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Automatic mapping of cracking patterns on concrete surfaces with biological stains using hyper-spectral images processing
摘要： Despite all technological advances, mapping cracks on concrete structures mostly remains to be evaluated through sketches based on on-site observation and photographs. Methods based on image processing have been developed with clear advantages. However, most studies rely on perfectly identified areas or on single cracks without any other pathologies, being therefore unsuitable for on-site application. In addition, the accuracy is not usually quantified due to the absence of ground-truth. Thus, methods for automatic mapping of cracking patterns, sufficiently robust to deal with the surrounding pathologies, are of great interest. The Super Cluster-Crack method (SC-Crack method) is herein presented. It was developed for crack detection in concrete surfaces, with biological stains, by processing hyperspectral images. SC-Crack performs k-means clustering, followed by grouping clusters to composing a super cluster that stands for the cracks. The method was calibrated and validated by classifying hyperspectral images of concrete specimens, within bandwidths of 25 nm in a wavelength range between 425 nm and 950 nm. Results are discussed by comparison with the ground-truth image. Finally, the super cluster composition is also validated. The SC-Crack method performs successfully both on clean and on surface with biological stains. In the latter case, hyperspectral images help to avoid mixing biological stains with crack pattern. Concerning the main goal of mapping the cracking pattern, the method performs perfectly on concrete clean surfaces, allowing to detect all the crack branches. In the case of surface with biological stains, the SC-Crack also detects the majority of cracking pattern, except for the thinner branches.
关键词： image processing,concrete surfaces,super cluster,cracking pattern,hyper-spectral image,automatic mapping
更新于2025-09-23 15:23:52
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Influence of Structure Modification of Silicon Carbide Materials on Their Dynamic Properties
摘要： SiC ceramic materials were prepared both by reactive and liquid-phase sintering. Structure was modified during preparation by introducing reinforcing SiC-filaments and by synthesizing grains self-reinforcing the structure. The armor-protection capacity was determined by estimating the bullet penetration delay time.
关键词： reinforced materials,bullet resistance of the ceramic material,cracking resistance,liquid-phase sintered silicon carbide (LPS-SiC),reaction-sintered silicon carbide (SiSiC)
更新于2025-09-23 15:21:21
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Application of distributed temperature sensing for cracking control of mass concrete
摘要： This paper presents a framework of cracking control for a mass concrete structure in a reservoir project, by taking advantage of Distributed Temperature Sensing (DTS) system. The DTS system in this project, mainly consisting of an Optical Backscatter Reflectometer (OBR) interrogation unit and a single fibre-optic cable, was deployed to measure and monitor concrete temperatures of an intake tower in block placement. The temperature measurements in concrete blocks were utilized as the fundamental data to determine the thermal properties of the cast-in-situ concretes, through the inverse analysis method based on temperature simulation. Based on thermal stress simulation using the thermal properties, cracking risks of each concrete block were predicted and evaluated under the modes of temperature control associated with the time-varying construction and ambient conditions, for appropriate modes before and after the concrete placement. The framework of cracking control, developed by integrating the DTS measurement with the temperature forecast and the cracking prediction based on thermal stress simulation and cracking risk evaluation, improves the efficiency of temperature regulation and cracking control in mass concrete construction, and can be further integrated into the intelligent construction management of concrete projects.
关键词： Cracking control,Fibre-optic,DTS,Mass concrete
更新于2025-09-23 15:21:21
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[IEEE 2019 20th International Conference on Electronic Packaging Technology(ICEPT) - Hong Kong, China (2019.8.12-2019.8.15)] 2019 20th International Conference on Electronic Packaging Technology(ICEPT) - Effects of Cracks on Interfacial Thermal Properties of LED Packages by Entropy Generation
摘要： Entropy generation is a kind of available energy loss. Evolution of thermodynamic entropy during accelerated test of die attach in LED is studied with transient analysis. The existing models on the study of heat transfer in the solder layer, mainly including the effect of voids on the mechanical properties and the heat transfer performance. However, there are few investigations that relating the second law of thermodynamics to the voids in the DA layer, transient heat distribution is less considered. In this work, based on the temperature distribution, the convection entropy rate of the chip to the ambient and the conduction entropy of the DA layer are studied. The results show that, as the length of the crack increases, both the convection entropy rate and the conduction entropy increase. Particularly, when the crack length was increased from 30% to 40%, the normalized conduction entropy of the DA layer showed a sharp increase, which indicates that the large crack (more than 30%) will pose a serious challenge to the quality of the LED packaging.
