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Investigation on the crack fracture mode and edge quality in laser dicing of glass-anisotropic silicon double-layer wafer
摘要： This work puts forward numerical and experimental investigations on laser dicing of glass-anisotropic single-crystal silicon double-layer wafer using laser induced thermal-crack propagation (LITP). A semiconductor continuous wave laser working at the defocusing mode serves as volumetric heat source for glass layer while as surface heat source for silicon layer. Based on the classical fracture theory, a static seam-type crack is introduced under the circumstance of ABAQUS to simulate the crack fracture modes in glass layer as well as silicon layer with crystal planes of (100), (110) and (111) during laser dicing in different dicing directions. In the experiments, processing parameters are kept the same as the simulations and typical dicing directions obtained from simulations are also used. The surface morphologies of crack edges are measured by the optical microscope and surface profiler. Through the comparison of numerical and experimental results it is discovered that for the specific substrate, the evolution of crack edge qualities in different dicing directions and different layers can be interpreted based on the corresponding stress distribution and stress intensity factor (SIF) ratio explicitly. And most important of all, the anisotropy of silicon layer has significant influence on the fracture mode and edge quality of crack in both layers.
关键词： Crack fracture mode,Laser induced thermal-crack propagation,Glass-anisotropic single-crystal silicon double-layer wafer,Crack edge quality,Static seam-type crack
更新于2025-11-21 11:24:58
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Study on mechanism of crack propagation of sapphire single crystals of four different orientations under impact load and static load
摘要： Sapphire has a wide range of applications due to its excellent physical properties. Sapphire is a typical anisotropic material, whose parts are usually employed in the complex conditions, including static and dynamic load. The mechanism of crack propagation under different loading conditions has important significance for successful application of sapphire. In this study, impact and static load tests have been performed on the A-plane, C-plane, M-plane and R-plane of sapphire by the high frequency cyclic impact test device, respectively. The force signals applied to sapphire have been obtained under different test conditions. The crack propagation has been analyzed based on the fracture morphology of specimen. It is found that sapphire will quickly crack and break under impact load, and then enter the fatigue stage. In the static load indentation tests, the force applied to sapphire seems to increase linearly with the linear increase of load, but this relationship is not yet linear in the unloading procedure. The crack propagation is affected by the crystal orientation, which leads to different characteristics of the surface morphology of the different crystal orientations sapphire after fracture. So four different models of crack system are proposed for A-plane, C-plane, M-plane and R-plane respectively. In addition, the three-dimensional morphology of sapphire is observed by a white-light interferometer. It seems that the Hertzian cone crack occurs only on the R-plane sapphire after impact load, but it cannot be sure whether the cone crack occurs when impacting A-, C-, and M-planes sapphire.
关键词： Impact load,Static load,Sapphire,Crystal orientations,Crack propagation,Crack system
更新于2025-09-23 15:23:52
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Methodology for diagnosing crack patterns in masonry structures using photogrammetry and distinct element modeling
摘要： Understanding the causes of damages on existing structures can augment preservation, renovation, and rehabilitation efforts. The aim of this work is to outline a method for diagnosing the most probable causes of cracks on existing structures using a combination of photogrammetry and distinct element modeling (DEM). Five experimental, masonry walls were constructed and cracked; the state of the wall before and after cracking was recorded using photogrammetry. Using distinct element modeling, each test wall was subjected to a variety of loading conditions including the same load case which was used to crack the wall during experimental testing. The crack patterns in the simulations were compared to the experimental crack patterns using a combined qualitative and quantitative method. The simulation which most closely reflected the existing damage patterns was selected as the most probable cause of the damages. For each of the test walls, the real simulated load had the closest fractional distance to the existing damage patterns captured by photogrammetry. This method was then applied to diagnose possible causes of cracking on a foundation wall in the Baptistery of San Giovani in Florence, Italy.
关键词： Distinct element modeling,Masonry,Building pathology,Diagnosis,Crack propagation,Photogrammetry
更新于2025-09-23 15:23:52
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Three-Dimensional Scanning Hall Probe Microscopy for Final Stage of Crack Growth of Chromium Molybdenum Steel SCM440
摘要： Crack propagation around the stress concentration area causes fatigue failure. Non-destructive method is necessary for monitoring structure fatigue before destruction. We focused on a magnetic non-destructive evaluation method for crack growth. In order to understand the relation between crack propagation and changes in magnetic flux density, we observed the position of the positive and negative magnetic flux density distributions around the crack of tool steel (SCM440) plate using a scanning Hall probe microscope (SHPM). We found that the vertical component of the three-dimensional magnetic flux density moved as the crack growth. Furthermore, the magnetic component which is parallel to the tensile stress appeared just before destruction of the specimen.
关键词： Crack propagation,Scanning Hall probe microscope,Magnetic flux density
更新于2025-09-23 15:22:29
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Atomic picture of crack propagation in Li <sub/>2</sub> Oa??2SiO <sub/>2</sub> glassa??ceramics revealed by molecular dynamics simulations
摘要： Fundamental understanding of the interaction between glass and ceramic phases with a running crack and the mechanisms by which propagation is hindered or altered as compared to the precursor parent glasses remains elusive for the lithium disilicate glass-ceramics. We herein conduct extensive molecular dynamics simulations to reveal some atomic details that are otherwise extremely challenging to be probed by experiments. The results show that the crack propagation pathway in glass-ceramics is dramatically different as compared to the precursor parent glass. In glassy sample, clean crack branching seems to be triggered by multiple cavitation events ahead of crack tip. In glass-ceramic samples, however, branching is characterized by microcracks at multiple glass-nanocrystal interface sites, clean nanocrystal cleavage along certain crystalline plane, and even secondary cracks due to the percolation of multiple microcracks. Additionally, the nanocrystal distribution, total volume fraction, and aspect ratio also have pronounced effects on the propagation of a primary crack and can lead to very diverse crack patterns.
