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- 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
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Effect of large-scale domain switching on intensity factors for a crack in 3D ferroelectric single crystals using the I-integral method
摘要： Due to their intrinsic brittleness, ferroelectric materials are prone to fracture under extreme electromechanical operational loads. The fracture of ferroelectric materials is usually accompanied by large-scale domain switching. This paper develops the interaction integral (I-integral) method for a crack in three-dimensional ferroelectrics through applying a virtual load increment to the current state. Unlike the widely-used switching-toughening model, the I-integral is not restricted to small scale switching. Due to designable choice of the virtual load increment, the I-integral allows to decouple the intensity factors of different fracture modes. The local intensity factors along the curved crack front can be directly extracted, since the I-integral is independent of integration volume. With these merits, the I-integral method is a very promising technique in fracture analysis of ferroelectrics under large-scale domain switching. Moreover, the I-integral method is used in combination with the phase field model to simulate a tensile test of nanoscale PbTiO3 ferroelectric single crystal with a semi-circular surface crack. Results show that various patterns of polarization pairs appear as soon as the applied load is increased beyond a critical value. The stable domain structures are divided into two layers by the plane where the crack is located and in each layers several polarization vortices formed eventually. Apart from the geometry and loading conditions, the position where the crack front is located with respect to the polarization vortex is a key factor affecting the switching-induced change of the stress intensity factor.
关键词： crack,interaction integral (I-integral),large-scale domain switching,phase field model,ferroelectric,intensity factor
更新于2025-09-10 09:29:36
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An Enhanced Time-Reversal Imaging Algorithm-Driven Sparse Linear Array for Progressive and Quantitative Monitoring of Cracks
摘要： A Lamb wave and linear piezoelectric lead zirconate titanate (PZT) array-based monitoring method for the detection and quantification of crack damage is presented in this paper. Because existing PZT array arrangements are not suitable for quantitative monitoring of crack damage both in orientation and in length, a sparse linear PZT array is introduced and applied to collect crack reflections. Based on this new array, a method for estimating crack orientation is proposed. An amplitude spectrum as a function of angle is mapped using time delayed and summed signals. By finding the peaks in the spectra, the central actuator element and corresponding orientation angle are determined. Furthermore, the time of flight imaging method is modified to display and evaluate cracks quantitatively. Validating experiments are conducted on a T6061 aluminum plate, monitoring and evaluating single and connected cracks with various orientations in different locations. As suggested by the experiments, the orientation of most cracks can be well recognized and all cracks can be quantitatively displayed by the proposed methods.
关键词： sensor arrays,waveguide theory,monitoring,Crack detection,signal processing
更新于2025-09-10 09:29:36
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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
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Numerical investigation of atherosclerotic plaque rupture using optical coherence tomography imaging and XFEM
摘要： Myocardial infarction contributes to most fatalities in which atherosclerotic plaque disruption is the underlying pathology. From the mechanics view point, the pulsatile blood flow in the arteries resembles a fatigue environment and generates stresses that affect the rupture of the atherosclerotic plaque. In this context, patient-specific optical coherence tomography (OCT) was used to develop the fatigue crack growth behavior. The impact of location specific morphological features and their relative effect on plaque life were discussed. EXtended Finite Element Method (XFEM) and Paris’ Law were employed to investigate the fatigue crack growth. Twelve 2D slices from six patients were reconstructed for studying the fatigue crack growth behavior. Our results indicate that plaque life decreases with an increase in pulse pressure and 53.5% of the total cracks initiated at various locations on the lumen lead to rupture. 73.7% of the rupture locations did not have calcifications. Correlation between the location specific morphology and the rupture indicates that for a 1 mm increase in the fibrous cap thickness there is a large decrease in the odds of rupture [0.163 (0.073; 0.363)], p-value < 0.0001; and for a 1 mm2 increase of the calcification area, there is a decrease in the odds of rupture by 0.719 (0.619; 0.835), p-value < 0.0001. In conclusion, the XFEM technique can be used to study the fatigue behavior of the atherosclerotic plaque that depends on the combined effects of plaque constituents and their morphology. It may help to better assess plaque vulnerability and make more accurate predictions for plaque rupture.
