Mesodamage Evolution in Polycrystals

2005 ◽  
Vol 127 (2) ◽  
pp. 214-221 ◽  
Author(s):  
M. Chadli ◽  
A. Abdul-Latif
Keyword(s):  
Fatigue Life ◽  
Micromechanical Model ◽  
Small Strain ◽  
Cyclic Stress ◽  
Damage Variable ◽  
Thermodynamic Force ◽  
Inelastic Behavior ◽  
Loading Paths ◽  
Localized Plastic Deformation ◽  
Phase Angles

A micromechanical model of damaged elasto-inelastic behavior is proposed to predict the plastic fatigue life for fcc metallic polycrystals under multiaxial loading paths. This model is expressed in the time-dependent plasticity for a small strain assumption. In order to generalize and then to increase the model applicability (with respect to other works of the author) in describing the cyclic stress-strain evolution during plastic fatigue, it is therefore assumed that a damage variable initiates and then evolves at the grain level where the phenomenon of the localized plastic deformation occurs. The associated thermodynamic force of the damage variable is determined as a total granular energy (elastic and inelastic). The transition of the elastic strain from the single to the polycrystal, which is classically performed by averaging procedures in this type of modeling, is modified due to the coupling of such a strain with damage. The developed model is tested under different multiaxial cyclic loading situations (tension-compression and tension-torsion with different out-of-phase angles). The effects the loading paths and the grains aggregate type on the fatigue life are appropriately investigated. It is demonstrated that the model can correctly describe the overall and local damaged behavior of polycrystals.

Determinist-Probabilistic Concept in Modeling Fatigue Damage Through a Micromechanical Approach

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
A. Abdul-Latif ◽  
M. Chadli
Keyword(s):  
Fatigue Life ◽  
Cyclic Loading ◽  
Elastic Strain ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Damage Variable ◽  
Cyclic Behavior ◽  
Thermodynamic Force ◽  
Mean Stress ◽  
Loading Paths

Motivated by a micromechanical determinist-probabilistic model coupled with damage recently developed by the authors, a new generalization is proposed to describe the nonlinear elasto-inelastic cyclic strain-stress behavior of polycrystals notably under biaxial cyclic loading paths. In this context, this generalization considers a compressible and linear anisotropic granular elastic strain behavior coupled with damage. The model is expressed in the framework of the time dependent plasticity for a small strain assumption. It is assumed that a damage variable initiates at the mesoscopic (granular) level where the plastic strain localization phenomenon takes place. The associated thermodynamic force of the damage variable is determined using the concept of total granular energy (elastic and inelastic). The transition of the elastic strain from the single to the polycrystal is modified due to its explicit coupling with damage. Comparisons between predicted and experimental results are conducted describing the low-cycle fatigue behavior of the aluminum alloy 2024 under different complex cyclic loading paths. It is demonstrated that the model has a reasonable ability in describing the cyclic behavior of this alloy. Qualitatively, the model is tested under different cyclic loading paths with stress-controlled condition describing especially the ratcheting behavior of the alloy. In fact, the effects of the applied mean stress on the predicted overall elasto-inelastic behavior and on the fatigue life are carefully studied. It shows the dependence of the fatigue life on the mean stress value.

Elastic-Inelastic Self-Consistent Model for Polycrystals

2002 ◽  
Vol 69 (3) ◽  
pp. 309-316 ◽  
Author(s):  
A. Abdul-Latif ◽  
J. P. Dingli ◽  
K. Saanouni
Keyword(s):  
Complex Loading ◽  
Small Strain ◽  
Elastic Behavior ◽  
Inelastic Behavior ◽  
Surface Evolution ◽  
Heterogeneous Distribution ◽  
Strain Behavior ◽  
Loading Paths ◽  
Nonlinear Stress ◽  
Nonlinear Elastic

Based on a well-established nonincremental interaction law for fully anisotropic and compressible elastic-inelastic behavior of polycrystals, tangent formulation-based and simplified interaction laws, of softened nature, are derived to describe the nonlinear elastic-inelastic behavior of fcc polycrystals under different loading paths. Within the framework of small strain hypothesis, the elastic behavior, which is defined at granular level, is assumed to be isotropic, uniform, and compressible neglecting the grain rotation. The heterogeneous inelastic deformation is microscopically determined using the slip theory. In addition, the granular elastic behavior and its heterogeneous distribution from grain to grain within a polycrystal are taken into account. Comparisons between these two approaches show that the simplified one is more suitable to describe the overall responses of polycrystals notably under multiaxial loading paths. Nonlinear stress-strain behavior of polycrystals under complex loading, especially a cyclic one, is of particular interest in proposed modeling. The simplified model describes fairly well the yield surface evolution after a certain inelastic prestraining and the principle cyclic features such as Bauschinger effect, additional hardening, etc.

scholarly journals Effect of Mean Stress on the Fatigue Life Prediction of Notched Fiber-Reinforced 2060 Al-Li Alloy Laminates under Spectrum Loading

2018 ◽  
Vol 2018 ◽  
pp. 1-16
Author(s):  
Weiying Meng ◽  
Liyang Xie ◽  
Yu Zhang ◽  
Yawen Wang ◽  
Xiaofang Sun ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Linear Model ◽  
Life Prediction ◽  
Piecewise Linear ◽  
Forecast Accuracy ◽  
Cyclic Stress ◽  
Fatigue Life Prediction ◽  
Fiber Reinforced ◽  
Piecewise Linear Model ◽  
Spectrum Loading

