Artykuły w czasopismach na temat „Crack”
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1
Han, Zhichao, Caifu Qian i Huifang Li. "Investigation of the Enhancement Interactions between Double Parallel Cracks on Fatigue Growth Behaviors". Materials 13, nr 13 (1.07.2020): 2952. http://dx.doi.org/10.3390/ma13132952.
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In this paper, interactions of double parallel cracks were studied by performing experiments and numerical simulations. Fatigue crack propagation tests were carried out to measure crack growth rates in the specimens with double parallel cracks or a single crack. Finite element method was adopted to calculate stress intensity factors at the crack tips. Results show that the double parallel cracks at different positions present a shielding effect or enhancement effect on crack growth rates and stress intensity factors. When the double parallel cracks are offset, crack interactions mostly behave as enhancement effects. Empirical formulas were obtained to calculate the stress intensity factor at the “dangerous” crack tip of the double parallel cracks. By modifying the material parameters in Paris equation of the single crack, the double parallel cracks are simplified into a single crack with the same crack growth rates.
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Wang, Chaolin, Yu Zhao, Yanlin Zhao i Wen Wan. "Study on the Interaction of Collinear Cracks and Wing Cracks and Cracking Behavior of Rock under Uniaxial Compression". Advances in Civil Engineering 2018 (2018): 1–10. http://dx.doi.org/10.1155/2018/5459307.
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This paper investigates the crack interaction, initiation, and propagation rules of rock-like materials containing two collinear cracks. Based on the Kachanov method, the formulations for stress intensity factors (SIFs) of two collinear cracks and two winged cracks are derived, respectively. The influences of bridge ligament and crack length on the crack interaction are analyzed theoretically. The results show that the propagation of a long crack is independent of crack interaction when d≥a2 and the same rule applies for a short crack when d≥a1. With the growth of wing cracks, the SIF of wings first remarkably decreases and then it tends toward a steady value. Subsequently, the propagation of collinear cracks and cracking processes under uniaxial compression are analyzed experimentally and numerically. Both the experimental results and simulation results demonstrate that shear cracks tend to initiate and propagate at higher inclination angle. The crack coalescence is affected by the inclination angle of bridge ligament. For increasing the inclination angle, the crack coalescence varies from wing crack failure to shear crack coalescence. As bridge ligament increases, the crack coalescence varies from shear crack coalescence to shear-wing crack coalescence and then to wing crack failure.
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Xu, Yan Hai. "Study on Crack Retardation with the Consideration of Crack Surface Roughness by FEM". Advanced Materials Research 97-101 (marzec 2010): 471–74. http://dx.doi.org/10.4028/www.scientific.net/amr.97-101.471.
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As one of the key factors to induce crack closure, crack surface roughness plays a dominated role in evaluating the characteristics of short fatigue cracks. The crack retardation induced by the crack surface roughness was investigated by numerical simulation in this paper. The influence of crack surface roughness on short fatigue cracks was directly applied into the numerical simulation procedure with the help of friction coefficients on the contacted crack surfaces. The driving forces of cracks represented by the two indicators such as crack tip displacement and plastic strain range were studied and used to characterize the retardation induced by crack surface roughness. It is shown that the evidence of crack surface roughness affecting on crack retardation is obvious and the influence of crack surface roughness on the characteristics of short fatigue cracks must account for in evaluating the performance of short fatigue cracks.
4
Xu, Yonglin, B. Moran i T. Belytschko. "Self-Similar Crack Expansion Method for Three-Dimensional Crack Analysis". Journal of Applied Mechanics 64, nr 4 (1.12.1997): 729–37. http://dx.doi.org/10.1115/1.2788976.
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The self-similar crack expansion method is developed to calculate stress intensity factors for three-dimensional cracks in an infinite medium or semi-infinite medium by the boundary integral element technique. With this method, the stress intensity factors at crack tips are determined by calculating the crack-opening displacements over the crack surface, and the crack expansion rate, which is related to the crack energy release rate, is estimated by using a technique based on self-similar (virtual) crack extension. For elements on the crack surface, regular integrals and singular integrals are evaluated based on closed-form expressions, which improves the accuracy. Examples show that this method yields very accurate results for stress intensity factors of penny-shaped cracks and elliptical cracks in the full space, with errors of less than one percent as compared with exact solutions. The stress intensity factors of subsurface cracks are in good agreement with other numerical solutions.
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Yoda, M. "Subcritical Crack Growth Characteristics on Compact Type Specimens and Indentation Cracks in Glass". Journal of Engineering Materials and Technology 111, nr 4 (1.10.1989): 399–403. http://dx.doi.org/10.1115/1.3226486.
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For the purpose of comparing crack growth characteristics on small indentation cracks with those for long cracks, subcritical crack growth data on soda-lime glass were obtained using the compact type (CT) specimens with long cracks and the indentation cracks. It was found that there is apparently a small crack effect in the as-indented cracks which increases crack growth. However, the annealed indentation crack shows the same trend of crack growth as that for the CT specimens. A residual stress effect can be used to explain this anomalous growth behavior of the as-indented cracks.
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Jin, Huijin, Bing Cui i Ling Mao. "Fatigue Growth Behaviour of Two Interacting Cracks with Different Crack Offset". Materials 12, nr 21 (28.10.2019): 3526. http://dx.doi.org/10.3390/ma12213526.
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Under cyclic fatigue load, multiple cracks would significantly deteriorate the service life of the components with respect to the case of a single crack owing to the crack interaction. The present study aims to explore the effect of crack interaction on the fatigue growth behaviour of samples with different crack offset. In this study, fatigue crack growth tests were performed for samples containing a single crack and non-collinear cracks of different crack offset in an aluminum–lithium alloy. It was shown that the two facing non-collinear cracks changed their growth direction when the cracks were overlapped, resulting in load mode transfers from mode I to I + II mixed mode. Then, the interaction behaviour was studied by establishing the finite element models to calculate the stress intensity factor K of samples with different crack offset. The results indicated that the K decreased, largely owing to the shielding effect as the two cracks overlapped, leading to retardation of crack growth in the position of overlap, especially for the specimens with a small crack offset. It was also shown that the interaction effect could change from positive to negative during the process of the multiple cracks’ growth, thus leading to the acceleration or deceleration of crack growth rates, suggesting that the influence of interaction on cracks’ growth behaviour could vary with the different stages of crack growth.
