- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2018
- Phase difference method
- UTM
- Crack mouth opening displacement
- FBGs
- Three point bend specimens
- Prenotched concrete
- Plastic optical fiber
- Optoelectronic Information Science and Engineering
- National Institute of Technology, Warangal
-
Recent advancements in micro-crack inspection of crystalline silicon wafers and solar cells
摘要： The move towards in-line instrumentation quality assurance in photovoltaic industry has triggered new interest in development of novel methods and instruments for defect detection. Among the many tests that need to be carried out on silicon wafers and solar cells during the manufacturing process is the detection of micro-cracks. To date, the optical transmission method and luminescence technologies like electroluminescence and photoluminescence are popularly used by silicon wafer and solar cell manufacturers primarily due to their practicality and speed advantages. However, the increase in production throughput speeds and the recent change in the wafer sawing process where slurry-based sawing is gradually being replaced with diamond-wire sawing presents new challenges to the industries. This short perspective presents these new challenges and highlights breakthrough inventions in response to recent development. This article concludes by identifying some research opportunities that has emerged as a result of these recent developments.
关键词： Image Processing,Micro-crack,Solar Cell,Silicon Wafer,Machine Vision
更新于2025-09-23 15:19:57
-
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
-
The effect of manufacturing defects on the fatigue life of selective laser melted Ti-6Al-4V structures
摘要： The manufacturing defects introduced by selective laser melting typically lead to lower fatigue strength and a larger variation in fatigue life compared to conventionally manufactured structures. X-ray micro computed tomography (μCT) is used to characterize the porosity and lack of fusion defects in terms of population, morphology, dimension and location. The defect size and location are combined with the NASA/FLACGRO (NASGRO) fatigue crack growth model to predict the likely fatigue life, in which an effective initial crack length is defined using the cyclic plastic zone and the defect radius. An eXtended defect zone (XDZ) describing the propensity for local plasticity during fatigue around a defect has been shown through numerical analysis to be a good indicator of the ranking of the threat to fatigue caused by differently located manufacturing defects. This indicates that the effect of a defect, initial radius, r0, is likely to be pronounced when its center is within 2r0 of the surface and maximal when it lies just beneath the surface.
关键词： Additive manufacturing,High cycle fatigue (HCF),Fatigue crack initiation and growth,Digital printing,Defect tolerance method
更新于2025-09-23 15:19:57
-
Eliminating the crack of laser 3D printed functionally graded material from TA15 to Inconel718 by base preheating
摘要： High quality manufacturing the functionally graded material (FGM) from TA15 to Inconel718 (IN718) has wide application prospects in the aerospace field. However, the crack always can be found in linear gradient structure of the FGM manufactured by laser 3D printing. In the present study, the crack-free FGM was fabricated by laser 3D printing via base preheating. The microstructure and mechanical properties were analyzed in detail to evaluate the mechanism that the preheating process prevented the formation of the crack. The microstructure of the unpreheated FGM presented that the crack mainly formed in the region between 60% and 80% IN718. Obviously, no cracks formed in the preheated sample because base preheating process made the level of internal stress to be below the yield strength. The tensile strength of the FGM with the preheating was 207 MPa. This is a noticeable improvement compared with that fabricated without the preheating, which could not be measured due to the formation of the crack. These research results indicate that the base preheating process can effectively prevent the formation of the crack during laser 3D printing FGMs from Ti- to Ni-based alloys.
