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low-cycle-fatigues
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Thermo-mechanical behaviours of light alloys in comparison to high temperature isothermal behaviours
, Article Materials at High Temperatures ; Vol. 31, issue. 1 , 2014 , pp. 12-17 ; ISSN: 09603409 ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
Abstract
In this article, out-of-phase thermo-mechanical fatigue (TMF) behaviours of light alloys were investigated in comparison to their high temperature low cycle fatigue (LCF) behaviours. For this objective, strain based fatigue tests were performed on the A356 aluminium alloy and on the AZ91 magnesium alloy. Besides, TMF tests were carried out, where both strain and temperature changed. The fatigue lifetime comparison demonstrated that the TMF lifetime was less than that one under LCF loadings at elevated temperatures for both light alloys. The reason was due to severe conditions in TMF tests in comparison to LCF tests. The temperature varied in TMF test but it was constant under LCF loadings....
A new analysis method of the dry sliding wear process based on the low cycle fatigue theory and the finite element method
, Article Journal of Materials Engineering and Performance ; Vol. 23, issue. 3 , 2014 , pp. 1096-1106 ; ISSN: 10599495 ; Taheri, A. K ; Bakhtiarydavijani, A ; Sharif University of Technology
Abstract
In the present work, a combination of a dynamic explicit finite element model and the low cycle fatigue theory is used to simulate the steady-state abrasive wear occurring between an as-cast eutectoid steel and a carbide-tungsten disk. While the low cycle fatigue theory has been used to model wear in softer non-ferrous alloys, this work shows its applicability and accuracy for use in harder alloys, such as the eutectoid steel used in this research which is strengthened with added chromium. The novelty of this work lies in calculating the Manson-Coffin relation constants from a coupled finite element model with experimental tests instead of the previously used Slip line method. The D...
A new energy-based isothermal and thermo-mechanical fatigue lifetime prediction model for aluminium-silicon-magnesium alloy
, Article Fatigue and Fracture of Engineering Materials and Structures ; Volume 36, Issue 12 , 2013 , Pages 1323-1335 ; 8756758X (ISSN) ; Azadi, M ; Winter, G ; Eichlseder, W ; Sharif University of Technology
2013
Abstract
In this paper, a new fatigue lifetime prediction model is presented for the aluminium-silicon-magnesium alloy, A356.0. This model is based on the plastic strain energy density per cycle including two correction factors in order to consider the effect of the mean stress and the maximum temperature. The thermal term considers creep and oxidation damages in A356.0 alloy. To calibrate the model, isothermal fatigue and out-of-phase thermo-mechanical fatigue (TMF) tests were conducted on the A356.0 alloy. Results showed an improvement in predicting fatigue lifetimes by the present model in comparison with classical theories and also the plastic strain energy density (without any correction...
An Investigation into the Wear of an Eutectoid Steel Based on the Low-Cycle Fatigue Theory with the Finite Element Method
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
In sliding wear, the process of making debris takes place with different mechanisms. Previous works estimating the wear rate have been carried out based on contact mechanics and material failure mechanisms. In present work, the possibility of existence of low-cycle fatigue as the dominant mechanism in the wear of an as-cast eutectoid steel is investigated. Moreover, wear coefficient and the the volume loss per distance of that steel was predicted. At first, wear tests were done in order to obtain the wear trend of the steel in different loads. Then, regarding the roughness of the disk surface, a finite element model was built to simulate the sliding of the pin surface over the asperities...
Low cycle fatigue mechanism of René 80 at high temperature-high strain
, Article Materials Science and Engineering A ; Volume 494, Issue 1-2 , 2008 , Pages 385-390 ; 09215093 (ISSN) ; Nategh, S ; Sharif University of Technology
2008
Abstract
The low cycle fatigue René 80, a Ni-base superalloy, was studied at temperature of 871 °C, R = (εmin/εmax) = 0 and strain rate of about 2 × 10-3 s-1. The dislocation structure and failure surface observations were evaluated through TEM and SEM. TEM studies showed that at Δεt = 0.8% during the first cycle the dislocations formed a hexagonal network in the γ-phase matrix. When the number of cycles increased, the density of dislocations increased as well. At N = Nf and Δεt = 0.8% the cutting of γ′ precipitates took place. SEM studies at Δεt = 0.8% and N = Nf showed that fatigue crack initiation generally occurred at the surface, where it is depleted of the γ′ phase as a result of oxidation by...
