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Finite-element inverse analysis of residual stress for laser welding based on a contour method
摘要： The thermal effect of laser welding degrades the local material properties, and this inevitably leads to thermal deformation and thermal residual stress in welded joints. In this study, the residual stress distribution of laser-welded Al–Li alloy parts was measured by a combination of the contour method and finite-element simulation. First, the contour deformation of the cutting surfaces of welded parts resulting from the release of residual stress was measured by a coordinator. Then, the reverse contour deformation was applied to the finite-element model as the displacement boundary condition to invert the full-field residual stress of the cutting surface. Furthermore, a thermal/structural sequential coupling analysis method was used to establish a complete three-dimensional finite-element model of a laser-welded plate and calculate the residual stress field, taking the actual weld morphology as the characteristic parameter of the heat source, using the improved conical heat source model of laser welding. The result is consistent with the results of the contour method.
关键词： Laser welding,Residual stress,Contour method,Thermal/structural finite-element analysis,Improved conical heat source model
更新于2025-09-23 15:19:57
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Numerical simulation of the surface morphology and residual stress field of IN718 alloy by Gaussian mode laser shock
摘要： Laser shock processing (LSP) is a new surface modification technology that can improve mechanical properties and extending fatigue life. The numerical simulation was utilized in this work, the IN718 alloy was treated by Gaussian mode laser with the laser pulse energy of 3?7 J, laser pulse width of 12 ns and laser spot in diameter of 3 mm. And the effects of laser pulse energy on the surface morphology and residual stress field of material was investigated. The numerical simulation results showed that after the treatment of LSP, the plastic deformation and compressive residual stress layer with a certain depth is formed on the near surface of material. The amount of the plasticity deformation of material was increased with the laser pulse energy. And the compressive residual stress in surface and the direction of depth are increased with the laser pulse energy too. With the laser pulse energy from 3?7 J, the maximum compressive residual stresses are appeared at the center of the surface corresponding to the laser spot. When the laser pulse energy is increased from 3 J–7 J, the plastic deformation in depth is increases from 0.50 μm–1.86 μm, and the maximum compressive residual stress is increased from 362 MPa–742 MPa. In conclusion, LSP can improve mechanical properties of IN718 significantly, and the laser pulse energy is the most important factor to affect the LSP effect. This work can provide a certain theoretical guidance for researchers to study the IN718 alloy treated by LSP.
关键词： Residual stress,Gaussian mode laser,Surface morphology,Laser shock processing,IN718 alloy,Laser pulse energy,Numerical simulation
更新于2025-09-23 15:19:57
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The effect of spot overlap ratio on femtosecond laser planarization processing of SiC ceramics
摘要： Silicon carbide ceramics are widely used in many fields owing to their excellent mechanical properties such as good wear resistance, thermal stability, and chemical corrosion resistance. The laser planarization processing can effectively achieve the functional, practical, and engineering process, satisfying the demands of the assembly precision. Therefore, different spot overlap ratios were utilized to investigate the effect of femtosecond laser planarization processing on silicon carbide ceramic samples. Various scanning speeds and laser repetition frequencies were matched to achieve different spot overlap ratios under the premise of fixed laser incident angle and single pulse energy. Under different parameters, the ablation depth, surface roughness, surface morphology, oxidation, and residual stress were compared. The result showed that at the same spot overlap ratio, the ablation depth and surface roughness are basically maintained at a stable value despite the difference in the scanning speed and repetition rate. The surface oxidation phenomenon remarkably decreased at the spot overlap ratio less than 90%. The decrease in the overlap ratio leads to the transition of the low frequency nano-ripple and the high frequency nano-ripple, and the surface residual stress converted from tensile stress to compressive stress. Combining processing requirements with ablation quality, the parameters are divided into three parts to fit three processes based on the spot overlap ratios. The variation in the spot overlap ratios as the guidelines had good potential in guiding the parameter range selection.
