Articoli di riviste sul tema "Defects propagation"
Segui questo link per vedere altri tipi di pubblicazioni sul tema: Defects propagation.
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 articoli di riviste per l'attività di ricerca sul tema "Defects propagation".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi gli articoli di riviste di molte aree scientifiche e compila una bibliografia corretta.
1
Salim, M. N., M. N. M. Khairy e T. Hayashi. "Effect of Oval Defect on Propagation of Fundamental Lamb Wave". Applied Mechanics and Materials 833 (aprile 2016): 49–58. http://dx.doi.org/10.4028/www.scientific.net/amm.833.49.
Abstract (sommario):
Complicated Lamb wave propagation in structures can cause a misinterpretation in defect location and sizing during nondestructive inspections. A visualization of Lamb wave interactions with oval defects was carried out in our study to investigate the phenomenon of fundamental Lamb wave interaction around defect by using a reduced model of plate in ABAQUS. The visualized wave propagations with oval shape of through defects in plates demonstrated different patterns of wave interactions for the symmetric and anti-symmetric modes. The results also visualized the mode conversions around defects which converted from the incident waves. The visualized changes on the wave structures due to wave interaction with defects is important to increase our understanding on the guided wave propagation and reduce misinterpretation in nondestructive inspection when using the wave modes during inspection on large structures.
2
Wang, Shang, Wei Qiang Wang, Ming Da Song e Hao Zhang. "The Fatigue and Fracture Analysis of Steam Turbine Rotor Shafts Containing Defects". Key Engineering Materials 795 (marzo 2019): 254–61. http://dx.doi.org/10.4028/www.scientific.net/kem.795.254.
Abstract (sommario):
In this study, the assessment and calculation methods for the crack propagation life of steam turbine rotor shafts containing defects are presented. The analytic methods for estimating the average stress and the alternating stress amplitude of the steam turbine rotor shafts are introduced. The defects on/in the rotor shafts were regularized by the method of fracture mechanics, and the high cycle fatigue crack propagation life and low cycle fatigue crack propagation life of the rotor shafts are estimated from Paris formula. Taking the 60MW turbine rotor shafts containing an initial surface defect and an initial internal defect as the examples respectively, the crack propagation life of them were calculated. The results indicated that the assessment method for the crack propagation life can preliminarily be both used to estimate the safety-operating life and to analyze the fracture reason of a steam turbine rotor shaft containing defects. This paper can provide reference for periodic maintenance and safety evaluation of turbine rotor shafts.
3
Huang, Yunqing, e Jichun Li. "Total Reflection and Cloaking by Triangular Defects Embedded in Zero Index Metamaterials". Advances in Applied Mathematics and Mechanics 7, n. 2 (23 marzo 2015): 135–44. http://dx.doi.org/10.4208/aamm.2014.m659.
Abstract (sommario):
AbstractIn this work, we investigate wave propagation through a zero index meta-material (ZIM) waveguide embedded with triangular dielectric defects. We provide a theoretical guidance on how to achieve total reflection and total transmission (i.e., cloaking) by adjusting the defect sizes and/or permittivities of the defects. Our work provides a systematical way in manipulating wave propagation through ZIM in addition to the widely studied dielectric defects with cylindrical and rectangular geometries.
4
Yu, Shuisheng, Leilei Niu, Jin Chen, Yawei Wang e Honghao Yang. "Study on Bond Defect Detection in Grouted Rock Bolt Systems under Pullout Loads". Advances in Materials Science and Engineering 2022 (31 agosto 2022): 1–9. http://dx.doi.org/10.1155/2022/3282211.
Abstract (sommario):
In grouted rock bolt systems, bond defects often occur, which seriously affects the safety of rock mass structures. Therefore, in this study, based on the existence of bond defects, laboratory tests were conducted to detect the location and length of bond defects and study the guided wave propagation in grouted rock bolt systems under different pullout loads. The guided wave signal was analysed in the time domain and frequency domain. In addition to the laboratory test, a numerical simulation of the effect of different bond defect locations on ultrasonic guided wave propagation in rock bolts was conducted using a damage-based model. The influence mechanism of bond defects on guided wave propagation under different pullout loads was explored. The study confirmed that there existed a stress platform in the rock bolt at the bond defect under a pullout load. The location and length of the bond defect could be detected by the stress platform and guided wave. The debonding length increased exponentially with the amplitude ratio (Q) of low frequency to high frequency, and the Q value could be used as the quantitative index of debonding length. As the pullout load increased, the impedance mismatch between the rock bolt and cement mortar (defect) increased, and the guided wave propagation in grouted rock bolt systems was irregular. The pullout load weakened the guided wave propagation law. The larger the pullout load is, the greater the weakening effect is.
5
Basmaci, Ayse. "The Behavior of Electromagnetic Wave Propagation in Photonic Crystals with or without a Defect". Applied Computational Electromagnetics Society 36, n. 6 (6 agosto 2021): 632–41. http://dx.doi.org/10.47037/2020.aces.j.360603.
Abstract (sommario):
In this study, the electromagnetic wave propagation behavior of two-dimensional photonic crystal plates with a defect is investigated. For this purpose, the partial differential equation for the electromagnetic wave propagation in various photonic crystal plates containing a defect or not is obtained by using Maxwell’s equations. The defect is also defined in the electromagnetic wave propagation equation appropriately. In order to solve the electromagnetic wave propagation equation, the finite differences method is used. The material property parameters of the photonic crystal plates are determined with respect to the defects. Accordingly, the effects of material property parameters on electromagnetic wave propagation frequencies, phase velocities, and group velocities are examined. The effects of the size and position of the defects on the electromagnetic wave propagation frequencies are also discussed. The highest electromagnetic wave propagation fundamental frequency value obtained from the analyses performed is 1.198 Hz. This fundamental frequency value is obtained for the electromagnetic wave propagation in the t-shaped photonic crystal plate. Electromagnetic field distribution maps for the fundamental frequencies of the photonic crystal plates whose electromagnetic wave propagation behaviors are examined are obtained with the ANSYS package program based on the finite differences time-domain (FDTD) method.
6
Bultel, Yann, Corine BAS, Florence Dubelley, Fabrice Micoud, Sébastien Rosini e Christine Nayoze-Coynel. "Anode Defects’ Propagation in Polymer Electrolyte Membrane Fuel Cells Stack". ECS Meeting Abstracts MA2023-02, n. 38 (22 dicembre 2023): 1835. http://dx.doi.org/10.1149/ma2023-02381835mtgabs.
