| 1. |
- Devotta, Ashwin Moris, 1984-, et al.
(author)
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A modified Johnson-Cook model for ferritic-pearlitic steel in dynamic strain aging regime
- 2019
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In: Metals. - : MDPI. - 2075-4701. ; 9:5
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Journal article (peer-reviewed)abstract
- In this study, the flow stress behavior of ferritic-pearlitic steel (C45E steel) is investigated through isothermal compression testing at different strain rates (1 s-1, 5 s-1, and 60 s-1) and temperatures ranging from 200 to 700 °C. The stress-strain curves obtained from experimental testing were post-processed to obtain true stress-true plastic strain curves. To fit the experimental data to well-known material models, Johnson-Cook (J-C) model was investigated and found to have a poor fit. Analysis of the flow stress as a function of temperature and strain rate showed that among other deformation mechanisms dynamic strain aging mechanism was active between the temperature range 200 and 400 °C for varying strain rates and J-C model is unable to capture this phenomenon. This lead to the need to modify the J-C model for the material under investigation. Therefore, the original J-C model parameters A, B and n are modified using the polynomial equation to capture its dependence on temperature and strain rate. The results show the ability of the modified J-C model to describe the flow behavior satisfactorily while dynamic strain aging was operative. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
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| 2. |
- Ehn, Andreas, et al.
(author)
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Setup for microwave stimulation of a turbulent low-swirl flame
- 2016
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In: Journal of Physics D: Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 49:18
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Journal article (peer-reviewed)abstract
- An experimental setup for microwave stimulation of a turbulent flame is presented. A low-swirl flame is being exposed to continuous microwave irradiation inside an aluminum cavity. The cavity is designed with inlets for laser beams and a viewport for optical access. The aluminum cavity is operated as a resonator where the microwave mode pattern is matched to the position of the flame. Two metal meshes are working as endplates in the resonator, one at the bottom and the other at the top. The lower mesh is located right above the burner nozzle so that the low-swirl flame is able to freely propagate inside the cylinder cavity geometry whereas the upper metal mesh can be tuned to achieve good overlap between the microwave mode pattern and the flame volume. The flow is characterized for operating conditions without microwave irradiation using particle imaging velocimetry (PIV). Microwave absorption is simultaneously monitored with experimental investigations of the flame in terms of exhaust gas temperature, flame chemiluminescence (CL) analysis as well as simultaneous planar laser-induced fluorescence (PLIF) measurements of formaldehyde (CH2O) and hydroxyl radicals (OH). Results are presented for experiments conducted in two different regimes of microwave power. In the high-energy regime the microwave field is strong enough to cause a breakdown in the flame. The breakdown spark develops into a swirl-stabilized plasma due to the continuous microwave stimulation. In the low-energy regime, which is below plasma formation, the flame becomes larger and more stable and it moves upstream closer to the burner nozzle when microwaves are absorbed by the flame. As a result of a larger flame the exhaust gas temperature, flame CL and OH PLIF signals are increased as microwave energy is absorbed by the flame.
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| 3. |
- Gao, Jinlong, et al.
(author)
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Visualization of instantaneous structure and dynamics of large-scale turbulent flames stabilized by a gliding arc discharge
- 2019
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In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:4, s. 5629-5636
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Journal article (peer-reviewed)abstract
- A burner design with integrated electrodes was used to couple a gliding arc (GA) discharge to a high-power and large-scale turbulent flame for flame stabilization. Simultaneous OH and CH2O planar laser-induced fluorescence (PLIF) and CH PLIF measurements were conducted to visualize instantaneous structures of the GA-assisted flame. Six different regions of the GA-assisted flame were resolved by the multi-species PLIF measurements, including the plasma core, the discharge-induced OH region, the post-flame OH region, the flame front, the preheat CH2O region and the fresh gas mixture. Specifically, the OH profile was observed to be ring-shaped around the gliding arc discharge channel. The formaldehyde (CH2O) was found to be widely distributed in the entire measurement volume even at a low equivalence ratio of 0.4, which suggest that long-lived species from the gliding arc discharge have induced low-temperature oxidations of CH4. The CH layer coincides with the interface of the OH and CH2O regions and indicates that the flame front and the discharge channel are spatially separated by a distance of 3-5 mm. These results reveal that the discharge column acts as a movable pilot flame, providing active radicals and thermal energy to sustain the flame. High-speed video photography was also employed to record the dynamics of the GA-assisted flame. This temporally resolved data was used to study the ignition and propagation behaviors of the flame in response to a temporally modulated burst-mode discharge. The results indicate that turbulent flame can be sustained by matching temporal parameters of the high-voltage bursts to the extinction time of flame.
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| 4. |
- Hurtig, Lars Tomas Gustav, et al.
(author)
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Investigation Into Relativistic Magnetic Flux Amplification
- 2016
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In: IEEE Transactions on Plasma Science. - : IEEE. - 0093-3813 .- 1939-9375. ; 44:1, s. 2-6
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Journal article (peer-reviewed)abstract
- Amplification of magnetic flux and electric polarization fields caused by a plasma streaming at relativistic velocity into a magnetic field is discussed. It is shown that the electrostatic polarization field that arises in a plasma beam streaming across magnetic field lines at relativistic velocities will cause amplification of the magnetic flux. This effect is in complete contrast to the expulsion of the magnetic field from the plasma interior that can be expected in high beta(K) plasmas, where beta(K) is the kinetic energy density in the plasma stream divided by the energy density in the magnetic field. The amplification is shown to be caused by the relativistic motion of the space charge layers setting up the polarization field. 3-D electromagnetic particle-in-cell simulations that support this theory are presented.
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