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.

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.

Fatigue Behavior of Ferritic-Pearlitic-Bainitic Steel – Effect of Positive Mean Stress

2009 ◽  
Vol 417-418 ◽  
pp. 577-580
Author(s):  
Jaroslav Polák ◽  
Martin Petrenec
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Strain Amplitude ◽  
Fatigue Behavior ◽  
Cyclic Creep ◽  
Plastic Strain Amplitude ◽  
Fatigue Properties ◽  
Mean Stress ◽  
Bainitic Steel ◽  
The Mean

The fatigue properties of ferritic-pearlitic-bainitic steel using specimens produced from massive forging were measured in stress controlled regime with positive mean stress. The cyclic creep curves and cyclic hardening/softening curves were evaluated. The fatigue life was plotted in dependence on the mean stress and on the plastic strain amplitude. The principal contribution to the drop of the fatigue life with the mean stress is due to the increase of the plastic strain amplitude in cycling with mean stress.

Fatigue-life prediction under irregular stress conditions

1970 ◽  
Vol 5 (3) ◽  
pp. 207-211 ◽  
Author(s):  
T H Erismann
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Stress Conditions ◽  
Fatigue Life Prediction ◽  
Mean Stress ◽  
Arbitrary Loading ◽  
Empirical Determination ◽  
The Mean ◽  
Standard Tests

The present work is a shorter version of a more detailed treatise by the author (1)∗. The method consists of two parts: the empirical determination of certain characteristics of a material by means of a relatively small number of well defined standard tests, and the arithmetical application of the results obtained to arbitrary loading histories. The following groups of parameters are thus taken into account: the variations of the mean stress; the interaction of these variations and the superposed oscillating stresses; the spectrum of the oscillating-stress amplitudes; the sequence of the oscillating-stress amplitudes.

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.

FATIGUE LIFE PREDICTION OF ROLLED AZ31 MAGNESIUM ALLOY USING AN ENERGY-BASED MODEL

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5503-5508 ◽  
Author(s):  
SUNG HYUK PARK ◽  
SEONG-GU HONG ◽  
BYOUNG HO LEE ◽  
CHONG SOO LEE
Keyword(s):  
Fatigue Life ◽  
Magnesium Alloy ◽  
Deformation Behavior ◽  
Strain Energy ◽  
Life Prediction ◽  
Fatigue Life Prediction ◽  
Az31 Magnesium Alloy ◽  
Stress And Strain ◽  
Mean Stress ◽  
The Mean

Fatigue behavior of rolled AZ31 magnesium alloy, which shows an anisotropic deformation behavior due to the direction dependent formation of deformation twins, was investigated by carrying out stress and strain controlled fatigue tests. The anisotropy in deformation behavior introduced asymmetric stress-strain hysteresis hoops, which make it difficult to use common fatigue life prediction models, such as stress and strain-based models, and induced mean stress and/or strain even under fully-reversed conditions; the tensile mean stress and strain were found to have a harmful effect on the fatigue resistance. An energy-based model was used to describe the fatigue life behavior as strain energy density was stabilized at the early stage of fatigue life and nearly invariant through entire life. To account for the mean stress and strain effects, an elastic energy related to the mean stress and a plastic strain energy consumed by the mean strain were appropriately considered in the model. The results showed that there is good agreement between the prediction and the experimental data.

scholarly journals Fatigue Life Prediction of Rolling Bearings Based on Modified SWT Mean Stress Correction

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Aodi Yu ◽  
Hong-Zhong Huang ◽  
Yan-Feng Li ◽  
He Li ◽  
Ying Zeng
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Sensitivity Coefficient ◽  
Fatigue Life Prediction ◽  
Stress Effect ◽  
Mean Stress ◽  
Rolling Bearings ◽  
Contact Loads ◽  
Compensation Factor ◽  
The Mean

