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A hybrid distributed optical fibre sensor for acoustic and temperature fields reconstruction
摘要： We have proposed and experimentally demonstrated a distributed optical fibre sensor (DOFS) based on the hybrid of phase-sensitive optical time domain reflectometry (Ф-OTDR) and Raman optical time domain reflectometry (ROTDR), which could reconstruct the acoustic and temperature fields all along the sensing fibre at the same time. The Rayleigh back scattering (RBS), Raman Stokes (RS) and Raman anti-Stokes (RAS) generated by the probe pulse were separated by a WDM filter. Then the RBS was received by a heterodyne balanced photo detector (BPD) for quantitative vibration measurement and the dynamic acoustic field reconstruction, while the RS and RAS components were received directly by avalanche photodiodes (APDs) for temperature demodulation. The experimental results have shown that the proposed hybrid system could measure the temperature profile along a 12km long standard single-mode fibre with a maximal temperature uncertainty of 0.95℃ and a linearity response of R2=0.9986, along with a periodical knocking event detected simultaneously. Meanwhile, a 100Hz sinusoidal vibration at 12km distance along the same fibre could be clearly identified. Distributed knocking vibration and temperature was achieved at the same time with high accuracy.
关键词： temperature field,Distributed optical fibre sensors,acoustic field,Phase-sensitive OTDR (Ф-OTDR),Raman
更新于2025-09-23 15:21:01
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Experimental Study of Thermomechanical Processes: Laser Welding and Melting of a Powder Bed
摘要： In this study, an experimental approach was developed to analyze and better understand the laser welding and melting of a powder bed process. Different optical diagnostics tools (high-speed camera, infrared camera, pyrometer, etc.) were applied to measure different physical quantities (molten pool morphology, temperature ?eld, residual stresses, and distortions). As a result, measurements during the laser welding process facilitated the building of a database of experimental results (experimental benchmarks). The study of the melting of a powder bed enabled a better understanding of the physics related to the formation and behavior of the molten pool. These results can be used by researchers to improve and validate numerical simulations of these processes.
关键词： optical diagnostics,molten pool,melting of a powder bed,residual stresses,laser welding,temperature field
更新于2025-09-23 15:21:01
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Numerical simulation of temperature field of B1500HS steel/Q235 laser tailored blanks by external thermal action
摘要： Taking high-strength B1500HS steel/Q235 laser tailored blanks as the research object, this paper established the finite element model of the laser welding process of high-strength B1500HS steel /Q235 laser tailored blanks based on the theoretical model of laser welding temperature field. The temperature field of laser tailored blanks was numerically simulated under the conventional condition and External Thermal Action (ETA). The thermal cycle curve of welded joints was compared and analyzed, and the influence of welding power and welding speed on the welding width was analyzed. The results show that, under ETA condition, the cooling rate of weld and heat affected zone decreases greatly, and the residence time above the phase transition temperature becomes longer. And it is conducive to the homogenization of austenite structure at high temperature and the coordination of mechanical properties of welded joints. In addition, under the same welding power, the welding width of ETA is wider than that of conventional welding, and the larger the welding speed is, the smaller the welding width is. In order to ensure the penetration of welding, the welding speed should between 2mm/s and 7mm/s.
关键词： laser welding,external thermal action,cooling rate,numerical simulation,temperature field
更新于2025-09-23 15:21:01
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Experimental and Numerical Simulation on Laser welding of High Manganese TWIP980 Steel
摘要： In this paper, the numerical simulation of laser tailoring process for the 2mm thickness TWIP980 steel sheet is carried out using Simufact welding software. The results show that the center of the laser welding heat source is small, and temperature is high. The front of the weld pool has a drop-shaped profile and a funnel-shaped cross section. The simulated weld joint has a high degree of conformity comparing to the actual weld joint. As the heat input (line energy) increases, the peak temperature of the thermal cycle and the weldment width increase. The simulated results indicate that the residual stress of the weld joint perpendicular to the weld along the surface is greater than that along the weld direction, and are both greater than the residual stress perpendicular to the weld along the thickness direction. The residual stress generated by welding is mainly concentrated in the direction perpendicular to the weld seam. With the heat input increase, the deformation after welding increases. For the studied TWIP980 steel, the recommending laser tailored blank (LTB) weld parameters are: power 3kW and welding speed 3m/min, which is the optimum welding process in the practical welding. The guiding significance of the software for laser welding simulation of TWIP980 steel was verified.