关键词： Residual stress,Spot overlap ratios,Femtosecond laser,Silicon carbide ceramics,Planarization processing
更新于2025-09-23 15:19:57
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633-nm InGaN-based red LEDs grown on thick underlying GaN layers with reduced in-plane residual stress
摘要： This work investigates the in?uence of residual stress on the performance of InGaN-based red light-emitting diodes (LEDs) by changing the thickness of the underlying n-GaN layers. The residual in-plane stress in the LED structure depends on the thickness of the underlying layer. Decreased residual in-plane stress resulting from the increased thickness of the underlying n-GaN layers improves the crystalline quality of the InGaN active region by allowing for a higher growth temperature. The electroluminescence intensity of the InGaN-based red LEDs is increased by a factor of 1.3 when the thickness of the underlying n-GaN layer is increased from 2 to 8 lm. Using 8-lm-thick underlying n-GaN layers, 633-nm-wavelength red LEDs are realized with a light-output power of 0.64 mW and an external quantum ef?ciency of 1.6% at 20 mA. The improved external quantum ef?ciency of the LEDs can be attributed to the lower residual in-plane stress in the underlying GaN layers.
关键词： InGaN,n-GaN layers,residual stress,red LEDs,electroluminescence
更新于2025-09-23 15:19:57
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Numerical analysis of the effect of the scan strategy on the residual stress in the multi-laser selective laser melting
摘要： The inevitably formed residual stress in the Selective Laser Melting (SLM) process leads to distortion, crack and even delamination of the workpiece. Single laser is commonly applied during SLM processing. However, its productivity is much lower than multiple lasers. In addition, the research of residual stress with multi-laser condition currently is limited in the open documents. In this paper, a three-dimensional (3D) thermo-mechanical model, with considerations of temperature dependent properties of Ti-6Al-4V, phase change and convective flow, is developed at first. Then, the numerical results of maximum temperature and dimensions of the molten pool are validated by available experimental data. Furthermore, a parametric study in regards to a series of scan strategies is investigated. According to the simulation results, the residual stress increases significantly when the laser number reaches four. The “two-zone technique” scan strategy decreases the equivalent residual stress by 10.6% compared to the successive scan strategy. With a shortening scan length, the residual stress first increases slightly, then decreases dramatically and attains the minimum when it is a quarter. Furthermore, for the multi-laser SLM process, carefully planning the scanning sequence and the sweeping direction to decrease heat concentration is beneficial in controlling the residual stress.
关键词： Scan strategy,Thermo-mechanical model,Residual stress,Selective laser melting,Multi-laser
更新于2025-09-23 15:19:57
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On the application of laser shock peening for retardation of surface fatigue cracks in laser beam-welded AA6056
摘要： The present study aims to investigate the extent to which the fatigue behaviour of laser beam-welded AA6056-T6 butt joints with an already existing crack can be improved through the application of laser shock peening. Ultrasonic testing was utilized for in situ (nondestructive) measurement of fatigue crack growth during the fatigue test. This procedure allowed the preparation of welded specimens with surface fatigue cracks with a depth of approximately 1.2 mm. The precracked specimens showed a 20% reduction in the fatigue limit compared with specimens without cracks in the as-welded condition. Through the application of laser shock peening on the surfaces of the precracked specimens, it was possible to recover the fatigue life to the level of the specimens tested in the as-welded condition. The results of this study show that laser shock peening is a very promising technique to recover the fatigue life of welded joints with surface cracks, which can be detected by nondestructive testing.
关键词： fatigue crack,aluminium alloys,laser beam welding,ultrasonic crack tip diffraction,residual stress,laser shock peening
更新于2025-09-23 15:19:57
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Fatigue Life of Materials Strengthened by Laser Shock Processing
摘要： The influence of the thickness of 03Х22Н6М2 stainless steel samples strengthened by laser shock processing on their fatigue life is investigated by finite-element modeling. This technology is found to increase the fatigue life of thin (2 mm) samples more than threefold.