Improvement of high temperature fatigue lifetime in AZ91 magnesium alloy by heat treatment
, Article Materials Science and Engineering A ; Volume 588 , December , 2013 , Pages 357-365 ; 09215093 (ISSN) ; Azadi, M ; Hossein Farrahi, G ; Winter, G ; Eichlseder, W ; Sharif University of Technology
2013
Abstract
In the present paper, an improvement in high temperature fatigue properties of the AZ91 magnesium alloy with rare earth elements has been obtained by a typical heat treatment, denoted by T6. For this objective, out-of-phase thermo-mechanical fatigue, room temperature and high temperature low cycle fatigue tests are performed to compare lifetimes. Several rare earth elements are initially added to the AZ91 alloy during a gravity casting process in permanent molds. Also, the type of the heat treatment is examined. Results of specimens with only the solution (the T4 heat treatment) and the solution with the ageing process (the T6 heat treatment) are compared under isothermal fatigue loadings....
Heat treatment effect on thermo-mechanical fatigue and low cycle fatigue behaviors of A356.0 aluminum alloy
, Article Materials and Design ; Volume 45 , 2013 , Pages 279-285 ; 02613069 (ISSN) ; Shirazabad, M. M ; Sharif University of Technology
2013
Abstract
In the present paper, the heat treatment effect on A356.0, a cast aluminum alloy which has been widely used in diesel engine cylinder heads, is investigated under out-of-phase thermo-mechanical fatigue and low cycle fatigue (at different temperatures) loadings. A typical heat treatment is applied to the material including 8. h solution at 535 °C, water quench and 3. h ageing at 180 °C. The experimental fatigue results show that the heat treatment process has considerable influence on mechanical and low cycle fatigue behaviors, especially at room temperature, but its effect on thermo-mechanical fatigue lifetime is not significant. The improvement in the strength can be explained by the...
A Thermo-Mechanical Fatigue Life Prediction Model for Aluminum Alloy (A356.0) with Thermal Barrier Coating
, Ph.D. Dissertation Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor)
Abstract
Thermal barrier coating (TBC) systems have been widely used in gas turbines and diesel engines. Their advantages include reducing the fuel consumption, improving the performance and increasing the fatigue lifetime at high temperatures. In the present thesis, the fatigue behavior of an aluminum alloy (the A356.0 alloy), with and without a typical TBC system is studied. The application of this research can be introduced as coating the cylinder head in diesel engines. Initially, coating process parameters (including the feed rate and the nozzle distance) of the plasma spraying, with the objective of bending strength are optimized. The optimum value of the TBC thickness is obtained based on...
Modeling Stress-strain Behavior of Aluminum Alloy (A356.0) under Thermo-mechanical Loading
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholam Hossein (Supervisor)
Abstract
Aluminum alloy (A356.0) is used in the production of cylinder head. Automobile engines are often subjected to thermo-mechanical loadings. In order to investigate the material performance, it is crucial to obtain fatigue properties of the material under thermo-mechanical and isothermal fatigue tests. The specimen is subjected to tensile and compressive stresses in a constant temperature. But in thermo-mechanical tests, the temperature and the strain vary in a specific span (between maximum and minimum values). By using the strain- stress hysteresis loop (obtained by fatigue tests), we can determine fatigue properties. Then, these properties are used in the simulation. In this thesis,...
Numerical Simulation of Al-Si Alloy Fatigue Behavior under Thermo-Mechanical and Isothermal Loads
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor) ; Asghari, Mohsen (Co-Advisor)
Abstract
The main purpose in this thesis is the finite element simulation of the stress-strain behavior in an aluminum-silicon-magnesium alloy, subjected to low cycle fatigue and thermo-mechanical fatigue loadings. This finite element modeling is performed in the ABAQUS software. Two time-dependent and time-independent models are used to simulate the behavior of the material. The time-independent model is the combined nonlinear isotropic/kinematic hardening model, which predicts the mean stress relaxation behavior, the cyclic softening or hardening and the translation of the yield surface, while it ignores the effect of the strain rate. Time-dependent models include Johnson-Cook and the two-layer...
