Energy-based damage descriptions to assess fatigue life of steel samples undergoing various multiaxial loading spectra

2017 ◽  
Vol 28 (1) ◽  
pp. 35-57 ◽  
Author(s):  
GR Ahmadzadeh ◽  
A Varvani-Farahani
Keyword(s):  
Fatigue Life ◽  
Mild Steel ◽  
Fatigue Damage ◽  
Hysteresis Loops ◽  
Growth Stress ◽  
Principal Strain ◽  
Stress Strain ◽  
Damage Models ◽  
Maximum Principal Strain ◽  
Loading Spectrum

The present study evaluates fatigue damage of four steel alloys, mild steel, SS347, SNCM439, and SNCM630, by means of Socie, Ellyin, and Varvani-Farahani damage models. The Socie model assesses fatigue damage through product of maximum principal strain amplitude and maximum normal stress on the maximum principal strain plane. Damage description by Ellyin was developed as both elastic and plastic strain energies over loading spectrum were integrated. The elastic–plastic response of materials is evaluated through use of Garud’s constitutive plasticity model to achieve components of stress/ strain and corresponding stress–strain hysteresis loops. Based on the Varvani-Farahani model, components of stress and strain calculated from largest Mohr’s circles over peak-valley events are employed to assess fatigue damage. Overall damage was calculated on the basis of energy-based models from counted reversals over entire loading blocks and related to fatigue life. The Socie approach overpredicted lives for steel samples. Predicted life data for mild steel and SS347 samples fell below the midline based on the Ellyin’s model. Both Ellyin and Varvani-Farahani models showed a good agreement of predicted lives for steel samples within factors ±3 as compared with experimental data. The choice of damage assessment was highly related to consistency of damage descriptions to crack formation and early growth, stress/strain components, material properties, and loading spectrum.

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.

Multi-Axial Fatigue Damage Models of Fiber Reinforced Composites

2004 ◽  
Author(s):  
N. H. Yang ◽  
H. Nayeb-Hashemi ◽  
A. Vaziri
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Fatigue Failure ◽  
Multiaxial Fatigue ◽  
Loading Frequency ◽  
Reinforced Composites ◽  
Damage Models ◽  
Failure Models ◽  
Axial Fatigue

Fiberglass reinforced composites are extensively used in various structural components. In order to insure their structural integrity, their monotonic and fatigue properties under multiaxial stress fields must be understood. Combined in-phase tension/torsion loading is applied to [±45°]4 E-glass/epoxy composite tubes under monotonic and fatigue conditions to determine the effects of multiaxial loading on its failure. Various monotonic and fatigue damage criteria are proposed. These models considered failure mode (failure plane), the energy method and the effective stress-strain method. It is observed for the majority of experiments, the failure initiated at the outer lamina layer at 45° to the tube axis. A damage criterion for multiaxial monotonic loading is proposed considering both normal and shear stress contributions on the plane of failure. The experimental data show an excellent agreement with this proposed model for various loading conditions. Other failure models are currently under investigation utilizing the stresses and strains at the composite laminate as well as stress and strain at the outer lamina layer. Multiaxial fatigue failure models are proposed considering again the plane of failure. Since the plane of the failure is subjected to mean and cyclic stresses (shear and normal) and mean and cyclic strains (shear and normal), the fatigue damage models consider the contributions of these stresses and strains to the fatigue life of the composite tube. In addition to the fatigue damage model based on the plane of failure, a multi-axial fatigue failure model is proposed considering the mean and cyclic energy during fatigue experiments. The experimental data show a good correlation between the proposed damage parameters and fatigue life of specimens with some scatter of the data. Other fatigue failure models are currently under investigation considering the loading frequency and visco-elastic properties of the composite.

Thermographic Determination of Fatigue Damage

1978 ◽  
Vol 100 (2) ◽  
pp. 200-203 ◽  
Author(s):  
J. A. Charles ◽  
F. J. Appl ◽  
J. E. Francis
Keyword(s):  
Fatigue Life ◽  
Mild Steel ◽  
Surface Temperature ◽  
Fatigue Damage ◽  
Fatigue Cracks ◽  
Temperature Distributions ◽  
Fatigue Failures

The energy released due to hysteresis effects in cyclically loaded materials can be used to predict where fatigue cracks are likely to initiate and to determine the stage of fatigue life. In the present study, thermography is used to monitor the surface temperature distributions on a series of double-notched, mild steel fatigue specimens cyclically loaded in bending. The results indicate that the fatigue life of the material encompasses three thermal stages, each of which is indicative of the fatigue damage the material has sustained. This information can be used to avoid in-service fatigue failures.

scholarly journals Maximum Entropy Models for Fatigue Damage in Metals with Application to Low-Cycle Fatigue of Aluminum 2024-T351

Entropy ◽  
2019 ◽  
Vol 21 (10) ◽  
pp. 967 ◽  
Author(s):  
Young ◽  
Subbarayan
Keyword(s):  
Maximum Entropy ◽  
Fatigue Damage ◽  
Low Cycle Fatigue ◽  
Hysteresis Loops ◽  
Distribution Functions ◽  
Cumulative Distribution ◽  
Cycle Fatigue ◽  
Damage Models ◽  
Cumulative Distribution Functions ◽  
Thermodynamic Entropy

