scholarly journals Analysis of Fatigue Strain, Fatigue Modulus and Fatigue Damage for the Model formulation of Concrete based on Strain Life Approach

2019 ◽  
Author(s):  
Indra Yadav ◽  
Kamal Bahadur Thapa
Keyword(s):  
Fatigue Damage ◽  
Residual Strain ◽  
Inelastic Deformation ◽  
Evaluation Model ◽  
Strain Curve ◽  
Fatigue Loading ◽  
Vital Role ◽  
Evolution Model ◽  
Stiffness Degradation ◽  
The Impact

Analysis of Fatigue Strain, Fatigue Modulus and Fatigue Damage for the modeling of concrete plays a vital role in the evolution material behaviour which is heterogeneous and anisotropic in nature. In this paper, the Level-S nonlinear fatigue strain curve, fatigue modulus curve, residual strain curve of concrete in compression, tension, flexure and torsional fatigue loading were proposed using strain life approach. The parameters such as physical meaning, the ranges, and the impact on the shape of the curve were discussed. Then, the evolution model of fatigue modulus was established based on the fatigue strain evolution model, fatigue modulus evaluation model, residual strain evaluation model, secondary strain evaluation model. The hypothesis of fatigue modulus is inversely related with the fatigue strain amplitude. The fatigue evolution of concrete damages the bond between material grains, changed the orientation of structure of molecules and affects the elastic properties resulting in the reduction of material stiffness and modulus by utilizing strain life analysis, regarding stiffness degradation and inelastic deformation by formation of microcracking, macro cracking, cracking which is heterogeneous and anisotropic in nature . This paper presents the Fatigue Strain Life Model and analyses of fatigue strain, fatigue modulus and damage parameters of concrete which is capable of predicting stiffness degradation, inelastic deformation, strength reduction under fatigue loading. Hence, the obtainable results were compared with experimental results for the validation of the proposed model.

scholarly journals Strain based approach in fatigue damage modeling of brittle material-application to concrete

2019 ◽  
Vol 2 (1) ◽  
pp. 49-60
Author(s):  
Indra Narayan Yadav
Keyword(s):  
Fatigue Damage ◽  
Brittle Material ◽  
Inelastic Deformation ◽  
Damage Mechanics ◽  
Fatigue Loading ◽  
Biaxial Stress ◽  
Stiffness Degradation ◽  
Experimental Result ◽  
Variable Theory ◽  
Strain Space

Due to very good compressive strength of concrete, it is used widely in all over the world during three decades. The Formulation of Concrete is through combination of Cement, stone aggregate, sand and water according to their design mix based on the ultimate strength required for the structural component. The Mixing of concrete is as mortar, the layer of cement, sand and water is wrapped around the aggregate. When the load is applied to the concrete, the weaker zone i.e. mortar of cement, sand is weaker than stone aggregate, damage by formulation of crack before crack in aggregate. The Damage behavior of Concrete is thus to be analyzed according to their fatigue behavior. Strain Based approach in Fatigue Damage Modelling of Brittle Material in Concrete is presented to describe the behavior and failure of con-crete by utilizing Damage Mechanics approach. Stiffness degradation and inelastic deformation are the essential features of concrete that develop due tothe formation of multitude of microcracks in the fatigue environment. Microcracking, which is anisotropic in nature, destroys the bond between material grains, and affects the elastic properties resulting in the reduction of material stiffness in elastic as well as plastic stage. This paper presents an anisotropic fatigue damage model for plain concrete subjected to cyclic tension. The model is developed, in strain space, using the general framework of internal variable theory of continuum thermodynamics and Damage Mechanics. It is argued that within the damage surface of given strain states the unloadingreloading cycles (fatigue loading) stimulate the nucleation and growth microcracks in concrete, which will result in stiffness degradation and inelastic deformation, and hence material is termed as damaged. Damage is reflected through the fourthorder stiffness tensor involving a damage parameter whose increment is governed by the consistency equation associated with a cycle dependent damage surface in strain space. The model is capable of predicting stiffness degradation, inelastic deformation and strength reduction under fatigue loading and compared against experimental result. By increasing the number of loading cycles, the strength of concrete gradually decreases and the limit surface is allowed to contract and form new curves representing residual strengths. The magnitude of loading, load range, and the load path are known to influence the fatigue life and hence are addressed in this formulation. In this paper, a strength softening function is proposed in order to address the re-duction in the strength of concrete due to fatigue. Separate softening functions are also proposed to account for the deformation characteristics in concrete under cyclic loading. Numerical simula-tions predicted by the model in both uniaxial and biaxial stress paths show a good correlation with the experimental data available in the literature.

