| 1. |
|
|
| 2. |
- Andersson, Björn, 1989, et al.
(författare)
-
Homogenization based macroscopic model of phase transformations and cyclic plasticity in pearlitic steel
- 2022
-
Ingår i: Journal of Thermal Stresses. - : Informa UK Limited. - 0149-5739 .- 1521-074X. ; 45:6, s. 470-492
-
Tidskriftsartikel (refereegranskat)abstract
- In this contribution macroscopic modeling of phase transformations and mechanical behavior of low alloy steels are developed and investigated. Such modeling is of importance in simulations of transient thermo-mechanical processes which can cause phase transformations, examples from the railway industry include train braking induced frictional heating as well as rail grinding and welding operations. We adopt a modeling approach which includes phase transformation kinetics and individual constitutive models for the phases in combination with different homogenization methods. Algorithmic implementations of the isostrain, isostress and self-consistent homogenization methods are presented and demonstrated in finite element simulations of a laser heating experiment. Stress field results from the different homogenization methods are compared against each other and also against experimental data. The importance of including transformation induced plasticity in the modeling is highlighted, as well as the multi-phase stages of the heating and cooling.
|
|
| 3. |
- Cao, Yu, 1969, et al.
(författare)
-
Mechanical Behaviour of a Rephosphorized Steel for Car Body Applications — Effects of Temperature, Strain Rate and Pre-treatment
- 2011
-
Ingår i: Journal of Engineering Materials and Technology, Transactions of the ASME. - : ASME International. - 1528-8889 .- 0094-4289. ; 133:2, s. 021019-1 - 021019-11-
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature and strain rate effects on the mechanical behaviour of a commercial rephosphorized, interstitial free steel have been investigated by uniaxial tensile testing, covering applicable temperatures (-60 – +100°C) and strain rates (1•10-4 – 1•102 s-1) experienced in automotive crash situations. The effect of prestraining to 3.5 % with or without successive annealing at 180°C for 30 min has also been evaluated. These treatments were used to simulate pressing of the plates and the paint-bake cycle in the production of car bodies. Yield and ultimate tensile strengths, ductility including uniform and total elongation and area reduction, thermal softening effect at high strain rate and strain rate sensitivity of stress were determined and discussed in all cases. It was found that the Voce equation [σ = σs- (σs -σ0) exp (ε/ε0)] can be fitted to the experimental true stress-true plastic strain data with good precision. The parameter values in this equation were evaluated and discussed. Furthermore, temperature and strain rate effects were examined in terms of thermal and athermal components of the flow stresses. Finally, a thermal activation analysis was performed.
|
|
| 4. |
- Cao, Yu, 1969, et al.
(författare)
-
Temperature and strain rate effects on the mechanical behavior of dual phase steel
- 2015
-
Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 636, s. 124-132
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature and strain rate on the mechanical behavior of a commercial dual phase steel (DP 800) has been investigated experimentally by uniaxial tensile tests in this study, covering temperatures (−60 °C to 100 °C) and strain rates (1×10–4 to 1×10+2 s−1) encompassing conditions experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity have been determined and discussed. It was found that the Voce equation [σ=σs−(σs−σ0)exp(−εθ0/σs))] can be satisfactorily applied to describe the tensile flow curves by means of a modified Kocks–Mecking model. In this model the parameter θ0 is fixed, whereas both σ0 and σs consist of athermal and thermal stress components. The athermal component is only weakly dependent on temperature through the elastic shear modulus μ. The thermal stress component is governed by temperature and strain rate. Statistical analysis based on the experimental data has allowed all parameters in the Voce equation to be quantified.
|
|
| 5. |
- Cao, Yu, 1969, et al.
(författare)
-
The influence of temperatures and strain rates on the mechanical behavior of dual phase steel in different conditions
- 2015
-
Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 4:1, s. 68-74
-
Tidskriftsartikel (refereegranskat)abstract
- This study deals with the mechanical behavior of DP steel. A commercial dual phase steel (DP 800) was strained to 3.5% followed by annealing at 180 degrees C for 30 min to simulate the pressing of the plates and the paint bake cycle involved in the manufacturing process of automobile body structures. The effect of temperarure and strain rate on the machanical behavior of this material was investigated by uniaxial tensile tests, covering applicable temperatures (-60 degree C to +100 degree C) and strain rates (1x10exp-4 s-1 to 1x10exp+2 s-1) experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity as well as strain rate hardening rate have been determined and discussed.