AbstractThe existing engineering empirical life analysis models are not capable of considering the constitutive behavior of materials under contact loads; as a consequence, these methods may not be accurate to predict fatigue lives of rolling bearings. In addition, the contact stress of bearing in operation is cyclically pulsating, it also means that the bearing undergo non-symmetrical fatigue loadings. Since the mean stress has great effects on fatigue life, in this work, a novel fatigue life prediction model based on the modified SWT mean stress correction is proposed as a basis of which to estimate the fatigue life of rolling bearings, in which, takes sensitivity of materials and mean stress into account. A compensation factor is introduced to overcome the inaccurate predictions resulted from the Smith, Watson, and Topper (SWT) model that considers the mean stress effect and sensitivity while assuming the sensitivity coefficient of all materials to be 0.5. Moreover, the validation of the model is finalized by several practical experimental data and the comparison to the conventional SWT model. The results show the better performance of the proposed model, especially in the accuracy than the existing SWT model. This research will shed light on a new direction for predicting the fatigue life of rolling bearings.

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.

Strain Ratio Effect on the Low Cycle Fatigue Behavior and Microstructure of High-Mn Austenitic Alloy Undergoing the Strain-Induced ε-Martensitic Transformation

2018 ◽  
Vol 941 ◽  
pp. 1065-1070
Author(s):  
Ilya Nikulin ◽  
Takahiro Sawaguchi
Keyword(s):  
Martensitic Transformation ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Control Mode ◽  
Total Strain ◽  
Lattice Rotation ◽  
Mean Stress ◽  
Total Strain Amplitude ◽  
Cycle Fatigue ◽  
The Mean

The effect of the strain asymmetry on low-cycle fatigue properties and microstructure of Fe–15Mn–10Cr–8Ni–4Si (in. wt. %) alloy undergoing the strain-induced ε-martensitic transformation (ε-MT) were investigated at strain ratios,R, of-1, -0.2, 0.2 and 0.5 under total strain-control mode with total strain amplitude of 0.01. At studied strain ratios the clear asymmetry in tension and compression stress providing tensile mean stress was observed in alloy deformed atRof-0.2, 0.2 and 0.5. The mean stress rapidly decreases to ~ 100 cycles and remain almost zero until failure. It was found that strain-induced ε-martensitic transformation and lattice rotation of austenite provide cyclic hardening of the studied alloy leading to the mean stress relaxation and provides the stability in hysteresis loops behavior at studiedR. As a consequence, the fatigue life,Nf, of the alloy remains on the level of the alloy deformed by LCF atR, of -1 (NfR=-1=9200 cycles). The details of the fatigue behavior, deformation mechanisms and microstructure evolution of the studied alloy are discussed.

Time-Dependent Response of Polymer Systems Under Cyclic Loading Conditions

2000 ◽  
Author(s):  
Shane Schumacher ◽  
Aleksandra M. Vinogradov ◽  
Zhiyu Liu ◽  
Christopher H. Jenkins ◽  
Isamu Kitahara ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Polyvinylidene Fluoride ◽  
Cyclic Creep ◽  
Nylon 6 ◽  
Time Dependent ◽  
Cyclic Loads ◽  
Mean Stress ◽  
Loading Conditions ◽  
Polymer Systems ◽  
The Mean

Abstract The paper concerns the time dependent response of polymer systems subjected to superimposed static and cyclic loads. An experimental study of two materials, Nylon 6/6 and a piezoelectric polyvinylidene fluoride (PVDF)-based composite, has been conducted with the objective to determine the degree of cyclic creep effects depending on the mean stress, cyclic stress amplitude and frequency. Creep acceleration due to cyclic loading effects has been observed in both materials even in the range of stresses well below their respective viscoelastic linearity limits. It is clear that these effects are essentially nonlinear, as the response of the materials to cyclic loading conditions does not represent a simple superposition of the responses to static and fully reversed cyclic loads applied separately. An increase of creep rates in both polymers has been observed consistently as frequencies and amplitudes of vibration tended to increase. However, the relation between cyclic creep effects and the mean stress appears to vary depending on the polymer type and loading conditions. Nylon 6/6 has demonstrated material hardening as a result of cycling. Considerable crack development in Nylon 6/6 has been detected only in the range of stresses approaching yield conditions.

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