关键词： numerical simulation,laser welding,residual stress,temperature field,TWIP980 steel
更新于2025-09-23 15:19:57
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Study on laser irradiation temperature field of carbon fiber reinforced plastic composites
摘要： Based on Abaqus software, the temperature profiles during laser heating CFRP materials in different fiber directions was investigated in this research. The 3D temperature distribution and temperature history of laminates with different ply directions were analyzed and compared through the homogenous model. It is found that the focusing characteristics of laser causes a large temperature gradient. Meanwhile, the temperature field of CFRP laminate extends toward the direction of fibers because of the large axial thermal conductivity of carbon fibers. The thermal conduction in the thickness direction is poor, so the lower layer will not reach the melting temperature. In order to verify the validity of the model, a real-time temperature field measurement device consisting of thermal imager and thermocouples was built. The results show that the model can effectively simulate the temperature field of composite materials irradiated by laser.
关键词： carbon fiber reinforced plastic composites,laser,finite element simulation,temperature field
更新于2025-09-23 15:19:57
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[IEEE 2019 Smart Grid Conference (SGC) - Tehran, Iran (2019.12.18-2019.12.19)] 2019 Smart Grid Conference (SGC) - Introducing a novel method for improving the design of off-grid photovoltaic systems
摘要： Two-color pyrometric methods have been widely used in noncontact temperature measurement area. However, it is difficult to get synchronous monochromatic images for two-color pyrometric formula. Some researches use beam splitter to obtain two or more optical paths to capture the different monochromatic images, but the complex optical paths will bring spatiotemporal matching errors. Another method uses color camera to capture the Red, Green, Blue (RGB) channel images as the RGB monochromatic images, but substituting the Dirac delta function for spectral response function will result in the inaccuracy of the measurement results. In fact, the RGB monochromatic images can be obtained from the color image if the irradiance attenuations from color channel to single wavelength are calibrated. In this paper, a novel 3-D reconstruction method is proposed to measure the temperature distribution of combustion flame. First, the irradiance attenuations are calibrated to calculate the synchronous monochromatic images at R and G wavelengths. Second, the tomographic reconstruction of flame monochromatic emissive power is improved with visual hull restriction so that the energy distribution is more reasonable. Finally, the 3-D temperature distribution is calculated from the reconstructed monochromatic emissive power fields at R and G wavelengths using two-color pyrometric method. The alcohol and butane flames are tested in the laboratory-scale test rig. The experimental results indicate that our approach performs well in flame temperature field reconstruction.
关键词： irradiance,3-D reconstruction,two-color pyrometry,flame temperature distribution,temperature field measurement
更新于2025-09-19 17:13:59
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An Analytical Model for Filler Wire Heating and Melting during Wire Feed Laser Deposition
摘要： Additive technologies, in particular, wire-feed laser deposition, can significantly reduce the production cycle of manufacturing large-sized parts or parts of complex shape due to partial or complete elimination of technological operations such as casting, machining and welding. The aim of the work is to develop an analytical model of heating and melting of the filler wire during wire-feed laser deposition. The heat conduction problem was solved by the functional-analytical methods. The practical effectiveness of the functional-analytical methods with respect to computational time is several orders of magnitude higher than numerical ones. Obtained analytical solution made it possible to determine the temperature field for heat flux arbitrarily distributed on the filler wire surface. It is established that at a higher feed rate, the wire tip is completely melted at a greater distance from the laser axis. The shape of the melting surface also depends on the feed rate. At a slow feed rate, a more uniform heating of the wire over the cross section occurs. The melting surface has a small angle of inclination.