关键词： XFEM,Fatigue crack growth,Atherosclerotic plaque rupture,Optical coherence tomography,Paris’ Law
更新于2025-09-10 09:29:36
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A methodology framework for retrieval of concrete surface crack′s image properties based on hybrid model
摘要： Regular concrete surface crack inspection is critical since cracks are one of the earliest signs of deteriorating in concrete structures. With recent digital imaging and processing techniques, computer vision-based inspection shows huge potential in this field. A novel image processing framework for automatically retrieving multiple crack properties from concrete surface images is proposed. The framework includes (1) a crack extraction algorithm which combines edge detecting and seed growing; (2) a skeleton optimizing method which contains short branch deleting and polyline approximation algorithm; (3) a hybrid crack model which classifies crack segments into disc-shaped and bar-shaped parts based on their skeleton topological information, and (4) a triad labelling method that indicates the interrelationships between different cracks. Contrast experiments showed that the proposed segmentation method can extract more complete crack segments. Real image experiments indicated that the framework is effective and helpful for subsequent concrete structure health assessment.
关键词： Hybrid model,Image analysis,Crack detection,Feature extraction,Concrete
更新于2025-09-10 09:29:36
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On crack propagation monitoring by using reflection spectra of AFBG and UFBG sensors
摘要： Due to their light weight, small size and immunity to electromagnetic interference, Fiber Bragg Gratings (FBG) have shown great potential in structural health monitoring (SHM) area. Ordinarily, FBGs are used as the quasi-distributed sensors to detect structural damage by central wavelengths shifting, which has robust problem in real engineering application. It is found that the FBG reflection spectra can also be distorted with the non-uniform strain field caused by crack. Multiple indices can be extracted from the reflection spectra which can provides more information on the crack propagation. However, till now no researches have been investigated regarding the behaviors of different kinds of FBGs for crack propagation monitoring based on the FBG reflection spectra. In this paper, behaviors of the apodized FBG (AFBG) and the uniform FBG (UFBG) sensors for structural crack propagation monitoring are investigated. The reflective spectral behaviors of both UFBG and AFBG sensors under crack-generated non-uniform strain are illustrated by simulation and experiment. Three spectra indices, namely the central wavelength shift, the ratio of side lobe to main lobe and the information entropy, are proposed to indicate the propagation of the crack. The results show the UFBG sensors have better performance than the AFBG sensors which are more suitable for crack propagation monitoring.
关键词： crack propagation monitoring,uniform fiber Bragg gratings,apodized fiber Bragg gratings,structural health monitoring,spectral distortion
更新于2025-09-10 09:29:36
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Facile fabrication and optimization of bowl-like ZnO/CdS nano-composite thin films with hierarchical nanopores and nano-cracks for high-performance photoelectrochemistry
摘要： A special nano-structured composite ZnO/CdS thin film with hierarchical nanopores and nano-cracks has been synthesized by a facile two-step method for the first time, in which both loadings of ZnO and CdS are optimized. We first fabricated the hierarchical nano-porous ZnO thin film through rapid gas/liquid interface assembly and layer-by-layer transfers of bowl-like ZnO nanoparticles for thirteen times. The ZnO nanobowls are prepared by a simple solution chemical reaction without using any templates. After annealing, the assembled ZnO film is sensitized with CdS nanoparticles by successive ionic layer adsorption and reactions for six cycles. Nano-cracks form for the ZnO/CdS nano-composite film by calcination, which is due to the different thermal expansion behavior between the ZnO film and the CdS layer. The facilely optimized ZnO/CdS films can serve as a promising photoanode in a photoelectrochemical cell, and it can generate a saturated photocurrent density as high as 7.8 mA cm?2 at ?0.9 V (vs. Hg|Hg2SO4|saturated K2SO4) under visible light illumination of 100 mW cm?2 in an aqueous solution of 0.5 M Na2S, corresponding to a solar-to-electricity conversion efficiency of 6.6%.
