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Inverse analysis of the residual stress in laser-assisted milling
摘要： In laser-assisted milling, higher temperature in shear zone softens the material potentially resulting in a shift of mean residual stress, which significantly affects the damage tolerance and fatigue performance of product. In order to guide the selection of laser and cutting parameters based on the preferred mean residual stress, inverse analysis is conducted by predicting residual stress based on guessed process parameters, which is defined as the forward problem, and applying iterative gradient search to find process parameters for next iteration, which is defined as the inverse problem. An analytical inverse analysis is therefore proposed for the mean residual stress in laser-assisted milling. The forward problem is solved by analytical prediction of mean residual stress after laser-assisted milling. The residual stress profile is predicted through the calculation of thermal stress, by treating laser beam as heat source, and plastic stress by first assuming pure elastic stress in loading process, then obtaining true stress with kinematic hardening followed by the stress relaxation. The variance-based recursive method is applied to solve inverse problem by updating process parameters to match the measured mean residual stress. Three cutting parameters including depth of cut, feed per tooth, and cutting speed, and two laser parameters including laser-tool distance and laser power, are updated with respected to the minimization of resulting residual stress and measurement in each iteration. Experimental measurements are referred on the laser-assisted milling of Ti–6Al–4 V and Si3N4. The percentage difference between experiments and predictions is less than 5% for both materials, and the selection is completed within 50 loops.
关键词： Residual stress,Ti–6Al–4V,Si3N4,Laser-assisted milling,Inverse analysis,Iterative gradient search
更新于2025-09-16 10:30:52
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Flexible CZTSSe thin film solar cells fabricated at low temperature with relieved residual stress by Sb incorporation
摘要： The troublesome residual stress is always a stumbling block that drags the progress pace of flexible CZTSSe thin film solar cells, which urgently needs to be noticed and solved. In this paper, low-temperature prepared CZTSSe absorber with relieved residual stress (0.558 GPa) is realized by Sb incorporation. Owing to the evaporated 20 nm Sb layer under CZTS precursor, the crystalline quality and band mismatching of CZTSSe/CdS interface are simultaneously improved. Additionally, the spatial potential fluctuation extracted from the PL results is found to decrease from 63.26 meV to 41.57 meV, indicating a reduction in band tailing and disorder of CZTSSe absorber. Compared with the general solar cells fabricated at 580 °C, flexible devices with Sb incorporation can maintain a slightly higher performance at a lower temperature about 60 °C. The best power conversion efficiency (PCE) of 4.41% is obtained in the solar cell with 550 °C-selenized CZTSSe absorber after incorporating 20 nm Sb layer, featuring 351.20 mV Voc, 25.73 mA/cm2 Jsc and 48.79% FF. Finally, low-temperature prepared flexible CZTSSe thin film solar cell can retain over 83% of the original PCE after bending at 180° for 40 cycles. The mechanical durability paves a promising way for flexible CZTSSe thin film solar cell in roll-to-roll production.
关键词： CZTSSe,Sb incorporation,Residual stress,Low temperature
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Zhenjiang, China (2019.8.4-2019.8.8)] 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - The Study on Surface Integrity on Laser-assisted Turning of SiCp/2024Al
摘要： An experimental study was conducted on laser-assisted turning (LAT) of SiCp/2024Al in order to investigate the effects of input variables of LAT and conventional turning (CT) on machining performance of SiCp/2024Al. An experimental study was conducted on LAT of SiCp/2024Al in order to investigate the effects of input variables of LAT and CT on machining performance of SiCp/2024Al. The process benefits of laser processing variables were analyzed by comparing the surface roughness, surface microstructure and residual stress. The variables in LAT are as follows: the cutting speed is 30 to 60 m / min, the feed rate is 0.01 to 0.1 mm/rev, and the laser power is between 0 W and 50 W. The experimental results show that under the same cutting parameters, the LAT outperforms the CT method by reducing the surface roughness value by up to 81.73%. Unlike in CT, LAT produces more residual compressive stress. Micro-structure analysis shows that there are no microcracks on the surface of the workpiece machined by LAT.
