Preheat Effect Research Articles

Island scan length effect on processability, microstructure, and mechanical property of laser powder bed fusion processed nickel matrix composites

Nickel matrix composites (NMCs) reinforced with WC particles were manufactured by laser powder bed fusion (LPBF) using island strategy with the variation of island scan length. The processability, microstructural evolution, and mechanical property were investigated. The results indicated that all samples showed high densification, while the surface morphology, molten pool geometry, and microstructures were distinct. With increasing scan length from 0.5 to 1 mm, the grain size was similar, while the high angle grain boundaries (HAGBs) decreased from 68.1% to 50.4%. With further increasing scan length, the residual stress increased from 206.3 to 308.8 MPa, the surface roughness and molten pool configurations were enlarged, and columnar/cellular dendrites became irregular. This change was related to the large temperature gradient and unstable thermal behaviors resulting from the weakened preheat effect under long scan length. Thus, the superior mechanical properties with wear rate of 4.09 × 10−5 mm3/N·m, ultimate tensile strength of 1132 MPa, and elongation of 16.1% were obtained at the moderate scan length of 1 mm. The high performance was related to smaller residual stress, fewer HAGBs and dislocation-carbides interactions along the columnar/cellular boundary.

Deep Drawing Behavior of Metal-Composite Sandwich Plates.

The deep drawing behavior of metal-composite sandwich plates, or fiber-metal laminates, in which aluminum or steel sheets are used as the face layer and composite materials are used as the core layer, is discussed in this work to find the workpieces without fractures and wrinkles. Two types of aluminum, 1050 and 6061, are considered their suitability as face sheets. The preheat effect of aluminum 6061 on formability is also investigated. When steel sheets are used, the effect of blank-holder pressure is included. In addition, to understand the deformation of fabric composite, pure composite laminates are deep drawn. The results of composite laminates show that after drawing, the weft and warp lines are shorter than the other radial lines, causing the specific deformed shape and the variation of the fiber intersection angle. For Al-composite sandwich plates, fractures and wrinkles are easy to occur. Even though the fracture and wrinkle conditions are released with the increase in preheating temperature of aluminum 6061, it may be not enough. For the deep drawing of the steel-composite sandwich plates, in which fractures are avoided, the increase of blank-holder pressure could reduce the wrinkle number. Hence, good quality workpieces without fracture and wrinkle could be obtained when the blank-holder pressure is high enough.

High order entropy stable and positivity-preserving discontinuous Galerkin method for the nonlocal electron heat transport model

The nonlocal electron heat transport model in laser heated plasmas plays a crucial role in inertial confinement fusion (ICF), and it is important to solve it numerically in an accurate and robust way. In this paper, we first develop an one-dimensional high-order entropy stable discontinuous Galerkin method for the nonlocal electron heat transport model. We further design our DG scheme to have the positivity-preserving property by using the scaling positivity-preserving limiter, which is shown, by a computer-aided proof, to have no extra time step constraint than that required by L2 stability. Next, we extend our one-dimensional scheme to two-dimensions on rectangular meshes and tensor product polynomial spaces. Numerical examples are given to verify the high-order accuracy and positivity-preserving properties of our scheme. By comparing the local and nonlocal electron heat transport models, we also observe more physical phenomena such as the flux reduction and the preheat effect from the nonlocal model.

Understanding effects of radiation from radiative shock on Richtmyer-Meshkov instability