关键词： Laser 3D printing,Functionally graded material,Crack,Microstructure,Preheating
更新于2025-09-23 15:19:57
-
Design of ultrathin OLEDs having oxide-based transparent electrodes and encapsulation with sub-mm bending radius
摘要： Highly flexible ultrathin organic light emitting diodes (OLEDs) hold vast potential as light sources particularly for wearable and imperceptible electronics. Most of the work demonstrated to date for highly flexible OLEDs, however, has relied on non-conventional transparent conductors such as conjugated polymers and has had no proper encapsulation or, if any, simple polymer-based encapsulation. We here demonstrate OLEDs that can be bent at a sub-mm radius even with conventional transparent conductive oxides (TCOs) and full encapsulation based on a multilayer gas barrier containing aluminum oxides, both of which are prone to strain-induced fracture. We realize such a small bending radius not only by adopting ultrathin substrates but also by exploiting the beneficial neutral plane shift toward the top of substrates identified in a system consisting of a ultrathin substrate and a multilayer device structure on its top. The proposed OLEDs exhibit stable performance after 1,000 bending iterations even at a bending radius far smaller than 1 mm and show similar reliability to that of glass-based reference devices even after two weeks in the acceleration test chamber.
关键词： Transparent conductive oxides,Ultrathin OLEDs,Multilayer encapsulation,Crack-onset strain,Neutral plane shift
更新于2025-09-23 15:19:57
-
A Real-Time Method to Detect the Deformation Behavior during Laser Solid Forming of Thin-Wall Structure
摘要： Laser solid forming (LSF) is a promising additive manufacturing technology. In the LSF process, deformation behaviors dictate the accuracy of the produced parts. In this study, by using a laser displacement detector based on laser triangulation principle, an accurate and effective real-time detection method was established to monitor the real-time deformation behavior of the key position during the LSF of a thin-wall structure. The results confirmed that increasing thin-wall length results in increasing final deformation of the edge. The displacement fluctuation range and value in the middle of thin wall are both smaller than that of the positions near the end, while the entire displacement changing direction in the middle is opposite to that of the end positions. When the deposition process is paused, the deformation of the thin wall during the cooling stage will deviate the position of the deposited thin wall, resulting in the dislocation between the subsequent deposited part and that before the pause, which affect the dimensional accuracy of the thin wall structure. This non-contact real-time detection method also confirmed the ability to monitor the initiation of cracking during the LSF process, and a potential to be used for the on-line feedback control of deformation of detected key position of deposited structure.
关键词： laser solid forming,real-time detection,accuracy,crack,additive manufacturing,deformation behaviors
更新于2025-09-23 15:19:57
-
Hot cracking in autogenous welding of 6061-T6 aluminum alloy by rectangular pulsed Nd:YAG laser beam
摘要： Due to high hot crack susceptibility of Al-Mg-Si alloys, autogenous welding by rectangular pulsed laser beam has not been generally successful in the removal of cracks. In this research, the effect of pulsed Nd:YAG laser parameters and preheating on the creation of hot cracks in the 6061-T6 aluminum alloy was investigated. The sample that was fabricated by the laser parameters including 1 Hz, 0.12 mm/s, 10 ms, and without preheating exhibited the highest cooling rate and the smallest dendrite arm spacing but no hot crack was observed. The tensile test specimens of this sample fractured at a point far from the weld metal and a decrease in the precipitation of silicon and magnesium in the inter-dendritic space and the reduction of thermal stresses resulted in the elimination of hot cracks. However, according to macro-scale models for the creation of hot cracks, preheating decreased the tensile stresses in the BTR (brittle temperature range), but increasing the preheating temperature led to increasing rather than decreasing the hot crack length. In this case, the formation of hydrogen porosity, the segregation of silicon and magnesium, and the creation of low melting point compounds were the important parameters affecting the hot crack initiation and growth.
