A Novel Nonlinear Kinematic Hardening Model for Uniaxial/Multiaxial Ratcheting and Mean Stress Relaxation

2017 ◽  
pp. 227-245
Author(s):  
Hao Wu ◽  
Zheng Zhong
Keyword(s):  
Stress Relaxation ◽  
Kinematic Hardening ◽  
Mean Stress ◽  
Hardening Model ◽  
Mean Stress Relaxation

A Cyclic Plasticity Model for Advanced Light Metal Alloys

2013 ◽  
Vol 391 ◽  
pp. 3-8 ◽  
Author(s):  
Kyriakos I. Kourousis
Keyword(s):  
Stress Relaxation ◽  
Automotive Industry ◽  
Preliminary Analysis ◽  
Light Metal ◽  
Metal Alloys ◽  
Cyclic Plasticity ◽  
Isotropic Hardening ◽  
Mean Stress ◽  
Mean Stress Relaxation ◽  
Cyclic Plasticity Model

Advanced light metals have recently attracted the interest of the aerospace and automotive industry. The need for accurate description of their cyclic inelastic response under various loading histories becomes increasingly important. Cyclic mean stress relaxation and ratcheting are two of the phenomena under investigation. A combined kinematic isotropic hardening model is implemented for the simulation of the behavior of Aluminum and Titanium alloys in uniaxial mean stress relaxation and ratcheting. The obtained results indicate that the model can perform well in these cases. This preliminary analysis provides useful insight for the evaluation of the models capabilities.

Mean stress relaxation during cyclic straining of high strength aluminum alloys

2009 ◽  
Vol 31 (11-12) ◽  
pp. 1742-1750 ◽  
Author(s):  
Attilio Arcari ◽  
Raffaella De Vita ◽  
Norman E. Dowling
Keyword(s):  
Aluminum Alloys ◽  
Stress Relaxation ◽  
High Strength ◽  
Mean Stress ◽  
Mean Stress Relaxation ◽  
High Strength Aluminum Alloys ◽  
Cyclic Straining

Fatigue Behavior of Stainless Steel 304L Including Strain Hardening, Prestraining, and Mean Stress Effects

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Julie Colin ◽  
Ali Fatemi ◽  
Said Taheri
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Stress Relaxation ◽  
Fatigue Behavior ◽  
Control Mode ◽  
Mean Stress ◽  
Continuous Increase ◽  
Stainless Steel 304L ◽  
Mean Stress Relaxation ◽  
Mean Strain

This paper discusses cyclic deformation and fatigue behaviors of stainless steel 304L and aluminum 7075-T6. Effects of loading sequence, mean strain or stress, and prestraining were investigated. The behavior of aluminum is shown not to be affected by preloading, whereas the behavior of stainless steel is greatly influenced by prior loading. Mean stress relaxation in strain control and ratcheting in load control and their influence on fatigue life are discussed. Some unusual mean strain test results are presented for SS304L, where in spite of mean stress relaxation fatigue lives were significantly longer than fully-reversed tests. Prestraining indicated no effect on either deformation or fatigue behavior of aluminum, while it induced considerable hardening in SS304L and led to different results on fatigue life, depending on the test control mode. Possible mechanisms for secondary hardening observed in some tests, characterized by a continuous increase in the stress response and leading to runout fatigue life, are also discussed. The Smith–Watson–Topper parameter was shown to correlate most of the experimental data for both materials under different loading conditions.

Experimental and Theoretical Study of the Cyclic Relaxation of Die Cast Magnesium Alloy

2009 ◽  
Vol 610-613 ◽  
pp. 991-998 ◽  
Author(s):  
Shu Sheng Xu ◽  
Xiang Guo Zeng ◽  
Zhan Hua Gao ◽  
Hua Yan Chen ◽  
Jing Hong Fan
Keyword(s):  
Magnesium Alloy ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Fatigue Testing ◽  
Weight Ratio ◽  
Mean Stress ◽  
R Ratio ◽  
The Mean ◽  
Mean Stress Relaxation ◽  
Magnesium Alloy Am60