<sec>Radiative shocks are ubiquitous in stellar environments and are characterized by high temperature plasma emitting a considerable fraction of their energy as radiation. Radiative shocks occur commonly in nature, especially in astronomical systems and inertial confinement fusion. The study of the effects of radiation on Richtmyer-Meshkov (RM) instability will improve our ability to understand and predict the evolution of RM instability under high energy density conditions.</sec><sec>A few experiments have been performed to compare the radiative case with the non-radiative case in Rayleigh-Taylor (RT) instability, thereby studying how the radiative effects change the evolution of RT instability, but the interplay between RM instability and radiative shock has been studied rarely. </sec><sec>This paper reports mainly the role of radiation in the changing of the RM instability. Two experiments are performed at Shenguang III prototype laser facility, the RM instability growth data are obtained by varying the laser intensity. The laser intensity for high-drive experiment is approximately 60% greater than that for low-drive experiment. The target consists of a multiple layer in the axial direction, in which the first layer is a 15μm-thick CH sample serving as an ablator, followed by a 10 μm-thick aluminum used as a shield layer to prevent the preheat effect. The next layer is a 350-μm-thick SiO<sub>2</sub> foam, which is used as a material to produce a radiative shock. The last layer is the CH perturbed sample. There is a sinusoidal perturbation on the surface of CH sample which is adjacent to the SiO<sub>2</sub> foam. The target is irradiated by four overlapping laser beams, and the laser beams produce a large pressure that drives a shock wave, whose velocity can be changed by varying the laser intensity, into the target package.</sec><sec>In the experiments, shock-generated radiative fluxes first ablate the unstable interface which the shock has not passed through, then the shock transmits the unstable interface to produce the RM instability. The images of unstable interface are captured using side-on x-ray radiography, and the experimental results show that the RM growth is suppressed in the experiment for the higher laser intensity. Radiation hydrodynamic code Multi1D is used to evaluate the electron temperature, shock velocity, and electron density. The simulations show that the foam temperature in the high-drive case can reach 80 eV in the front of shock, this energy flows away from the shock front, generating a radiative precursor ahead of the shock. The radiative precursor velocity of 270 km/s is much larger than the shock velocity of 170 km/s, the radiative precursor arrives at the unstable interface before the shock and ablates the unstable interface, so the radiative flux changes the initial conditions of unstable interface. When the shock propagates through the unstable interface, the ablation increases the density gradient length scale and reduces the Atwood number of the unstable interface, so the RM growth is suppressed in the high-drive case because of the ablation of the radiative precursor.</sec>

Nonlocal electron heat transport under the non-Maxwellian distribution function

In laser plasmas, the electron distribution function is not Maxwellian but super-Gaussian due to the inverse bremsstrahlung heating, and the electron heat transport is generally nonlocal because of the large Knudsen number. Starting from the Fokker–Planck equation, we develop a nonlocal electron heat transport model based on the non-Maxwellian distribution function. In our study, we follow the method in Schurtz et al. [Phys. Plasmas 7, 4238 (2000)] and derive a differential equation for calculating the nonlocal electron heat flux based on the non-Maxwellian distribution function. The numerical results show that the non-Maxwellian distribution function would reduce the nonlocal heat flux in the laser heated region. The preheat effect due to nonlocal electron heat transport in the conduction region is also reduced by the non-Maxwellian distribution function. This nonlocal electron heat transport model can be easily implemented in two-dimensional and three-dimensional hydrodynamics codes.

Computational fluid dynamic on the temperature simulation of air preheat effect combustion in propane turbulent flame

this paper presents results obtained from the application of a computational fluid dynamics (CFD) code Fluent 6.3 to modelling of temperature in propane flames with and without air preheat. The study focuses to investigate the effect of air preheat temperature on the temperature of the flame. A standard k-ε model and Eddy Dissipation model are utilized to represent the flow field and combustion of the flame being investigated, respectively. The results of calculations are compared with experimental data of propane flame taken from literature. The results of the study show that a combination of the standard k-ε turbulence model and eddy dissipation model is capable of producing reasonable predictions of temperature, particularly in axial profile of all three flames. Both experimental works and numerical simulation showed that increasing the temperature of the combustion air significantly increases the flame temperature.