关键词： Laser welding,6061 aluminum alloy,Stress simulation,Solidification microstructure,Hot crack modeling,Rectangular pulse
更新于2025-09-23 15:19:57
-
A comparative study of microstructure and hydrogen embrittlement of selective laser melted and wrought 17a??4??PH stainless steel
摘要： In this study, the microstructure and hydrogen embrittlement of 17–4 PH stainless steel produced by Selective Laser Melting (SLM) were investigated. The microstructure of SLM-ed 17–4 PH stainless steel was found to be fully ferritic, in contrast to the wrought martensitic steel. This finding was correlated to the high cooling and heating rates of the SLM process that suppressed the austenite formation and retained the delta ferrite to room temperature. The SLM-ed steel shows grains elongated in the building direction and its grain size is higher than the prior austenitic grain size of the wrought steel. The two steels present nanoscale copper precipitation after ageing 4 h at 580°C. The yield strength of the SLM-ed steel was found lower by only 10% with respect to the wrought steel. The hydrogen embrittlement was evaluated by performing slow strain rate tensile tests under cathodic charging after ageing 4 h at 580°C. It was found that SLM-ed 17–4 PH steel was more susceptible to hydrogen embrittlement compared to its wrought counterpart. This was attributed to the difference in microstructures, more specifically grain size. The crack initiation and propagation was much easier in the ferritic SLM-ed steel than in the martensitic wrought steel because of the higher grain size. The fracture in both steels was due to a significant subcritical crack growth followed by fast overload fracture of the remaining ligament. The fracture surface of the wrought steel showed a brittle intergranular fracture mode close to the surface and a ductile mode at the center. The brittle intergranular fracture mode was associated with the slow subcritical crack growth, while the ductile mode was due to the final fast overload fracture. On the other hand, in the SLM-ed steel, both the subcritical crack growth and the final fast overload fracture were obtained by transgranular cleavage. This shows that under hydrogen the martensitic wrought steel is prone to brittle intergranular fracture in contrast to the ferritic SLM-ed steel which is subject to brittle transgranular cleavage. The same tendency is obtained under air when notched specimens are used. This propensity of the martensitic steel to fracture along prior austenite grain boundaries can be interpreted in terms of the easiest fracture path.
关键词： Cleavage,Subcritical crack growth,Martensitic stainless steels,Selective laser melting,Additive manufacturing,Hydrogen cracking,Hydrogen embrittlement,Intergranular
更新于2025-09-23 15:19:57
-
Examination of internal stress by photoelasticity in laser cleaving of glass
摘要： Laser cleaving is a glass-cutting technique in which thermal stress induced by laser heating and cooling produces cracks in the glass. Stress measurement during the laser cleaving process is critical in elucidating the crack-propagation mechanism and solving the problems of the laser cleaving method. In this study, we measured the birefringence retardation using a high-speed polarization camera and evaluated the relevance and accuracy of the measured values by comparing them with the results of a numerical calculation. The birefringence retardation at the crack tip was also observed in the experimental process. For the experiment, a soda lime glass was cleaved using CO2 laser irradiation. Then, the birefringence retardation and azimuthal angle obtained using the polarization camera were compared with the numerical calculation results. The birefringence retardation around the crack tip corresponded with that of the deformation caused by mode I. The crack propagation was arrested when the crack tip approached the edge of the glass. The birefringence retardation observed using the polarization camera confirmed that the mode I deformation decreased as the crack approached the edge.
关键词： Glass,Laser cleaving,Crack propagation,Numerical calculation,Photoelasticity
更新于2025-09-23 15:19:57
-
[IEEE 2018 26th European Signal Processing Conference (EUSIPCO) - Rome (2018.9.3-2018.9.7)] 2018 26th European Signal Processing Conference (EUSIPCO) - Road Surface Crack Detection using a Light Field Camera
摘要： During traditional road surveys, inspectors capture images of pavement surface using cameras that produce 2D images, which can then be automatically processed to get a road surface condition assessment. This paper proposes a novel crack detection system that uses a light field imaging sensor, notably the Lytro Illum camera, instead of a conventional 2D camera, to capture road surface light field images. Light field images capture the light rays originating from different directions, thus providing a richer representation of the observed scene. The proposed system explores the disparity information, which can be computed from the light field, to obtain information about cracks observable in the pavement images. A simple processing system is considered, to show the potential use of this type of sensors for crack detection. Encouraging experimental crack detection results are presented based on a set of road pavement light field images captured over different pavement surface textures. A performance comparison with a state-of-the-art 2D image crack detection system is included, confirming the potential of using this type of sensors.
关键词： Light field imaging,image processing,road crack detection
更新于2025-09-19 17:15:36