then the number of cavities nucleated in a cycle is proportional to the fatigue effect, i.e. the amplitude of loading stress. As the creep process is composed of the static creep and the cyclic creep during the fatigue-creep interaction, then the equivalent stress causing cavity growth should be proportional to the maximum hold stress (static creep) and the mean stress (cyclic creep). Therefore, this model is applicable to stress control mode and includes the effects of fatigue, static creep and cyclic creep during the fatigue-creep interaction. By employing this method, the fatigue-creep lives are assessed for 1.25Cr0.5Mo steel at 520°C and 540°C. The predicted lives are compared with the tested ones and a good agreement is found between them. Moreover, it is found that the coefficient of the mean stress is 3-order larger than that of the stress amplitude, which means the effect of static creep is much punier than that of cyclic creep. Considering the detailed test parameters, the short hold duration for peak load may be responsible for this.

scholarly journals An Energy-Based Experimental-Analytical Torsional Fatigue Life-Prediction Method

2010 ◽  
Author(s):  
John N. Wertz ◽  
M.-H. Herman Shen ◽  
Tommy George ◽  
Charles Cross ◽  
Onome Scott-Emuakpor
Keyword(s):  
Fatigue Life ◽  
Strain Energy ◽  
Life Prediction ◽  
Fatigue Testing ◽  
Pure Shear ◽  
Prediction Method ◽  
Strain Curve ◽  
Fatigue Life Prediction ◽  
Torsional Fatigue ◽  
Shear Fatigue

An energy-based fatigue life prediction framework for calculation of torsional fatigue life and remaining life has been developed. The framework for this fatigue prediction method is developed in accordance with our previously developed energy-based axial and bending fatigue life prediction approaches, which state: the total strain energy dissipated during a monotonic fracture and cyclic processes is the same material property, where each can be determined by measuring the area underneath the monotonic true stress-strain curve and the area within a hysteresis loop, respectively. The energy-based fatigue life prediction framework is composed of the following entities: (1) development of a shear fatigue testing procedure capable of assessing strain energy density per cycle in a pure shear stress state and (2) incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials subjected to pure shear fatigue.

Fatigue-Creep Damage Evolution Model and Life Prediction Methods Under Stress Controlled Mode

2007 ◽  
Author(s):  
Zhichao Fan ◽  
Xuedong Chen ◽  
Ling Chen ◽  
Jialing Jiang
Keyword(s):  
Damage Evolution ◽  
Life Prediction ◽  
Cyclic Creep ◽  
Evolution Model ◽  
Control Mode ◽  
Frequency Separation ◽  
Control Factor ◽  
Static Creep ◽  
Mean Strain ◽  
Mean Stresses

Damage evolution of stress controlled fatigue-creep interaction actually is the ductility exhaustion process induced by cyclic creep and static creep. Based on the ductility dissipation theory and effective stress concept of the continuum damage mechanism (CDM), a new fatigue-creep interaction damage evolution model and life prediction method under stress control mode are proposed, in which mean strain is the damage parameter to define damage variable D, and mean strain rate at half life is the control factor related to fracture lives. As for 1.25Cr0.5Mo steel, stress-controlled fatigue-creep tests with different combination of stress amplitudes and mean stresses at 540°C were conducted to investigate fatigue-creep interaction. The results of damage descriptions indicate that, the damage model and mean strain parameter are applicable to describe damage evolution of cyclic creep-static creep interaction when ductility exhaustion is dominant. The life prediction results are found to be quite satisfactory relative to test data with a ±1.25 error factor, which is much better than that for the Frequency Separation method (FS) and Strain Energy Frequency Modified approach (SEFS). Further more, it is found that, when stress amplitudes are less than mean stresses, drastic interaction between cyclic creep and static creep will accelerate the material damage rate, so that the damage exponent reaches its peak value.

