- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Density Functional Theory Study on the Donating Strength of Donor Systems in Dye-Sensitized Solar Cells
摘要： The electron-donating strength of donor (D) moieties in thirteen donor-π-acceptor systems (D1-π-A to D13-π-A wherein -π- and A represent butadiene and cyanoacrylic acid units, respectively) have been studied using B3LYP/cc-pVDZ level density functional theory (DFT) calculations. The selected D moieties are encountered as a part of an organic sensitizer molecule in dye-sensitized solar cell (DSSC) applications. When D moiety is joined with π-A, a certain amount of electron donation from D to A occurs leading to increase in electron density at the A site of D-π-A compared to A site of π-A. This electron reorganization is quantified in terms of the change in molecular electrostatic potential (MESP) minimum (ΔVmA) at the acceptor site, the CN group of the cyanoacrylic acid. The ΔVmA is always negative, in the range -11.0 to -2.6 kcal/mol which provides a quick assessment of the rank order of the electron-donating nature of the D moieties in the ground state of D-π-A. The optical, and photovoltaic properties of D and D-π-A systems are also determined at TD-CAM-B3LYP/cc-pVDZ//B3LYP/cc-pVDZ level. An absorption red shift (Δλmax) in the range 81 – 242 nm is observed when D moieties change to D-π-A systems. The ground state property ΔVmA showed a strong linear correlation with the excited state property Δλmax. Further, ΔVmA is found to be proportional to the open-circuit voltage (Voc). The resemblance of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of the D-π–A system with the respective energies of donor and π-A systems shows that donor tunes HOMO, while π-A tunes LUMO. Among the thirteen D-π-A systems, N,N-dialkylaniline, and julolidine are rated as the best donors for the photovoltaic applications. This study shows that MESP based assessment of donating strength of donor systems offers a powerful rational design strategy for the development of efficient dyes for DSSC applications.
关键词： donor-π-acceptor systems,electron-donating strength,molecular electrostatic potential,dye-sensitized solar cells,density functional theory
更新于2025-09-23 15:21:01
-
Effect of light absence or attenuation on biaxial flexural strength of dual-polymerized resin cements after short- and long-term storage
摘要： Objective: To evaluate whether biaxial flexural strength (BFS) of dual resin cements is affected by light absence or attenuation, storage time, or cements' chemical nature. Materials and methods: One hundred and twenty disk-shaped specimens were made from each cement (non-self-adhesive cement and self-adhesive cement) using Teflon molds on a controlled temperature surface (35°C). Specimens were polymerized as follows (N = 30): self-cured, directly light-cured, light-cured at a distance of 6 mm between the light tip and the specimen, and through a 6-mm thick composite resin barrier (indirectly light-cured). Each group was divided (N = 10) for storage purposes (15 minutes, 24 hours, and 6 months). Specimens were placed into a biaxial-flexure jig and a vertical load was applied until failure. The BFS values were subjected to generalized linear models statistical analysis and Weibull distributions (α = 0.05). Results: After 15 minutes aging, neither material achieved enough polymerization to perform the BFS test when polymerized using the self-curing mode. The self-adhesive product demonstrated much lower variation in strength with storage time than did the non-self-curing cement. Conclusions: Attenuated/light-curing reduced BFS values only for 15-minutes storage period for both materials. Flexural strength of the self-adhesive cement was less affected by light absence/attenuation and storage time.
关键词： resin cements,Weibull analysis,biaxial flexural strength,physical properties,polymerization
更新于2025-09-23 15:21:01
-
Laser-arc hybrid welding of 12- and 15-mm thick structural steel
摘要： High-power lasers are very effective in welding of plates thicker than 10 mm due to the keyhole mode. High-power intensity generates a vapor-filled cavity which provides substantial penetration depth. Due to the narrow and deep weld geometry, there is susceptibility to high hardness and weld defects. Imperfections occur due to keyhole instability. A 16-kW disk laser was used for single-pass welding of 12- to 15-mm thick plates in a butt joint configuration. Root humping was the main imperfection and persisted within a wide range of process parameters. Added arc source to the laser beam process may cause increased root humping and sagging due to accelerated melt flow. Humping was mitigated by balancing certain arc and other process parameters. It was also found that lower welding speeds (< 1.2 m/min) combined with lower laser beam power (< 13 kW) can be more positive for suppression of humping. Machined edges provided more consistent root quality and integrity compared with plasma cut welded specimens. Higher heat input (> 0.80 kJ/mm) welds provided hardness level below 325 HV. The welded joints had good Charpy toughness at ? 50 °C (> 50 J) and high tensile strength.
