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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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Effect of thermal stress induced by femtosecond laser on fracture toughness of fine-grained alumina
摘要： The ultra-sharp V-notch with tip radius smaller than 0.5 μm was cut by femtosecond laser on the fine-grained alumina ceramic bars to measure the fracture toughness by single-edge V-notched beam (SEVNB) method. In order to relieve the effect of thermal stresses induced by laser on fracture toughness testing, the samples with V-notch were annealed before measurement. The morphologies of the notch tip were analyzed by SEM and micro-Raman spectra. Results reveal that the fracture toughness value of this fine-grained alumina with thermal stresses on the V-notch is equal to that after annealing, and the effect of thermal stresses induced by laser on the fracture toughness can be ignored.
关键词： SEVNB,Fracture toughness,Laser processing,Thermal stress,Alumina
更新于2025-11-21 11:18:25
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Micromechanical simulation of ferroelectric domain processes at crack tips
摘要： The electromechanical loading situation at cracks in ferroelectric ceramics is essentially affected by domain switching. Under high electrical and/or mechanical external fields, the state of polarization and remanent strains is substantially changed at the crack tip. These irreversible dissipative processes influence the fracture toughness of the cracked ferroelectric material. In the present paper, the micromechanical domain switching processes at the crack tip are studied by numerical simulation and compared with the in situ experimental results obtained by Jones et al. (Acta Mater 55(16):5538–5548, 2007) using X-ray diffraction analyses in synchrotron. Main attention is payed to the spatial distribution of preferred domain orientation in a mechanically loaded compact tension specimen made of a soft tetragonal lead zirconate titanate ceramics. It is found that the mechanically induced favored domain orientation distribution depends on position within the plane of the CT specimen and correlates with projected deviatoric stresses and strains. Some issues concerning shortcomings in the experimental and simulation results are raised and discussed. The outcome of this type of simulations forms the basis for more realistic fracture mechanical evaluations in future.
关键词： Domain switching,Crack tip,Ferroelectric/piezoelectric materials,Fracture,Process zone
更新于2025-09-23 15:23:52
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Effect of Object Position in Cone Beam Computed Tomography Field of View for Detection of Root Fractures in Teeth with Intra-Canal Posts
摘要： Background: Vertical root fracture (VRF) is a common problem in endodontically treated teeth. Due to its poor prognosis, a reliable technique must be used to make an accurate diagnosis. Cone beam computed tomography (CBCT) has been recently introduced for maxillofacial imaging. Despite the high diagnostic value of this method, metal artifacts resulting from intra-canal posts still make the detection of VRFs challenging. Objectives: This study aimed to assess the effect of object position in the field of view (FOV) of CBCT on detection of VRFs in teeth with intra-canal posts. Materials and Methods: The crowns of 60 extracted premolar teeth were cut at the level of cementoenamel junction (CEJ). Root canals were filled with gutta-percha and filling of the coronal 2/3 of the root canals was subsequently removed to fabricate intra-canal cast posts. The teeth were randomly divided into two groups of 30. Fracture was induced in group one using an Instron machine. Group two was considered as the control group with no fracture. All teeth were then randomly positioned and scanned in five different positions starting at the center of the FOV as well as right, left anterior and posterior relative to the center (3, 9, 12, and 6 O’clock) via the New Tom VGI CBCT unit. Two observers evaluated images for VRFs. Sensitivity and specificity of fracture diagnosis in each position was calculated in comparison with the gold standard. Wilcoxon test was used for data analysis. Results: Considering deterministic and probabilistic diagnostic parameters, probabilistic sensitivity was similar in all positions; but probabilistic specificity of the center position (65.1%) was significantly higher than that of 6 and 12 O’clock positions. Considering the deterministic diagnostic parameters, the overall sensitivity and specificity values decreased in all positions in FOV, but sensitivity of the center position of FOV was significantly higher than that of other positions; specificity was significantly higher at the 3 O’clock position (58.5%). Conclusion: Concerning the positions in FOV, the center position is suitable for detection of VRF in teeth with intra-canal posts due to significantly higher sensitivity at this position. The 3 O’clock position would be suitable for assessment of intact teeth without fractures due to significantly higher specificity at this position.
关键词： Post and Core Technique,Position,Tooth Fracture,Cone-Beam Computed Tomography
更新于2025-09-23 15:23:52
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Fracture behavior of carbon fiber reinforced polymer composites: An optical study of loading rate effects
摘要： Crack initiation and growth in single-edge notched unidirectional T800s/3900-2 CFRP laminates are studied under stress wave and quasi-static loading conditions. An optical technique called reflection-mode Digital Gradient Sensing is also extended to study fracture mechanics of CFRP by using it in conjunction with ultrahigh-speed photography to perform full-field measurement of crack-tip deformations in the pre- and post-crack initiation regimes. DGS is capable of measuring two orthogonal surface slopes in the crack-tip vicinity as angular deflection of light rays. A method for extracting crack-tip parameters - the instantaneous crack speed and stress intensity factor (SIFs) histories - associated with the stationary and propagating cracks using measured surface slopes is presented. The effect of fiber orientation in the range 0°-60° relative to the initial notch and two loading rates are investigated. Nominally mode-I fracture occurs when the fiber orientation is 0° whereas mixed-mode fractures ensue in others. Besides crack initiation occurrence at higher loads as fiber orientation increases, the SIF histories imply strong fiber bridging at low fiber orientations under quasi-static conditions. Furthermore, this CFRP shows significant loading rate dependence during crack growth. Unlike stress wave loading conditions, an increasing crack growth resistance immediately after crack initiation is seen under quasi-static conditions.