|
|
| 6. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
A methodology to predict thermomechanical cracking of railway wheel treads: From experiments to numerical predictions
- 2017
-
Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 105, s. 71-85
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, thermomechanical cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The main goal of the paper is to perform thermomechanical rolling contact fatigue life predictions. The wheel tread material is subjected to simultaneous mechanical and thermal loads due to rolling contact and stop braking, respectively. Full-scale tests featuring three series of repeated stop braking cases have been performed in a brake rig featuring a tread braked wheel that is in rolling contact with a so-called rail-wheel. The brake rig test conditions have been simulated numerically using the finite element method where the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Stresses induced by temperature from braking as well as tractive rolling contact loading on the tread are considered. The mechanical response of the wheel material ER7 is obtained from a plastic Chaboche material model calibrated against data from cyclic experiments at room temperature and up to 625 °C. Finally, a strategy for prediction of fatigue life with respect to ratchetting failure is discussed.
|
|
| 7. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
Modelling of cyclic plasticity and phase transformations during repeated local heating events in rail and wheel steels
- 2018
-
Ingår i: Proceedings - 11th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. - 9789461869630 ; , s. 245-252
-
Konferensbidrag (refereegranskat)abstract
- Short term local friction heating in railway operation might occur when a railway wheelset skids along the rail. The consequent temperature elevation is significant and in the pearlitic rail and wheel steels results in phase transformations. The temperature dependent differences in thermal expansion, density and mechanical properties of the phases result in residual stresses which can cause thermal damage in rail and wheel steels. This study is an improvement of Finite Element (FE) modelling incorporating phase transformation kinetics law describing transformation and evolution of volume fraction of phases. The FE modelling has included coupled thermal and mechanical analysis to compute residual stresses near the wheel-rail contact.
|
|
| 8. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
Modelling of cyclic plasticity and phase transformations during repeated local heating events in rail and wheel steels
- 2021
-
Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 151
-
Tidskriftsartikel (refereegranskat)abstract
- Short term local friction heating events in railway operations might lead to phase transformations in pearlitic rail and wheel steels. A modelling framework for phase transformations combined with cyclic plasticity for the individual phases is presented. The phase transformation kinetics include e.g. austenitization due to heating, martensite formation due to rapid cooling and martensite tempering. The modelling framework has been calibrated against cyclic dilatometry test data and cyclic mechanical experiments. Simulations of a double heating event followed by rolling contact loadings show phase transformations and how cyclic residual stresses develop in the different phases.
|
|
| 9. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
Modelling of temperature and strain rate dependent behaviour of pearlitic steel in block braked railway wheels
- 2021
-
Ingår i: Railway Engineering Science. - : Springer. - 2662-4745 .- 2662-4753. ; 29:4, s. 362-378
-
Tidskriftsartikel (refereegranskat)abstract
- Block braked railway wheels are subjected to thermal and rolling contact loading. The thermal loading results in high temperatures and thermal stresses which cause slow time dependent processes such as creep, relaxation and static recovery of the wheel material. At the same time, the rolling contact loading implies a very fast mechanical load application. This paper is focused on material modeling of pearlitic steel for a wide range of loading rates at elevated temperatures. The starting point is a viscoplasticity model including nonlinear isotropic and kinematic hardening. The Delobelle overstress function is employed to capture strain rate dependent response of the material. The model also includes static recovery of the hardening to capture slower viscous (diffusion dominated) behaviour of the material. Experiments for the pearlitic wheel steel ER7 in terms of cyclic strain-controlled uniaxial tests with hold-time, uniaxial ratchetting tests including rapid cycles and biaxial cyclic tests with tension/compression and torsion are used to calibrate the material model. These experiments were performed under isothermal conditions at different temperatures. In the ratchetting tests, higher loading rates are obtained and these have been used to calibrate the high strain rate response of the viscoplasticity model. The paper is concluded with a numerical example of a block braked wheel where the importance of accounting for the viscoplasticity in modelling is highlighted.
|
|
| 10. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
Thermomechanical cracking of railway wheel treads: a combined experimental and numerical approach
- 2015
-
Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015). ; , s. 8-
-
Konferensbidrag (refereegranskat)abstract
- In the present study, thermal cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The focus is on thermomechanical rolling contact fatigue (RCF) life predictions. The wheel tread material is subjected to simultaneous mechanical and thermal loads due to rolling contact and stop braking, respectively. Full-scale tests featuring three series of repeated stop braking cases have been performed at the Railway Technical Research Institute (RTRI) in Japan in a brake rig featuring a tread braked wheel that is in rolling contact with a railwheel. The brake rig test conditions have been simulated numerically using the finite element method. To this end, the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Thermomechanical stresses induced by braking as well as Hertzian contact loading on the tread including tractive loads based on a partial slip assumption are considered. The mechanical response of the wheel material ER7 is obtained from a viscoplastic Chaboche material model calibrated against data from cyclic experiments with hold-time from room temperatures up to 650 °C. Finally, a strategy for prediction of fatigue life with respect to ratcheting failure is discussed.
|
|
