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Effect of thermal stress induced by femtosecond laser on fracture toughness of fine-grained alumina
摘要： The ultra-sharp V-notch with tip radius smaller than 0.5 μm was cut by femtosecond laser on the fine-grained alumina ceramic bars to measure the fracture toughness by single-edge V-notched beam (SEVNB) method. In order to relieve the effect of thermal stresses induced by laser on fracture toughness testing, the samples with V-notch were annealed before measurement. The morphologies of the notch tip were analyzed by SEM and micro-Raman spectra. Results reveal that the fracture toughness value of this fine-grained alumina with thermal stresses on the V-notch is equal to that after annealing, and the effect of thermal stresses induced by laser on the fracture toughness can be ignored.
关键词： SEVNB,Fracture toughness,Laser processing,Thermal stress,Alumina
更新于2025-11-21 11:18:25
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Joining of AlN and Al with Compositional Graded Layer by Centrifugal Mixed-Powder Method
摘要： In this study, joining of AlN and Al with compositional graded layer is made by centrifugal mixed-powder method (CMPM). The mixed-powder of AlN particles and Al particles is inserted into a spinning mold with bulk-shaped AlN, and then molten Al is poured into the spinning mold with the mixed-powder and bulk-shaped AlN. As a result, the molten Al penetrates into the space between the mixed-powder by the centrifugal force, and at the same time, the Al particles can be melted by heat from the molten Al. Then AlN and Al can be joined with compositional graded layer after solidification. Micromechanics-based analysis is also employed to understand the thermal stress relaxation by the compositional graded layer.
关键词： Joining,Ceramics/metal joining,Thermal stress relaxation,Functionally graded materials (FGMs),Micro-mechanics,Centrifugal mixed-powder method (CMPM)
更新于2025-09-23 15:22:29
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[IEEE 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Shanghai (2018.8.8-2018.8.11)] 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Simulation research on wafer warpage and internal stress in the First Passivation process of eSiFO package
摘要： In the electronics packaging process, warpage and thermal stress are two important causes which lead to packaging failure. In this paper, ABAQUS is used to perform three-dimensional numerical simulation of eSiFo packaging products from the thermodynamic point of view. The effects of different structural parameters on wafer warpage and thermal stress in electronic packages are simulated. In the simulation part, single factor analysis, Taguchi orthogonal experiment design and finite element analysis are combined to obtain the optimized process parameters and perform simulation analysis. The result shows that the structural parameter that has the greatest influence on the von Mises stress value of the wafer is the window size. And the structural parameter that has the greatest influence on the wafer warpage is the Die thickness. The thickness of the adhesive layer and the thickness of the passivation layer have a relatively small effect on the von Mises stress and the warpage value of the wafer. Under the optimized process parameters, the maximum von Mises stress and the maximum warpage value are much smaller than the initial process.
关键词： Taguchi orthogonal experiment,optimization of process parameters,numerical simulation,Warpage,thermal stress
更新于2025-09-23 15:21:01
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Crack behavior in ultrafast laser drilling of thermal barrier coated nickel superalloy
摘要： Quantitative analysis is required to explore the mechanism of crack generation in ultrafast laser drilling of thermal barrier coated nickel superalloy. In this study, a simple thermo-mechanical coupled model is established to obtain temperature history, phase transformation stress and thermal stress during drilling process, in which laser beam scanning, laser intensity attenuation, the nonlinear relationship between drilling depth and drilling time are involved. The induced stress obtained from the present model is compared with the results by digital image correlation (DIC) method. According to the crack distribution around the drilled hole, the present model is used to explain the mechanism of crack behavior in drilling of multilayer materials. Finally, the strategy using low pulse repetition rate or water jet assisted method is suggested to reduce the thermal effect in ultrafast laser drilling process.