This paper presents a study on the fatigue life prediction of notched fiber-reinforced 2060 Al-Li alloy laminates under spectrum loading by applying the constant life diagram. Firstly, a review on the state of the art of constant life diagram models for the life prediction of composite materials is given, which highlights the effect on the forecast accuracy. Then, the fatigue life of notched fiber-reinforced Al-Li alloy laminates (2/1 laminates and 3/2 laminates) is tested under cyclic stress, which has different stress cycle characteristics (constant amplitude loading and Mini-Twist spectrum loading). The introduced models are successfully realized based on the available experimental data of examined laminates. In the case of Mini-Twist spectrum loading, the effect of the constant life diagram on the life prediction accuracy of examined laminates is studied based on the rainflow-counting method and Miner damage criteria. The results show that the simple Goodman model and piecewise linear model have certain advantages compared to other complex models for the life prediction of notched fiber metal laminates with different structures under Mini-Twist loading. From the engineering perspective, the S-N curve prediction based on the piecewise linear model is most applicable and accurate among all the models.

scholarly journals Influence of the microstructure on the cyclic stress-strain behaviour and fatigue life in hypo-eutectic Al-Si-Mg cast alloys

2018 ◽  
Vol 165 ◽  
pp. 15004 ◽  
Author(s):  
Jochen Tenkamp ◽  
Alexander Koch ◽  
Stephan Knorre ◽  
Ulrich Krupp ◽  
Wilhelm Michels ◽  
...  
Keyword(s):  
Solid Solution ◽  
Fatigue Life ◽  
Cyclic Loading ◽  
Weight Ratio ◽  
Cyclic Stress ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Eutectic Morphology ◽  
Cast Alloys ◽  
Incremental Step

Aluminium alloys are promising candidates for energy-and cost-efficient components in automotive and aerospace industries, due to their excellent strength-to-weight ratio and relatively low cost compared to titanium alloys. As modern cast processing and post-processing, e.g. hot isostatic pressing, result in decreased frequency and size of defects, the weakest link depends on microstructural characteristics, e.g. secondary dendrite arm spacing (SDAS), Si eutectic morphology and α-Al solid solution hardness. Hereby, fatigue investigations of the effect of the microstructure characteristics on the cyclic stress-strain behaviour as well as fatigue mechanisms in the low cycle and high cycle fatigue regime are performed. For this purpose, samples of the aluminium cast alloy EN AC-AlSi7Mg0.3 with different Si eutectic morphology and α-Al solid solution hardness were investigated. To compare the monotonic and cyclic stress-strain curves, quasistatic tensile tests and incremental step tests were performed on two microstructure conditions. The results show that the cyclic loading leads to a hardening of the material compared to monotonic loading. Based on damage parameter Woehler curves, it is possible to predict the damage progression and fatigue life for monotonic and cyclic loading in hypo-eutectic Al-Si-Mg cast alloys by one power law.

The Reliability of a Component Under Multiple Cyclic Stress Levels With Distributed Cyclic Numbers

2016 ◽  
Author(s):  
Xiaobin Le
Keyword(s):  
Fatigue Life ◽  
Probabilistic Models ◽  
Random Variable ◽  
Fatigue Loading ◽  
Cyclic Stress ◽  
Initial Crack ◽  
Stress Levels ◽  
Single Constant ◽  
Unsolved Issue ◽  
Loading Spectrum

Fatigue damage is initiated through some “defects” on the surfaces of and/or inside the component and induced by the fatigue cyclic loadings. These “defects” are randomly scattered in components, and one of these “defects” will be randomly “activated” and finally developed to become the initial crack which causes the final fatigue failure. Therefore, the fatigue strength is inherently a random variable and should be treated by probabilistic models such as typical P-S-N curves. The fatigue cyclic loading could be presented or described in any form. But the fatigue loading spectrum can generally be grouped as and described by these five models: (1) a single constant cyclic stress (loading) with a given cyclic number, (2) a single constant cyclic stress with a distributed cyclic number, (3) a distributed cyclic stress (loading) at a given fatigue life (cyclic number), (4) multiple constant cyclic stress levels with given cyclic numbers, and (5) multiple constant cyclic stress levels with distributed cyclic numbers. The approaches for determining the reliability of components under fatigue loading spectrum of the models 1∼4 are available in literature and books. But few articles and books have addressed an approach for determining the reliability of components under the fatigue loading spectrum of the model 5. This paper will propose two approaches for addressing this unsolved issue. Two examples will be presented to implement the proposed approaches with detailed procedures.

Application of the Cyclic Strain Approach to the Fatigue Failure of Ship Structural Details

1987 ◽  
Vol 31 (03) ◽  
pp. 177-185
Author(s):  
Wolfgang Fricke ◽  
Hans Paetzold
Keyword(s):  
Fatigue Life ◽  
Plastic Region ◽  
Steel Structure ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Damage Parameter ◽  
Elastic Plastic ◽  
Strain Behavior ◽  
Structural Details ◽  
The Relationship

The cyclic strain approach is useful for determining the fatigue life of notches strained in the elastic-plastic region. Examples are the flame-cut edges of cutouts in the ship steel structure. After the description of the cyclic stress-strain behavior of the usual mild steel, the individual elements of the approach are described: the probability distribution of load amplitudes, the relationship between load and local elastic-plastic strain, the relationship between the damage parameter and fatigue life, and finally the damage accumulation law. The approach is illustrated by two examples of longitudinal/transverse web intersections. In the first, the predicted life is confirmed by experimental results. The second example shows the approach for complicated load combinations. It is hoped that this paper will contribute to sound and crack-free ship structural details, particularly if unusual loads are applied to well-tried details or if simplified designs are introduced.

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