关键词： thermal effect,DA layer,cracking,transient,entropy generation
更新于2025-09-23 15:21:01
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20a??kW laser welding applied on the international thermonuclear experimental reactor correction coil case welding
摘要： International thermonuclear experimental reactor correction coil cases are made of heavy, thick, high strength, and high toughness austenitic stainless steel 316LN. The BTCC (bottom and top correction coils) case has the dimension of 2.5 × 7 m2 and cross section of 239.8 × 146.7 mm2, side correction coil case has the dimension of 7.2 × 7.6 m2 and cross section of 147.8 × 168 mm2, and they will be closure welded after winding pack insertion. The 20 mm welding depth, dozens of meter of welding length, strict welding requirements, large size, and complex configuration bring a big challenge to this closure welding work. 20 kW high power laser welding is selected as the main welding method because of the advantage of potential welding deformation control and its penetrating ability and cracking resistance. The welding parameter is developed that can cover the assembly gap from 0 to 0.5 mm with a good welding quality. A special test coupon is designed for the welding procedure qualification, and related tests are carried out to qualify the joint properties of bend, tensile, and impact. Finally, a full-scale BTCC case is welded. After welding, ultrasonic testing confirms that almost all welds satisfy the weld seam quality requirement. The recorded temperatures less than 250° indicate that the temperature induced by welding will not harm the internal winding pack. The dimensional deviation of the inner face is less than 4 mm and also satisfies the tolerance requirement of ±2 mm for the BTCC case.
关键词： austenitic stainless steel,ITER,welding deformation,cracking,20kW laser welding
更新于2025-09-23 15:21:01
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Prediction of solidification cracking by an empirical-statistical analysis for laser cladding of Inconel 718 powder on a non-weldable substrate
摘要： This paper presents an empirical-statistical approach to predict solidification cracking during laser cladding of Inconel 718 powder on A-286 Fe-based superalloy. This approach is based on a linear regression analysis and empirical-statistical correlations between the key processing parameters (laser power, P; powder feed rate, F; and scanning speed, V) and the geometrical attributes of single laser cladding tracks. These correlations were used for the development of a processing map which assesses the effects of the geometrical characteristics on the solidification cracking and the required conditions to obtain crack-free clads. Scanning electron microscopy was used for microstructural characterization. Thermodynamic calculations using the non-equilibrium Scheil solidification model were also employed. The empirical-statistical analysis showed that the processing parameters directly associated with the height and angle of single laser cladding tracks are and, respectively. The processing map revealed that the dilution ratio is the governing macrostructural attribute required to avoid solidification cracking. Indeed, a substrate dilution ratio lower than 25% shifts the cladding composition to an alloy regime, which has lower susceptibility to solidification cracking. The role of this macrostructural feature in reducing the susceptibility of the fusion zone to solidification cracking is thoroughly discussed.