Abstract (sommario):
Reliability and durability are key considerations to successfully deploy Proton Exchange Membrane Fuel Cells (PEMFCs). Defects induced by manufacturing processes and fuel cell operating conditions may shorten the lifetime of PEMFC due to membrane electrode assembly (MEA) components degradations. If the degradation mechanisms occurring along ageing are now well-known, the propagation of these defects to other materials or to other locations in the stack was poorly investigated in the literature. Recently, we investigated a defect-propagation in MEA via accelerated stress tests combining load and load-driven humidity cycling, and open-circuit voltage. Results highlighted a defect propagation in term of anode and cathode ECSA losses. Significant membrane thinning is also observed for the defective segments. If, the defect propagation was investigated at the cell scale, it has been barely studied in the literature at the stack level. The objective of this work is to quantify the impact of MEA manufacturing defects on the performance and durability in stack and to analyze how these defects can propagate within healthy areas of the same MEA or to healthies MEAs within a stack. Tests were carried out on two stacks with metallic bipolar plates. The stacks were assembled using 35 defect-free MEAs for the healthy stack and using 30 homogeneous MEAs and 5 MEAs with controlled anode defects over 25% of the active area (absence of anode catalyst layer) for the faulty one. The two stacks were operated on a test bench able to control operating conditions and electrochemical characterizations were regularly made in order to evaluate the impact of the defects on the stack behavior. The initial characterization of the stack contained faulty MEAs showed, as expected, that the defects in the anode active layers have a significant effect on the performance of the cells from the conditioning stage. The analysis of the degradation rate showed that the cells directly in contact with the defected MEAs were the ones whose performance degraded the fastest, which implies that the presence of defects within the stack induces a propagation of the performance decrease. This phenomenon could be linked to a significant increase in hydrogen leakage through the membrane identified both by off-line electrochemical characterization and by thermal camera measurements in post-mortem analysis. The mechanism of degradation is still difficult to understand but the presence of defects within the stack could lead to constriction of the current lines around the defect and to localized heating which could degrade the membrane relatively rapidly. Figure 1
7
Huang, Chen, Zong-Xian Zhang, Adeyemi Aladejare, Xianbo Guan, Bingbing Yu e Liyun Yang. "The Effect of Preloaded Compressive Stress and Curvature of Defect on Blast-Induced Fracture Behavior by Caustic and Numerical Models". Mathematics 11, n. 21 (3 novembre 2023): 4532. http://dx.doi.org/10.3390/math11214532.
Abstract (sommario):
In this study, the effects of preloaded uniaxial compressive stress and defect (prefabricated by laser cutting) curvature on blast-induced cracks and stress wave propagation were investigated in polymethyl methacrylate (PMMA) specimens using caustics theory. Based on the mathematical relationship between stress and optics, the fracture behavior (the propagation path, dynamic stress intensity factors (DSIFs), propagation velocity, initiation angle of the main crack, and damage degree between the defect and the blasthole) was calculated and analyzed quantitatively. The results show that the preloaded stress could mainly restrain the main crack propagation in the horizontal direction and reduce the initiation angle and damage degree at the defects. Meanwhile, the crack initiation position of the positive curvature defect was not at the end of the defect. In addition, the curvature of the defect significantly affected the blast-induced fracture compared to preloaded stresses. Comparing the main crack with other curvature defects, the DSIFs, velocity, crack arrest time, crack length, and horizontal offset distance of the main crack with negative curvature defect were the largest. The variation in the full stress field in the specimen under blasting and preloaded stress was simulated by a numerical model. The results show that the curvature of the defect has a significant effect on tensile waves at the end of defects, and the tensile stress from high to low was C-25, C0, and C25, in that order.
8
Cao, Andong, Zhen Zhang e Qian Li. "Frequency shifting of transmitted ultrasound in thick composites containing fiber wrinkles and its application in non-destructive evaluation". Journal of the Acoustical Society of America 154, n. 4_supplement (1 ottobre 2023): A246. http://dx.doi.org/10.1121/10.0023434.
Abstract (sommario):
Thick composite structures are prone to defects such as fiber wrinkles and voids during manufacturing. It is challenging to accurately evaluate the forming quality of the structures using conventional ultrasonic inspection, due to the coupling effects between time-frequency features of ultrasound and mixed-type defects. Propagation behaviors of through-thickness transmitted ultrasound in thick composites with fiber wrinkles, voids and no defects were comparatively investigated by both simulation and experiment in this study. Influence of out-of-plane fiber wrinkles on the ultrasonic frequency shifting was studied by comparing the time-frequency characteristics of simulated ultrasonic signals after propagating different distances in the intact and wavy composites. Changes of transmission coefficients of converted transverse waves caused by fiber wrinkles were concluded be the reason for the appearance of high-frequency components above the excitation frequency in the transmitted ultrasound signal. Thereby ultrasonic defect inspection indices based on the phenomenon of ultrasonic frequency shifting were defined. Effects of interaction angles between ultrasonic propagation direction and fibers on the defined inspection indices was further investigated quantitatively. The thick composites with diverse defects were successfully diagnosed using the ultrasound frequency shifting and energy dissipation behaviors.
9
Yilmaz, Ayca, Dilek Helvacioglu-Yigit, Cansu Gur, Handan Ersev, Gullu Kiziltas Sendur, Egemen Avcu, Canan Baydemir e Paul Vincent Abbott. "Evaluation of Dentin Defect Formation during Retreatment with Hand and Rotary Instruments: A Micro-CT Study". Scanning 2017 (2017): 1–7. http://dx.doi.org/10.1155/2017/4868603.
Abstract (sommario):
The purpose of this study was to compare the incidence and longitudinal propagation of dentin defects after gutta-percha removal with hand and rotary instruments using microcomputed tomography. Twenty mandibular incisors were prepared using the balanced-force technique and scanned in a 19.9 μm resolution. Following filling with the lateral compaction technique, gutta-percha was removed with ProTaper Universal Retreatment (PTUR) or hand instruments. After rescanning, a total of 24,120 cross-sectional images were analyzed. The numbers, types, and longitudinal length changes of defects were recorded. Defects were observed in 36.90% of the cross sections. A total of 73 defects were comprised of 87.67% craze lines, 2.73% partial cracks, and 9.58% fractures. No significant difference in terms of new defect formation was detected between the retreatment groups. The apical and middle portions of the roots had more dentin defects than the coronal portions. Defects in three roots of the PTUR instrument group increased in length. Under the conditions of this in vitro study, gutta-percha removal seemed to not increase the incidence of dentin defect formation, but the longitudinal defect propagation finding suggests possible cumulative dentinal damage due to additional endodontic procedures. Hand and rotary instrumentation techniques caused similar dentin defect formation during root canal retreatment.
10
Xie, Mingjiang, Yifei Wang, Weinan Xiong, Jianli Zhao e Xianjun Pei. "A Crack Propagation Method for Pipelines with Interacting Corrosion and Crack Defects". Sensors 22, n. 3 (27 gennaio 2022): 986. http://dx.doi.org/10.3390/s22030986.
Abstract (sommario):
Corrosion and crack defects often exist at the same time in pipelines. The interaction impact between these defects could potentially affect the growth of the fatigue crack. In this paper, a crack propagation method is proposed for pipelines with interacting corrosion and crack defects. The finite element models are built to obtain the Stress Intensity Factors (SIFs) for fatigue crack. SIF interaction impact ratio is introduced to describe the interaction effect of corrosion on fatigue crack. Two approaches based on extreme gradient boosting (XGBoost) are proposed in this paper to predict the SIF interaction impact ratio at the deepest point of the crack defect for pipelines with interacting corrosion and crack defects. Crack size, corrosion size and the axial distance between these two defects are the factors that have an impact on the growth of the fatigue crack, and so they are considered as the input of XGBoost models. Based on the synthetic samples from finite element modeling, it has been proved that the proposed approaches can effectively predict the SIF interaction impact ratio with relatively high accuracy. The crack propagation models are built based on the proposed XGBoost models, Paris’ law and corrosion growth model. Sensitivity analyses regarding corrosion initial depth and axial distance between defects are performed. The proposed method can support pipeline integrity management by linking the crack propagation model with corrosion size, crack size and the axial distance. The problem of how the interaction between corrosion and crack defects impacts crack defect growth is investigated.
11
Wei, Chihang, e Zhihuan Song. "Real-Time Forecasting of Subsurface Inclusion Defects for Continuous Casting Slabs: A Data-Driven Comparative Study". Sensors 23, n. 12 (7 giugno 2023): 5415. http://dx.doi.org/10.3390/s23125415.