关键词： Mechanical properties,Toughness,Thick steel,Hybrid welding,High strength steel,Laser welding
更新于2025-09-23 15:21:01
-
Effect of numerical aperture on molten area characteristics in micro-joining of glass by picosecond pulsed laser
摘要： Glass products with precise and sophisticated shapes are highly demanded in the field of MEMS due to their excellent properties. Ultrashort pulsed laser has been expected to be a powerful and reliable tool for micro-welding of glass. Focusing condition such as numerical aperture (N.A.) is a critical parameter that controls how ultrashort laser pulses interact with and propagate in glass, and it has a great influence on the laser micro-welding characteristics of glass. In order to investigate the quality of welding process, it is important to understand the dependence of the mechanical strength of molten area created in glass specimen with various numerical apertures. Therefore, the mechanical strength of molten area with various numerical apertures was evaluated in micro-welding of glass by picosecond pulsed laser. Higher bending strength could be obtained under an appropriate volume ratio of molten area and glass specimen, when continuous molten areas were formed. In addition, high density and large size of molten area without crack led to higher breaking stress. It is concluded that superior focusing characteristics such as N.A. 0.65 enable a long region of high power density in beam axis, which can satisfy both high mechanical strength and high processing speed.
关键词： Picosecond pulsed laser,Breaking stress,Bending strength,Glass material,Numerical aperture
更新于2025-09-23 15:19:57
-
Filler metal distribution and processing stability in laser-arc hybrid welding of thick HSLA steel
摘要： Welds made by high power laser beam have deep and narrow geometry. Addition of filler wire by the arc source, forming the laser-arc hybrid welding (LAHW) process, is very important to obtain required mechanical properties. Distribution of molten wire throughout the entire weld depth is of concern since it tends to have low transportation ability to the root. Accurate identification of filler metal distribution is very challenging. Metal-cored wires can provide high density of non-metallic inclusions (NMIs) which are important for acicular ferrite nucleation. Accurate filler distribution can be recognized based on statistical characterization of NMIs in the weld. In the present study, it was found that the amount of filler metal decreased linearly towards the root. The filler metal tends to accumulate in the upper part of the weld and has a steep decrease at 45–55 % depth which also has wavy pattern based on longitudinal cuts. Substantial hardness variation in longitudinal direction was observed, where in the root values can reach > 300 HV. Excessive porosity was generated at 75 % depth due to unstable and turbulent melt flow based on morphology of prior austenite grains. The delicate balance of process parameters is important factor for both process stability and filler metal distribution.
关键词： Filler metal distribution,Microstructure,Thick steel,Non-metallic inclusions,High strength steel,Mechanical properties,Laser-arc hybrid welding
更新于2025-09-23 15:19:57
-
Nanosecond-pulsed laser welding of metallic glass
摘要： This study explores nanosecond-pulsed (ns-pulsed) laser welding on the metallic glass (MG) ribbons of four compositions: Fe78Si9B13, Zr65Cu15Ni10Al10, La55Ni20Al25 and Ce65Al10Cu20Co5. All MGs can be welded in the air by the ns-pulsed laser, and the crystallization of the welding joints can be avoided by proper control of the laser parameters. By varying the travel speed, pulse duration and repetition frequency, the critical crystallization time of MG can be quickly detected in a high-throughput way by ns-pulsed laser welding. At the optimal processing conditions, 70–90% of the tensile strength of the parent melt-spun ribbon can be preserved in the welded MG ribbons. The mechanical strength is well linked to the pro?le of the welding joint, which suggests a simple method to evaluate the welding quality. A welding parameter map has been established based on the experiments, and it is concluded that the laser power-density per sample thickness and the interaction time are the key factors that control the crystallization and strength of the welding joints. The map is valid for a broad range of MG compositions of all sample thickness, and thus the optimal processing conditions may be extended to all MGs with equivalent glass-forming ability.
