scholarly journals Analysis of Fatigue Life of PMMA at Different Frequencies Based on a New Damage Mechanics Model

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Aifeng Huang ◽  
Weixing Yao ◽  
Fang Chen
Keyword(s):  
Fatigue Life ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Low Frequency ◽  
Creep Damage ◽  
Cyclic Creep ◽  
Continuum Damage Mechanics ◽  
Creep Tests ◽  
Damage Evolution Equation ◽  
Load Rate

Low-cycle fatigue tests at different frequencies and creep tests under different stress levels of Plexiglas Resist 45 were conducted. Correspondingly, the creep fracture time,S-Ncurves, cyclic creep, and hysteresis loop were obtained. These results showed that the fatigue life increases with frequency at low frequency domain. After analysis, it was found that fatigue life is dependent on the load rate and is affected by the creep damage. In addition, a new continuum damage mechanics (CDM) model was established to analyze creep-fatigue life, where the damage increment nonlinear summation rule was proposed and the frequency modification was made on the fatigue damage evolution equation. Differential evolution (DE) algorithm was employed to determine the parameters within the model. The proposed model described fatigue life under different frequencies, and the calculated results agreed well with the experimental results.

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.

Creep Behaviors Calculated by Varying Material Constants Obtained from Different Stress Regions for a Closed-End P91 Pipe

2016 ◽  
Vol 35 (5) ◽  
pp. 441-447
Author(s):  
Zhao Yanping ◽  
Gong Jianming ◽  
Wang Xiaowei ◽  
Li Qingnan
Keyword(s):  
Damage Mechanics ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Creep Tests ◽  
Material Constants ◽  
Mechanics Model ◽  
Stress Region ◽  
Wide Range ◽  
Tertiary Stage

AbstractIn order to predict the creep life of a component at high temperature both accurately and economically, continuum damage mechanics approach is used based on experimental creep data. However, material constants used in the models have a great relationship with the performed stress range of creep tests. In this paper, several sets of material constants were obtained from a wide range of stresses on P91 steel. The creep damage tolerance parameter was used to classify these sets, and the modified continuum damage mechanics model was used to investigate a pipe under closed-end condition. Results have illustrated the main difference lies on the tertiary stage while slight difference on the primary and secondary stages, and the contribution of the tertiary stage to the total damage decreased when using material constants from higher stress region.

Continuum damage mechanics-based ductile behavior and fatigue life estimation of low carbon steels: AISI 1020 and AISI 1030

2019 ◽  
Vol 233 (10) ◽  
pp. 2057-2071
Author(s):  
Abhinav Gautam ◽  
Prabir Kumar Sarkar
Keyword(s):  
Fatigue Life ◽  
Strain Hardening ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Continuum Damage Mechanics ◽  
Strain Hardening Exponent ◽  
Cycle Fatigue ◽  
Ductile Flow ◽  
Ductile Behavior

This paper presents an experimental estimation of the ductile behavior and low-cycle fatigue life for widely used structural steels AISI 1020 and AISI 1030 based on continuum damage mechanics approach. This method identifies the deterioration in stiffness of a material arising from micromechanisms of formation, growth, and coalescence of microvoids. This helps the characterization of the ductile flow behavior of metals through a damage variable D, evaluated via load–unload cyclic tensile test. The influence of strain hardening exponent, commonly treated as a constant in ductile flow characterization, is also explored in the current investigation. Its determination uses the Hollomon constitutive relation. Estimated D at different strain levels defines the corresponding effective stress. Application of this stress to the strain equivalence theory then enables the prediction of the stress–strain curve. The model-based results closely approximate the experimental stress–strain curve up to the onset of necking. The agreement of experimental results for fatigue life of the materials from low-cycle fatigue tests with damage-based low-cycle fatigue model demonstrates the correctness of the experimental findings. The damage-based model additionally helps in the prediction of microcrack nucleation and crack propagation life separately. Fractographic examinations of test specimen exhibit usually observed morphology of involved failure mechanisms. The present study emphasizes the experimental means of damage-based ductile flow assessment involving strain hardening exponent term and also the low-cycle fatigue life estimation. The significance of varying strain hardening exponent is further expressed in terms of the corresponding damage magnitude. The material data obtained from this study depicts the damage state at different levels of plastic strain that may serve as a useful information for metal-forming process design.

scholarly journals Anisotropic Elastoplastic Damage Mechanics Method to Predict Fatigue Life of the Structure

2016 ◽  
Vol 2016 ◽  
pp. 1-12
Author(s):  
Hualiang Wan ◽  
Qizhi Wang ◽  
Zheng Zhang
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Damage Evolution ◽  
Present Method ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Engineering Application ◽  
Damage Evolution Equation ◽  
Material Parameters ◽  
Elastoplastic Damage

New damage mechanics method is proposed to predict the low-cycle fatigue life of metallic structures under multiaxial loading. The microstructure mechanical model is proposed to simulate anisotropic elastoplastic damage evolution. As the micromodel depends on few material parameters, the present method is very concise and suitable for engineering application. The material parameters in damage evolution equation are determined by fatigue experimental data of standard specimens. By employing further development on the ANSYS platform, the anisotropic elastoplastic damage mechanics-finite element method is developed. The fatigue crack propagation life of satellite structure is predicted using the present method and the computational results comply with the experimental data very well.