Abstract (sommario):
Subsurface inclusions are one of the most common defects that affect the inner quality of continuous casting slabs. This increases the defects in the final products and increases the complexity of the hot charge rolling process and may even cause breakout accidents. The defects are, however, hard to detect online by traditional mechanism-model-based and physics-based methods. In the present paper, a comparative study is carried out based on data-driven methods, which are only sporadically discussed in the literature. As a further contribution, a scatter-regularized kernel discriminative least squares (SR-KDLS) model and a stacked defect-related autoencoder back propagation neural network (SDAE-BPNN) model are developed to improve the forecasting performance. The scatter-regularized kernel discriminative least squares is designed as a coherent framework to directly provide forecasting information instead of low-dimensional embeddings. The stacked defect-related autoencoder back propagation neural network extracts deep defect-related features layer by layer for a higher feasibility and accuracy. The feasibility and efficiency of the data-driven methods are demonstrated through case studies based on a real-life continuous casting process, where the imbalance degree drastically vary in different categories, showing that the defects are timely (within 0.01 ms) and accurately forecasted. Moreover, experiments illustrate the merits of the developed scatter-regularized kernel discriminative least squares and stacked defect-related autoencoder back propagation neural network methods regarding the computational burden; the F1 scores of the developed methods are clearly higher than common methods.
12
Lim, Seong-Sik, Je-Pyo Hong, Minki Kim, Young-Chul Park, Sang-Mock Lee, Dae-Yeon Cho e Chang-Hee Cho. "Study on Rolling Defects of Al-Mg Alloys with High Mg Content in Normal Rolling and Cross-Rolling Processes". Materials 16, n. 18 (18 settembre 2023): 6260. http://dx.doi.org/10.3390/ma16186260.
Abstract (sommario):
This study investigated defect formation and strain distribution in high-Mg-content Al-Mg alloys during normal rolling and cross-rolling processes. The finite element analysis (FEA) revealed the presence of wave defects and strain localization-induced zipper cracks in normal cold rolling, which were confirmed by the experimental results. The concentration of shear strain played a significant role in crack formation and propagation. However, the influence of wave defects was minimal in the cross-rolling process, which exhibited a relatively uniform strain distribution. Nonetheless, strain concentration at the edge and center regions led to the formation of zipper cracks and edge cracks, with more pronounced propagation observed in the experiments compared to FEA predictions. Furthermore, texture evolution was found to be a crucial factor affecting crack propagation, particularly with the development of the Goss texture component, which was observed via electron backscattered diffraction analysis at bending points. The Goss texture hindered crack propagation, while the Brass texture allowed cracks to pass through. This phenomenon was consistent with both FEA and experimental observations. To mitigate edge crack formation and propagation, potential strategies involve promoting the formation of the Goss texture at the edge through alloy and process conditions, as well as implementing intermediate annealing to alleviate stress accumulation. These measures can enhance the overall quality and reliability of Al-Mg alloys during cross-rolling processes. In summary, understanding the mechanisms of defect formation and strain distribution in Al-Mg alloys during rolling processes is crucial for optimizing their mechanical properties. The findings of this study provide insights into the challenges associated with wave defects, strain localization, and crack propagation. Future research and optimization efforts should focus on implementing strategies to minimize defects and improve the overall quality of Al-Mg alloys in industrial applications.
13
Valentini, M., S. K. Serkov, D. Bigoni e A. B. Movchan. "Crack Propagation in a Brittle Elastic Material With Defects". Journal of Applied Mechanics 66, n. 1 (1 marzo 1999): 79–86. http://dx.doi.org/10.1115/1.2789172.
Abstract (sommario):
A two-dimensional asymptotic solution is presented for determination of the trajectory of a crack propagating in a brittle-elastic, isotropic medium containing small defects. Brittleness of the material is characterized by the assumption of the pure Mode I propagation criterion. The defects are described by Po´lya-Szego¨ matrices, and examples for small elliptical cavities and circular inclusions are given. The results of the asymptotic analysis, which agree well with existing numerical solutions, give qualitative description of crack trajectories observed in brittle materials with defects, such as porous ceramics.
14
THATCHER, M. J., e M. J. MORGAN. "BIREFRINGENT ELECTROWEAK DEFECTS". International Journal of Modern Physics A 17, n. 14 (10 giugno 2002): 1953–64. http://dx.doi.org/10.1142/s0217751x02010583.
Abstract (sommario):
In this paper we examine the propagation of electromagnetic waves through electroweak textures and W-strings. The photon is associated with a negative mass squared term as a consequence of its coupling to the intermediate vector bosons from which the electroweak defect is constructed. The photon pseudo-mass depends on the polarization of the photon and results in electroweak defects exhibiting birefringent properties. We calculate the effective refractive index and birefringence length scale. The cosmological implications of birefringent electroweak defects are discussed.
15
Jiang, Yin Fang, Zhen Ning Guo, Yong Qi Yan e Qin Huang. "Study on Inside and Outside Circumferential Defects of Pipes and Ultrasonic Guided Wave". Advanced Materials Research 460 (febbraio 2012): 411–14. http://dx.doi.org/10.4028/www.scientific.net/amr.460.411.
Abstract (sommario):
The difference between inside circumferential defects and outside circumferential defects was proved using the theory of reflection waves, the course of propagation and reflection from inside circumferential defects and outside circumferential defects in steel pipes was simulated with L(0,2) mode by the numerical simulation program ANSYS, and the curves of the reflection waves were obtained. The investigation indicated that the relationship between reflection coefficient of each kind of circumferential defects and the circumference of the defects was linear; in additional, it was found that the reflection coefficient of outside circumferential defects was a little higher than the reflection coefficient of inside circumferential defects; the difference between inside and outside circumferential defect became more obvious as the thickness of the defect increases. So the results provide a basis for detecting and distinguishing circumferential defects of pipes.
16
Fang, Chunhua, Junjie Lv, Ziheng Pu, Peng Li, Tian Wu e Tao Hu. "Electromagnetic Ultrasonic Shear-Horizontal Wave to Detect Corrosion Defect of Flat Steel for Grounding Device of Transmission Pole Tower". Applied Sciences 13, n. 12 (8 giugno 2023): 6947. http://dx.doi.org/10.3390/app13126947.
Abstract (sommario):
Detecting defects in grounded flat steel is essential for ensuring the safety and reliability of transmission tower grounding devices. However, traditional inspection methods, such as physical excavation and verification, are costly and time-consuming. This paper proposes a corrosion defect detection method for flat steel transmission tower grounding devices based on electromagnetic ultrasonic SH waves. In addition, using commercial software, a three-dimensional finite element simulation model of grounded flat steel with simulated pitting corrosion defects is constructed. The specified displacements applied to multiple surface sources mimic the horizontal shear vibrations generated by the electromagnetic ultrasonic transducer on the surface of the grounded flat steel during actual inspection. A simulation was used to investigate the propagation and attenuation characteristics of shear-horizontal ultrasonic SH0guided waves for simulated corrosion defects with various geometric configurations in grounded flat steel. The simulation investigated the propagation and attenuation characteristics of the SH0 wave in grounded flat steel and the detection of various defects for linear analysis of the results. The simulation results show that the attenuation of the electromagnetic ultrasonic guided wave is small, at only 0.0016 dB/mm, and the displacement amplitude of the echo signal decreases with the increase of the SH0 wave propagation distance. Increasing the depth and length of corrosion defects increases the echo signal amplitude. At the same time, the width of corrosion defects has little effect on the echo amplitude. Finally, a flat steel defect detection experiment was conducted, and the experimental results fit with the simulation to verify the accuracy of the simulation model. This detection method introduces a new idea for the on-site detection and quantitative identification of corrosion defects in grounded flat steel, which has significant reference value and can provide a more effective and economical method for ensuring the safety and dependability of transmission tower grounding devices.