Magnesium alloys are among the best light-weight structural material with a relatively high strength-to-weight ratio end excellent technological properties. Therefore, magnesium attracts special attention of researchers working in automotive and aircraft industry. This work paid the efforts to the structural components made out of magnesium alloy AM60 such as chassis, transmission case in automotive, where the components are subject to cyclic loading after being pre-loaded. In this study, the cyclic stress-strain behaviors were investigated by strain-controlled fatigue testing. In order to investigate the effects of R-ratio on mean stress relaxation, the R-ratio ranged from 0.1 to 0.7 at the strain amplitude of 0.3%. The experimental results indicate that the mean stress relaxation increases with the increasing R-ratio. A constitutive model was proposed to simulate the mean stress relaxation. The calculation results show that the constitutive model developed in this work is capable of reproducing the stress relaxation behaviors of magnesium alloy AM60 under strain control.

scholarly journals Optimising the multiplicative AF model parameters for AA7075 cyclic plasticity and fatigue simulation

2018 ◽  
Vol 90 (2) ◽  
pp. 251-260 ◽  
Author(s):  
Dylan Agius ◽  
Mladenko Kajtaz ◽  
Kyriakos I. Kourousis ◽  
Chris Wallbrink ◽  
Weiping Hu
Keyword(s):  
Experimental Data ◽  
Stress Relaxation ◽  
Cyclic Plasticity ◽  
Model Parameters ◽  
Mean Stress ◽  
Multiobjective Optimisation ◽  
Simulation Accuracy ◽  
Content Type ◽  
Starting Point ◽  
Mean Stress Relaxation

Purpose This study presents the improvements of the multicomponent Armstrong–Frederick model with multiplier (MAFM) performance through a numerical optimisation methodology available in a commercial software. Moreover, this study explores the application of a multiobjective optimisation technique for the determination of the parameters of the constitutive models using uniaxial experimental data gathered from aluminium alloy 7075-T6 specimens. This approach aims to improve the overall accuracy of stress–strain response, for not only symmetric strain-controlled loading but also asymmetrically strain- and stress-controlled loading. Design/methodology/approach Experimental data from stress- and strain-controlled symmetric and asymmetric cyclic loadings have been used for this purpose. The analysis of the influence of the parameters on simulation accuracy has led to an adjustment scheme that can be used for focused optimisation of the MAFM model performance. The method was successfully used to provide a better understanding of the influence of each model parameter on the overall simulation accuracy. Findings The optimisation identified an important issue associated with competing ratcheting and mean stress relaxation objectives, highlighting the issues with arriving at a parameter set that can simulate ratcheting and mean stress relaxation for load cases not reaching at complete relaxation. Practical implications The study uses a strain-life fatigue application to demonstrate the importance of incorporating a technique such as the presented multiobjective optimisation method to arrive at robust parameters capable of accurately simulating a variety of transient cyclic phenomena. Originality/value The proposed methodology improves the accuracy of cyclic plasticity phenomena and strain-life fatigue simulations for engineering applications. This study is considered a valuable contribution for the engineering community, as it can act as starting point for further exploration of the benefits that can be obtained through material parameter optimisation methodologies for models of the MAFM class.

Modeling of Cyclic Ratchetting Plasticity, Part II: Comparison of Model Simulations With Experiments

1996 ◽  
Vol 63 (3) ◽  
pp. 726-733 ◽  
Author(s):  
Y. Jiang ◽  
H. Sehitoglu
Keyword(s):  
Stress Relaxation ◽  
Biaxial Tension ◽  
Computational Procedure ◽  
Mean Stress ◽  
Plasticity Model ◽  
Virgin Material ◽  
Model Simulations ◽  
Material Constants ◽  
Mean Stress Relaxation ◽  
Multiple Step

The material constants of the new plasticity model proposed in the first part of the paper can be divided into two independent groups. The first group, c(i) and r(i) (i = 1, 2, ..., M), describes balanced loading and the second group, χ(i) (i = 1,2, . . ., M), characterizes unbalanced loading. We define balanced loading as the case when a virgin material initially isotropic will undergo no ratchetting and/or mean stress relaxation, and unbalanced loading as the loading under which a virgin material initially isotropic will produce strain ratchetting and/or mean stress relaxation. The independence of the two groups of material constants and the interpretation of the model with a limiting surface concept facilitated the determination of material constants. We describe in detail a computational procedure to determine the material constants in the models from simple uniaxial experiments. The theoretical predictions obtained by using the new plasticity model are compared with a number of multiple step ratchetting experiments under both uniaxial and biaxial tension-torsion loading. In multiple step experiments, the mean stress and stress amplitude are varied in a stepwise fashion during the test. Very close agreements are achieved between the experimental results and the model simulations including cases of nonproportional loading. Specifically, the new model predicted long-term ratchetting rate decay more accurately than the previous models.

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