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Improved stress-cracking resistance of laser welded amorphous thermoplastics by means of adapted wavelengths
摘要： Laser transmission welding is widely used for the creation of strong, hermetic and optically appealing joints between thermoplastic parts. Amorphous polymers like polycarbonate and poly(methyl methacrylate) offer excellent optical properties, making them suitable for this joining technique and especially attractive for lighting and decorative applications, for example in the automotive industry. However, the rapid and non-uniform temperature changes during the process can lead to residual stresses, which can impair weld strength and result in part failure due to environmental stress cracking. In this work it was found, that the application of 2 μm laser radiation can lead to reduced stress-cracking-susceptibility compared to conventional laser transmission welding with wavelengths of ~1 μm.
关键词： amorphous polymers,residual stresses,environmental stress cracking,laser transmission welding
更新于2025-09-16 10:30:52
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Coupled Thermal-Mechanical Analysis of CO<sub>2</sub> Laser Irradiation on Fused Silica
摘要： To grind fused silica in ductile mode, it was proposed to repair surface and subsurface micro cracks of fused silica by CO2 laser irradiation. However, excessive residual stress remains on the surface because the melt fused silica on the surface quenches in air. It causes the critical depth of cut for ductile grinding fused silica to be smaller than 0.2μm. To investigate the distribution of the residual stress and look for an optimal manner of irradiation to control residual tensile stress, a numerical model of was built for simulating the dynamic behavior of fused silica when irradiated by CO2 laser. Laser energy absorption, heat transmission, viscoelastic behavior of fused silica and thermally induced stress were considered in the numerical simulation. The results show how the residual stress is formed and distributed. We found that an appropriate control of the temperature field as a function of time and position in the laser process is the key to reduce the residual stress. Therefore, three kinds of processes were proposed to reduce residual tensile stress on the surface of fused silica introduced by laser irradiation. The residual stress distributions of these three processes were compared by numerical analysis to decide a better method of laser irradiation.
关键词： fused silica,laser irradiation,ductile grinding,viscoelastic,residual stress
更新于2025-09-16 10:30:52
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Reliability investigation on CdTe solar cells submitted to short-term thermal stress
摘要： In this paper, we investigate the effect of short-term thermal stresses in CdTe thin film solar cells. The CdTe solar cells under test are manufactured with physical vapour deposition on soda lime glass in superstrate configuration. Different characterization techniques were used to study the reliability of the solar cells. In particular, external quantum efficiency (EQE) and electroluminescence (EL) measurement were applied in order to investigate the physical processes responsible for degradation. Through this analysis, we give a broad overview of degradation effects using both electrical and optical measurement and correlating the results. We show that (i) during short-term thermal stresses a soft degradation occurs, (ii) the series resistance of the cells increases and (iii) degradation is preliminarily ascribed to the generation of crystal defects due to the diffusion of copper or oxygen atoms in the CdTe solar cells.
关键词： degradation,EL,reliability,CdTe solar cells,EQE,thermal stress
更新于2025-09-16 10:30:52
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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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Performance, Limits, and Thermal Stress Analysis of High Concentrator Multijunction Solar Cell under Passive Cooling Conditions
摘要： Concentration of solar radiation onto the surface of triple-junction solar cells causes high cell temperature and system failure. Recently, several cooling methods were proposed for these systems. However, quantitative evaluation of the essential heat transfer coefficients to maintain stable operation of these systems at different meteorological and operating conditions is not found in the literature. Therefore, in this study, a comprehensive three-dimensional coupled thermal and structural model is proposed for the latest triple-junction AZUR SPACE solar cell. The model is used to investigate the performance of an HCPV system under different solar concentration ratios (CRs), ambient temperature, direct solar irradiance, wind speed, backside heat transfer coefficient, and copper-II substrate area ratios. In addition, a new structure of the solar cell is proposed by modifying the typical solar cell assembly by changing the area of the rear copper layer. The results indicate that by increasing the ambient temperature, CR and direct solar irradiance significantly increase the predicted cell temperature at the same backside heat transfer coefficient. In addition, increasing copper-II substrate area ratios significantly reduces the average cell temperature at the same backside heat transfer coefficient and CR. At the highest backside heat transfer coefficient, when the copper-II substrate area increased, the cell temperature decreased to a certain limit and subsequently remained constant. Critical values of the highest backside heat transfer coefficient were about 200, 600, 1000, and 1600 W/m2 K at CRs of 50, 500, 1000, and 1500 Suns, respectively. In addition, at the highest backside heat transfer coefficient of 1600 W/m2 K, the critical area ratio values were about 2, 3, 4, and 6 at CRs of 50, 500, 1000, and 1500 Suns, respectively.
关键词： Passive cooling,Concentrator photovoltaic,Thermal stress,Triple-junction solar cell
更新于2025-09-16 10:30:52
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Finite Element Modelling and Analysis for Dynamic Investigation of a Laser Spot Welded Hat-Plate Structure under Initial Stress Influence
摘要： This paper presents the finite element modelling and analysis of the dynamic behaviour of a laser spot welded structure under the influence of initial stress. Modal based updating with a new scheme was used to improve the finite element model of the structure. Element connectors with CWELD ELPAT format were used to represent the laser spot welded in the structure. The modal parameters of the structure were measured using impact hammer testing and roving accelerometers under free-free boundary conditions. NASTRAN SOL 200 was used in updating the finite element model in light of the experimental results. In this study, it was found that modal updating with the new scheme has successfully matched the finite element model of the welded structure with the experimental model. The achievement demonstrates the accuracy and efficiency of the proposed new scheme.
关键词： Finite Element Analysis,Initial Stress,Experimental Modal Analysis,Model Updating
更新于2025-09-16 10:30:52
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Thermo-elastic stress in high-power laser bars
摘要： This article presents the results of three-dimensional modeling of thermo-elastic stresses arising during the operation of a powerful laser diode bars mounted on a CuW thermal compensator using AuSn soldering alloy in a wide range of thermal loads up to extreme values. Calculated distributions of thermo-elastic stresses at the output and highly reflective mirror of the laser bar is compared. An interpretation of the results obtained, in particular, higher values of thermo-elastic stresses on a less hot highly reflective mirror, in comparison with a hotter output mirror, is proposed.
关键词： thermal loads,three-dimensional modeling,thermo-elastic stress,laser diode bars,high-power laser bars
更新于2025-09-16 10:30:52
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Numerical Modelling on Modified Directional Solidification Process of Multi-crystalline Silicon Growth for Photovoltaic Applications
摘要： A transient global model was used to investigate the effect of bottom grooved furnace upon the directional solidification (DS) process of multi-crystalline silicon (mc-Si). The numerical simulation assumed geometry is perfect 2D axis-symmetry. The temperature distribution, crystal-melt (c-m) interface, thermal stress and dislocation density have been simulated. The modified heat exchanger block system was used for controlling the temperature gradient at the bottom of the crucible. The obtained result shows convex shape of the c-m interface. The von Mises stress and dislocation density were reduced while using the bottom grooved furnace. This work was carried out in the different grooves of radius 30 and 60 mm of the heat exchanger block of the DS furnace.
关键词： Directional solidification,Dislocation density,Thermal stress,Silicon,Solar cells,Numerical simulation
更新于2025-09-16 10:30:52