17
Hou, Ning, Li Zhou, Shu Tao Huang e Li Fu Xu. "Finite Element and Experimental Analysis of Edge Defects Formation during Orthogonal Cutting of SiCp/Al Composites". Advanced Materials Research 500 (aprile 2012): 146–51. http://dx.doi.org/10.4028/www.scientific.net/amr.500.146.
Abstract (sommario):
In this paper, a finite element method was used to dynamically simulate the process of the edge defects formation during orthogonal cutting SiCp/Al composites. The influence of the cutting speed, cutting depth and rake angle of the PCD insert on the size of the edge defects have been investigated by using scanning electron. According to the simulated results, it can be provided that the cutting layer material has an effect on transfer stress and hinder the chip formation in the critical transition stage, and the critical transition point and distance are defined in this stage. The negative shear phenomenon is found when the chip transit to the edge defects in the flexure deformation stage, so the process of the chip formation is the basis of the edge defects formation. In addition, the relationship between the nucleation and propagation direction of the crack and the variation of the edge defect shape on the workpiece was investigated by theory, and it found that the negative shear angle formation is the primary cause of the edge defect formation. A mixed mode crack is found in the crack propagation stage. The sizes of edge defects were measured by the experiment and simulation, and the edge defect size decrease with the increasing of tool rake angle, while increase with increasing cutting depth and cutting speed.
18
Ishikawa, Yukari, Koji Sato, Yoshihiro Okamoto, Noritaka Hayashi, Yong Zhao Yao e Yoshihiro Sugawara. "Dislocation Formation in Epitaxial Film by Propagation of Shallow Dislocations on 4H-SiC Substrate". Materials Science Forum 717-720 (maggio 2012): 383–86. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.383.
Abstract (sommario):
Shallow defects, which were induced by mechanical treatment, on 4H-SiC wafers were investigated. The density and the distribution in depth of shallow defects on the wafers were depended on wafer venders. Most of serious defects such as dislocation array (DA), triangular stacking fault (TRSF) and triangular defect (TRD) in epitaxial film were demonstrated to be caused by shallow dislocations on the surface of the wafers. Revised mechanical polish can reduce the densities of DA, TRSF and TRD in epitaxial film.
19
CASTREJON-M, C., V. GRIMALSKY, S. KOSHEVAYA e A. ZAMUDIO-LARA. "PROPAGATION OF TRANSVERSELY BOUNDED NONLINEAR ELECTROMAGNETIC PULSES THROUGH PERIODIC MEDIA". Journal of Nonlinear Optical Physics & Materials 21, n. 02 (giugno 2012): 1250022. http://dx.doi.org/10.1142/s0218863512500221.
Abstract (sommario):
Nonlinear propagation of optical pulses of finite transverse widths through periodic structures with and without defects is investigated numerically and the subject of investigation is a stack of alternating linear and cubically nonlinear layers of submicron thicknesses is considered. The simulations are based on a modified equation for the pulse envelope and modified boundary conditions where both the diffraction and possible focusing of the pulse are taken into account. The simulations demonstrate an essential influence of defects within the periodic structure on the nonlinear propagation of optical pulses when the carrier frequency is chosen within the stop-band of the structure with the defect.
20
Song, Shi Quan, Hua Dong Xu e Li Hai Wang. "Application of Ultrasonic Wave and Resistograph for Nondestructive Testing of Defects in Standing Trees". Applied Mechanics and Materials 48-49 (febbraio 2011): 265–69. http://dx.doi.org/10.4028/www.scientific.net/amm.48-49.265.
Abstract (sommario):
In order to carry out non-destructive testing on standing trees, explore the propagation characteristics and the influence factors of the ultrasonic wave spreading in the standing trees. Take simon poplar as the research object, Resistograph were employed to test 30 sample (simon polar) standing trees and it gave a preliminary estimate of the internal defects in the samples, and RSM-SYS5 ultrasonic device were employed to test the ultrasonic propagation velocity spreading in simon poplar standing trees, with the statistics of the ultrasonic propagation velocity spreading separately in the health trees and standing trees with defects, and did a regression analysis of the relationship between the size of the defacts and the ultrasonic propagation velocity. The results show that: 1) When the diameter of sample trees are between 30 and 55cm, the radial velocity of ultrasonic spreading in healthy simon poplar standing trees are in the range of 1029.96m/s ~ 1200m/s, all more than 1000m/s; however, when there are defects in simon poplar standing trees, the ultrasonic radial velocity are less than 1000m/s. 2) The defacts in standing trees have an significant influence on the ultrasonic radial propagation velocity spreading in simon poplar standing trees, defect size and the radial velocity is significantly negatively correlated, and the correlation coefficient R is 0.887.
21
Chang, Wen Yeau. "Application of Back Propagation Neural Network for Partial Discharge Pattern Recognition". Applied Mechanics and Materials 577 (luglio 2014): 511–14. http://dx.doi.org/10.4028/www.scientific.net/amm.577.511.
Abstract (sommario):
This paper proposes a pattern recognition approach based on the back propagation (BP) neural network for identifying insulation defects of high-voltage electrical apparatus arising from partial discharge (PD). Pattern recognition of PD is used for identifying defects causing the PD, such as internal discharge, external discharge, corona, etc. This information is vital for estimating the harmfulness of the discharge in the insulation. Since an insulation defect, such as one resulting from PD, would have a corresponding particular pattern, pattern recognition of PD is significant means to discriminate insulation conditions of high-voltage electrical apparatus. To verify the proposed approach, experiments were conducted to demonstrate the field-test PD pattern recognition of model insulators with artificial defects are purposely created to produce the common PD activities of insulators by using feature vectors of field-test PD patterns. The experimental data are found to be in close agreement with the recognized data. The experimental results show that the proposed approach is very effective for recognizing the defects of high-voltage electrical apparatus.
22
Wei, Xiwen, Liping Sun, Quansheng Sun, Shuzheng Xu, Hongjv Zhou e Chunxiao Du. "Propagation velocity model of stress wave in longitudinal section of tree in different angular directions". BioResources 14, n. 4 (24 settembre 2019): 8904–22. http://dx.doi.org/10.15376/biores.14.4.8904-8922.
Abstract (sommario):
In order to detect the size and shape of defects inside wood, a propagation velocity model of stress wave in the longitudinal section of trees in different direction angles was proposed and evaluated. The propagation velocity model was established through theoretical analysis. Four representative tree species in the northeast region of China were taken as test samples. The propagation velocity of stress wave in the longitudinal section of trees in different directions was measured using a nondestructive testing instrument. The corresponding regression model was obtained, which was in good agreement with the theoretical mathematical model. For the larch log samples, a healthy multiple regression model (z = 109.2×2 – 182.1y2 + 36.78x2y2 – 34.76x2y4 + 1627) with correlation coefficient R2 = 0.97 and root mean square error RMSE =17.81 was used to conduct two-dimensional imaging of defective logs. Based on the results of two-dimensional imaging, the highest fitness of the images was 94.24%, and the lowest error rates of defect cavities was 6.11%. The imaging results showed that this method accurately detected the internal defects of trees and was not affected by the size of defects.
23
Hempel, Martin, Jens W. Tomm, Ute Zeimer e Thomas Elsaesser. "Defect Propagation in Broad-Area Diode Lasers". Materials Science Forum 725 (luglio 2012): 101–4. http://dx.doi.org/10.4028/www.scientific.net/msf.725.101.