Experimental Study of Mechanical Behavior of a Particular Metallic Material under Cyclic Loading
, M.Sc. Thesis Sharif University of Technology ; Khonsari, Vahid (Supervisor)
Abstract
One of the requirements of designing structures is the properties of their materials. The behavior of the material should be studied under the same conditions (loading regime) as it would be in practice. Regarding the structures which are subjected to cyclic loading, usually the results of monotonic tests on their material are used for their analysis under cyclic loads. Taking this fact into account that the behavior of materials under cyclic loading is normally much different from that under monotonic loading, one should doubt the results of the analyses of structures subjected to cyclic loading for which monotonic test results are used. In this project, the properties of steel rebars under...
Research on Influences of Coating on Low Cycle Fatigue Properties of Ni-Base Superalloy René 80
, Ph.D. Dissertation Sharif University of Technology ; Nategh, Saeed (Supervisor)
Abstract
In this thesis, based on the taking-off and landing of aircraft with GE 21-J85 turbine, the low cycle fatigue (LCF) test for superalloy used in first stage blades is considered. The LCF tests were performed on both coated and uncoated Rene 80 which are used in GE 21-J85 turbine at R = (min/max) = 0, strain rate of 2 10-3 s-1 and 760oC, 871oC and 982oC. To produce specimens, an investment casting method was used so that adequate amount of polycrystalline round bars could be obtained. The specimens were all homogenized and solution treated. After the inspection, some specimens were coated with pack cementation method in CODEP-B powder in H2 atmosphere. The coated and uncoated specimens all...
Fatigue lifetime of AZ91 magnesium alloy subjected to cyclic thermal and mechanical loadings
, Article Materials and Design ; Vol. 53, issue , 2014 , pp. 639-644 ; ISSN: 02613069 ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
Abstract
In the present paper, thermo-mechanical fatigue (TMF) and low cycle fatigue (LCF) or isothermal fatigue (IF) lifetimes of a cast magnesium alloy (the AZ91 alloy) were studied. In addition to a heat treatment process (T6), several rare elements were added to the alloy to improve the material strength in the first step. Then, the cyclic behavior of the AZ91 was investigated. For this objective, strain-controlled tension-compression fatigue tests were carried out. The temperature varied between 50 and 200. °C in the out-of-phase (OP) TMF tests. The constraint factor which was defined as the ratio of the mechanical strain to the thermal strain, was set to 75%, 100% and 125%. For LCF tests,...
Stress–strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings
, Article Mechanics of Time-Dependent Materials ; Vol. 18, issue. 3 , 2014 , p. 475-491 ; Ghodrati, M ; Azadi, M ; Rezvani Rad, M ; Sharif University of Technology
Abstract
This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening...
Experimental fatigue lifetime of coated and uncoated aluminum alloy under isothermal and thermo-mechanical loadings
, Article Ceramics International ; Volume 39, Issue 8 , December , 2013 , Pages 9099-9107 ; 02728842 (ISSN) ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
2013
Abstract
This paper presents the fatigue lifetime of an aluminum-silicon-magnesium alloy, widely used in diesel engine cylinder heads, both with and without a thermal barrier coating (TBC) system. The coating system in this study consists of two layers including a 150 μm thick metallic bond coat and a zirconium oxide top coat 350 μm thick. These coating layers were applied on the substrate of A356.0 alloy by air plasma thermal spraying. The isothermal fatigue tests were conducted in low cycle fatigue (LCF) regime at various temperatures. Out-of-phase thermo-mechanical fatigue (OP-TMF) tests were also performed at different maximum temperatures and constraint factors. Experimental results demonstrate...