关键词： Nano-crack,CdS,Bowl-like ZnO nanoparticle,Gas/liquid interface assembly,Hierarchical nanopores,Photoelectrochemistry
更新于2025-09-10 09:29:36
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Slow crack growth in silica aerogels: A review
摘要： The sub-critical crack growth in hydrophobic (as prepared) and hydrophilic (oxidized) silica aerogel was studied using the Dynamic fatigue experiment and the Double-Cleavage-Drilled-Compression test (DCDC). The effect of oxidation treatment is clearly evidenced. The temperature and water vapor content dependence on the crack growth rate is measured between 22 °C and 110 °C with relative air moisture ranging from 5 to 80% RH. Like dense silica, crack growth velocities were found to decrease when increasing the temperature at a constant water vapor concentration. Surprisingly, the crack velocity also decreases when increasing water vapor content at constant temperature. Such a behavior is contrary to expected results usually encountered in glasses. We assume that a capillary condensation phenomenon of water vapor inside the aerogel porosity takes place, inducing internal compressive stresses.
关键词： Silica aerogels,Slow crack growth,Stress corrosion effect
更新于2025-09-09 09:28:46
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Materials Science and Technology of Optical Fabrication || Increasing Yield: Scratch Forensics and Fractography
摘要： If a workpiece falls and breaks catastrophically, the cause of failure is obvious. But a workpiece may fracture catastrophically (or noncatastrophically) for many reasons far more difficult to diagnose and hence, prevent or mitigate. For such purposes, the field of fractography – the science of means and methods of characterizing a fractured component by examining its fracture pattern and surface – can be very useful. The theory and practice of fractography are well described by Frechette [1], Varner and Frechette [2], Quinn [3], Freiman and Mecholsky [4], and Bradt and Tressler [5]. This chapter first provides a fractography introduction, describing the major features observed on the fracture surfaces and what information they provide about failure. Next, the fractography is extended to diagnosing yield loss due to scratching a workpiece, using a technique called scratch forensics and to insights on the time-dependent fracture failure caused by slow crack growth. Finally, some relevant case studies of the fractured workpieces during optical fabrication analyzed by fractography and scratch forensics are presented.
关键词： fracture analysis,fractography,optical fabrication,slow crack growth,scratch forensics
更新于2025-09-09 09:28:46
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Effects of polymeric filler on polarization fatigue of 1-3 0.74Pb(Mg <sub/>1/3</sub> Nb <sub/>2/3</sub> )O <sub/>3</sub> -0.26PbTiO <sub/>3</sub> single crystal/polymer composites
摘要： Polarization fatigue tests have been conducted on both bulk Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals and two 1-3 PMN-xPT/polymer composites with both “soft” and “hard” epoxy fillers, respectively. The variations of remnant polarization, coercive electric field, and micro-crack morphology under 10 Hz cyclic electric loading were studied. It was found that the magnitude of coercive field for both composites was higher compared to that of single crystals. However, as the number of cycles increases, the degradation ratio of remnant polarization and the increased portion of coercive field for both composites were lower than that of single crystals; the sequence is PMN-0.26PT bulk single crystal > 1-3 PMN-0.26PT/soft epoxy composites > 1-3 PMN-0.26PT/hard epoxy composites. In addition, the observed micro-crack propagation morphology shows that 1-3 PMN-0.26PT/hard epoxy composites can substantially improve fatigue-resistance owing to the lower stretching strain benefiting from the polymeric filler. Our results indicated that 1-3 PMN-0.26PT/polymer composites present much better electric polarization stability.
关键词： epoxy fillers,PMN-xPT single crystals,polymer composites,micro-crack morphology,polarization fatigue
更新于2025-09-09 09:28:46