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Kamaya, Masayuki. "Evaluation of Fatigue Crack Growth of Interacting Surface Cracks". Advanced Materials Research 33-37 (marzec 2008): 187–98. http://dx.doi.org/10.4028/www.scientific.net/amr.33-37.187.
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Since mechanical interaction between multiple cracks affects the rate of crack growth due to fatigue and stress corrosion cracking, it is important to consider its influence when predicting growth. In this study, a procedure predicting the growth of interacting surface cracks was developed. First, using the results of fatigue crack growth tests performed in a previous study, the transient growth behavior during coalescence and growth under interaction was evaluated based on area of crack face. It was shown that the area is a representative parameter of the growth of interacting surface cracks as well as independent cracks. The growth in area showed good correlation with the crack driving force defined using size of area. Then, in order to investigate the relationship between growth of interacting cracks and their relative spacing, crack growth simulations were carried out. The body force method was used to evaluate the change in stress intensity factors (SIF) during crack growth under interaction, and the simulation could reproduce the crack configurations obtained in the fatigue crack growth test. SIF of an interacting crack tip converges to that of a coalesced crack as the distance between cracks decreases. It was concluded that when the distance between cracks is small enough, the cracks can be replaced with a semi-elliptical crack of the same area of crack face for a growth evaluation. The threshold offset distance for the replacement was suggested to be less than 0.1Rx, where Rx is the span length of two cracks on the surface.
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Luo, Xiaoyan, Guoyan Zhao, Peng Xiao i Wengang Zhao. "Fracture Process and Failure Mode of Brazilian Discs with Cracks of Different Angles: A Numerical Study". Mathematics 10, nr 24 (17.12.2022): 4808. http://dx.doi.org/10.3390/math10244808.
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In order to determine the effect of internal cracks on the tensile failure of materials, a hybrid finite–discrete element method was used to analyze the Brazilian disc test with cracks of different angles. When the pre-crack angle is between 0° and 60°, the wing crack is initiated from the pre-crack end. When the pre-crack is 90°, the crack initiated from the pre-crack center. When the pre-crack angle is between 0° and 60°, the maximum principal stress and plastic strain are concentrated at the pre-crack end. When the pre-crack angle is 90°, the maximum principal stress and plastic strain are concentrated in the pre-crack center. As the crack angle increased from 0° to 90°, the failure mode of Brazilian discs with cracks transits from splitting into two parts to splitting into four parts. The influence of crack length is further studied. When the crack length is less than 5 mm, the crack angle has little influence on the disc failure mode; Brazilian discs with cracks of different angles undergoes splitting failure along the loading axis. When the crack length is larger than 5 mm, the crack angle has a great effect on the disc failure mode.
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Han, Zhichao, Caifu Qian i Huifang Li. "Study of the Shielding Interactions between Double Cracks on Crack Growth Behaviors under Fatigue Loading". Metals 10, nr 2 (31.01.2020): 202. http://dx.doi.org/10.3390/met10020202.
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In this paper, the interactions between double cracks with a co-bisector-line were investigated theoretically and experimentally. Fatigue crack growth tests of specimens with a single crack or double cracks were carried out to measure the crack growth rates, and finite element calculations were performed to obtain the stress intensity factors at crack tips. It was found that when the double cracks are in co-bisector-line, they present shielding interactions which reduce the stress intensity factors at crack tips as well as the crack growth rates. By modifying the stress intensity factors and the Paris equation considering the shielding interactions, a new simplification method was proposed to simplify the double cracks into a single crack with the same crack growth rates.
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Kim, D. S., i K. H. Lo. "Crack Interaction Criteria in Pressure Vessels and Pipe". Journal of Offshore Mechanics and Arctic Engineering 117, nr 4 (1.11.1995): 260–64. http://dx.doi.org/10.1115/1.2827232.
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An attempt was made to define a new crack interaction criterion for pressurized cylinders with two co-planar surface cracks. Elastic-plastic finite element method with line spring concept (line spring element method) was used to verify the validity of the new interaction criterion and to establish the relative conservatism built into various codes/standards. The crack interaction criteria of two co-planar surface cracks as defined by ASME Section XI and BS PD6493 were studied and a new interaction criterion which accounts for crack shape and load factor was introduced. The basic idea behind the crack interaction criteria for co-planar surface cracks was the plastic zone and stress interaction near crack tips. To verify the new crack interaction criterion, comparisons of J-integral values were made for various crack sizes with different distances between cracks and loading conditions. Based upon these comparisons, the new crack interaction criteria, comparing a physical distance, s, to a characteristic distance d=(σ/σy)2(c1Q1 + c2Q2), proved to be a reasonable parameter for indication of the crack driving force interaction for co-planar cracks. The characteristic distance also represents a rigorous measure of an equivalent crack driving force for interacting cracks.
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Cui, Zhendong, i Weige Han. "In SituScanning Electron Microscope (SEM) Observations of Damage and Crack Growth of Shale". Microscopy and Microanalysis 24, nr 2 (kwiecień 2018): 107–15. http://dx.doi.org/10.1017/s1431927618000211.
