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.

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 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.

Creep-Fatigue Behavior and Life Prediction of 316L Stainless Steel Under Different Loading Levels

2009 ◽  
Author(s):  
Huifeng Jiang ◽  
Xuedong Chen ◽  
Zhichao Fan ◽  
Jie Dong ◽  
Heng Jiang
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Cyclic Deformation ◽  
Life Prediction ◽  
316L Stainless Steel ◽  
Control Mode ◽  
Creep Fatigue ◽  
Material Creep ◽  
Minimum Stress ◽  
Mean Strain

Stress controlled creep-fatigue interaction tests were carried out for 316L stainless steel under different loading levels at 550°C. Cyclic properties such as material life and mean strain were investigated for 316L stainless steel. When the maximum stress is keeping fixed, with increasing minimum stress, the material creep-fatigue life increases first and then decreases. When the stress amplitude is equal to 167.5MPa (minimum stress is equal to 50MPa), material creep-fatigue life reaches its maximum value. Moreover, under stress control mode, dynamic strain aging was found to manifest itself macroscopically as displacement or mean strain abrupt jumps during cyclic deformation. When the minimum stress is less than 0MPa, abrupt displacement jumps occur at the early stage of cyclic deformation and there are many jumps during the whole process. While the minimum stress is larger than 0MPa, displacement only jumps once at the end of deformation. Additionally, by employing a life prediction method on the basis of the Hull-Rimmer creep cavity growth theory, the creep-fatigue life was assessed for 316L stainless steel at 550°C under different loading levels. The predicted lives were compared with the tested ones and a good agreement was found between them.

scholarly journals A Strain Rate-Dependent Damage Evolution Model for Concrete Based on Experimental Results

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Bin Xu ◽  
Xiaoyan Lei ◽  
P. Wang ◽  
Hui Song
Keyword(s):  
Strain Rate ◽  
Uniaxial Compression ◽  
Damage Evolution ◽  
Damage Model ◽  
Evolution Model ◽  
Experimental Results ◽  
Strain Rates ◽  
Compression Tests ◽  
Stress Strain ◽  
Actual Damage

There are various definitions of damage variables from the existing damage models. The calculated damage value by the current methods still could not well correspond to the actual damage value. Therefore, it is necessary to establish a damage evolution model corresponding to the actual damage evolution. In this paper, a strain rate-sensitive isotropic damage model for plain concrete is proposed to describe its nonlinear behavior. Cyclic uniaxial compression tests were conducted on concrete samples at three strain rates of 10−3s−1, 10−4s−1, and 10−5s−1, respectively, and ultrasonic wave measurements were made at specified strain values during the loading progress. A damage variable was defined using the secant and initial moduli, and concrete damage evolution was then studied using the experimental results of the cyclic uniaxial compression tests conducted at the different strain rates. A viscoelastic stress-strain relationship, which considered the proposed damage evolution model, was presented according to the principles of irreversible thermodynamics. The model results agreed well with the experiment and indicated that the proposed damage evolution model can accurately characterize the development of macroscopic mechanical weakening of concrete. A damage-coupled viscoelastic constitutive relationship of concrete was recommended. It was concluded that the model could not only characterize the stress-strain response of materials under one-dimensional compressive load but also truly reflect the degradation law of the macromechanical properties of materials. The proposed damage model will advance the understanding of the failure process of concrete materials.

On the Development of Physically Based Life Prediction Models in the Thermo Mechanical Fatigue of Ni-Base Superalloys

2011 ◽  
Vol 465 ◽  
pp. 47-54 ◽  
Author(s):  
Stephen D. Antolovich ◽  
Robert L. Amaro ◽  
Richard W. Neu ◽  
A Staroselsky
Keyword(s):  
High Temperature ◽  
Damage Evolution ◽  
Life Prediction ◽  
Prediction Models ◽  
High Temperature Fatigue ◽  
Mechanical Fatigue ◽  
Use Of Resources ◽  
Physically Based ◽  
Creep Fatigue ◽  
Materials Used

In a world increasingly concerned with environmental factors and efficient use of resources, increasing operating temperatures of high temperature machinery can play an important role in meeting these goals. In addition, the cost of failure of such devices is rapidly becoming prohibitive. For example, in an airline crash airframe and engine manufacturers are, on average, held liable for 1,000,000 euros per fatality excluding the loss of property. Thus there is considerable pressure to make machinery that can operate much more safely at high temperatures. This means that the old ways of guarding against high temperature fatigue failure (e.g. factor of safety, S/N curves, creep life) are no longer acceptable; more reliable, accurate, and efficient means are needed to manage life, durability and risk. In this paper, high temperature fatigue is considered in terms of past successes and current challenges. Particular emphasis is placed on understanding damage mechanisms and their interactions both in terms of scientific interest and technological importance. Materials used in nuclear reactors (e.g. selected steels and solid solution Ni-base alloys) and in hot sections of jet engines (e.g. superalloys) are used as vehicles to illustrate damage evolution and interaction. Phenomenological life prediction models are presented and compared with physics-based damage evolution/interaction models which are based on observed physical processes such as creep/fatigue/environment interactions. It is shown that in many cases, in spite of the emphasis on creep-fatigue interactions, the most damaging forms of damage that occur under thermo-mechanical fatigue (TMF) loading result from the interaction of slip bands with oxidized boundaries.

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