Preheat effect on titanium plate fabricated by sputter-free selective laser melting in vacuum

The dynamics of titanium (Ti) melted by laser irradiation was investigated in a synchrotron radiation experiment. As an indicator of wettability, the contact angle between a selective laser melting (SLM) baseplate and the molten Ti was measured by synchrotron X-rays at 30 keV during laser irradiation. As the baseplate temperature increased, the contact angle decreased, down to 28° at a baseplate temperature of 500 °C. Based on this result, the influence of wettability of a Ti plate fabricated by SLM in a vacuum was investigated. It was revealed that the improvement of wettability by preheating suppressed sputtering generation, and a surface having a small surface roughness was fabricated by SLM in a vacuum.

Measuring impact of M-band and soft X-rays on radiation-driven ablation performance

M-band and soft X-rays play different roles in radiation-driven ablation. In the SGIII-prototype laser facility, experiments were performed to deduce the absorbed M-band and soft X-rays at different angles. Both the absorbed energy and the absorption rate of the M-band and soft X-rays were studied. The results showed that the M-band (1.6–4.4 keV) and soft (0.1–1.6 keV) X-rays performed differently in radiation-driven ablation. The difference was determined by the radiation source, the state of the ablator, and the field of view. A time-varying radiation source, the opacity change of the ablator, and fields of view at different angles were studied by using the one-dimensional multi-group radiation hydrodynamic code Multi-1D and the three-dimensional view-factor code IRAD3D. Radiation-driven ablation is the interaction between X-rays and the ablator. These studies are useful for understanding the ablation process and provide guidance for increasing the ablation rate and reducing the preheat effect.

A study on the effects of air preheat on the combustion and heat transfer characteristics of Bunsen flames

Existing designs of small-scale burners and domestic cookers have relied on open flame, where a large amount of heat is lost with flue gas. Flue Gas Recirculation (FGR) has been an effective technique for energy saving for large-scale industrial furnaces. Against this background, an experimental study was conducted to investigate the thermal, emission and heating performance of CH4-H2/air flames in terms of their dependence on both dilution effect (CO2 and N2) and preheat effect (initial reactant temperature from 20°C to 100°C).Testing of flame stability showed detrimental and favorable effects of dilution and preheat, respectively. Examination of flame height showed that under constant Re and Ф, the reaction cone is shorter at higher initial reactant temperature, indicative of enhanced burning velocity caused by preheat. Emission of CO and NOx was monotonically increased as the result of higher flame temperature due to preheat.The key question whether flame heating performance can be promoted or not is answered by detailed analysis of the radial heat flux configurations. The data reveals that the combined effects of dilution and preheat indeed induce higher heat transfer rate, thus theoretical evidence is provided for feasibility of adoption of FGR in domestic cookers.

Measurement of preheat in aluminium target in indirect drive using the SGIII prototype facilities

The velocity interferometer system for any reflector (VISAR) is used to demonstrate preheat effect in aluminium in indirect drive. The rear surface motion prior to shock front was observed and compared with a multi-group calculation. By properly adjusting the hard x-ray portion of the radiation source, the calculated rear surface motion fits well with the experimental results, which gives us confidence to predict the preheated temperature of the sample by hard x-rays. Further, the effect of hohlraum geometry is compared and discussed experimentally. The result suggests gas-filled hohlraum or hohlraum with low Z substrates should be considered to further reduce preheating.

Thermomechanical Analysis of Preheat Effect on Grade P91 Steel During GTA Welding

Effect of preheat on the thermal cycles, residual stress, and distortion during autogenous GTA welding of Grade P91 steel has been analyzed using FEM. Phase transformation effect on the residual stresses is also analyzed. Thermomechanical analysis has shown that preheat reduced the peak temperatures, cooling rate, and the distortion values. The phase transformation involving martensite during cooling resulted in typical “M” shaped residual stress profile with a reduction in peak tensile residual stress value and a wider distribution of residual stress. There is good agreement between the predicted and measured thermal cycles, residual stresses, and distortion of the P91 steel weld joint.