scholarly journals Research on Fatigue Strain and Fatigue Modulus of Concrete

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Fangping Liu ◽  
Jianting Zhou
Keyword(s):  
Strain Analysis ◽  
Correlation Coefficients ◽  
Vital Role ◽  
Evolution Model ◽  
Linear Change ◽  
Advantages And Disadvantages ◽  
Strain Evolution ◽  
Left Corner ◽  
The Impact ◽  
Evolution Curve

Concrete fatigue strain and fatigue modulus evolution play a vital role in the evaluation of the material properties. In this paper, by analyzing the advantages and disadvantages of existing concrete strain analysis methods, the level-S nonlinear fatigue strain model was proposed. The parameters’ physical meaning, the ranges, and the impact on the shape of the curve were all discussed. Then, the evolution model of fatigue modulus was established based on the fatigue strain evolution model and the hypothesis of fatigue modulus inversely related fatigue strain amplitude. The results indicate that the level-S model covered all types of fatigue strain evolution. It is very suitable for the description of strain evolution of concrete for its strong adaptability and high accuracy. It was found that the fitting curves coincided with the experimental curves very well, and the correlation coefficients were all above 0.98. The evolution curves of fatigue strain modulus both have three stages, namely, variation phase, linear change stage, and convergence stage. The difference is that the fatigue strain evolution curve is from the lower left corner to the upper right corner, but the fatigue modulus evolution curve is from the upper left corner to the right lower corner.

scholarly journals Fatigue Strain and Damage Analysis of Concrete in Reinforced Concrete Beams under Constant Amplitude Fatigue Loading

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Fangping Liu ◽  
Jianting Zhou
Keyword(s):  
Reinforced Concrete ◽  
Fatigue Damage ◽  
Concrete Beams ◽  
Nonlinear Evolution ◽  
Fatigue Loading ◽  
Evolution Model ◽  
Reinforced Concrete Beams ◽  
Constant Amplitude ◽  
Bending Fatigue ◽  
Strain Evolution

Concrete fatigue strain evolution plays a very important role in the evaluation of the material properties of concrete. To study fatigue strain and fatigue damage of concrete in reinforced concrete beams under constant amplitude bending fatigue loading, constant amplitude bending fatigue experiments with reinforced concrete beams with rectangular sections were first carried out in the laboratory. Then, by analyzing the shortcomings and limitations of existing fatigue strain evolution equations, the level-S nonlinear evolution model of fatigue strain was constructed, and the physical meaning of the parameters was discussed. Finally, the evolution of fatigue strain and fatigue damage of concrete in the compression zone of the experimental beam was analyzed based on the level-S nonlinear evolution model. The results show that, initially, fatigue strain grows rapidly. In the middle stages, fatigue strain is nearly a linear change. Because the experimental data for the third stage are relatively scarce, the evolution of the strain therefore degenerated into two phases. The model has strong adaptability and high accuracy and can reflect the evolution of fatigue strain. The fatigue damage evolution expression based on fatigue strain shows that fatigue strain and fatigue damage have similar variations, and, with the same load cycles, the greater the load level, the larger the damage, in line with the general rules of damage.

scholarly journals Performance of CRTS-II Ballastless Track–Bridge Structural System Rebars under Fatigue Loading Test

2021 ◽  
Vol 11 (11) ◽  
pp. 4858
Author(s):  
Lingyu Zhou ◽  
Lifan Zou ◽  
Lei Zhao ◽  
Yahui Yuan ◽  
Akim D. Mahunon ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fatigue Damage ◽  
Strain Amplitude ◽  
Amplitude Ratio ◽  
Strain Curve ◽  
Fatigue Loading ◽  
Structural System ◽  
Ballastless Track ◽  
Cumulative Strain ◽  
Track Bridge