Abstract (sommario):
A simple model is presented for the propagation of macroscopic defects within the quantum well (QW) plane of broad-area high power diode lasers. The catastrophic optical damage (COD) effect is considered the mechanism for creating an initial damage site and further development of defect pattern. The relations between the parameters used in the model and the actual physical properties of the semiconductor materials are discussed. Experimentally observed damage patterns are well described.
24
Yao, Zong Jian, Gui Lan Yu, Yue Sheng Wang e Jian Bao Li. "Flexural Vibration in a Ternary Locally Resonant Phononic Crystal Thin Plate with Defects". Advanced Materials Research 150-151 (ottobre 2010): 1282–85. http://dx.doi.org/10.4028/www.scientific.net/amr.150-151.1282.
Abstract (sommario):
The improved supercell plane wave expansion method is applied to theoretically study the propagation of flexural waves in a ternary locally resonant phononic crystal thin plate with a point defect and linear defects. The thin concrete plate composed of a square array of steel cylinders hemmed around by rubber is considered here. Absolute band gaps in low frequency are obtained. For the point defect, the defect mode is localized around the defect, and the magnitude of the resonant defect mode is strongly dependent on the defect filling fraction, mass density and Young’s modulus of the defect cylinder. For the straight linear defects, several resonant linear defect bands appear inside the absolute band gap. And the displacement distributions show that the flexural waves could well propagate along the linear defects.
25
Ishikawa, Masashi, Sou Ishihara, Hideo Nishino, Masashi Koyama, Hideyuki Kasano, Hiroshi Hatta e Shin Utsunomiya. "Relationship between Inspection Time and Frequency Components of Input and Reflected Thermal Waves in Active Thermographic Non-Destructive Inspection". Proceedings 27, n. 1 (21 settembre 2019): 16. http://dx.doi.org/10.3390/proceedings2019027016.
Abstract (sommario):
Experiments and numerical simulations for a carbon fiber reinforced plastic specimen were performed to investigate the relationship between the time required for detecting subsurface defects and the frequency components of the thermal waves propagating within the specimen. Experimental results showed that the required inspection time was shortened by increasing the frequency of the input thermal wave. However, if the attenuation during thermal wave propagation is large enough to render the detection of the thermal wave reflected at the subsurface defect impossible, the inspection time exceeds the time estimated by theoretical calculation.
26
Dlhý, Pavol, Jan Poduška, Michael Berer, Anja Gosch, Ondrej Slávik, Luboš Náhlík e Pavel Hutař. "Crack Propagation Analysis of Compression Loaded Rolling Elements". Materials 14, n. 10 (19 maggio 2021): 2656. http://dx.doi.org/10.3390/ma14102656.
Abstract (sommario):
The problem of crack propagation from internal defects in thermoplastic cylindrical bearing elements is addressed in this paper. The crack propagation in these elements takes place under mixed-mode conditions—i.e., all three possible loading modes (tensile opening mode I and shear opening modes II and III) of the crack are combined together. Moreover, their mutual relation changes during the rotation of the element. The dependency of the stress intensity factors on the crack length was described by general parametric equations. The model was then modified by adding a void to simulate the presence of a manufacturing defect. It was found that the influence of the void on the stress intensity factor values is quite high, but it fades with crack propagating further from the void. The effect of the friction between the crack faces was find negligible on stress intensity factor values. The results presented in this paper can be directly used for the calculation of bearing elements lifetime without complicated finite element simulations.
27
Dong, Jiwei, e Yaohua Gong. "Influence of void defects on progressive tensile damage of three-dimensional braided composites". Journal of Composite Materials 52, n. 15 (30 ottobre 2017): 2033–45. http://dx.doi.org/10.1177/0021998317737829.
Abstract (sommario):
A meso-finite element model with random voids in matrix is developed to simulate the tensile progressive damage of three-dimensional braided composites. A stiffness degradation method for generating the random void defect element in finite element method is presented. Proper criteria are adopted as initial damage of components, and stiffness degradation is implemented for damage propagation. The tensile strengths are predicted from calculated stress–strain curves. From simulation, void defects in matrix make the redistribution of micro-stress and accelerate the damage propagation of three-dimensional braided composites. Furthermore, void defects reduce the strength and ductility of the composites, but the reduction is not obvious if the porosity is controlled within a range.
28
Yang, Jing Gang, Yong Yong Jia, Ke Zhao e Shan Gao. "Simulation Study of Partial Discharge UHF Wave Transmission Characteristic in GIS Typical Structure". Applied Mechanics and Materials 672-674 (ottobre 2014): 787–92. http://dx.doi.org/10.4028/www.scientific.net/amm.672-674.787.
Abstract (sommario):
Defects inside the gas-insulated switchgear (GIS) will produce ultra-high frequency (UHF) electromagnetic waves. The waves will be affected by the shell of GIS when propagating inside the GIS cavity. In the 0-3GHz frequency range, propagation characteristic of electromagnetic which is excited by partial discharge in GIS is simulated based on the method of finite difference time domain (FDTD). This paper designs the GIS simulation models with and without insulator according to the size of a 220kV single phase GIS bus and sets a metal protrusion defect on the bus as the PD source. The transmission characteristics of model waves inside typical GIS structures, and the influence of the insulator to the propagation of electromagnetic wave was studied via setting the different directions of electromagnetic, comparing the time and frequency domain results of electromagnetic wave in different structures and measurement angles.
29
Sevost'yanov, P. A. "MODELLING OF AGING OF THREADS AND FIBRES WITH COMPUTER SIMULATION METHODS". Technologies & Quality, n. 4 (2019): 36–39. http://dx.doi.org/10.34216/2587-6147-2019-4-46-36-39.
Abstract (sommario):
The article proposes an algorithm for computer statistical simulation of the formation and development of areas of defects and aging in one-dimensional fibrous materials of arbitrary finite length. The software implementation of the algorithm in the Matlab environment allowed to obtain a visual picture of the aging regions propagation dynamics, taking into account the probabilistic nature of the occurrence and propagation of defects. The model combines factors affecting the location of defect sources along the threads and fibres length, the violation intensity of the fibrous material properties in the defective areas, and the speed of its propagation along the threads and fibres length. The developed model allows to study the influence of numerous factors on the aging effects dynamics in one-dimensional materials, to rank the degree of their influence, to determine the area of efforts for the aging processes study in full-scale experiments. An example is given for realisations of defects along the length of the sample for stationary and non-stationary conditions of the thread aging, when within a short period of time the thread was subjected to intense exposure, which contributed to the acceleration of aging and destruction.
30
Berteaux, Olivier, Roger Valle, Monique Raffestin, Marc Thomas e G. Henaff. "An Investigation of Fracture Origins in Heat-Treated Ti49Al47Cr2Nb2 Powder Compacts". Materials Science Forum 638-642 (gennaio 2010): 1422–27. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.1422.
Abstract (sommario):
The fatigue behaviour of a powder-metallurgy (PM) + heat-treated Ti49Al47Cr2Nb2 alloy is investigated using detailed SEM characterization. Based on the results of comparative static and cyclic loadings at RT, the fracture origins for the different test specimens is investigated. Conventional fractographic analyses revealed that internal structural defects inherent to powder metallurgy such as compaction defects, porosities and non-metallic inclusions can promote crack initiation. However, the fracture surface of test specimens is markedly affected by the microstructure, which is indicative of the microstructure dependence on crack initiation and propagation. In sub-transus heat treatment conditions, the detrimental effect of structural defects is illustrated by clear crack initiation sites onto the fracture surfaces. In super-transus conditions, crack propagation from defects can be blunted due to crack deflection, branching through lamellar interfaces, thus leading to lower defect sensitivity. Correlation of the results of these microfractographic examinations with the stress-strain curves corresponding to the various specimens allows identifying the role of such structural defects on the static and cyclic deformation behaviours. Finally, implications of such dependencies will be assessed relative to the requirements for aerospace gas turbine applications.