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AbstractTo better understand the formation and evolution of hierarchical crack networks in shales, observations of microscopic damage, and crack growth were conducted using anin situtensile apparatus inside a scanning electron microscope. An arched specimen with an artificial notch incised into the curved edge was shown to afford effective observation of the damage and crack growth process that occurs during the brittle fracturing of shale. Because this arched specimen design can induce a squeezing effect, reducing the tensile stress concentration at the crack tip, and preventing the brittle shale from unstable fracturing to some extent. Both induced and natural pores and cracks were observed at different scales around the main crack path or on fractured surfaces. Observations indicate that the crack initiation zone develops around the crack tip where tensile stresses are concentrated and micro/nanoscale cracks nucleate. Crack advancement generally occurs by the continuous generation and coalescence of damage zones having intermittent en echelon microscopic cracks located ahead of the crack tips. Mineral anisotropy and pressure build-up around crack tips causes crack kinking, deflection, and branching. Crack growth is often accompanied by the cessation or closure of former branch cracks due to elastic recovery and induced compressive stress. The branching and interactions of cracks form a three-dimensional hierarchical network that includes induced branch cracks having similar paths, as well as natural structures such as nanopores, bedding planes, and microscopic cracks.
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Zhao, Jinghe, Ying Zhang i Bo Jiang. "A Study on Mode Shape and Natural Frequency of Rotating Flexible Cracked Annular Thin Disk". Shock and Vibration 2021 (17.09.2021): 1–15. http://dx.doi.org/10.1155/2021/6533487.
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As an important rotating component, the flexible annular thin disk is widely used in mechanical engineering. Cracks may occur in some weak disk parts, which will greatly shorten the equipment service life and even cause equipment failure. Due to the centrosymmetric structure of the flexible annular disk, two typical cracks are studied in this paper; one is radial crack parallel to diameter, including radial closed crack (RC-crack) and radial opening crack (RO-crack); the other one is vertical crack perpendicular to diameter, including circumferential crack (CF-crack) and tangential crack (TG-crack). The effect of crack parameters, such as crack length, direction, and position, on disk vibration characteristics are studied through theoretical simulation and experimental verification. The research shows that the effect of cracks on vibration characteristic gets more obvious with cracks extending in most cases, RO-crack decreases the natural frequency obviously, and vertical cracks would affect mode shapes. In addition, the bigger the nodal diameter is, the more obvious the effect gets. Meanwhile, the most obvious effect appears in the mode of a nodal diameter locating on the crack. The research possesses some guiding significance in industrial production; by comparing with the vibration characteristics of the flawless disk, the integrity of the rotating flexible disk can be judged to prevent possible equipment damage.
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Gao, Ruipeng, Mengmeng Liu, Bing Wang, Yiran Wang i Wei Shao. "Influence of Stress Intensity Factor on Rail Fatigue Crack Propagation by Finite Element Method". Materials 14, nr 19 (30.09.2021): 5720. http://dx.doi.org/10.3390/ma14195720.
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Wheel rail rolling contact fatigue is a very common form of damage, which can lead to uneven rail treads, railhead nuclear damage, etc. Therefore, ANSYS software was used to establish a three-dimensional wheel–rail contact model and analyze the effects of several main characteristics, such as the rail crack length and crack propagation angle, on the fatigue crack intensity factor during crack propagation. The main findings were as follows: (1) With the rail crack length increasing, the position where the crack propagated by mode I moved from the inner edge of the wheel–rail contact spot to the outer edge. When the crack propagated to 0.3–0.5 mm, it propagated to the rail surface, causing the rail material to peel or fall off and other damage. (2) When the crack propagation angle was less than 30°, the cracks were mainly mode II cracks. When the angle was between 30 and 70°, the cracks were mode I–II cracks. When the angle was more than 70°, the cracks were mainly mode I cracks. When the crack propagation angle was 60°, the equivalent stress intensity factor reached the maximum, and the rail cracks propagated the fastest.
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Shen, Jane-Sang, Julie P. Harmon i Sanboh Lee. "Thermally-induced Crack Healing in Poly(Methyl Methacrylate)". Journal of Materials Research 17, nr 6 (czerwiec 2002): 1335–40. http://dx.doi.org/10.1557/jmr.2002.0199.
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A microscopic theory of thermally induced crack healing in poly(methyl methacrylate) is presented. Both laser-induced cylindrical cracks and knife-induced surface cracks were analyzed. For a given temperature, the crack closure rate was constant for both types of cracks. However, the crack closure rate was lower for samples with cylindrical cracks than for those with surface cracks. The former exhibited higher activation energy for crack closure than the latter, because the knife-induced cracks had sharper crack tips. Fracture stress was proportional to surface crack healing time to the one-fourth power for thermal healing at a given temperature. Based on the reptation model of polymer chains, the activation energy of chain diffusion was calculated. The healing process was monitored via fractography and crack closure was confirmed. The results were compared with solvent healing and thermal healing in the literature.
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Takahashi, Akiyuki, Ayaka Suzuki i Masanori Kikuchi. "Fatigue Crack Growth Simulation Using S-Version FEM: Application to Interacting Subsurface Cracks". Key Engineering Materials 741 (czerwiec 2017): 82–87. http://dx.doi.org/10.4028/www.scientific.net/kem.741.82.
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In this paper, fatigue crack growth simulation of interacting subsurface cracks using the s-version finite element method (SFEM) is presented. In order to evaluate the accuracy and reliability of the proximity rules published by the ASME, during the fatigue crack growth simulations, the subsurface cracks are approximated to either a single elliptical crack or semi-elliptical surface crack in accordance with the proximity rules. Then, the proximity rules are slightly modified for improving the accuracy and reliability. The results of crack depth evolution calculated by the SFEM with the use of the new proximity rules suggest that the approximation to deep cracks drastically improves the accuracy of the fatigue crack growth evaluation. Thus, the approximation to deep cracks must be a promising approach for having better evaluation of fatigue crack growth of subsurface cracks.
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Li, Xiaoke, Songwei Pei, Kunpeng Fan, Haibin Geng i Fenglan Li. "Bending Performance of Steel Fiber Reinforced Concrete Beams Based on Composite-Recycled Aggregate and Matched with 500 MPa Rebars". Materials 13, nr 4 (19.02.2020): 930. http://dx.doi.org/10.3390/ma13040930.