To study the evolution of mechanical properties of steel rebars in the China Railway Track System Type II (CRTS II) ballastless track–bridge structural system under repeated train loads, a 1/4 scale three-span ballastless slab track simple-supported bridge structural system specimen was manufactured and subjected to a multistage fatigue test with 18 million cycles. The experimental results show that the strain amplitude of the steel bar changes proportionally to the fatigue stress amplitude, and there is an obvious strain increase in the loading stage 4, where the fatigue stress amplitude is the largest. During the test, the cumulative strain–amplitude ratio first decreases then increases. At the end of the test, the cumulative strain–amplitude ratio increases by 5.46% and 5.32%, respectively, at L/2 and L/4 sections. The load–strain curve of the steel rebar keeps the shape of an oblique straight line. The slope increases first and then decreases with a degradation at the end of the test of 5.14% and 4.82%, respectively, at L/2 and L/4 sections. The mechanical properties of the rebar are enhanced under the first three million fatigue loading cycles: this is the fatigue strengthening stage. The mechanical properties of reinforcement gradually degrade from the three millionth cycle to the end of the test: this is the fatigue damage stage. Finally, based on the material fatigue damage model and the multistage cumulative damage criterion, the change rule of the load–strain curve slope of steel rebars in the fatigue damage stage is obtained by finite element simulation. The simulation results agree well with the experimental data, proving the validity of the calculation method proposed in this paper.

The Impact Of Emotional Intelligence On Leadership Excellence Of Executive Empoloyees In Public Sector Organizationin Ampara District Of Sri Lanka

2019 ◽  
Vol 118 (9) ◽  
pp. 52-60
Author(s):  
Dr.S. Gunapalan ◽  
Dr.K. Maran
Keyword(s):  
Emotional Intelligence ◽  
Public Sector ◽  
Vital Role ◽  
Public Organization ◽  
Self Awareness ◽  
Public Sector Organization ◽  
Expression Of Emotion ◽  
Asking Questions ◽  
Private Sector Organizations ◽  
The Impact

Emotional Intelligence is play a vital role to decide  leadership excellence. So this paper to study the  impact of emotional intelligence on leadership excellence of executive employee in public sector organization.Hence the objective of this  research   is to identify the  impact of emotional intelligence on leadership excellence of executive employee in Public Sector Organization in Ampara districtof Sri Lanka.emotional intelligence includes the verbal and non-verbal appraisal and expression of emotion, the regulation of emotion in the self and others, and the utilization of emotional content in problem solving. Cook (2006)[1]. Emotional intelligence is one of the  essential skill for leaders to manage their subordinate. Accordingly although there is some research done under “Emotional intelligence on leadership excellence of the executive employee in the public organization in Ampara district so this study full filed the gap. Based on the analysis, Self-awareness, Self-management, Social-awareness and Relationship management are the positively affect to the Leadership excellence. So, executive employees should consider about the Emotions of their subordinators when they completing their targets. leaders should pay the attention for recognize the situation, hove to impact their feelings for the performance & recognized their own feelings. Leaders should consider and see their own emotions when they work with others by listening carefully, understand the person by asking questions, identifying non-verbal expressions and solving problems without helming someone’s. Leadersshould consider their subordinators emotions when they find a common idea, government should give to moderate freedom to executive employees in public organization to take the decision with competing the private sector organizations.

Studies on Related ms Magnitude Rate Models in Triangular Wave Unloading Section of Calcium Medium-Fine Sandstone

2010 ◽  
Vol 152-153 ◽  
pp. 164-170
Author(s):  
Jie Liu ◽  
Jian Lin Li ◽  
Ying Xia Li ◽  
Shan Shan Yang ◽  
Ji Fang Zhou ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Strain Curve ◽  
Experimental System ◽  
Constant Term ◽  
Lag Time ◽  
Vertical Force ◽  
Time Segment ◽  
Triangular Wave ◽  
Apparent Modulus ◽  
The Impact