Damage prediction for un-coated and coated aluminum alloys under thermal and mechanical fatigue loadings based on a modified plastic strain energy approach
, Article Materials and Design ; Volume 66, Issue PB , 2015 , Pages 587-595 ; 02613069 (ISSN) ; Farrahi, G. H ; Winter, G ; Huter, P ; Eichlseder, W ; Sharif University of Technology
Abstract
In this article, a novel energy-based lifetime prediction model has been presented for uncoated and coated aluminum alloys, subjected to thermal and mechanical fatigue loadings. For this objective, isothermal and thermo-mechanical fatigue tests were performed on the A356.0 alloy, with and without thermal barrier coating systems. This model, which was based on the plastic strain energy, had three correction factors including temperature, strain and mean stress effects. The predicted lifetime showed a proper agreement with experimental data. By the present model, higher accuracy was obtained in comparison to other existed approaches. Besides, the present model had lower number of material...
Cyclic Behavior Modeling of Magnesium Alloy (AZ91) Under Thermo-Mechanical and Low Cycle Fatigue Loadings
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor)
Abstract
Magnesium alloys have been used in the production of light weight components in automobile industries (for example: the ladder frame and the valve cover) due to a good combination of low density (1740 kg/m3), the tensile strength (160-365 MPa) and the elastic modulus (45 GPa). For the design and the optimization of these components under various loadings and different conditions, it is necessary to determine fatigue properties of the material by using thermo-mechanical and low cycle fatigue tests at different temperatures. In thermo-mechanical fatigue tests, the temperature varies in a specific range with the mechanical strain. The goal of this research is to investigate low cycle fatigue...
Experimental and Numerical Study of Low Fatigue Cycle Behavior of Magnesium-Lithium Alloy
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholam Hossein (Supervisor) ; Kashyzadeh, Kazem Reza (Co-Supervisor)
Abstract
Application of light metals such as Magnesium alloys due to proper mechanical behavior is increasing in industries such as automotive, electronics and so on. In this project, ingot of Mg-9Li-1Zn alloy with 10 mm thickness were produced by casting, then hot rolled at 300oC to reach 2mm thickness. Annealing at 350oC for 3 hours resulted homogenous properties in the final sheet.Study of monotonic and cyclic behavior of Mg-Li alloy by experiments and FE simulation was the goal of this project. Experimental monotonic and cyclic test were carried out in order to obtain the hysteresis loops and cyclic stress-strain curve. The Chaboche constant were extracted from the experimental test and used to...
Constitutive modeling of elastic-visco-plastic behaviors in aluminum alloys subjected to cyclic loadings at various strain rates
, Article Journal of Strain Analysis for Engineering Design ; Volume 50, Issue 2 , December , 2015 , Pages 103-124 ; 03093247 (ISSN) ; Azadi, M ; Farrahi, G. H ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
In this article, simulations of the stress-strain behavior in aluminum alloys were investigated under cyclic loadings at various strain rates. Four plasticity approaches were applied to simulate cyclic behaviors. To validate obtained results, strain-controlled tensile-compressive fatigue tests were performed in the low cycle fatigue regime. Isothermal fatigue experiments were conducted at various strain rates. Thermo-mechanical fatigue experiments were carried out at different rates of cooling and heating processes. Numerical results demonstrated a good agreement with experimental data at the mid-life cycle of the material. Material constants for different models were also presented for...
Mechanical properties of uncoated and aluminide-coated rené 80
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 41, Issue 1 , 2010 , Pages 125-137 ; 10735623 (ISSN) ; Nategh, S ; Sharif University of Technology
Abstract
Nickel-base superalloys such as René 80 are widely used in manufacturing aircraft turbine blades. They are usually coated in order to increase their wear, oxidation, erosion, and hot corrosion properties against environmental degradation. In this article, the mechanical behavior (tensile and low-cycle fatigue (LCF)) of uncoated and aluminide-coated (CODEP-B) René 80 has been studied at 871 °C and 982 °C. Experimental results show that the tensile properties of coated specimens are relatively lower than those of uncoated ones in the same conditions, but application of coating increases the LCF life of René 80 at T = 871 °C, 982 °C, R = (εmin/εmax) = 0, strain rate of 2 × 10-3 s-1, and Δεt =...