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To promote the engineering application of recycled aggregate for concrete production with good adaptability and economic efficiency, this paper performed a campaign to investigate the flexural performance of steel fiber reinforced composite-recycled aggregate concrete (SFR-CRAC) beams matched with 500 MPa longitudinal rebars. The composite-recycled aggregate has features of the full use recycled fine aggregate and small particle recycled coarse aggregate, and the continuous grading of coarse aggregate ensured by admixing the large particle natural aggregate about 35% to 45% in mass of total coarse aggregate. The properties of SFR-CRAC have been comprehensively improved by using steel fibers. With a varying volume fraction of steel fiber from 0% to 2.0%, 10 beam specimens were produced. The flexural behaviors of the beams during the complete loading procedure were experimentally studied under a four-point bending test. Of which the concrete strain at mid-span section, the appearance of cracks, the crack distribution and crack width, the mid-span deflection, the tensile strain of longitudinal rebars, and the failure patterns of the beams were measured in detail. Results indicated that the assumption of plane cross-section held true approximately, the 500 MPa longitudinal rebars worked at a high stress level within the limit width of cracks on reinforced SFR-CRAC beams at the normal serviceability, and the typical failure occurred with the yield of 500 MPa longitudinal rebars followed by the crushed SFR-CRAC in compression. The cracking resistance, the flexural capacity, and the flexural ductility of the beams increased with the volume fraction of steel fiber, while the crack width and mid-span deflection obviously decreased. Finally, by linking to those for conventional reinforced concrete beams, formulas are suggested for predicting the cracking moment, crack width, and flexural stiffness at normal serviceability, and the ultimate moment at bearing capacity of reinforced SFR-CRAC beams.
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Gardin, Catherine, Saverio Fiordalisi, Christine Sarrazin-Baudoux i Jean Petit. "3D Numerical Study on how the Local Effective Stress Intensity Factor Range Can Explain the Fatigue Crack Front Shape". Advanced Materials Research 891-892 (marzec 2014): 295–300. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.295.
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The plasticity-induced crack closure of through-thickness cracks, artificially obtained from short cracks grown in CT specimens of 304L austenitic stainless steel, is numerically simulated using finite elements. Crack advance is incremented step by step, by applying constant ΔK amplitude so as to limit the loading history influence to that of crack length and crack wake. The calculation of the effective stress intensity factor range, ΔKeff, along curved shaped crack fronts simulating real crack fronts, are compared to calculation previously performed for through-thickness straight cracks. The results for the curved crack fronts support that the front curvature is associated to constant ΔKeffamplitude, thus assumed to be the propagation driving force of the crack all along its front.
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Shi, Nan Nan, i Da Hai Huang. "Experimental Study on Early-Age Crack of RC Using TSTM". Advanced Materials Research 919-921 (kwiecień 2014): 119–22. http://dx.doi.org/10.4028/www.scientific.net/amr.919-921.119.
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Thermal stress is a major cause of early-age crack of massive concrete structures. In order to analyze the influencing factors of concrete crack under thermal loads, a series of tests were conducted using the improved Temperature Stress Testing Machine (TSTM). Effects of temperature on crack resistance of concrete were studied on different concrete placing temperatures and curing temperatures. Meanwhile, the roles of reinforcement on concrete crack resistance and crack-width limitation were quantitative analyzed, which compare cracks of plain concrete and reinforced concrete with the same mix proportion. The results indicate that reinforcement can improve the crack resistance of the structures by approximately twenty percents, which against the engineering experience. After concrete cracks, the cracks photos show that reinforcement can induce the smaller cracks formation, and the crack width of reinforced concrete is about 1/10 of the plain concrete crack width.
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Chang, Yan Jun, Shuang Feng Zeng, Ke Shi Zhang i Zhuo Li. "Study of Q345 Steel under Tensile Failure with Bilateral Parallelcracks". Applied Mechanics and Materials 574 (lipiec 2014): 368–72. http://dx.doi.org/10.4028/www.scientific.net/amm.574.368.
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The parallel crackswere prefabricated on both sides of theQ345 steel specimensand the tensile failure tests were performed.The effects of parallel crack spacing and crack length on the crack propagation behavior were studied and the fracture modes were investigated with electronic scanning microscope.The finite element analysis of tensile fracture process was also fulfilled based on the ductile metal damage theory, and the crack propagation and the crack stress field evolution around the crack tips were studied. The simulation was agreed with experimental results, and these analysis shows that the crack propagation related with double crack tip of horizontal distance ratio. When the longitudinal and horizontal distance ratio of the two crack tip is less than 1, the linkage between two cracks occurs, or two cracks expand independently. Simulation analysis shows that cracks deflect and connect with another one when the two high Mises plastic stress zones are met with each other; on the contrary, cracks propagate separately.
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Loukil, Mohamed Sahbi, Janis Varna i Zoubir Ayadi. "Applicability of solutions for periodic intralaminar crack distributions to non-uniformly damaged laminates". Journal of Composite Materials 47, nr 3 (22.03.2012): 287–301. http://dx.doi.org/10.1177/0021998312440126.
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Stiffness reduction simulation in laminates with intralaminar cracks is usually performed assuming that cracks are equidistant and crack density is the only parameter needed. However, the crack distribution in the damaged layer is very non-uniform, especially in the initial stage of multiple cracking. In this article, the earlier developed model for general symmetric laminates is generalized to account for non-uniform crack distribution. This model, in which the normalized average crack-opening and crack-sliding displacements are the main characteristics of the crack, is used to calculate the axial modulus of cross-ply laminates with cracks in internal and surface layers. In parametric analysis, the crack-opening displacement and crack-sliding displacement are calculated using finite element method, considering the smallest versus the average crack spacing ratio as non-uniformity parameter. It is shown that assuming uniform distribution, we obtain lower bond to elastic modulus. A ‘double-periodic’ approach presented to calculate the crack-opening displacement of a crack in a non-uniform case as the average of two solutions for periodic crack systems is very accurate for cracks in internal layers of cross-ply laminates, whereas for high crack density in surface layers, it underestimates the modulus reduction.
