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Effect of Nd:YAG pulsed laser welding process on the liquation and strain-age cracking in GTD-111 superalloy
摘要： The weldability of GTD-111 nickel-based superalloy by Nd:YAG pulse laser with an average power of 250 W was studied using several pre- and post-weld heat treatment cycle, and the characteristics of liquation, solidification and strain-age cracks were also investigated. The results revealed that liquation cracks in the GTD-111 Nickel-Based Cast Superalloy were associated with the constitutional liquation of γ′ particle, MC carbides, inter-dendritic γ-γ? eutectic and melting of Cr-rich boride. Also, cracking during welding occurred at the places that the concentration of Al and Ti is high. Crack-free laser welds were observed in the MT1 conditions (1200 ℃ for 2 h) owing to dissolution of deleterious phases before welding. γ′ phase had little effect on the incidence of cracking in the MT1 condition. An analysis of the microstructures indicated that the cracking was caused primarily by liquation in the as-welded condition and was exacerbated by post-weld heat treatment cracking during the subsequent heat treatment. aging heat treatment of samples which were undergone aging heat treatment before welding, resulted in the formation of strain-age cracking due to γ? and γ-γ? eutectic phases precipitation. The results of micro-hardness indicated that the hardness of fusion zone (FZ) was higher than that of HAZ and base metal zone (BMZ). The liquation cracking in the heat affected zone (HAZ) was observed to be affected by the hardness of base-alloy.
关键词： Laser beam welding,GTD-111 superalloy,Liquation cracking,Strain age cracking
更新于2025-09-19 17:13:59
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CNN based automatic detection of photovoltaic cell defects in electroluminescence images
摘要： Automatic defect detection is gaining huge importance in photovoltaic (PV) field due to limited application of manual/visual inspection and rising production quantities of PV modules. This study is conducted for automatic detection of PV module defects in electroluminescence (EL) images. We presented a novel approach using light convolutional neural network architecture for recognizing defects in EL images which achieves state of the art results of 93.02 % on solar cell dataset of EL images. It requires less computational power and time. It can work on an ordinary CPU computer while maintaining real time speed. It takes only 8.07 milliseconds for predicting one image. For proposing light architecture, we perform extensive experimentation on series of architectures. Moreover, we evaluate data augmentation operations to deal with data scarcity. Overfitting appears a significant problem; thus, we adopt appropriate strategies to generalize model. The impact of each strategy is presented. In addition, cracking patterns and defects that can appear in EL images are reviewed; which will help to label new images appropriately for predicting specific defect types upon availability of large data. The proposed framework is experimentally applied in lab and can help for automatic defect detection in field and industry.
关键词： PV cell cracking,Automatic defect detection,Convolutional neural network (CNN),Electroluminescence,Deep learning,Photovoltaic (PV) modules
更新于2025-09-19 17:13:59
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Plasmon‐Enhanced InGaZnO Ultraviolet Photodetectors Tuned by Ferroelectric HfZrO
摘要： Allene (C3H4) gas is produced and separated on million-metric-ton scale per year during petroleum refining but is rarely employed in organic synthesis. Meanwhile, the addition of an allyl group (C3H5) to ketones is among the most common and prototypical reactions in synthetic chemistry. Herein, we report that the combination of allene gas with inexpensive and environmentally benign hydrosilanes, such as PMHS, can serve as a replacement for stoichiometric quantities of allylmetal reagents, which are required in most enantioselective ketone allylation reactions. This process is catalyzed by copper salts and commercially available ligands, operates without specialized equipment or pressurization, and tolerates a broad range of functional groups. Furthermore, the exceptional chemoselectivity of this catalyst system enables industrially relevant C3 hydrocarbon mixtures of allene with methylacetylene and propylene to be applied directly.
关键词： enantioselective allylation,allene,copper catalysis,hydrosilanes,petroleum cracking byproduct,ketones
更新于2025-09-19 17:13:59
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Drivers for the cracking of multilayer polyamidea??based backsheets in field photovoltaic modules: Ina??depth degradation mapping analysis
摘要： There is a lack of understanding on the root cause of cracking of photovoltaic (PV) backsheets due to the challenge of multilayer characterization and the complicated failure modes at the submodule level. In this work, the in-depth degradation mapping of field-exposed polyamide-based (PA-based) PV module backsheets was studied, with the major focus on the identification of underlying drivers for the through cracking (in between the solar cells). PV modules were retrieved from five different locations, comprising a variety of climates, including humid subtropical, hot-summer Mediterranean, tropical savanna climate, and hot arid. A suite of microscale cross-sectional characterizations, including chemical changes, fluorescence intensity, and modulus as a function of distance from the air surface of the backsheet, was performed. Results showed more advanced signs of degradation of the inner layer than the outer layer in the cracking region. Increases in the modulus were identified as the major indicator for the cracking. Moreover, a rudimentary test by immersion in acetic acid, which forms during photodegradation of the ethylene-vinyl acetate copolymer (EVA) encapsulant, showed the first-time direct evidence that acetic acid can largely accelerate the chemical degradation and facilitate the cracking of PA inner layer. This study suggests that the field cracking of PA-based backsheet can be attributed to the combined effects of chemical degradation and physical reorganization (chemi-crystallization) under cyclic thermomechanical stresses. Therefore, it is important to consider effects of local microclimates and interlayer infection to understand the heterogeneous nature of backsheet failures.