In the present work, we propose using the cumulative distribution functions derived from maximum entropy formalisms, utilizing thermodynamic entropy as a measure of damage to fit the low-cycle fatigue data of metals. The thermodynamic entropy is measured from hysteresis loops of cyclic tension–compression fatigue tests on aluminum 2024-T351. The plastic dissipation per cyclic reversal is estimated from Ramberg–Osgood constitutive model fits to the hysteresis loops and correlated to experimentally measured average damage per reversal. The developed damage models are shown to more accurately and consistently describe fatigue life than several alternative damage models, including the Weibull distribution function and the Coffin–Manson relation. The formalism is founded on treating the failure process as a consequence of the increase in the entropy of the material due to plastic deformation. This argument leads to using inelastic dissipation as the independent variable for predicting low-cycle fatigue damage, rather than the more commonly used plastic strain. The entropy of the microstructural state of the material is modeled by statistical cumulative distribution functions, following examples in recent literature. We demonstrate the utility of a broader class of maximum entropy statistical distributions, including the truncated exponential and the truncated normal distribution. Not only are these functions demonstrated to have the necessary qualitative features to model damage, but they are also shown to capture the random nature of damage processes with greater fidelity.

scholarly journals Fatigue Life Assessment of Filled Rubber by Hysteresis Induced Self-Heating Temperature

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 846 ◽  
Author(s):  
Wenbo Luo ◽  
Youjian Huang ◽  
Boyuan Yin ◽  
Xia Jiang ◽  
Xiaoling Hu
Keyword(s):  
Steady State ◽  
Fatigue Life ◽  
Temperature Increase ◽  
Fatigue Testing ◽  
Heating Temperature ◽  
Life Assessment ◽  
Principal Strain ◽  
Filled Rubber ◽  
Maximum Principal Strain ◽  
Steady State Temperature

As a viscohyperelastic material, filled rubber is widely used as a damping element in mechanical engineering and vehicle engineering. Academic and industrial researchers commonly need to evaluate the fatigue life of these rubber components under cyclic load, quickly and efficiently. The currently used method for fatigue life evaluation is based on the S–N curve, which requires very long and costly fatigue tests. In this paper, fatigue-to-failure experiments were conducted using an hourglass rubber specimen; during testing, the surface temperature of the specimen was measured with a thermal imaging camera. Due to the hysteresis loss during cyclic deformation, the temperature of the material was found to first rise and then level off to a steady state temperature, and then it rose sharply again as failure approached. The S–N curve in the traditional sense was experimentally determined using the maximum principal strain as the fatigue parameter, and a relationship between the steady state temperature increase and the maximum principal strain was then established. Consequently, the steady state temperature increase was connected with the fatigue life. A couple of thousand cycles was sufficient for the temperature to reach its steady state value during fatigue testing, which was less than one tenth of the fatigue life, so the fatigue life of the rubber component could be efficiently assessed by the steady state temperature increase.

Fatigue Life Prediction of Composite Pin Joints

2014 ◽  
Vol 697 ◽  
pp. 57-61
Author(s):  
Peng Gang Mu ◽  
Xiao Peng Wan
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Composite Structures ◽  
Degradation Process ◽  
Damage State ◽  
Damage Propagation ◽  
Damage Models ◽  
Damage Quantification ◽  
Arbitrary Loading ◽  
Damage Process

In this research, new progressive fatigue damage models are established to calculate the fatigue life and simulate damage process of composite pin joints. The proposed models based on residual strength and residual stiffness of unidirectional laminates, have three parameters to present the different damage state, which can accurately describe the growth process of fatigue damage propagation by the mathematical method. The fatigue damage models combining with stress analysis, failure analysis, and material property degradation process, can predict the fatigue life, damage state and residual material properties of composite structures under arbitrary loading conditions. Using the models, composite pin joints with different stacking sequence are analyzed, fatigue life and damage quantification are concluded simultaneously. The proposed models and the process of analysis provide a way to solve the fatigue durability of composite structures.

Assessment of the Uncertainties Introduced by Different Fatigue Damage Models for Ship Structural Details

2010 ◽  
Author(s):  
Yordan Garbatov ◽  
C. Guedes Soares
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Climatic Data ◽  
Stress Effect ◽  
Damage Models ◽  
Notch Stress ◽  
Operational Profile ◽  
Structural Details ◽  
Stress Concentration Factors

The objective of this work is to assess the uncertainties introduced by different approaches for fatigue damage of ship structural details including discrete, closed-form and spectral approaches. The fatigue life is predicted by S-N approach based on the long-term notch stress range. The influence of ship main characteristics, operational profile based on a mission or loading condition, wave climatic data including the use of different scatter diagrams, wave spectra, heading distributions and consider the random origin of the mean stress effect, imperfection, weld shape improvement, hot spot calculation and resulting notch stress concentration factors to the fatigue life of a but welded ship structural component are accounted for.

scholarly journals A Modified Model for Nonlinear Fatigue Damage Accumulation of Turbine Disc Considering the Load Interaction Effect

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 919 ◽  
Author(s):  
Huang ◽  
Ding ◽  
Li ◽  
Zhou ◽  
Huang
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Damage Accumulation ◽  
Damage Model ◽  
Modified Model ◽  
Damage Models ◽  
Fatigue Damage Accumulation ◽  
Turbine Disc ◽  
Damage Accumulation Model ◽  
Nonlinear Damage Model

Fatigue damage accumulation theory is one of the core contents in structure fatigue strength design and life prediction. Among them, the nonlinear damage model can overcome the shortcomings of the linear damage model, which takes the loading sequence effect into account. Besides, the loading interaction cannot be ignored for its profound influence in damage accumulation behavior. In the paper, some commonly-used methods of the linear and nonlinear fatigue damage accumulation theory are investigated. In particular, a modified nonlinear fatigue damage accumulation model which considers the effects of loading sequences as well as loading interactions on fatigue life is developed, and a load interaction parameter is obtained by analyzing damage models which assumes that the load logarithm ratio between adjacent stress levels can characterize this phenomenon. Finally, the modified model is employed to predict the fatigue life of high pressure turbine disc. Moreover, comparison is made between the experimental data as well as the predicted lives using the Miner’s rule, the Ye’s model, and the modified model.

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