Three-dimensional Heat Source Research Articles

Numerical simulation and testing of laser-MIG hybrid-welding angle-structure sheets.

Numerical simulation and experimental investigation of laser-MIG hybrid angle-welding low-carbon 1.5-mm-thin SPCC steel sheets are presented in this work. The transient simulation analysis provides an access to the thermal-fluid phenomena prediction by employing a hybrid three-dimensional heat source model. Special attention is paid to the melt dynamic behaviors within the triangular molten pool affected by the Marangoni convection. The simulation results show that the temperature and its gradient distribution are symmetrical with respect to the laser beam, which is validated well by the experimental study. The microstructure of the welded joints was analyzed by scanning electron microscopy and transmission electron microscopy. The results show that the cross-section microstructures of welded joint are mainly composed of the weld zone, narrow heat-affected zone, and substrate. The semielliptic-like molten pool shape is consistent with that of the simulated results. The finer microstructure in the weld bead results from the rapid cooling rate of laser welding confirmed by the FEM calculation. The columnar and equiaxed dendrites are formed in the peripheral and central region of the molten pool, which is beneficial for the improvement of the microhardness.

An investigation on heat transfer analysis of Micro-Plasma arc welds using finite element method

Predicting temperature distribution and controlling cooling rate to mitigate welding defects and residual stresses using a high-density arc welding process is quite significant. Therefore, choosing the right process parameters is very vital. However, performing experimental trials and deciding process parameters is quite expensive and time-consuming. Hence, a numerical investigation has been put forth using two different heat source models using the Finite element-based method. The three-dimensional heat source model has been solved using COMSOL Multiphysics. The study unfolds the most suitable heat source model for calculating temperature distribution around weld bead for the micro-plasma arc welding process. This study also lays the foundation for further analysis of residual stress.

High-performance compliant thermoelectric generators with magnetically self-assembled soft heat conductors for self-powered wearable electronics

Softening of thermoelectric generators facilitates conformal contact with arbitrary-shaped heat sources, which offers an opportunity to realize self-powered wearable applications. However, existing wearable thermoelectric devices inevitably exhibit reduced thermoelectric conversion efficiency due to the parasitic heat loss in high-thermal-impedance polymer substrates and poor thermal contact arising from rigid interconnects. Here, we propose compliant thermoelectric generators with intrinsically stretchable interconnects and soft heat conductors that achieve high thermoelectric performance and unprecedented conformability simultaneously. The silver-nanowire-based soft electrodes interconnect bismuth-telluride-based thermoelectric legs, effectively absorbing strain energy, which allows our thermoelectric generators to conform perfectly to curved surfaces. Metal particles magnetically self-assembled in elastomeric substrates form soft heat conductors that significantly enhance the heat transfer to the thermoelectric legs, thereby maximizing energy conversion efficiency on three-dimensional heat sources. Moreover, automated additive manufacturing paves the way for realizing self-powered wearable applications comprising hundreds of thermoelectric legs with high customizability under ambient conditions.

A semi-analytical solution for the transient temperature field generated by a volumetric heat source developed for the simulation of friction stir welding

The accurate prediction of transient temperature fields, induced in alloy systems during advanced manufacturing processes, is critical. These fields influence the magnitude and distribution of residual stresses, the evolution of material microstructures, and material properties such as fracture toughness. Such predictions in the vicinity of a concentrated heat source require precise knowledge of the associated heat flux as a function of position and time. If the applied thermal load is time-dependent this can have a significant effect on the resulting temperature fields and microstructures. In this work a novel three-dimensional heat source is proposed to represent the friction stir welding process along with the semi-analytical solution for the temperature field. The volumetric heat source model has a nontrivial spatial distribution constructed from physical arguments and may account for complex mass transfer, and the associated thermal effects, without explicitly solving the flow equations. A method for incorporating a time-dependent heating scenario into analytical solutions generated by this heat source is also presented. Predicted temperatures are compared with those measured experimentally for two cases reported in the literature and good agreement is observed. Example solutions for various time-dependent heat inputs are also presented.