关键词： Strength,Metallic glass,Thickness,Laser welding,Welding parameter map
更新于2025-09-23 15:19:57
-
Modelling and optimization of process parameters to obtain maximum tensile strength for laser butt welding of 316L austenitic stainless steel sheets
摘要： The attribute of high power density but low energy-input in Laser welding offers exciting solutions to the commonly encountered disadvantages with conventional joining techniques. In this paper, 316L Austenitic Stainless Steel metal sheets were butt welded using Nd:YAG Laser welding system. Owing to its low cost and specific properties such as excellent toughness, higher creep, stress to rupture at elevated temperatures, 316L A.S.S finds wide range of applications in the industrial arena especially in the automobile and marine sectors. Hence, it becomes imperative to examine its post weld properties after performing laser welding and find optimized values of the parameters. The prominent process parameters like Laser Power, Travel speed and Focal length were analysed and optimised. Design of experiment statistical tool was embraced for the systematic conduct of the tests. Response Surface Methodology (RSM) and analysis of variance (ANOVA) techniques were employed to identify the significant process parameters affecting the weld. An empherical relationship involving the parameters was developed to predict the ultimate tensile strength. The 3D response surface plot and contour plots were generated for this model to elucidate the interaction effect of Laser parameters (Travel speed and Focal length), (Laser Power and Focal Length) & (Laser Power and Travel Speed) on Ultimate Tensile Strength. The welded specimens cut by electric discharge machining were prepared for tensile testing as per the ASTM standard. The Universal Testing Machine was used to test the welded specimen. Microhardness Testing was also carried out on the base material and the Heat Affected Zone (HAZ) using Vickers Hardness Testing machine. The tensile tested specimens were used for metallurgical analysis using Scanning Electron Microscope (S.E.M.). Specimen prepared for metallurgical analysis were sectioned, mounted, ground and polished in accordance with recommended procedures in ASTM practice E 3-11. The metallurgical observations showed the existence of undulating topography of ductile fracture surfaces. The investigations reveals that the actual values of the Ultimate tensile strength of the weld were falling close with the predicted strength obtained through the proposed model. It can be concluded that the proposed model in this work can be utilised to predict tensile strength of the weld with more precision.
关键词： Design of Experiments,Ultimate tensile strength,316 L A.S.S,Response Surface Methodology (RSM),Nd:YAG Laser welding
更新于2025-09-23 15:19:57
-
Tailoring the plasmonic Fano resonance in metallic photonic crystals
摘要： Periodically arranged metallic nanowires on top of a waveguide layer show a strong coupling between the particle plasmon of the wires and the waveguide mode. By introducing a dielectric spacer layer between the metallic structures and the waveguide layer, this coupling can be reduced. Here, the thickness of this spacer layer is varied and the coupling strength is determined for each spacer layer thickness by fitting an effective energy matrix to the energy positions of the resonance peaks. It is found that the coupling strength can be very well described by the electric field amplitude of the waveguide mode at the location of the nanowires. We carried out experiments and found very good agreement with theory and our simple model. Using this method, we achieved experimentally an extremely small mode splitting as small as 25 meV leading to very sharp spectral features. Our pathway and design for tailoring the coupling strength of plasmonic Fano resonances will enable the design of highly sensitive plasmonic sensor devices and open the door for narrow plasmonic spectral features for nonlinear optics and slow light propagation.
关键词： photonic crystals,coupling strength,Fano resonance,plasmonic,waveguide
更新于2025-09-23 15:19:57
-
Development of technology for robotic laser welding of thin-walled products from heat-resistant alloys
摘要： The results of testing the modes of robotic laser welding of spatial welded joints of thin-walled products from heat-resistant steels are considered. Comparative studies of the influence of the parameters of various methods of industrial welding on the metallography of the weld and the technological strength of the welded joint are presented. The resistance of welded joints against the formation of crystallization (hot) cracks is evaluated.
关键词： heat-resistant alloys,robotic laser welding,technological strength,metallography,crystallization cracks,thin-walled products
更新于2025-09-23 15:19:57
-
Laser transmission welding of thermoplastic with beam wobbling technique using particle swarm optimization
摘要： Laser transmission welding is growing day by day with an increase of the uses of thermoplastic materials. This article presents the effect of various process parameters on weld strength and weld seam width obtained. The transparent polycarbonate and black carbon filled PMMA, each of 2.8 mm thickness have been joined by using low power laser. Here, effect of wobble frequency and wobble width are studied along with other process parameters. It is observed that weld seam width much depends upon the wobble width and the effect of wobble frequency is minimum. It has been observed that laser beam wobbling provides the greater weld strength by enlargement of joint area. Moreover, Beam wobbling plays a significant role to achieve better weld strength and weld width. Response surface methodology has been used to model the laser welding process parameters and responses of welding through regression analysis. The results of ANOVA reveal that the models formed appropriately predict the responses within the range of process parameters. A confirmation experiment has also been conducted to validate the results. A multi objective optimization has been used to find the optimum solution by Particle swarm optimization technique.
关键词： Polycarbonate,Acrylic,Low power laser,Weld strength,Beam wobbling,Particle swarm optimization
更新于2025-09-23 15:19:57