关键词： Carbon fiber reinforced plastics,Loading rate effects,Crack growth behavior,Dynamic fracture,Digital Gradient Sensing
更新于2025-09-23 15:23:52
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Automatic fracture–vug identification and extraction from electric imaging logging data based on path morphology
摘要： We present a path morphology method to separate total rock pore space into matrix, fractures and vugs and derive their pore structure spectrum. Thus, we can achieve fine pore evaluation in fracture–vug reservoirs based on electric imaging logging data. We automatically identify and extract fracture–vug information from the electric imaging images by adopting a path morphological operator that remains flexible enough to fit rectilinear and slightly curved structures because they are independent of the structuring element shape. The Otsu method was used to extract fracture–vug information from the background noise caused by the matrix. To accommodate the differences in scale and form of the different target regions, including fracture and vug path, operators with different lengths were selected for their recognition and extraction at the corresponding scale. Polynomial and elliptic functions are used to fit the extracted fractures and vugs, respectively, and the fracture–vug parameters are deduced from the fitted edge. Finally, test examples of numerical simulation data and several measured well data have been provided for the verification of the effectiveness and adaptability of the path morphology method in the application of electric imaging logging data processing. This also provides algorithm support for the fine evaluation of fracture–vug reservoirs.
关键词： Path morphology,Electric imaging logging,Fracture–vug reservoir,Image automatic identification
更新于2025-09-23 15:23:52
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Topology and polarity of dislocation cores dictate the mechanical strength of monolayer MoS2
摘要： In contrast to homoelemental graphene showing common dislocation dipole with pentagon-heptagon (5|7) core, heteroelemental MoS2 is observed to contain diverse dislocation cores that tune the chemical and physical properties. Yet, how the inevitable dislocation cores in MoS2 affect the mechanical behaviours remains virtually unexplored. Herein, we report direct atomistic simulations of mechanical characteristics of isolated dislocation-embedded MoS2 monolayers under tensile load. All isolated dislocation cores in MoS2 monolayer rise polar stress-concentration, while those with larger Burgers vector are less energetically-favorable configurations but show local wrinkling behaviour. It is revealed that the intrinsic tensile strength of MoS2 is dictated by topology and polarity of dislocation cores. There is a strong inverse correlation between the maximum residual stresses induced by the dislocation cores and the strength of MoS2 monolayers. Mechanical failure initiates from the bond at dislocation polygon on which side there is a missing atomic chain. Armchair-oriented 4|8 dislocation exhibits sole brittle failure, however, dual brittle/ductile fractures occur in zigzag-oriented dislocations; Mo-S-Mo angle-oriented crack is brittle, while the S-Mo-S angle-oriented crack becomes ductile. Our findings shed sights on mechanical design of heteroelemental 2D materials via dislocation engineering for practical application.
关键词： Mechanical strength,Fracture characteristics,Monolayer MoS2,Molecular dynamics simulations,Dislocation cores
更新于2025-09-23 15:23:52
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Electric field-induced toughening in GaN piezoelectric semiconductor ceramics
摘要： In this paper, the effect of an applied electric field on fracture toughness of polarized GaN piezoelectric semiconductor ceramics was studied by using experimental and numerical methods. The results show that fracture toughness increases by 22% under a field intensity of 0.83 kV cm?1, and with further increase of the electrical filed, fracture toughness remains unchanged. This is completely different from the fracture characteristics of traditional piezoelectric ceramics that is thought to decrease with an applied electric field. The reason for such a difference is attributed to the redistribution of free electrons. It is expected that this finding will be instructive to the reliability design of piezoelectric semiconductor structures and devices.
关键词： GaN,Electric field,Fracture toughness,Piezoelectric semiconductor ceramics,Toughening
更新于2025-09-23 15:23:52
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Fracture strength of silicon torsional mirror resonators fully coated with submicrometer-thick PECVD DLC film
摘要： In this work, we attempted to enhance the torsional fracture strength of single crystal silicon (SCS) resonators for micro mirrors application by introducing a 300 nm-thick diamond-like carbon (DLC) coating. The SCS torsional beams of the resonators were 20 μm wide and 9 μm thick, and fully coated with DLC films using plasma enhanced chemical vapor deposition (PECVD) at three different deposition bias voltages. The resonators were driven by a piezoelectric actuator and their angular amplitude was measured by a custom-made torsional test system. Average nominal torsional fracture strength of DLC coated resonators was 11.1–30.0% higher than that of bare SCS, reaching a value of 2.93 GPa. The torsional fracture strength of resonators exhibited a good agreement with the tensile fracture strength. Deviations in torsional strength were reduced with increasing deposition bias voltage due to the compressive residual stress of DLC films.
关键词： Single crystal silicon,Micro mirror resonator,Diamond-like carbon film,Strength deviation,Torsional fracture strength
更新于2025-09-23 15:23:52
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Localized Deformation and Fracture Behaviors in InP Single Crystals by Indentation
摘要： The indentation-induced deformation mechanisms in InP(100) single crystals were investigated by using nanoindentation and cross-sectional transmission electron microscopy (XTEM) techniques. The results indicated that there were multiple “pop-in” events randomly distributed in the loading curves, which were conceived to arise primarily from the dislocation nucleation and propagation activities. An energetic estimation on the number of nanoindentation-induced dislocations associated with pop-in effects is discussed. Furthermore, the fracture patterns were performed by Vickers indentation. The fracture toughness and the fracture energy of InP(100) single crystals were calculated to be around 1.2 MPa·m1/2 and 14.1 J/m2, respectively.
关键词： InP(100) single crystal,nanoindentation,fracture toughness,transmission electron microscopy,Pop-in
更新于2025-09-23 15:23:52