关键词： TBC,Phase transformation stress,Thermal stress,Crack behavior,Ultrafast laser,Laser drilling
更新于2025-09-23 15:19:57
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Correlation between laser energetic parameters and magnetic properties of GO laminations under surface treatments with long, short or ultra-short pulsed lasers
摘要： Electromagnetic components mostly incorporate soft magnetic materials used as flux multipliers. Hence, any reduction in iron loss of the magnetic core yields in saving energy. Among the techniques, the local laser treatment is a non-contact method applied for 180° domain refinement (Patri et al. [1]). The present study reassessed the impact of laser treatment on the magnetic properties of grain oriented silicon steels. Various laser pulse widths are used: an ultra-short pulse laser mainly adapted to the ablation process and a long and short pulse durations used for both irradiation and scribing processes [2]. The power loss is measured with a Single Sheet Tester (150 × 150 mm2). Each type of treatment resulted in a power loss reduction of 15–35% at peak induction 1.5 T and frequency 50 Hz. However, only the scribing and the ablation improved also the apparent permeability. In this work, the laser energy parameters are used to estimate the laser impact on the heat affected zone, the groove depth, the induced thermal stress, and on the internal properties of a magnetic behavioral model: static permeability and dynamic magnetization property [3].
关键词： Groove depth,Heat affected zone,GO laminations,Induced thermal stress,Laser treatment,Magnetic properties
更新于2025-09-23 15:19:57
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Transformation of a liquid electrolyte to a gel inside dye sensitized solar cells for better stability and performance
摘要： A gel electrolyte based on a metal-organic framework (MOF), comprised of Al3+ and trimesic acid, was used in dye-sensitized solar cells. The electrolyte was gelated inside the solar cell to ensure the best interfacial connection between the TiO2 photoanode and electrolyte ingredients. The photovoltaic performance of the solar cells showed that the gel has a good ability to preserve the function of liquid electrolytes. By optimizing the ratio of MOF and liquid electrolyte, the current density was improved, which was due to the increase in the redox couple I-/I3- content in the gel electrolyte. The open-circuit voltage was affected because of the change in the conduction band of TiO2 by the introduction of Al3+ ions and also because of electron recombination. Thus, a slightly higher efficiency was achieved using the gel electrolyte compared to the liquid electrolyte based cells. A superior stability was achieved with the MOF gel electrolyte under thermal stress at 60 °C for 250 h, while the efficiency of cells with liquid electrolyte deteriorated continuously under the same conditions. The drop in efficiency in the liquid electrolyte cells, was 24%, compared to only a 6% drop in the MOF gel electrolyte cells.
关键词： Stability,Metal organic framework,Dye sensitized solar cells,Thermal stress,Gel electrolyte
更新于2025-09-23 15:19:57
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Transient thermoelastic response in a cracked strip of functionally graded materials via generalized fractional heat conduction
摘要： This work is devoted to analyzing a thermal shock problem of an elastic strip made of functionally graded materials containing a crack parallel to the free surface based on a generalized fractional heat conduction theory. The embedded crack is assumed to be insulated. The Fourier transform and the Laplace transform are employed to solve a mixed initial-boundary value problem associated with a time-fractional partial differential equation. Temperature and thermal stresses in the Laplace transform domain are evaluated by solving a system of singular integral equations. Numerical results of the thermoelastic fields in the time domain are given by applying a numerical inversion of the Laplace transform. The temperature jump between the upper and lower crack faces and the thermal stress intensity factors at the crack tips are illustrated graphically, and phase lags of heat flux, fractional orders, and gradient index play different roles in controlling heat transfer process. A comparison of the temperature jump and thermal stress intensity factors between the non-Fourier model and classical Fourier model is made. Numerical results show that wave-like behavior and memory effects are two significant features of the fractional Cattaneo heat conduction, which does not occur for the classical Fourier heat conduction.
关键词： functionally graded materials,thermal stress,crack,time-fractional heat conduction,phase lag of heat flux
更新于2025-09-19 17:15:36
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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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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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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