关键词： laser-assisted micro-turning,microscopic morphology,SiCp/2024Al,residual stress,surface roughness
更新于2025-09-16 10:30:52
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A novel method of laser surface hardening treatment inducing different thermal processing condition for Thin-sectioned 100Cr6 steel
摘要： Hardness, microstructure and residual stresses induced on the engineered steel surface have a significant effect on the manufacturing process and the life time of the components. In the present work, these are analysed on laser-treated layer obtained on 100Cr6 bearing steel surface involving different thermal processing conditions. Prior to laser surface hardening treatment, the steel was spheroidized and hardened and tempered with resulting microstructure comprising of globular carbides in the matrix of martensite and retained austenite. A 20-mm wide diode laser beam was employed with a fixed peak laser power in both continuous wave and pulsed wave modes. Additionally, the treatment was carried out with an arrangement to induce fluid contact beneath the workpiece to enhance the heat transfer coefficient. Results indicated maximum improvement in hardness (1050–1100 HV) and compressive residual stress (?630 ± 20 MPa) with retention of core properties on treated surface processed with pulsed-wave mode under fluid contact owing to formation of refined microstructure constituting refined globular carbides (alloy nano-carbides) and retained austenite in martensite matrix. The extent of increase in compressive residual stress and treated layer microhardness was found to depend on the extent of martensite refinement and alloy nano-carbides dispersed in the matrix. Sliding wear tests conducted in both unlubricated and lubricated conditions indicated gradual improvement in wear resistance of the treated surface with increase in cooling rate governed by the thermal processing condition employed with conventionally hardened and tempered one being lowest and laser processed with pulsed wave mode under fluid contact being highest. Apparently, the laser treated surface processed with pulsed-wave mode under fluid contact exhibited reduction in friction coefficient with retention of core properties as compared to untreated counterpart.
关键词： Pulsed-wave,Spheroidized carbides,Laser surface hardening,100Cr6 bearing steel,Residual stress,Continuous-wave
更新于2025-09-16 10:30:52
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Effects of laser peening on the fatigue strength and defect tolerance of aluminum alloy
摘要： The effects of laser peening (LP) on the bending fatigue strength of the 7075-T651 aluminum alloy were investigated. Accordingly, the defect tolerance of the aluminum alloy subjected to LP is discussed on the basis of fracture mechanics. The results indicate that a deeper compressive residual stress was induced by LP compared with the case of shot peening (SP). The fatigue strengths increased when both peening types were used. Semicircular slits with depths less than 0.4 and 0.1 mm were rendered harmless on the basis of the applications of LP and SP, respectively. The apparent threshold stress intensity factor range ΔKth,ap increased by approximately five and two times owing to LP and SP, respectively. The increase of the ΔKth,ap was caused by the compressive residual stress induced by the peening. The Kitagawa-Takahashi diagram of the laser-peened specimens shows that the defect tolerance of the aluminum alloy was improved by LP.
关键词： fatigue strength,laser peening,residual stress,shot peening,defect tolerance,aluminum alloy
更新于2025-09-16 10:30:52
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Crystal defects in monocrystalline silicon induced by spot laser melting
摘要： Laser processing of monocrystalline silicon has become an important tool for a wide range of applications. Here, we use microsecond spot laser melting as a model experiment to investigate the generation of crystal defects and residual stress. Using Micro-Raman spectroscopy, defect etching, and transmission electron microscopy, we find no dislocations in the recrystallized volume for cooling rates exceeding jdT=dtj ? 2 (cid:2) 107 K/s, and the samples remain free of residual stress. For cooling rates less than jdT=dtj ? 2 (cid:2) 107 K/s, however, the experiments show a sharp transition to a defective microstructure that is rich in dislocations and residual stress. Moreover, transmission electron microscopy indicates dislocation loops, stacking-fault tetrahedra, and voids within the recrystallized volume, thereby indicating supersaturation of intrinsic point defects during recrystallization. Complementing photoluminescence spectroscopy indicates even three regimes with decreasing cooling rate. Spectra of regime 1 do not contain any defect related spectral lines. In regime 2, spectral lines appear related to point defect clusters. In regime 3, the spectral lines related to point defect clusters vanish, but dislocation-related ones appear. We propose a quantitative model explaining the transition from dislocation-free to dislocation-rich recrystallization by means of the interaction between intrinsic point defects and dislocations.