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Wang, Qiannan, Guoshuai Zhang, Yunyun Tong i Chunping Gu. "A Numerical Study on Chloride Diffusion in Cracked Concrete". Crystals 11, nr 7 (25.06.2021): 742. http://dx.doi.org/10.3390/cryst11070742.
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The cracks in concrete are a fast transport path for chlorides and influence the service life of concrete structures in chloride environments. This study aimed to reveal the effect of crack geometry on chloride diffusion in cracked concrete. The chloride diffusion process in cracked concrete was simulated with the finite difference method by solving Fick’s law. The results showed that the apparent chloride diffusivity was lower in more tortuous cracks, and the cracks with more narrow points also showed lower apparent chloride diffusivity. For tortuous cracks, a higher crack width meant relatively more straight cracks, and consequently, higher apparent chloride diffusivity, while a lower crack width resulted in more tortuous cracks and lower apparent chloride diffusivity. The crack depth showed a more significant influence on the chloride penetration depth in cracked concrete than crack geometry did. Compared with rectangular and V-shaped cracks, the chloride diffusion process in cracked concrete with a tortuous crack was slower at the early immersion age. At the same crack depth, the crack geometry showed a marginal influence on the chloride penetration depth in cracked concrete during long-term immersion.
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Le, Chengjun, Xuhua Ren, Haijun Wang i Shuyang Yu. "Experimental and Numerical Study on the Failure Characteristics of Brittle Solids with a Circular Hole and Internal Cracks". Materials 15, nr 4 (14.02.2022): 1406. http://dx.doi.org/10.3390/ma15041406.
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A stress analysis of a circular hole is one of the classical problems in mechanics. Internal cracks are inherent properties of materials, and they are mostly three-dimensional in form. However, studies on hole problems with three-dimensional internal cracks are still lacking. In this paper, internal cracks were generated in brittle materials containing circular holes based on 3D internal laser-engraved crack technology. Then, uniaxial compression tests were performed. The experimental results were compared with the existing literature, and theoretical and numerical simulation studies were carried out. The results show that: (1) The main crack shapes are the primary cracks and remote cracks. (2) The dynamic fracture characteristics existed in the formation of primary cracks and the surface of remote cracks. The tips of primary cracks were arc-shaped, and the surfaces of the remote cracks were curved. Remote cracks were tangential to the orifice where type III spear-like characteristics appeared. (3) The stress birefringence technology can be combined with 3D internal laser-engraved crack technology for internal crack stress information monitoring, the moire around the orifice was “flamboyant”, and the moire at the tip of the prefabricated crack was “petallike”. (4) The existence of internal cracks reduced the cracking and breaking load of the specimen, and compared with the intact orifice specimen, the upper primary crack, the lower primary crack, the remote crack and the failure load were reduced by 41.2%, 31.7%, 15.9%, and 32.3%, respectively. (5) The results of qualitative stress analysis of the orifice specimen were consistent with the initiation law of primary cracks and remote cracks. The K distribution based on M integral and the numerical simulation of crack propagation process based on the maximum tensile stress criterion were consistent with the law of primary crack growth. Compared with the current mainstream method of transparent rock research, 3D internal laser-engraved crack technology has certain advantages in terms of brittleness, crack authenticity, stress field visualization, and fracture characteristics, and the result will provide experimental and theoretical references for research on three-dimensional problems and internal cracks in fracture mechanics.
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Cui, Wei, Zhongmin Xiao, Jie Yang, Mi Tian, Qiang Zhang i Ziming Feng. "Multi-Crack Dynamic Interaction Effect on Oil and Gas Pipeline Weld Joints Based on VCCT". Energies 15, nr 8 (12.04.2022): 2812. http://dx.doi.org/10.3390/en15082812.
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In pipelines for transporting oil and gas, multiple cracks often exist in weld joints. The interaction among the cracks should be considered as it directly affects the life span of the pipeline structures. In the current investigation, based on the fluid–solid magnetic coupling model, the virtual crack-closure technique (VCCT) is applied to systematically study the multi-crack dynamic interaction effect on pipeline welds during the crack propagation process. The results show that the existence of an auxiliary crack accelerates the main crack’s propagation. When the auxiliary crack is nearer to the main crack tip, the enhancement effect of the auxiliary crack on the main crack increases. Further, when the initial length of the auxiliary crack increases, the main crack becomes easier to propagate. Two important parameters, the distance between the two interacting crack tips and the initial size of the auxiliary crack, are studied in detail. Their interference effect on the main crack has been quantified, which is very user-friendly for engineers to conduct failure assessment and prevention for oil and gas pipes with multiple cracks at weld joints.
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Sun, Xizhen, Fanbao Meng, Ce Zhang, Xucai Zhan i He Jiang. "Progressive Failure and Acoustic Emission Characteristics of Red Sandstone with Different Geometry Parallel Cracks under Uniaxial Compression Loading". Advances in Materials Science and Engineering 2021 (11.03.2021): 1–11. http://dx.doi.org/10.1155/2021/5569091.