An Energy-Based Method for Uni-Axial Fatigue Life Calculation

2009 ◽  
Author(s):  
Hakan Ozaltun ◽  
Jeremy Seidt ◽  
M.-H. Herman Shen ◽  
Tommy George ◽  
Charles Cross
Keyword(s):  
Fatigue Life ◽  
Gas Turbine ◽  
Life Prediction ◽  
Prediction Method ◽  
Strain Curve ◽  
Fatigue Life Prediction ◽  
Cyclic Process ◽  
Model Approximation ◽  
Plastic Energy ◽  
Remaining Fatigue Life

An energy based fatigue life prediction framework has been developed for calculation of remaining fatigue life of in-service gas turbine materials. The purpose of the life prediction framework is to account for the material aging effect on fatigue strength of gas turbine engines structural components which are usually designed for infinite life. Previous studies [1–7] indicate the total strain energy dissipated during a monotonic fracture process and a cyclic process is a material property that can be determined by measuring the area underneath the monotonic true stress-strain curve and the sum of the area within each hysteresis loop in the cyclic process, respectively. The energy-based fatigue life prediction framework consists of the following entities: (1) development of a testing procedure to achieve plastic energy dissipation per life cycle and (2) incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials. The accuracy of the remaining fatigue life prediction method was verified by comparison between model approximation and experimental results of Aluminum 6061-T6 (Al 6061-T6). The comparison shows promising agreement, thus validating the capability of the framework to produce accurate fatigue life prediction.

Damage Evolution and Life Prediction of a P91 Longitudinal Welded Tube Under Internal Pressure Creep

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Takashi Ogata ◽  
Takayuki Sakai ◽  
Masatsugu Yaguchi
Keyword(s):  
Internal Pressure ◽  
Void Growth ◽  
Damage Evolution ◽  
Life Prediction ◽  
Prediction Method ◽  
Creep Damage ◽  
Triaxial Stress ◽  
Creep Tests ◽  
P91 Steel ◽  
Welded Tube

The clarification of creep damage mechanism and the establishment of remaining life prediction methods of longitudinal welded piping of P91 steel are important subjects to maintain a reliable operation of boilers in thermal power plants. Internal pressure creep tests were conducted on P91 steel longitudinal welded tubes to characterize the evolution of creep damage with time and to evaluate a life prediction method. Interrupted creep tests were performed for damage observation in addition to rupture tests. Three dimensional finite element creep analyses of the longitudinal welded tube specimens were conducted to identify the stress and creep strain distributions within the specimen during creep. Failure occurred at a heat affected zone (HAZ) without a significant macroscopic deformation. It was found that the initiation of creep voids had concentrated at the midthickness region in the HAZ rather than in the surface. The creep analysis results indicated that the triaxial tensile stress yielded at the midthickness region in the HAZ due to difference of creep deformation property among the base metal, the HAZ, and the weld metal. It was suggested that the triaxial stress state caused acceleration of the creep damage evolution in the HAZ, resulting in internal failure of the tube specimens. A rupture time prediction method of the welded tube is proposed based on the maximum principal stress and the triaxial stress factor in the HAZ. The void growth behavior in the HAZ was well predicted by the previously proposed void growth simulation method by introducing a void initiation function to the method.

Static and cyclic creep behavior of in situTiB2 particulate reinforced aluminum composite

1999 ◽  
Vol 14 (12) ◽  
pp. 4541-4550 ◽  
Author(s):  
Z. Y. Ma ◽  
S. C. Tjong ◽  
S. X. Li
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Cyclic Creep ◽  
Creep Tests ◽  
Aluminum Composite ◽  
Self Diffusion ◽  
True Activation Energy ◽  
Static Creep ◽  
Particulate Reinforced

Static and cyclic creep tests of Al–15 vol% TiB2in situ composite were carried out at 573–623 K. The values of apparent stress exponent and activation energy for cyclic creep of the composite were much higher than that for static creep. Furthermore, the cyclic creep rate tended to decrease with increasing percentage of unloading amount but was independent of the loading frequencies under the frequency ranges investigated. Finally, the true stress exponent of the composite was equal to 8, and the true activation energy was close to the value for the lattice self-diffusion of aluminum by incorporating a threshold stress for the analysis.

Hybrid remaining useful life prediction method. A case study on railway D-cables

2021 ◽  
pp. 107746
Author(s):  
Yu Zang ◽  
Wei Shangguan ◽  
Baigen Cai ◽  
Huasheng Wang ◽  
Michael. G. Pecht
Keyword(s):  
Life Prediction ◽  
Prediction Method ◽  
Remaining Useful Life ◽  
Useful Life
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