关键词： acetic acid,cross section,degradation,photovoltaic backsheet,cracking
更新于2025-09-19 17:13:59
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Cracking behavior and control of β-solidifying Ti-40Al-9V-0.5Y alloy produced by selective laser melting
摘要： A β-solidifying Ti-40Al-9V-0.5Y (at.%) alloy with a high cracking sensitivity has been successfully fabricated by selective laser melting (SLM) in this study. The influence factors for cracking sensitivity, cracking behavior and crack inhibition mechanism were investigated. The results show that the effects of process parameters on cracking sensitivity strongly depend on the cooling rate in molten pool with different heat transfer modes. The conduction mode with higher cooling rates exhibits a higher cracking sensitivity in comparison to the keyhole mode. Microstructure characteristics and phase transformations controlled by cooling rate determine the inherent ductility of β-solidifying γ-TiAl alloys during SLM. On this basis, the formation and inhibition mechanism of solidification and cold cracking are proposed. Finally, the crack-free Ti-40Al-9V-0.5Y sample with fine equiaxed microstructures and favorable mechanical properties (microhardness of 542±19 HV, yield strength of 1871±12 MPa, ultimate strength of 2106±13 MPa and ultimate compressive strain of 10.89±0.57 %) can be produced by SLM. The strengthening mechanism can be attributed to grain refinement and precipitation strengthening.
关键词： Phase transformation,Selective laser melting,Cracking behavior,Microstructure,β-solidifying γ-TiAl alloy,Cracking control
更新于2025-09-16 10:30:52
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Phase and Structural Transformations in Heat Resistant Alloys during Direct Laser Deposition
摘要： DLD, also known as Direct Laser Deposition, is an approached manufacturing technology. It is used to build full density metal parts directly from CAD files without using any modules or tools. A close look over the chemical composition and the microstructure of nickel based alloys will be shown in this paper.
关键词： X-Ray analysis,heat treatment,heat resistant alloys,cracking,Direct laser fabrication,nickel based alloys,direct laser deposition
更新于2025-09-16 10:30:52
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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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Experimental and numerical study on the influence of the laser hybrid parameters in partial penetration welding on the solidification cracking in the weld root
摘要： The aim of the present study is to investigate the influence of the laser hybrid welding parameters on the solidification cracks in the weld root for partial penetration welding. Welding trials were performed on thick-walled high-strength steels of grade S690QL under the same critical restraint intensity, with a variation of the welding velocity, wire feeding rate, and the focal position of the laser beam. It was ascertained that the welding velocity has a high impact on the solidification cracking phenomenon. A decrease in the welding speed leads to a reduction of the number of cracks in the weld root. The arc power has also a slight influence on the solidification cracking, while the change of the focal position of the laser beam shows also a remarkable effect. Besides, numerical simulation was performed to understand the thermomechanical behavior of the welds for different welding parameters to assist the interpretation of the experimental results.
关键词： Thick-walled steels,Solidification cracking,High-power laser beam,Partial penetration,Laser hybrid welding
更新于2025-09-16 10:30:52
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Performance of Distributed Optical Fiber Sensors (DOFS) and Digital Image Correlation (DIC) in the monitoring of RC structures
摘要： Distributed Optical Fiber Sensors (DOFS) are strain measuring tools whose potential related to the civil engineering field has been discovered in the latest years only. A unique utility lies in the possibility of bonding these extremely thin sensors to steel reinforcement bars which will later be embedded in concrete elements (RC) in order to monitor its mechanical strains. The present paper presents the results of an experimental campaign that saw the tensing of two RC tensile members (ties) with DOFS-instrumented steel rebars providing strain readings every 7.5mm. Their cracking behavior allows to gain insight on the steel rebar’s strain profile when surrounded by cracking concrete. The described results are novel as measurements that are accurate, completely distributed, experimentally extracted, both before and after concrete cracking, have been impossible up until now. The internal strain measurements are additionally integrated with an external Digital Image Correlation (DIC) monitoring which provides data on the displacements and strains of the members’ surfaces. The present research represents the beginning of an in-depth experimental campaign aimed at providing reinforcement strain data for multiple loaded RC ties encompassing different geometrical features (concrete cover, reinforcement ratio, bar diameter).
关键词： strain monitoring,concrete cracking,Digital Image Correlation (DIC),Distributed Optical Fiber Sensors (DOFS),RC structures
更新于2025-09-16 10:30:52
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Porosity and solidification cracking in welded 45 mm thick steel by fiber laser-MAG process
摘要： Porosity and solidification cracking in joining of thick sections are very common issues in deep penetration keyhole laser-arc hybrid welding (LAHW). In the present work, 45 mm thick high strength steel was joined by a double-sided technique. With combined use of fast welding speeds and larger air gap between plates, higher amount of porosity was found because of the dynamic behavior of the keyhole walls. Solidification cracking formed at the centerline in the bottom of the weld due to high-depth-to-width geometrical ratio. Numerical simulations have been performed and showed very high cooling rate and stresses occurred in the root of the deep welds, which corresponds with higher cracking tendency.
关键词： hybrid welding,mechanical properties,porosity,Laser welding,thick steel,solidification cracking
更新于2025-09-12 10:27:22