关键词： monocrystalline silicon,transmission electron microscopy,laser melting,micro-Raman spectroscopy,crystal defects,residual stress,photoluminescence spectroscopy
更新于2025-09-16 10:30:52
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In-Fiber Production of Laser-Structured Stress-Mediated Semiconductor Particles
摘要： The ability to generate stressed semiconductor particles is of great importance in the development of tunable semiconductor and photonic devices. However, existing methods including both bottom-up synthesis and top-down fabrication for producing semiconductor particles are inherently free of stress effects. Here, we report a simple approach to generate controllable stress effects on both encapsulated and free-standing semiconductor particles using laser-structured in-fiber materials engineering. The physical mechanism of the thermally induced in-fiber built-in stress is investigated, and the feasibility of precisely tuning the stress state during the particle formation is experimentally demonstrated by controlling the laser treatment. Gigapascal-level built-in stress, which is a sufficiently strong stimulus to enable inelastic deformations on the fabricated semiconductor particles, has been achieved via this approach. Both encapsulated and free-standing stressed semiconductor particles are generated for a wide range of in-fiber and out-fiber optoelectronic and biomedical applications.
关键词： Built-in stress control,Laser cooling rate,Residual stress,Stressed semiconductor particles,In-fiber material engineering
更新于2025-09-12 10:27:22
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Residual Stresses in Ultrasonic-Assisted Laser Sintered Grinding Diamond Materials
摘要： Special processing, viz ultrasonic vibration-assisted laser sintering of diamonds was studied. This process would eliminate the drawbacks pertaining to existing super-hard grinding wheels. The composite process fully utilized the odds of laser sintering and ultrasonic vibration to homogenize the structure and reduce residual stresses. Diamond particles were added to a 45 steel matrix using a Ni–Cr alloy via ultrasonic vibration-assisted laser sintering in argon. Metallographic microscopy, and were used to examine the microstructure of a Ni–Cr alloy and abrasive diamond particle bonding interface microstructure, Raman spectrometry was applied to evaluate residual stresses. Acoustic flow and cavitation effects generated by ultrasonic vibration refine crystal grains in the cladding layer and the microstructure is more homogeneous than the microstructure without ultrasonic treatment. A Cr3C2 layer formed on the surface of abrasive diamond particles enhances the bonding ability of a Ni–Cr alloy to diamond, which ensures the diamond isolation and protection, ultrasonic vibration reduces residual stresses inside abrasive diamond particles.
关键词： diamond,laser sintering,ultrasonic vibration,interfacial microstructure,residual stress
更新于2025-09-12 10:27:22
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Analysis of distortion during laser metal deposition of large parts
摘要： Laser Metal Deposition (LMD) of large parts is very challenging technology for aerospace industry. Due to high productivity of several kilograms per hour and nearly unlimited part size, this technology becomes competitive to traditional production technologies of casting, welding and rolling. One of the main problem of large parts manufacturing is the high distortion. Estimation of residual stresses and distortion is necessary to obtain required dimensional accuracy and prevent fracture of additively manufactured parts. Effects of layer-by-layer evolution of stresses and strains was studied by finite-element simulation. It was shown that distortion of axially symmetrical parts can be successfully predicted by the developed simulation procedure. It was established that the effect of increasing cylinder radius is to increase residual radial displacement and curvature of the sidewall. The highest tension hoop and axial stress amounted to 1.15-1.2 times of yield stress near the substrate. If deposited material have a weak ductility (e.g. titanium alloys) there is a high probability that the fracture could occurs in the sidewall near the substrate. Several experimental trials was carried out for validation of accuracy of developed simulation procedure. Shape of build parts was analysed by 3D laser scanner.
关键词： residual stress,laser metal deposition,distortion,finite element method.
更新于2025-09-12 10:27:22
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High energy femtosecond laser peening of 2024 aluminum alloy
摘要： A femtosecond laser with a pulse energy of up to 100 mJ is used to investigate the feasibility of laser peening of a 2024 aluminum alloy that is widely used in aerospace industry. Laser beam directly irradiates the as-received aluminum sample surface in air without any protective coating for laser absorption and transparent overlay for plasma confinement. The effects of pulse energy, pulse duration and beam spot size on peening performance are studied. Optical microscope and SEM are used to examine the surface morphology of laser peened samples. Vickers hardness test is used to determine the microhardness on the surface. Residual stresses on the surface and at selected depths are measured using x-ray diffraction method. It is found that femtosecond laser can impart compressive residual stresses to a depth of more than 100 μm for this material, but the surface stress condition is not altered significantly.
关键词： residual stress,aluminum alloy,hardness,femtosecond laser,surface texture,laser peening
更新于2025-09-12 10:27:22