31
Wagih, Ahmed, Hassan A. Mahmoud, Ran Tao e Gilles Lubineau. "Towards Tough Thermoplastic Adhesive Tape by Microstructuring the Tape Using Tailored Defects". Polymers 15, n. 2 (4 gennaio 2023): 259. http://dx.doi.org/10.3390/polym15020259.
Abstract (sommario):
This paper presents a strategy towards achieving thermoplastic adhesive tapes with high toughness by microstructuring conventional tapes using tailored defects. Toughened tape was manufactured using two layers of a conventional tape where the bondline between the two adhesive layers was microstructured by embedding tailored defects with specific size and gap between them using PTFE film. Mode I toughness of the toughened tape was characterized experimentally. A high-fidelity finite element model was implemented to describe the toughening mechanisms using double cantilever beam simulations and end notch flexural tests. The model considers for the plasticity of the adhesive layer, the decohesion at the adherend–adhesive and adhesive–adhesive interfaces and progressive damage inside the adhesive layer. The adhesive–adhesive interface with the tailored defects inside the adhesive layer enables crack migration between adherend–adhesive interfaces, crack propagation at adhesive–adhesive interface, backward crack propagation under the defect, and plastic deformation of the adhesive ligament. The maximum toughness improvement of the tape with tailored defects of equal width and gap between two successive defects of 2 mm reached 278% and 147% for mode I and II, respectively, compared to conventional tape.
32
Wang, Ying, Wenhui Zhang, Xu Pan e Yuqian Zheng. "Experimental Study on Fatigue Crack Propagation of High-Strength Steel Wire with Initial Defects for Bridge Cables". Applied Sciences 10, n. 12 (12 giugno 2020): 4065. http://dx.doi.org/10.3390/app10124065.
Abstract (sommario):
In order to study the effect of initial defects on fatigue crack propagation law, a test method to identify fatigue crack propagation rate and path based on load waveform variation was presented, and a new test device was designed to apply fatigue pulsation loads to multiple wires for bridge cables simultaneously in this paper. To simplify the corrosion defect formation process, a machine-cut notch was used to describe the initial defect on the steel wire surface. Firstly, fatigue crack propagation tests were conducted on the surface notched steel wire specimens. By using crack front marking technique, the “beach-like patterns” visible to the naked eyes on the cross sections of the steel wires were formed, and the process of fatigue crack propagation can be tracked and reproduced. Then Autodesk Computer Aided Design (AutoCAD) software was used to describe the morphology of “beach-like patterns” and accurately measure the depth and width of cracks. Finally, the influence of initial defect morphology on fatigue crack propagation rate was investigated according to the relationship between fatigue cracks depth and cyclic loading numbers. The results show that the test device designed in this paper can effectively realize the synchronous fatigue crack propagation test of multiple wires, and significantly shorten the fatigue test period. By observing and analyzing the change of load waveform, the moment of fatigue crack propagation can be directly and accurately determined. The larger the depth, the smaller the width and the sharper the morphology of initial defect, the faster the crack propagation rate and the shorter the life of notched wire specimens under the combined action of fatigue loads and corrosive medium.
33
Anthony, Denis M., Evor L. Hines, David A. Hutchins e J. T. Mottram. "Ultrasound Tomography Imaging of Defects Using Neural Networks". Neural Computation 4, n. 5 (settembre 1992): 758–71. http://dx.doi.org/10.1162/neco.1992.4.5.758.
Abstract (sommario):
Simulations of ultrasound tomography demonstrated that artificial neural networks can solve the inverse problem in ultrasound tomography. A highly simplified model of ultrasound propagation was constructed, taking no account of refraction or diffraction, and using only longitudinal wave time of flight (TOF). TOF data were used as the network inputs, and the target outputs were the expected pixel maps, showing defects (gray scale coded) according to the velocity of the wave in the defect. The effects of varying resolution and defect velocity were explored. It was found that defects could be imaged using time of flight of ultrasonic rays.
34
Uvaysov, S. U., N. T. Luu, C. D. Nguyen, Th H. Vo e A. V. Dolmatov. "Detection of defects in printed circuit boards by the acoustic emission method". Russian Technological Journal 12, n. 1 (1 febbraio 2024): 15–29. http://dx.doi.org/10.32362/2500-316x-2024-12-1-15-29.
Abstract (sommario):
Objectives. Defects in the form of layering may occur during lamination in the production of multilayer printed circuit boards (MPCB). These defects cannot be detected by optical and electrical methods of output control. However, they can lead to breaches of the mechanical mode of operation and failures while running radioelectronic devices. In order to detect such defects, the acoustic emission (AE) method is proposed. This is based on the occurrence and propagation of acoustic waves in MPCBs caused by the presence of defects. The aim of this study is to investigate the possibility of using the AE method to detect defects in multilayer printed circuit boards. These defects can occur, in particular, in the lamination process.Methods. A mechanical processes modeling program (for research on the MPCB model) and various samples of two-layer printed circuit boards with pre-introduced defects (for experimental studies) were used to study the propagation of acoustic signals in the MPCB in the presence of defects. A solenoid mounted on the MPCB was used as a source of acoustic signals, while a piezoelectric sensor was used to receive signals. Data processing was carried out by comparing AE signals obtained for a serviceable MPCB sample and for MPCB samples with defects.Results. Simulation of the acoustic signal propagation in MPCBs in serviceable and faulty (with a rectangular defect in the form of delamination) states was carried out to show the difference in the received signals at the sensor installation point. Experimental studies were also conducted to examine the AE method applicability for detecting defects of various sizes and quantities.Conclusions. The studies demonstrated that the AE method allows the presence of defects in MPCB occurring during the lamination process to be detected effectively and reliably. This study proposes a new approach to non-destructive testing of MPCB using the AE method. This method significantly increases the reliability of MPCBs and the efficiency of their production processes.
35
Raišutis, Renaldas, Olgirdas Tumšys, Egidijus Žukauskas, Vykintas Samaitis, Lina Draudvilienė e Audrius Jankauskas. "An Inspection Technique for Steel Pipes Wall Condition Using Ultrasonic Guided Helical Waves and a Limited Number of Transducers". Materials 16, n. 15 (2 agosto 2023): 5410. http://dx.doi.org/10.3390/ma16155410.
Abstract (sommario):
This research utilizes Ultrasonic Guided Waves (UGW) to inspect corrosion-type defects in steel pipe walls, providing a solution for hard-to-reach areas typically inaccessible by traditional non-destructive testing (NDT) methods. Fundamental helical UGW modes are used, allowing the detection of defects anywhere on the pipe’s circumference using a limited number of transducers and measurements on the upper side of the pipe. Finite element (FE) modeling and experiments investigated generating and receiving UGW helical waves and their propagation through varying corrosion-type defects. Defect detection is based on phase delay differences in the helical wave’s signal amplitude peaks between defective and defect-free regions. Phase delay variations were noted for the different depths and spatial dimensions of the defects. These results highlight the phase delay method’s potential for NDT pipeline inspection.
36
Das, Subrata, Amitabh Wahi e Suresh Jayaram. "Defect detection in textiles using back propagation neural classifier". Zastita materijala 64, n. 3 (2023): 308–13. http://dx.doi.org/10.5937/zasmat2303308d.