The importance of the transmission flux in evaluating the preheat effect in x-ray driven ablation

In x-ray driven ablation, the preheat effect is caused by the high energy x-rays that pass through the ablator. Thus, the transmission flux can be used to characterize preheat effect in a certain degree. With the radiation temperature being 200 eV, the transmission flux and preheat temperature of pure polymer (CH) have been studied by using the one-dimensional multi-group radiation hydrodynamic code MULTI-1D. By studying the spectrum of the transmitted x-rays, it is found that the energy of the transmitted x-rays is in the range of 2–5 keV for pure CH ablator. This is of importance for selecting a dopant for CH ablator. We also calculated both the preheat temperature of CH near the surface of thick target (47.66 μm) and the transmission flux of a thinner target (38.66 μm). It is found that the more transmission flux leads to the higher preheat temperature. Preheat effect of graded Si-doped CH targets with different doped concentrations has also been studied. The results are consistent with this phenomenon. By analyzing the relationship between the transmission flux and the preheat temperature, we have presented a novel method to evaluate preheat effect in x-ray driven ablation.

The radiation temperature andM-band fraction inside hohlraum on the SGIII-prototype laser facility

The radiation temperature TR and M-band fraction fM inside the vacuum Au hohlraum have been experimentally determined by a shock wave technique and a broadband soft x-ray spectrometer (SXS) on the SGIII-prototype laser facility. From the results of the shock wave technique, TR is about 202 eV, and fM is about 9% for the hohlraums driven by a 1 ns flattop pulse of 6 kJ laser energy. The Continuous Phase Plate (CPP) for beam smoothing is applied in the experiment, which increases TR to 207 eV while has almost no influence on fM. Comparisons between the results from the two kinds of technologies show that TR from the shock wave technique is lower than that from SXS whether with CPP or not. However, fM from the shock wave technique is consistent with that from SXS without CPP, but obviously lower than the SXS's result with CPP. The preheat effect on exterior surface of witness plate is reduced by thicker thickness of witness plate designed for higher laser driven energy.

Analysis preheat effect on thermal cycle and residual stress in a welded connection by FE simulation

Preheat effect on thermal cycle and residual stress was studied by employing a 3D finite-element method. A circumferential multi-pass butt weld of pipes based on ASME section IX was investigated and the experiment for thermal cycle validation was carried out. A spherical heat source density with a Gaussian distribution was employed and by an appropriate coordinate system, the rotation of electrode around the pipe was modeled reasonably. Sequentially coupled, thermal–mechanical analysis was applied using temperature-dependent thermo-mechanical behavior for material properties and the variation in peak temperature, cooling rate, and the axial residual stress due to the preheat effect were evaluated.The simulation results revealed that the pattern of final residual stress was influenced by the preheat temperature. However the thermal cycle experienced in the welding zone seems to be significantly affected by the preheat temperature.

Analysis for the angular deformation of steel plates in a high-frequency induction forming process with a triangle heating technique

A triangle heating technique with the use of a heat source of high-frequency induction heating to make a steel plate deformed into a curved shape was modeled and analyzed using the numerical analysis of the finite element method in order to predict the angular deformation of the steel plate formed by the technique. For the analysis of the deformation, heat generation by an electromagnetic field was first analyzed with consideration of the preheat effect, and heat flow using the heat generated from the plate as the heat source was then analyzed. Thermal history of the plate predicted by numerical analysis was compared with that measured in an experiment of triangle heating on a steel plate. Deformations of the plates were then analyzed with changes of heating parameters including heating dimensions and plate thickness. The analyses were also verified with a series of experiments. In order to derive a simplified equation to readily predict deformation from the triangle heating technique, deformations predicted by numerical analyses and measured by the experiments were synthesized in association with the heating parameters using a statistical method of recursion analysis. The equation was verified to be able to predict the deformations conversely and expected to be practically used in the industry to select the heating parameters for the desired shapes of curved plates.