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The geometric distribution of initial damages has a great influence on the strength and progressive failure characteristics of the fractured rock mass. Initial damages of the fractured rock were simplified as parallel cracks in different geometric distributions, and then, the progressive failure and acoustic emission (AE) characteristics of specimens under the uniaxial compression loading were analyzed. The red sandstone (brittle materials) specimens with the parallel preexisting cracks by water jet were used in the tests. The energy peak and stress attenuation induced by the energy release of crack initiation were intuitively observed in the test process. Besides, three modes of rock bridge coalescence were obtained, and wing crack was the main crack propagation mode. The wing crack and other cracks were initiated in different loading stages, which were closely related to the energy level of crack initiation. The propagation of wing crack (stable crack) consumed a large amount of energy, and then, the propagation of shear crack, secondary crack, and anti-wing crack (unstable crack) was inhibited. The relationship between the crack propagation mode and the geometric distribution of existing cracks in the specimen was revealed. Meanwhile, the strength characteristic and failure mode of fractured rock with the different geometric distributions of preexisting crack were also investigated. The energy evolution characteristics and crack propagation were also analyzed by numerical modeling (PFC2D).
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Wang, Siyao, i Shaowei Hu. "Experimental Study of Crack Propagation in Cracked Concrete". Energies 12, nr 20 (12.10.2019): 3854. http://dx.doi.org/10.3390/en12203854.
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The intersection of cracks has an important role in the key technology of hydraulic fracturing for enhancing the recovery of tight hydrocarbon reservoirs. On the basis of digital image correlation technology, three-point bending tests of concrete beams with an edge crack and a central preset crack were conducted to investigate the propagation of cracks after intersection in concretes. Concrete beams with cracks of different positions, lengths, and approach angles were tested, and results were analyzed. In conclusion, the crack positions, crack lengths, and approach angles significantly influence the crack propagation in naturally cracked concrete. A large distance between the crack tip and central point at the preset transverse crack and crack length indicate a high possibility of the edge crack vertically crossing the preset crack. In particular, the crack restarts from the preset crack tip after intersection when the distance between two cracks is smaller than 30 mm and when the preset crack length is smaller than 40 mm. A large approach angle corresponds to a large carrying capacity of the beam and a high possibility of the crack propagating perpendicularly. An improved criterion of restart cracking after interaction is proposed, and the restart points of all tested beams are predicted and compared with the experimental results. A good agreement is observed, which proves that this criterion is reliable.
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Moan, Torgeir, Ole T. Va˚rdal, Nils-C. Hellevig i Knut Skjoldli. "Initial Crack Depth and POD Values Inferred From In-Service Observations of Cracks in North Sea Jackets". Journal of Offshore Mechanics and Arctic Engineering 122, nr 3 (14.04.2000): 157–62. http://dx.doi.org/10.1115/1.1286676.
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Observations made during more than 4000 in-service nondestructive examinations of tubular joints in North Sea jackets are utilized to determine the initial crack depth and probability of detecting (POD) cracks in magnet particle and eddy current inspections. Based on exponential distributions of the initial crack size and POD, it was found that the mean initial crack size and detectable crack depth was 0.94 and 1.95 mm, respectively. This initial crack size is referred to one crack occurrence per three joints and corresponds to a mean crack depth of 0.38 mm with a frequency of one crack per hot-spot area. The predicted number and size of undetected cracks are found to correspond well with actually reported “second inspection” cracks. The estimated depth of undetected cracks is used to estimate how deep the post-inspection grinding should be, to establish a certain residual fatigue life. [S0892-7219(00)00503-3]
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Wang, Jianming, Zhonghui Chen i Lingfan Zhang. "Unloading-Induced Crack Propagation of Two Collinear Unequal Length Flaws in Brittle Rocks". Geofluids 2020 (5.06.2020): 1–18. http://dx.doi.org/10.1155/2020/9385749.
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The propagation and coalescence of numerous discontinuous joints significantly contribute to landslide instability during excavation unloading. The tip expression of stress intensity factors of two collinear unequal length cracks in a typical rock mass under unloading conditions was calculated based on the superposition principle and fracture mechanics to determine the meso-influence law of intermittent joint interaction in the slope under the action of excavation. The effects of many factors on this interaction were also analyzed theoretically. Unloading tests were conducted on rock-like specimens with two collinear unequal length cracks in addition to numerical simulation and theoretical analysis. The results show decreased interaction between the two cracks with increased crack distance, increased influence of the main crack on a secondary crack with increased length of the main crack, and decreased influence of the secondary crack on the main crack with decreased length of the secondary crack. Wing tensile cracks first appear at the tip of flaws, and the propagation of these cracks occurs with the generation of secondary tensile cracks and shear cracks during unloading. Propagation and coalescence between cracks lead to tension and shear mixed failure of a rock bridge, and tensile cracks appear near the unloading surface. The axial initiation and peak stress of a crack increase with increased flaw distance, and the theoretical calculations were confirmed by lateral unloading test results.
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Khalid H. Almitani, Khalid H. Almitani. "https://marz.kau.edu.sa/Files/320/Researches/70650_43625.pdf". journal of King Abdulaziz University Engineering Sciences 28, nr 1 (7.01.2017): 67–90. http://dx.doi.org/10.4197/eng.28-1.5.
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A crack is a type of damage that can lead to catastrophic failure when it grows in a structure. Thus prediction of cracks is a very important problem that has to be addressed. Some studies have been done on non-destructive techniques to identify cracks. Research interest in this area has been growing up quickly. In this study, a beam made of aluminum was used for detecting cracks using vibration characteristics. A method to identify cracks in an aluminum beam was derived from the equation of the dynamic stiffness. Rotational springs were used to model the cracks in the beam and the frequency response function was calculated using a spectral element model using Finite Element Model (FEM). This procedure provides a relationship between the frequency response and crack structure. The inverse problem was solved repetitively for crack positions and sizes using the Newton-Raphson method. The finite element model was formulated to simulate the results and to provide vibration overall amplitude measurements. The results showed at certain crack size, the amplitude increases with increasing crack depth for all crack positions. At crack size of 12 mm, an increase of 4.5% in amplitude was obtained for 60 mm crack position at a depth of 1.6 mm compared to its value at a depth of 0.16 mm. Similarly, it was 8.4% at crack size of 16 mm. Also, the amplitude varies inversely with position. Furthermore, at certain crack position, the amplitude increases with increasing crack depth for all crack sizes. At crack position of 75 mm, an increase of 12.6% in amplitude was obtained for 20 mm crack size at a depth of 1.6 mm compared to its value at a depth of 0.16 mm. Similarly, it was 5.4% at crack position of 150 mm. Finally, the amplitude increases as crack size increases at a certain depth.