Abstract (sommario):
The textile products are affected by the defects during the manufacturing processes. It is also waste of the resources used for the production and in turn it affects the business. The manual inspection in defect detections is not encouraged these days in manufacturing process. The computer vision with machine learning algorithms in automated quality control system plays an important role in detecting defects in manufacturing process as well as analyzing the quality of products. Classification of defects in knitted fabric is an active area of research around the globe. This paper presents a classification method to detect defects such as holes and thick places in knitted fabric by applying artificial neural network algorithm. The artificial neural network algorithms learn from the input data after successful training process, it predicts the nature of the unknown samples in very fast and accurate way. The proposed work has been carried out in two phases. In the first phase the images of the defective samples of two classes were collected by a high-resolution camera. The color images of the samples were converted into grey scale images. The features were extracted from each grey scale image and stored in a database. In the second phase a neural classifier was trained with back-propagation neural Network (BPNN) algorithm on the training dataset. After successful training of the neural network on train dataset, the performance of the trained neural network was evaluated on the test dataset. Different experiments were carried out by increasing the number of training data samples; it was found that the best evaluation performance was obtained as 83.3%.
37
Kutsenko, Anton A. "Wave propagation through periodic lattice with defects". Computational Mechanics 54, n. 6 (1 ottobre 2014): 1559–68. http://dx.doi.org/10.1007/s00466-014-1076-3.
38
Gopalakrishnan, S. "Wave Propagation in Structures with Periodic Defects". Proceedings of the Indian National Science Academy 79, n. 4 (16 settembre 2013): 615. http://dx.doi.org/10.16943/ptinsa/2013/v79i4/47986.
39
Haragus, Mariana, e Arnd Scheel. "Corner defects in almost planar interface propagation". Annales de l'Institut Henri Poincare (C) Non Linear Analysis 23, n. 3 (maggio 2006): 283–329. http://dx.doi.org/10.1016/j.anihpc.2005.03.003.
40
Ferro, Gabriel, Olivier Kim-Hak, Jean Lorenzzi, Nikoletta Jegenyes, Maya Marinova, Maher Soueidan, Davy Carole e Efstathios K. Polychroniadis. "On the Mechanism of Twin Boundary Elimination in 3C-SiC(111) Heteroepitaxial Layers on α-SiC Substrates". Materials Science Forum 679-680 (marzo 2011): 71–74. http://dx.doi.org/10.4028/www.scientific.net/msf.679-680.71.
Abstract (sommario):
This paper deals with the formation and propagation of twin boundaries (TBs) inside 3C-SiC layers grown heteroepitaxially on -SiC substrate. The equivalent probability of nucleating 60° rotated 3C islands on such substrate lead to the systematic formation of TB upon coalescence of these islands. Elimination of these defects should occur by bending of the propagation direction. Bending through incoherent TBs is usually encountered during both VLS and CVD growth and it generates crystalline defects due to high built-in energy. One would prefer coherent TBs, formed by two-by-two annihilation of neighbouring TBs, which do not form new defect except microtwin inclusion at the interface. Such TB annihilation seems to be a specificity of growth by VLS mechanism. The mechanism of such bending is discussed
41
Krenckel, Patricia, Yusuke Hayama, Florian Schindler, Theresa Trötschler, Stephan Riepe e Noritaka Usami. "Propagation of Crystal Defects during Directional Solidification of Silicon via Induction of Functional Defects". Crystals 11, n. 2 (22 gennaio 2021): 90. http://dx.doi.org/10.3390/cryst11020090.
Abstract (sommario):
The introduction of directional solidified cast mono silicon promised a combination of the cheaper production via a casting process with monocrystalline material quality, but has been struggling with high concentration of structural defects. The SMART approach uses functional defects to maintain the monocrystalline structure with low dislocation densities. In this work, the feasibility of the SMART approach is shown for larger ingots. A G2 sized crystal with SMART and cast mono silicon parts has been analyzed regarding the structural defects via optical analysis, crystal orientation, and etch pit measurements. Photoluminescence measurements on passivated and processed samples were used for characterization of the electrical material quality. The SMART approach has successfully resulted in a crystal with mono area share over 90% and a confinement of dislocation structures in the functional defect region over the whole ingot height compared to a mono area share of down to 50% and extending dislocation tangles in the standard cast mono Si. Cellular structures in photoluminescence measurements could be attributed to cellular dislocation patterns. The SMART Si material showed very high and most homogeneous lifetime values enabling solar cell efficiencies up to 23.3%.
42
YAMASHITA, Kentaro, Kunio GOKUDAN e Tomoaki SAKAI. "OS11F060 Detection of Internal Defects in Concrete Structures by Analyzing Elastic Wave Propagation". Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics 2011.10 (2011): _OS11F060——_OS11F060—. http://dx.doi.org/10.1299/jsmeatem.2011.10._os11f060-.
43
Jones, K. M., R. J. Matson, M. M. Al-Jassim e S. M. Vernon. "Defect generation and propagation in GaAs solar cells". Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 926–27. http://dx.doi.org/10.1017/s0424820100106697.
Abstract (sommario):
It is well known that dislocations have deleterious effects on the performance of minority carrier semiconductor devices. In a previous study(1), the results of an EBIC examination of GaAsP wide bandgap solar cells was reported. The effects of defects in the 106-108 cm-2 range on various cell parameters were investigated. However, the equally important 104-106 range was not studied. In this work, we report a study on defects in low bandgap (1.4 eV) GaAs cells in the 104-108 cm-2 range. These cells were grown by low pressure MOCVD on GaAs substrates. In order to introduce dislocations with such a wide range of densities, an intermediate mismatched layer of GaAs1_xPx was introduced into the structure (Fig. 1). Five different device-type structures were grown in which the P concentration (x) was varied from 2% to 32%. These concentrations correspond to a lattice mismatch of 7.3x10-4 and 1.2xl0-2respectively. As expected, the higher the P concentration the larger the mismatch being introduced into the system and therefore, the higher the defect density.
44
Minnetyan, L., e C. C. Chamis. "Damage Tolerance of Large Shell Structures". Journal of Pressure Vessel Technology 121, n. 2 (1 maggio 1999): 188–95. http://dx.doi.org/10.1115/1.2883685.
Abstract (sommario):
Progressive damage and fracture of large shell structures is investigated. A computer model is used for the assessment of structural response, progressive fracture resistance, and defect/damage tolerance characteristics. Critical locations of a stiffened conical shell segment are identified. Defective and defect-free computer models are simulated to evaluate structural damage/defect tolerance. Safe pressurization levels are assessed for the retention of structural integrity at the presence of damage/defects. Damage initiation, growth, accumulation, and propagation to fracture are included in the simulations. Damage propagation and burst pressures for defective and defect-free shells are compared to evaluate damage tolerance. Design implications with regard to defect and damage tolerance of a large steel pressure vessel are examined.
45
Zheng, Zhupeng, Zihao Zhang e Cheng Huang. "Damage Monitoring of Steel Bars Based on Torsional Guided Waves". Sensors 24, n. 7 (22 marzo 2024): 2047. http://dx.doi.org/10.3390/s24072047.