关键词： lithium disilicate glass-ceramics,crack branching,microcracks,crack propagation
更新于2025-09-23 15:21:01
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Influence of laser weld shape on mechanical and fatigue behaviour of single lap laser welded joints
摘要： Traditional manufacturing processes, like arc welding and resistance spot welding, are still the main welding processes to join structural components used across the on/o?-road vehicle industry. Due to the abundance of data, experiences and insights over the decades of usage, lot of fatigue design data has been generated for different joint geometries produced using these methods. The laser welding process has excellent capabilities to join thin sheet metal structures with minimum heat input resulting into lower deformation and improved productivity that offers significant benefit as compared to the arc and resistance welding processes. However, due to the agility of designing joint configurations and limited availability of understanding regarding the fatigue behaviour of laser welded joints, the need arises for the fatigue design data. Most of the research presents the use of straight linear shape laser welds and limited knowledge exist regarding the influence of shape of laser welds on mechanical and fatigue performance of the laser welded joints. The laser welded joints produce small notch like radius at the root of laser weld which could act as a stress raiser causing early crack initiation. For this work, C-shape laser weld has been selected as the geometric shape in comparison to the straight linear shape of laser weld produced on a series of single lap joints. Detailed fatigue experimental investigation has been carried out for linear and C-shape laser welded joints tested in 3 different orientations with respect to the applied cyclic load and several different R-ratio’s and the results are compared. The metallurgical studies have been carried out to understand the failure mode and micro-hardness variations across the weld and heat affected zone. Further, the residual stress profiles have been compared for the C-shape laser weld with the linear welds using detailed X - Ray Diffraction based residual stress measurement.
关键词： Laser Weld,Ultra-high strength steel,C Shape,Crack propagation,High strength low alloy steel,Crack initiation
更新于2025-09-23 15:21:01
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Study on high-efficiency separation of laminated glass by skillfully combining laser-induced thermal-crack propagation and laser thermal melting
摘要： Laminated glass has a wide range of applications, but the cutting process is too cumbersome. In this paper, a novel laser composite separation method was proposed to separate the laminated glass by one time and simplify the cutting process from five steps to two steps for the first time by skillfully combining laser-induced thermal-crack propagation and laser thermal melting. This method generated three laser foci, and each laser focus is acting on one layer of laminated glass. Then, the composite mechanism combining laser-induced thermal-crack propagation for glass layers and laser thermal melting separation for PVB layer was realized to separate entire laminated glass. The experiments of separating laminated glass with thickness of 5 + 0.38 + 5 mm were carried out by laser composite separation successfully, and the separation side wall was very smooth (roughness of glass layer reached 10.24 nm) without any separation defects such as chipping, micro-cracks or subsurface damage. A mathematical model was also established to analyze the separation mechanism.
关键词： Laser melting,Numerical simulation,Laser-induced thermal-crack propagation,Laser separation,Laminated glass
更新于2025-09-23 15:21:01
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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
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Thermo-mechanical analysis of blister formation on a rigid substrate in blister-actuated laser-induced forward transfer
摘要： The paper presents an analytic model of glass-interface-polyimide structure for predicting the blister formation during blister-actuated laser-induced forward transfer. In order to investigate the dynamic process of the heating and vaporizing of polymer in laser/matter interaction and crack propagation of glass/polymer interface in blister expansion, a discrete quasi-static analysis method is proposed. In the frame of fracture mechanics, the energy release rate is calculated and introduced to analyze interfacial crack propagation of glass/polymer interface. In additional, the blister expansion and formation are also computed based on a finite element model, and the analytical predictions are shown to be in good agreement with simulated results. The results show that blister height and crack length are sensitive to laser fluence. A higher laser fluence is much easier to induce higher blister height. The crack will propagate as the laser fluence is larger than the critical laser fluence.
关键词： polymer,blister formation,virtual crack closure technique,blister-actuated laser-induced forward transfer,crack propagation
更新于2025-09-16 10:30:52
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Microstructure evolution and crack propagation feature in thermal fatigue of laser-deposited Stellite 6 coating for brake discs
摘要： In order to reveal the mechanism of microstructure evolution and crack propagation in laser-deposited Stellite 6 alloys, a quenching thermal fatigue test was conducted. Various detection methods were applied to observe differences between the coatings as deposited and after thermal fatigue. The results showed that the γ → ε martensitic transformation occurred in the as-deposited γ-Co matrix during the thermal fatigue process, driven by a fast cooling and thermal stress. The generated ε-Co phase presented variant selection, obeying Schmidt's law. In the ε-Co phase, the slip activity derived from different slipping systems that produced stacking faults and planar defects during the phase transformation. In addition, the stacking faults on {1 1 1}γ planes promoted the precipitation of directional M7C3 fine particle carbides. The net-like eutectic structures and γ/ε interfaces acted as paths for thermal crack propagation.
关键词： Martensitic transformation,Thermal fatigue,Crack propagation,Stellite 6 coating
更新于2025-09-10 09:29:36