scholarly journals Fatigue Failure Model for Polymeric Compliant Systems

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Theddeus T. Akano ◽  
Omotayo A. Fakinlede
Keyword(s):  
Fatigue Life ◽  
Damage Mechanics ◽  
Compliant Mechanisms ◽  
Elastic Strain Energy ◽  
Continuum Damage Mechanics ◽  
Fatigue Tests ◽  
Theoretical Formula ◽  
Damage Evolution Equation ◽  
Safety And Reliability ◽  
Stress Cycles

Fatigue analysis and lifetime evaluation are very important in the design of compliant mechanisms to ensure their safety and reliability. Earlier models for the fatigue prediction of compliant mechanisms are centred on repeated and reversed stress cycles. Compliant mechanisms (CMs) are now being applied to situations where the fatigue is caused by random varying stress cycles. It is, therefore, necessary to consider fatigue resulting from random varying stress cycles and damage caused to the compliant material. A continuum damage mechanics (CDM) model is proposed to assess the fatigue life of polymeric compliant mechanisms. The elastic strain energy is computed on the basis of a nearly incompressive hyperelastic constitution. The damage evolution equation is used to develop a mathematical formula that describes the fatigue life as a function of the nominal strain amplitude under cyclic loading. Low density polypropylene (LDP) is used for the fatigue tests conducted under displacement controlled condition with a sine waveform of 10 Hz. The results from the theoretical formula are compared with those from the experiment and fatigue software. The result from the prediction formula shows a strong agreement with the experimental and simulation results.

Assessment of Low Cycle Fatigue Life of Steam Turbine Rotor Based on a Thermodynamic Approach

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Yong-Jian Sun ◽  
Li-Sheng Hu
Keyword(s):  
Fatigue Life ◽  
Steam Turbine ◽  
Nonlinear Model ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Continuum Damage Mechanics ◽  
Turbine Rotor ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Steam Turbine Rotor

A new nonlinear model is proposed to assess the low cycle fatigue life of a 300 MW steam turbine rotor. Manson-Coffin equation and cyclic stress-strain relationship are employed to eliminate the unmeasured parameters, so all the parameters in model are measurable. Through comparison with that from the linear accumulation theory and continuum damage mechanics theory the results show this new nonlinear model describes the damage accumulation well and precisely in accordance with the practical test data. This approach supplies a new way to assess the damage of steam turbine rotor with satisfactory precision in engineering.

Continuum damage mechanics application in low-cycle thermal fatigue

2012 ◽  
Vol 22 (2) ◽  
pp. 285-300 ◽  
Author(s):  
M Mashayekhi ◽  
A Taghipour ◽  
A Askari ◽  
M Farzin
Keyword(s):  
Fatigue Life ◽  
Thermal Fatigue ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Isothermal Condition ◽  
Continuum Damage Mechanics ◽  
Life Assessment ◽  
Continuum Damage ◽  
Fatigue Damage Accumulation

In this article, a fatigue model for low-cycle thermal fatigue formulated in a continuum damage mechanics framework is presented. The model is based on a unified damage law presented by Lemaitre for low-cycle fatigue, which has been extended to low-cycle thermal fatigue. The temperature dependencies of material parameters are considered in the damage evolution integration to take the non-isothermal condition of loading into account. This model considers the stress triaxiality and non-linearity of damage evolution, and it is developed to a fatigue damage accumulation rule in which the load sequence effect is also included. The stabilized structural response under thermomechanical loading motivates the use of uncoupled analysis approach making the model a fast tool suitable for design purposes in the costly and time-consuming field of thermomechanical fatigue life assessment. To demonstrate the capability and ease of use of this model for real industrial applications, the low-cycle thermal fatigue life of a stainless steel engine exhaust manifold which is in an early stage of design is assessed.

Fatigue Life of the Human Teeth: A Continuum Damage Approach

2019 ◽  
Vol 43 ◽  
pp. 1-19
Author(s):  
Theddeus Tochukwu Akano
Keyword(s):  
Fatigue Life ◽  
Damage Mechanics ◽  
Stress Amplitude ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Elastoplastic Model ◽  
Human Teeth ◽  
Proposed Model ◽  
Number Of Cycles ◽  
Cycles To Failure

Normal oral food ingestion processes such as mastication would not have been possible without the teeth. The human teeth are subjected to many cyclic loadings per day. This, in turn, exerts forces on the teeth just like an engineering material undergoing the same cyclic loading. Over a period, there will be the creation of microcracks on the teeth that might not be visible ab initio. The constant formation of these microcracks weakens the teeth structure and foundation that result in its fracture. Therefore, the need to predict the fatigue life for human teeth is essential. In this paper, a continuum damage mechanics (CDM) based model is employed to evaluate the fatigue life of the human teeth. The material characteristic of the teeth is captured within the framework of the elastoplastic model. By applying the damage evolution equivalence, a mathematical formula is developed that describes the fatigue life in terms of the stress amplitude. Existing experimental data served as a guide as to the completeness of the proposed model. Results as a function of age and tubule orientation are presented. The outcomes produced by the current study have substantial agreement with the experimental results when plotted on the same axes. There is a notable difference in the number of cycles to failure as the tubule orientation increases. It is also revealed that the developed model could forecast for any tubule orientation and be adopted for both young and old teeth.

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