关键词： finite-element modeling,fatigue life,residual stress,laser shock processing
更新于2025-09-23 15:19:57
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Dimensional Deviation Management for Selective Laser Melted Ti6Al4V Alloy Blade
摘要： This article presents a systematically study through experimental and theoretical methods to better understand the mechanism of the geometric deformation produced during selective laser melting (SLM) treatment of the Ti6Al4V blade. Ti6Al4V blade was prepared by SLM. Microstructure, dimensional deviation and residual stress were investigated. The microstructure observation illustrates that the acicular α(cid:48) martensite formed in prior β grain, in addition, the smaller the grain size, the larger the dimensional deviation. The geometric deviation demonstrates that the directions of dimensional deviation at the leading and trailing edges of the blade are opposite to those in the middle. The distribution of dimensional deviation exhibits a parabolic change at the trailing edge of blade. The thermal stresses along the edges are much larger than that of the blade body, which cause the severe deformation of the edges toward the suction side of the blade. This conclusion is further veri?ed by the XRD method. The residual stress distribution measured through X-ray diffraction is consistent with the simulation results.
关键词： microstructure,dimensional deviation,residual stress,thermal elasto-plastic theory,selective laser melting
更新于2025-09-23 15:19:57
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Analytical mechanics modeling of residual stress in laser powder bed considering flow hardening and softening
摘要： Residual stress builds up during the fabrication of components via laser powder bed fusion (L-PBF) process which causes parts to fail due to the crack initiation and growth, low fatigue life, and fall outside of the specified dimensions. During the thermal loading, the grain size affected by strain hardening and flow softening is altered at the subsurface through dynamic recrystallization (DRx) and subsequent recovery. The yield strength of the alloys is largely determined by the size of nucleated grains, and it has a substantial influence on flow stress and residual stress build-up. In this work, a physics-based analytical model is proposed to predict the residual stress affected by the strain hardening, flow softening, and microstructural evolution during L-PBF process with IN718 as a material system for exploration. The temperature field is predicted using a transient moving point heat source approach. Due to the non-uniform heating, materials experience high thermal stress which may exceed the yield strength of the material. The thermal stress is obtained from Green’s functions of stresses due to the point body load. A material constitutive flow stress model known as Johnson-Cook is used to determine the yield surface. This flow stress model is modified to incorporate the effects of flow softening and grain size. The dynamic recrystallization and grain refinement models are used to calculate the grain size using recrystallized volume fraction from nucleation and growth rates. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. Results from the analytical residual stress model showed good agreement with X-ray diffraction measurements used to determine the residual stresses in the IN718 specimens built via L-PBF.
关键词： Residual stress,Microstructure evolution,Strain hardening,Flow softening,Laser powder bed fusion
更新于2025-09-23 15:19:57
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Analysis of Residual Stress in Electrical Penetration Assembly Based on a Fiber Bragg Grating Sensor
摘要： An important factor for maintaining hermeticity of a metal-to-glass sealed electrical penetration assembly (EPA) is the residual stress in the sealing glass, which is generated during the EPA sealing process. A novel method to investigate and optimize the sealing process of EPAs, based on a fiber Bragg grating (FBG) sensor, is proposed in this research. An FBG was well bonded with sealing glass to measure the parameters of the glass during the sealing process. The temperature change during the heating process was able to be measured by Bragg wavelength shift. After the sealing glass solidified and dropped to room temperature, the residual stress was determined and the effect of temperature was minimized because the temperature before and after the sealing process was the same as room temperature. The curing temperature of the sealing glass was evaluated to specifically investigate the solidification process of the EPA. This study provides a basis for online stress and temperature monitoring of EPAs under external loads in nuclear power plants.
关键词： electrical penetration assembly,embeddable technology,sealing process analysis,residual stress,fiber Bragg grating
更新于2025-09-19 17:15:36