Three-dimensional analysis of medium-frequency induction heating of steel pipes subject to motion factor

As hydrocarbon resource exploration will extend towards deep sea and alpine cold areas in future, the corresponding welded pipes for oilfield use will face increasingly adverse operating environment. Acquisition of more precise heat source for medium-frequency heat treatment of welded pipes is fundamental to postweld residual stress analysis, weld microstructure improvement and performance research. However, as a pipe billet is subjected to movement factor, it is very tough to solve for a three-dimensional heat source closer to real pattern with complex process parameters. In this paper, the authors utilized a computing method of sequential coupling combining electromagnetic-thermal coupling and relative motion between steel pipe and coils, and designed the corresponding computation flowchart, and by computing pipe billet heat treatment process, they found that the steady-state temperature field formed around a weld appears double ellipsoidal. Further analysis shows that the root cause of the double ellipsoidal temperature field is asymmetric distribution of magnetic flux density and induction current, generated in the weld zone due to electromagnetic effect, within the steel pipe in axial direction. Moreover, stability and hysteresis of pipe billet temperature field were studied. It’s found that there is a certain hysteresis between the maximum temperature of inner surface and that of outer surface, because of two different heat sources undergone by the inner and outer surfaces of the weld, as well as relative motion between induction coil and welded pipe. The unique heat transfer process and temperature distribution pattern in wall-thickness direction is the immediate cause of the double ellipsoidal three-dimensional temperature field. This study offers a referenceable analysis method for further exploring steel pipe induction heating process under complex process parameters and optimization of the process parameters.

Analytical model for the temperature field around a nonuniform three-dimensional moving heat source: friction stir welding modelling

A transient semi-analytical solution is devised to find the temperature distribution around a nonuniform three-dimensional heat source in a finite rectangular plate with cooling surfaces and nonhomogenous boundary conditions. This solution can serve as a viable tool to find the temperature field and consequently provides useful insights into material modelling and response in a variety of industrial applications, including friction welding processes. As a numerical example, the established solution is applied to the friction stir welding as a solid-state welding method. The comparison between the obtained analytical results and the results found through FEM and experiment showed that the analytically obtained results and the numerical and experimental data are in good agreement.

Anisotropic effect of natural convection on the temperature field in an enclosure in the presence of stable temperature stratification

Unsteady natural convection in a vertical cylindrical enclosure is numerically modeled in the case of heat input from above and from the side. The anisotropic effect of intense convection on the temperature field is established. It is shown that in the stratified region the temperature is well described by the time-dependent one-dimensional heat conduction equation with a three-dimensional heat source.

Evaluation of nonlinear absorptivity in internal modification of bulk glass by ultrashort laser pulses

Thermal conduction model is presented, by which nonlinear absorptivity of ultrashort laser pulses in internal modification of bulk glass is simulated. The simulated nonlinear absorptivity agrees with experimental values with maximum uncertainty of ± 3% in a wide range of laser parameters at 10 ps pulse duration in borosilicate glass. The nonlinear absorptivity increases with increasing energy and repetition rate of the laser pulse, reaching as high as 90%. The increase in the average absorbed laser power is accompanied by the extension of the laser-absorption region toward the laser source. Transient thermal conduction model for three-dimensional heat source shows that laser energy is absorbed by avalanche ionization seeded by thermally excited free-electrons at locations apart from the focus at pulse repetition rates higher than 100 kHz.

Reflection of disturbances produced by a three-dimensional heat source from a plane shock wave

The flow in the shock layer between a plane wedge and a plane attached shock is considered. The flow two-dimensionality is violated by the presence of a weak heat source in the shock layer. The relation between the mechanical actions of the disturbances singly reflected from the shock and those proceeding from the source and directly incident on the wedge surface is analyzed. The three-dimensional features of the field of the disturbances reflected from the shock are illustrated with reference to several examples.

Analysis of pulsed Nd:YAG laser welding of AISI 304 steel

Pulsed laser welding of AISI 304 stainless steel plate was simulated using commercial finite element software to determine the optimal welding conditions. Due to geometric symmetry, only one plate was modeled to reduce the simulation computation time. User subroutines were created to account for a moving three-dimensional heat source and to apply boundary conditions. The material properties such as conductivity, specific heat, and mass density were determined as functions of temperature. The latent heat was considered within the given temperature range. The three-dimensional heat source model for pulsed laser beam butt welding was designed by comparing the finite element analysis results and experimental data. This successful simulation of pulsed Nd:YAG laser welding for AISI 304 stainless steel will prove useful for determining optimal welding conditions.

Generalized Three-Dimensional Heat Source Problem for Small Time

This paper is concerned with the three-dimensional fundamental solutions in the generalized thermoelastic infinite body subjected to a continuous source of heat by using the inverse Laplace transform in an approximate manner for small values of time. It is found that there exist two coupled waves, of which is predominantly elastic wave and the other is predominantly thermal. Exact expressions for discontinuities in the field functions that occur at the wavefronts are computed and analyzed. Numerical results are presented graphically along with a comparison of the three theories due to Lord and Shulman, Green and Lindsay, and the classical coupled thermoelasticity. A discussion concerning which of the three theories is the most physically acceptable is given, and conclusions are stated.

Heat transfer between an eddying flow and a three-dimensional heat source

Heat transfer between an eddying flow and a three-dimensional heat source