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Liu, Bang, Zheming Zhu, Ruifeng Liu, Lei Zhou i Duanying Wan. "Study on the Fracture Behavior of Cracks Emanating from Tunnel Spandrel under Blasting Loads by Using TMCSC Specimens". Shock and Vibration 2019 (20.05.2019): 1–13. http://dx.doi.org/10.1155/2019/2308218.
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Radial cracks may exist around tunnel edge, and these cracks may propagate and weaken tunnel stability under nearby blasting operations. In order to study the blast-induced fracture behavior of radial cracks emanating from a tunnel spandrel, a tunnel model containing a spandrel crack (TMCSC) with different inclination angles was proposed in this paper. Crack propagation gauges (CPGs) and strain gauges were used in the experiments to measure crack initiation moment and propagation time. Finite difference models were established by using AUTODYN code to simulate crack propagation behavior and propagation path. ABAQUS code was used to calculate dynamic stress intensity factors (SIFs). The results show that (1) crack inclination angles affect crack initiation angles and crack propagation lengths significantly; (2) critical SIFs of both mode I and mode II decrease gradually with the increase of the crack propagation speed; (3) the dynamic energy release rates vary during crack propagation; and (4) there are “crack arrest points” on the crack propagation paths in which the crack propagation speed is very small.
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Lin, Bin, Hong Tao Zhu, Hui Wu, Z. F. Wang i S. Y. Yu. "Evaluation and Measurement of Surface/Subsurface Crack Damage of Ground Ceramics". Materials Science Forum 471-472 (grudzień 2004): 47–51. http://dx.doi.org/10.4028/www.scientific.net/msf.471-472.47.
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While be ground, ceramic is prone to engender surface/subsurface crack damage layer because of great grinding force and high brittle of the material. The crack damage layer was investigated in this research. In experiment, it is observed that the surface/subsurface crack damage layer consists of three kinds of cracks: surface micro-cracks, surface macro-cracks and subsurface crack system. To evaluate expediently the degree of damage to the machined components, the index of surface/subsurface crack damage - Dc, is defined.
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Aratani, Shin’ichi. "New crack generation phenomena by crack collision in 10 mm thick tempered glass". Strength, Fracture and Complexity 14, nr 1 (20.10.2021): 45–57. http://dx.doi.org/10.3233/sfc-210280.
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High speed photography by Caustics method using Cranz–Schardin camera was used to study crack propagation and divergence in thermally tempered glass. Tempered 10 mm thick glass plates were used as a specimen. New crack generation by two crack collision was observed. Regarding the presence/absence of new cracks, the dependence of the two cracks on the collision angle was confirmed. Considering that it is based on the synthesis of stress 𝜎CR generated at the crack tip, tensile stress necessary for the generation of new cracks could be created.
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Kamaya, Masayuki, i Toshihisa Nishioka. "Finite Element Alternating Method for Interacting Surface Cracks". Solid State Phenomena 120 (luty 2007): 147–53. http://dx.doi.org/10.4028/www.scientific.net/ssp.120.147.
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The finite element alternating method (FEAM), in conjunction with the finite element analysis (FEA) and the analytical solution for an elliptical crack in an infinite solid subject to arbitrary crack-face traction, can derive the stress intensity factor (SIF) of surface cracks by using the FEA results for an uncracked body. In the present study, the FEAM was applied to evaluations of SIF for noncoplanar multiple surface cracks. The SIF was evaluated for two surface cracks of dissimilar size, and three crack of the same size. The results suggested that the interaction is greatly affected by the relative crack size and negligible when the difference in the crack size is large enough, and the interaction can be evaluated by taking into account the adjacent cracks even if there are many cracks around them. Finally, the crack growth simulations were conducted and a possibility of the direct evaluation of influence of interaction between adjacent crack without using the combination rules was revealed.
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Daud, Ruslizam, Ahmad Kamal Ariffin, S. Abdullah, M. S. Abdul Majid i M. A. Rojan. "Mathematical Model of Elastic Crack Interaction and Two-Dimensional Finite Element Analysis Based on Griffith Energy Release Rate". Advanced Materials Research 795 (wrzesień 2013): 587–90. http://dx.doi.org/10.4028/www.scientific.net/amr.795.587.
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Stress shielding interaction effect of two parallel edge cracks in finite body under uniaxial loading is analysed using developed finite element (FE) analysis program. In present study, the stress shielding interaction is formulated as a mathematical model called stress shielding damage (SSD) model. SSD model used to define the combination and re-characterization of crack interaction from multiple cracks to single crack. Focus is given to weak crack interaction state as the crack interval exceed the length of cracks (b>a). The crack interaction factors are evaluated based on Griffith strain energy release rate and mode I SIF usingJ-integral analysis. For validation, the stress shielding factor parameters are compared to single edge crack SIF as a state of zero interaction in a form of crack unification limit (CUL) and crack interaction limit (CIL).
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Kuo, C. H., L. M. Keer i M. P. Bujold. "Effects of Multiple Cracking on Crack Growth and Coalescence in Contact Fatigue". Journal of Tribology 119, nr 3 (1.07.1997): 385–90. http://dx.doi.org/10.1115/1.2833499.
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A three-dimensional fracture analysis is applied to investigate the interaction effects of multiple cracking on the crack growth in contact fatigue and to simulate the process of crack coalescence that leads to pitting failure. The rolling contact fatigue is simulated by a cyclic Hertzian contact loading moving across the surface of an elastic half-space containing several planar cracks. The body force method is applied to determine the three modes of stress intensity factors around the three-dimensional crack fronts. The fatigue crack propagation under contact loading is estimated based on the modified Paris law for mixed mode crack growth. For coplanar cracks, the growth rate increases significantly as the adjacent cracks are very close while parallel cracks appear to constrain the cracks from coalescing. A numerical simulation for the propagation of crack fronts versus contact cycles is shown to agree with the pitting cracks observed in gears.