关键词： Temperature field,Green’s function,Heat source,Laser deposition,Filler wire
更新于2025-09-16 10:30:52
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Effect of Inter-Layer Dwell Time on Distortion and Residual Stresses of Laser Metal Deposited Wall
摘要： The laser metal deposition is an advanced manufacturing technology enabling the production of large-sized parts and partially or completely elimination of machining and welding. The process is characterised by a non-uniform local heating of the buildup leading to a stress distribution, which may exceed the yield strength of the material and leads to loss of dimensional accuracy. The interlayer dwell time has a strong influence on the temperature field. The effect of the interlayer dwell time on the distortion and the stress distribution during laser metal deposition of a single-pass wall on the edge of 2 mm thick plate was studied experimentally and numerically. The deposited material was IN625 and the substrate material was AISI 316. A decrease of the residual displacement, due to a uniform shrinkage after the deposition of the last layer and a lower level of the residual compressive longitudinal plastic strain, has been observed in the studies without a dwell time. The peak increment of the free edge displacement corresponds to the first layer and hence the subsequent layers will be deposited on the already plastically deformed buildup. The tensile residual longitudinal stress near the top of the buildup and transverse stress near the edges of the buildup is higher than yield strength in the studies with dwell time.
关键词： Temperature field,Laser metal deposition,Residual stresses,Simulation,Distortion
更新于2025-09-16 10:30:52
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Numerical simulation of selective laser melting temperature conduction behavior of H13 steel in different models
摘要： With considering the latent heat of melting and the temperature-dependent thermo-physical properties, a Gauss body heat source is employed to analyze the temperature field and the morphology of molten pool with a single-track and multi-track scan strategy in Substrate-Powder (SP) model, Full-Powder (FP) model and Partial-Solid model (PS), respectively. It is shown that the maximum temperature (Tmax) and maximum cooling rate (vcmax) of single-track increase with preheating temperature, while the maximum heating rate (vhmax) presenting an opposite trend. The preheating temperature has the greatest influence on the length and depth of the molten pool of SP model and the width of FP model. For the reason of heat accumulation, the Tmax of each track increases with the decrease of solid volume in the model and increases with the number of scan tracks in a multi-track scan strategy. Due to prominent thermal conductivity of SP model, heat accumulation of multi-track scanning has the smallest effect on the size of pool, but it drives the molten pool length of PS model and FP model increasing seriously. The verification experiment of SP model was in good agreement with the simulation results, proved that numerical simulation is capable of predicting the temperature field and molten pool morphology during the SLM process.
关键词： numerical simulation,H13 steel,temperature field,molten pool morphology,selective laser melting
更新于2025-09-16 10:30:52
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[IEEE 2019 25th International Conference on Automation and Computing (ICAC) - Lancaster, United Kingdom (2019.9.5-2019.9.7)] 2019 25th International Conference on Automation and Computing (ICAC) - Temperature Field Simulation and Experimental Analysis of Laser Cladding 45 Steel
摘要： In order to explore the influence in temperature field change on the cladding quality and substrate deformation during laser cladding, adopt the APDL parametrization design language in ANSYS finite element analysis software to establish the laser cladding process model and the cladding process. The dynamic simulation and the temperature field distribution during the simulation cooling process were carried out, and the experimental verification and comparison were carried out under the same process parameters. The results showed that the single-pass cladding layer has the best shape under the process parameters that laser power of 1800w, powder feeding capacity of 20g/min and scanning speed of 8mm/s. During the cladding simulation process, the temperature of the molten pool and the peak temperature of the time-course curve are basically constant, and the temperature field distribution takes on a steady-state distribution. After the cladding,the temperature of cladding layer diffuses to the both ends, the temperature field changes gradually decrease during the cooling process, and the temperature is in an unsteady state. As the cooling time increases, the temperature drop gradient gradually decreases. The temperature field cooling analysis is carried out under the same process parameters. The error between the experimental results and the simulation results is less than 10%, which is very consistent and has guiding significance for practical experiments.
关键词： temperature field,finite element analysis,laser cladding
更新于2025-09-12 10:27:22