关键词： Thermodynamic simulation,Inconel 718,Processing map,Solidification cracking,Laser cladding,Dilution ratio
更新于2025-09-23 15:21:01
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[Laser Institute of America ICALEO? 2015: 34th International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - Atlanta, Georgia, USA (October 18–22, 2015)] International Congress on Applications of Lasers & Electro-Optics - Microstructural effects induced by laser shock peening for mitigation of stress corrosion cracking
摘要： Stress corrosion cracking is a phenomenon that can lead to rapid, sudden failure of metallic products. In this paper we examine the mechanisms of SCC mitigation of stainless steel and brass samples using laser shock peening (LSP). The behavior of hydrogen within the crystal lattice is one of the most dominant contributors to SCC, where uptake of hydrogen strains the lattice and increases its hardness. Cathodic charging of the metallic samples in 1M sulfuric acid was performed in order to accelerate hydrogen uptake. Non-treated samples underwent hardness increases of 28%, but LSP treated samples only increased in the range of 0 to 8%, indicative that LSP keeps hydrogen from permeating into the metal. Mechanical U-bends subjected and MgCl2 environments are analyzed, to determine changes in fracture morphology. Surface chemical effects are addressed via Kelvin Probe Force Microscopy, which is used for finding changes in the work function caused by LSP treatment. A finite element model of material deformation from U-bending was developed to analyze and compare the induced stresses. With LSP, there is a potential for overprocessing the samples, whereby negative effects refinement, to corrosion martensite formation) can arise. Detection of any martensite phases formed is performed using x-ray diffraction. We find LSP to be beneficial for stainless steel but does not improve brass’s SCC resistance. With our analysis methods we provide a further understanding of the process whereby LSP reduces subsequently highlight SCC for important implementation of the process.
关键词： Brass,Stainless steel,Hydrogen uptake,Stress corrosion cracking,Cathodic charging,Kelvin Probe Force Microscopy,Laser shock peening,Finite element model
更新于2025-09-23 15:21:01
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Investigation on solidification cracks in pulsed laser spot welding of an AZ31 magnesium alloy
摘要： A direction-dependent model of solidification crack initiation and propagation is established to analyze the influence of the melt pool shape on the distribution of solidification cracks in pulsed laser spot welding. The formation direction of the initial crack is related to the variation of the solidification parameters. When the aspect ratio of the spot welds with a default Rectangular pulse is greater than 0.3 and less than 0.8, an initial crack is formed in the 45° direction of the mushy zone, and then the crack propagates along the grain boundary. That is, the solidification cracks are distributed in the direction of 45° on both sides of the surface center of the welding cross-section. When the aspect ratio of the spot welds is less than 0.3 or greater than 0.8, an initial crack is formed in the 90° direction of the mushy zone, and then the solidification crack is vertically distributed at the center of the welding cross-section. The Step-Down-10ms-0.3P pulse can significantly reduce the solidification rate of the melt pool interface, preventing the formation of initial cracks in the sensitive directions of the spot welds with an aspect ratio less than 0.8, thereby eliminating solidification cracks.
关键词： Molten pool shape,Solidification cracking prevention,Cracking distribution,Nd:YAG laser spot welds,Cracking initiation direction
更新于2025-09-23 15:19:57
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The effect of preliminary heat treatment on the durability of reaction bonded silicon nitride crucibles for solar cells applications
摘要： Silicon nitride crucibles have the potential to replace silica crucibles and reduce the cost of silicon crystallization because of their reusability potential. Till date, crucibles’ heat treatment before each use is a prerequisite to achieve non-wetting conditions that is needed to facilitate the ingot release and hence enable reusability. Yet, no studies have examined the heat treatment influence on the crucibles’ durability. The present investigation focuses on the crucibles’ heat treatment and its impact on the crucibles’ lifetime. Repeated heat-treatments of silicon nitride crucibles in the air at above 1100 °C leads to crucible fracture. Therefore, this study identifies the cause and the mechanism of such failures by applying different heat treatment procedures in the air. The mass gain and the oxidation rates of the crucibles at different temperatures are measured via Thermogravimetry (TG) and Differential Thermal Analyzer (DTA). The results show that the porosity and phase distribution along the crucible wall thickness, play a key role in the crucible’s behavior during oxidation. Moreover, excessive internal oxidation in the tested crucibles results in severe thermal stresses which cause cracking during cooling.
关键词： B1. Nitrides,A1. Heat treatment,A1. Crucible cracking,A1. Characterization
更新于2025-09-23 15:19:57
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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