Specific to the improvement in the present research of mechanical response under cyclic loading, this paper, taking the calcareous middle- coarse sandstone as the research subject and the RMT-150C experimental system in which data is recoded by ms magnitude as the platform, develops several related models concerning the unloading rate of triangle waves. The unloading process is divided into lag time segment and non-lag time segment, with criterions and related parameters provided as well. The term apparent elastic modulus is defined. The test data analysis shows that there exist a linear relationship between the apparent modulus and instant vertical force before load damage in non-lag time segment. On the preceding basis, a rate-dependent model of triangular wave un-installation section in non-lag time segment is established. Due to the inability of the loading equipment to accurately input the triangle wave, the average loading rate is amended and a constant term is added into it. The model is proved to be reliable, as the predicted value of the deformation rate and the stress strain curve coincides with measured value. At the same time, the impact of the lag time is pointed out quantitatively and a predication model of lag time segment is set up.

scholarly journals Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2738
Author(s):  
Roland Pawliczek ◽  
Tadeusz Lagoda
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Strain Curve ◽  
Mean Value ◽  
Fatigue Properties ◽  
Stress Strain ◽  
Reference Case ◽  
Block Loading ◽  
The Mean ◽  
Mean Strain

The literature in the area of material fatigue indicates that the fatigue properties may change with the number of cycles. Researchers recommend taking this into account in fatigue life calculation algorithms. The results of simulation research presented in this paper relate to an algorithm for estimating the fatigue life of specimens subjected to block loading with a nonzero mean value. The problem of block loads using a novel calculation model is presented in this paper. The model takes into account the change in stress–strain curve parameters caused by mean strain. Simulation tests were performed for generated triangular waveforms of strains, where load blocks with changed mean strain values were applied. During the analysis, the degree of fatigue damage was compared. The results of calculations obtained for standard values of stress–strain parameters (for symmetric loads) and those determined, taking into account changes in the curve parameters, are compared and presented in this paper. It is shown that by neglecting the effect of the mean strain value on the K′ and n′ parameters and by considering only the parameters of the cyclic deformation curve for εm = 0 (symmetric loads), the ratio of the total degree of fatigue damage varies from 10% for εa = 0.2% to 3.5% for εa = 0.6%. The largest differences in the calculation for ratios of the partial degrees of fatigue damage were observed in relation to the reference case for the sequence of block n3, where εm = 0.4%. The simulation results show that higher mean strains change the properties of the material, and in such cases, it is necessary to take into account the influence of the mean value on the material response under block loads.

scholarly journals High Expression of KLF10 Is Associated with Favorable Survival in Patients with Oral Squamous Cell Carcinoma

Medicina ◽  
2020 ◽  
Vol 57 (1) ◽  
pp. 17
Author(s):  
Chung-Min Yeh ◽  
Yi-Ju Lee ◽  
Po-Yun Ko ◽  
Yueh-Min Lin ◽  
Wen-Wei Sung
Keyword(s):  
Survival Rate ◽  
Oral Cancer ◽  
Cancer Patients ◽  
Protective Factor ◽  
Female Gender ◽  
Vital Role ◽  
Cancer Stage ◽  
Independent Prognostic Marker ◽  
Oral Cancer Patients ◽  
The Impact

Background and objectives: Krüppel-like transcription factor 10 (KLF10) plays a vital role in regulating cell proliferation, including the anti-proliferative process, activation of apoptosis, and differentiation control. KLF10 may also act as a protective factor against oral cancer. We studied the impact of KLF10 expression on the clinical outcomes of oral cancer patients to identify its role as a prognostic factor in oral cancer. Materials and Methods: KLF10 immunoreactivity was analyzed by immunohistochemical (IHC) stain analysis in 286 cancer specimens from primary oral cancer patients. The prognostic value of KLF10 on overall survival was determined by Kaplan–Meier analysis and the Cox proportional hazard model. Results: High KLF10 expression was significantly associated with male gender and betel quid chewing. The 5-year survival rate was greater for patients with high KLF10 expression than for those with low KLF10 expression (62.5% vs. 51.3%, respectively; p = 0.005), and multivariate analyses showed that high KLF10 expression was the only independent factor correlated with greater overall patient survival. The significant correlation between high KLF10 expression and a higher 5-year survival rate was observed in certain subgroups of clinical parameters, including female gender, non-smokers, cancer stage T1, and cancer stage N0. Conclusions: KLF10 expression, detected by IHC staining, could be an independent prognostic marker for oral cancer patients.

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