Abstract (sommario):
Ultrasonic guided waves represent a new development in the field of non-destructive testing. Longitudinal guided waves are mostly used to monitor the damage of steel bars, but the received signal is usually degraded and noisy owing to its dispersive propagation and multimodal behavior, making its implementation and location challenging. The torsional mode of T (0, 1) is not dispersive in the propagation of a steel bar and only produces circumferential displacement. It was chosen, in this study, to conduct guided wave-based damage monitoring on steel bars to reduce the signal processing complexity. The defects of steel bars, including circular surface defects, internal defects, and uniform damage defects, were thoroughly investigated, respectively, using numerical simulation. The waves were excited and received using the pitch-and-catch technique and the collected monitoring signals were processed using Hilbert transformation to highlight the amplitude and time-of-flight values of the wave signals, which were used for defect identification. In this paper, the reflectivity of guided waves is compared between torsional waves and longitudinal waves, in each case. The impact of defect size changes on damage monitoring is studied and the sensitivity of both the wave frequency and the wave mode (L and T) is also discussed. The results show that the monitoring method based on the torsional wave T (0, 1) is more sensitive to surface defects than the conventional method based on longitudinal waves. The reflectivity of the torsional wave T (0, 1) can be twice that of the longitudinal wave L (0, 1) when the depth of the defect in the circumferential grooves is less than 50% of the diameter of the steel bar. It is more sensitive to shallow surface defects within half of the bar’s radius, and it can also effectively identify defects under the conditions of the uniform damage defects of steel bars, even when the measurements are heavily noise-polluted. This proves the superiority of the torsional guided wave T (0, 1) in defect monitoring and provides a theoretical basis for the application of the torsional guided wave T (0, 1) in actual monitoring.
46
Chen, Guan, Hong Ping Zhao, Shao Hua Ji, Xi Qiao Feng e Hui Ji Shi. "Experimental Study of the Effects of Surface Defects on Rolling Contact Fatigue Behavior". Key Engineering Materials 353-358 (settembre 2007): 254–57. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.254.
Abstract (sommario):
Rolling contact fatigue (RCF) cracks initiated from surface and subsurface defects are typical failure modes of bearing systems. In this paper, the effects of surface defects on RCF behavior of M50NiL and M50 steels were studied experimentally. Artificial dents were introduced on the rolling surface by using Rockwell hardness tester. The influences of dent shape and dent shoulders were examined by thrust-type RCF tests. Surface cracks initiation, propagation and spalling were monitored by scanning electron microscope (SEM) observation. The results showed that artificial dents reduce RCF lives of M50NiL and M50 steels with mineral oil lubrication. The fatigue failure initiates at the surface defect with the effects of dent shape and dent shoulder. M50NiL steel has higher contact fatigue resistance than M50. The features of surface and sub-surface cracks propagation during RCF tests were also observed.
47
Benkhedda, Fatima, Ismail Bensaid, Abderrahim Benmoussat, Sid Ahmed Benmansour e Abdeldjelil Amara Zenati. "Corrosion of API 5L X60 Pipeline Steel in Soil and Surface Defects Detection by Ultrasonic Analysis". Metals 14, n. 4 (26 marzo 2024): 388. http://dx.doi.org/10.3390/met14040388.
Abstract (sommario):
The corrosion steels phenomenon is one of the main problems in the oil industry, such as in buried transmission pipelines used for high gas pressure for long distances. Steels are protected from the external soil corrosion through a bituminous coating, whose action is coupled with a cathodic protection system, which aims to maintain steel in its protection field and thus to avoid any corrosion risk. However, steels in service may experience external surface defects like corrosion pitting and cracking due to electrochemical or mechanical interactions of bare steel with an aggressive soil solution after steel protection failure. These are concerning phenomena and are the major threats of the pipeline transmission system’s reliability and ecological safety. Corrosion mechanisms are varied and can be evaluated by different methods, such as electrochemical measurements, which are influenced by various factors like temperature, pH, soil characteristics, resistivity, water content, and as well mechanical stresses. Corrosion results from simulated artificial soil solutions showed that steel is sensitive to corrosion by soil. Surface defects detection was carried out using an ultrasonic non-destructive method such as C-Scan Emission testing and the time of flight diffraction technique (TOFD) ultrasonic non-contact testing method. After propagation of the ultrasonic waves, the diffracted ultrasonic reflected wave occurring at the edges of the defects appears due to the presence of a corrosion defect by generating defect echoes. The C-Scan ultrasonic image shows surface reflection, including corrosion defects on interfaces with varying acoustic impedances. The cross-transverse speed ultrasonic propagation through the plate including defect is modified, revealing more surface defects, and cross-transverse speed is shown to increase ultrasonic detection presents some advantages, such as precision and speed of detection without alteration to the structure. This method can be used in the industrial context as an intelligent industrial robotics technique.
48
Wang, Zhentao, Shanglei Yang, Yubao Huang, Cong Fan, Zeng Peng e Zihao Gao. "Microstructure and Fatigue Damage of 316L Stainless Steel Manufactured by Selective Laser Melting (SLM)". Materials 14, n. 24 (8 dicembre 2021): 7544. http://dx.doi.org/10.3390/ma14247544.
Abstract (sommario):
In this paper, 316L stainless steel powder was processed and formed by selective laser melting (SLM). The microstructure of the sample was studied using an optical microscope, and the fatigue failure of the sample and the characteristics of crack initiation and propagation were analyzed, providing a research basis for the application of SLM-316L. Due to the influence of microstructure and SLM process defects, the fatigue cracks of SLM-316L mainly emerged due to defects such as lack of fusion and pores, while the cracks of rolled 316L initiated at the inclusions near the surface of the specimen. After fatigue microcrack initiation of the SLM-316L specimen, due to the existence of shear stress and tear stress, the crack tip was passivated and Z-shaped propagation was formed. The existence of internal defects in SLM-316L made the microcrack initiation random and diverse. At the same time, the existence of defects affected the crack propagation in the form of bending, bifurcation and bridge, which made the main crack propagation deviate from the maximum load direction.
49
Zhu, Long Xiang, Yue Min Wang e Feng Rui Sun. "Numerical Simulation on Detecting Defects in Pipes Using T(0,1) Mode Guided Wave". Advanced Materials Research 823 (ottobre 2013): 456–60. http://dx.doi.org/10.4028/www.scientific.net/amr.823.456.
Abstract (sommario):
The guided-wave technology is very efficient in inspecting a large portion of pipe. In order to study the propagation property of guided wave in pipe and the interaction between guided waves and defects, pipe model was established using 3D solid finite element in the software ANSYS. Tangential displacements were prescribed on the nodes in the pipe end and the propagating of T(0,1) mode guided wave in pipes was simulated. The detecting signals for the pipe model with different defects were extracted, which matched very well with experimental result.
50
Chapetti, Mirco D., Nenad Gubeljak e Dražan Kozak. "Intrinsic Fatigue Limit and the Minimum Fatigue Crack Growth Threshold". Materials 16, n. 17 (28 agosto 2023): 5874. http://dx.doi.org/10.3390/ma16175874.
Abstract (sommario):
In the field of long-life fatigue, predicting fatigue lives and limits for mechanical components is crucial for ensuring reliability and safety. Fracture mechanics tools have enabled the estimation of fatigue lives for components with small cracks or defects. However, when dealing with defects larger than the microstructural characteristic size, estimating the fatigue resistance of a material requires determining the cyclic resistance curve for the defect-free matrix, which depends on knowledge of the material’s intrinsic fatigue limit. This study focuses on the experimental evidence regarding the intrinsic fatigue limit and its correlation with naturally nucleated non-propagating cracks. Fracture mechanics models for small crack propagation are introduced, and their disparities and limitations are analyzed. The concept of intrinsic fatigue limit is then introduced and applied to reanalyze a recent publication. Methods for estimating the intrinsic fatigue limit are explored and applied to experimental results reported in the literature. The need to clarify and accurately predict the intrinsic fatigue limit is highlighted in alloys where the processing generates defects larger than the microstructural size of the matrix, as often observed in materials and components produced using additive manufacturing.