A line-imaging velocity interferometer technique for shock diagnostics without x-ray preheat limitation

A study was conducted with a line-imaging velocity interferometer on sandwich targets at the Shen Guang-III prototype laser facility in China, with the goal of eliminating the preheat effect. A sandwich target structure was used to reduce the x-ray preheat limitation (radiation temperature ~170 eV) in a radiative drive shock experiment. With a thick ablator, the preheat effect appeared before the shock arrived at the window. After adding a shield layer of high-Z material on the ablator, x-rays which penetrated the ablator were so weak that the blank-out effect could not be measured. This experiment indicates that the sandwich target may provide a valuable technique in experiments such as equation of state and shock timing for inertial confinement fusion studies.

G0600-6-1 壁面の影響を受けるブンゼン火炎先端部の熱発生速度に関する実験的検討(熱工学部門一般講演(6):燃焼(1))

In this study, we used OH/HCHO simultaneous PLIF measurement for qualitative evaluation of heat release rate. The effects of the wall on flame curvature and heat loss are investigated. The propane- and methaneair premixed gas are considered. It is shown that the preheat effect is more significant than Lewis number effect due to flame curvature for the maximum value of heat release rate. The heat loss to downstream stagnation plate is also effective for heat release rate in the condition that there are flame front near the stagnation plate.

Effect of Process Parameters on the Melting Ratio in Overlap Pulsed Laser Welding

A study of melting ratio in overlap pulsed laser welding has been done on St14 carbon steel sheet to investigate the effect of process parameters. Pulse duration, pulse energy, pulse frequency, and travel speed were varied in the experimental procedure. The results of the melting ratio have been presented by reforming the related formulas. Formulas have been modified based on overlapping and preheat effect factors. A new parameter is defined to show the actual energy entrance to the spot region in overlapping pulsed laser welding. It is shown that keyhole formation in pulsed laser welding has an essential role in increasing the melting ratio. Moreover, it is shown that the role of pulse energy is more effective on the melting ratio than pulse duration and overlapping process variables. The effect of overlapping has been studied by varying the travel speed and pulse frequency separately, and an optimum range of overlapping for maximizing the melting ratio in the full penetration keyhole mode was established.

Weak Nonlinearity of Ablative Rayleigh–Taylor Instability

The weakly nonlinear regime of single mode ablative Rayleigh–Taylor instability is studied, with consideration of preheat effect and the width of the ablation front. The Rayleigh–Taylor linear growth rate agrees well with the direct numerical simulation. For the density perturbation, the amplitude distribution of the fundamental mode has one peak value whereas those of the second and third harmonics have two and three peak values, respectively. Harmonics generation versus wave number is also given and it is close to the result of direct numerical simulation.

Effect of preoxidation of titanium on the titanium–ceramic bonding

To improve the titanium–ceramic bonding is a challenged theme because the bonding plays an important role in long-term performance of dental prosthetic implants. This study focused on the pre-heat treatment effect on the surface characteristics of titanium and the bond strength of the porcelain–titanium system. Phase, morphology, and oxide layer thickness of the pre-heat-treated titanium were evaluated. In particular, the bond strength of porcelain fused to pre-treated titanium was measured by using three-point bending test. Statistical analyses were made using one-way analysis of variance (ANOVA). The results revealed that with an increase in treatment temperature, the intensity of diffraction peaks of rutile-type titania formed on pre-treated titanium surface increased. With regard to the thickness of the oxide layer, a monotonous change with increasing treatment temperature was observed. The bond strength of the porcelain–titanium system was 27.6 MPa for untreated titanium, which is above the minimum value of 25 MPa specified in ISO 9693 standard for the three-point bending test. When titanium subjected to pre-heat-treatment at 600–850 °C, the values became the range of 23.7–34.5 MPa, indicating significant differences ( p < 0.05). The highest value resided in the optimal pre-treatment temperature of 750 °C at which specimens also presented greater amounts of remained porcelains on the titanium side among all tested groups after bending test. On the basis of the data, the pre-heat treatment in air for titanium substrates might be a simple and effective method for strengthening the titanium–ceramic bonding.