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Yang, Zheng, Wan Lin Guo, Chun Yong Huo i Yi Wang. "Fracture Appearance Evaluation of High Performance Pipeline Steel DWTT Specimen with Delamination Cracks". Key Engineering Materials 324-325 (listopad 2006): 59–62. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.59.
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The delamination cracks and its effects on the fracture of pipeline steel are investigated experimentally by using of Drop-Weight Tear Test (DWTT). The delamination cracks are produced by the stress perpendicular to the weak interfaces before main crack beginning or accelerating, no new delamination crack is produced during the stabile propagation of fracture. The quantity, splay degree of delamination crack and the space between two delamination cracks are influenced by the stress state of the crack tip at beginning or accelerating point of main crack and the length of delamination crack is influenced by the stress state of the crack tip during the propagation of fracture. The surface of delamination crack is cleavage fracture appearance with large cleavage facet. There is no delamination crack on the brittle fracture surface below the brittle-to-ductile temperature or on the brittle fracture region of mix-mode fracture surface with ductile and brittle region. The part of fracture surfaces with delamination crack ought to be evaluated as the shear area because the delamination cracks are produced only on the ductile fracture surface or on the ductile part of fracture surface.
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Niazi, Hamid, Greg Nelson, Lyndon Lamborn, Reg Eadie, Weixing Chen i Hao Zhang. "Crack Growth Sensitivity to the Magnitude and Frequency of Load Fluctuation in Stage 1b of High-pH Stress Corrosion Cracking". Corrosion 77, nr 6 (8.03.2021): 618–31. http://dx.doi.org/10.5006/3711.
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Pipelines undergo sequential stages before failure caused by high-pH stress corrosion cracking. These sequential stages are the incubation stage, intergranular crack initiation (Stage 1a), crack evolution to provide the condition for mechanically driven crack growth (Stage 1b), sustainable mechanically driven crack propagation (Stage 2), and rapid crack propagation to failure (Stage 3). The crack propagation mechanisms in Stage 1b are composed of the nucleation and growth of secondary cracks on the free surface and crack coalescence of secondary cracks with one another and the primary crack. These mechanisms continue until the stress intensity factor (K) at the crack tip reaches a critical value, known as KISCC. This investigation took a novel approach to study Stage 1b in using precracked compact tension (CT) specimens. Using precracked specimens and maintaining K at less than KISCC provided an opportunity to study crack initiation on the surface of the specimen under plane stress conditions in the presence of a pre-existing crack. In the present work, the effects of cyclic loading characteristics on crack growth behavior during Stage 1b were studied. It was observed that the pre-existing cracks during Stage 1b led to the initiation of secondary cracks. The initiation of the secondary cracks at the crack tip depended on loading characteristics, i.e., the amplitude and frequency of load fluctuations. The secondary cracks at the crack tip can be classified into four categories based on their positions with respect to the primary crack. Low R-ratio cycles generated an evident cyclic plastic zone, where high density of intergranular cracks were formed. The higher the frequency of the low R-ratio cycles, the higher the density of the intergranular cracks forming in the cyclic plastic zone. The crack growth rate increased with an increase in either the amplitude or the frequency of the load fluctuations. The minimum and maximum crack growth rates were 8 × 10−9 mm/s and 4.2 × 10−7 mm/s, respectively, with the R-ratio varying between 0.2 and 0.9, frequency varying between 10−4 Hz and 5 × 10−2 Hz, and at a fixed stress intensity factor of 15 MPa√m. It was found that avoiding rapid and large load fluctuations slowed down crack geometry evolution and delayed the onset of Stage 2. The implication of these results for pipeline operators is that reducing internal pressure fluctuations by reducing the frequency and/or amplitude of the fluctuations can expand Stage 1 and increase the reliable lifetime of operating pipelines.
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Peng, Yanyan, Xiao Cheng, Nan Song, Qi Qin, Xiaoyun Zhang i Manchao He. "Study on Crack Propagation and Coalescence in Fractured Limestone Based on 3D-DIC Technology". Energies 15, nr 6 (9.03.2022): 2007. http://dx.doi.org/10.3390/en15062007.
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To deeply understand the influence of crack inclination angle on crack propagation and coalescence in fractured limestone, uniaxial compression tests were carried out on limestone specimens with prefabricated cracks. The strain field evolution diagram of the failure process of the specimens was obtained using 3D digital image correlation technology (3D-DIC technology). This, in combination with the crack propagation diagram, was used to analyze the entire failure process of the limestone specimens. The test results show that the evolution process of the principal strain field agrees well with the process of crack initiation, propagation, and coalescence. The crack development process is the process of the high strain zones consistently propagating and also the process of micro-cracks appearing, developing, and nucleating to form macro-cracks. With the increase in the parallel crack inclination angle, the stress concentration zone of the intermediate crack transfers from both ends of the crack to the middle. Meanwhile, the coalescing crack type between the parallel crack and the intermediate crack changes from a coexisting tensile crack and tensile-shear crack to a single tensile crack. With the increase in the parallel crack inclination angle, the failure of the fractured limestone specimens changes from simple splitting or tensile failure to the coexistence of tensile-shear fracture and splitting. 3D-DIC technology provides an effective method to study crack propagation and coalescence during rock failure.
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Xu, Yan Hai, i Yong Xiang Zhao. "Modelling the Behavior of Short Fatigue Cracks under Variable Amplitude Loading Using FEM". Key Engineering Materials 353-358 (wrzesień 2007): 985–88. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.985.
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The behavior of short fatigue cracks under variable amplitude loading (VA) was investigated by FEM. The crack closure induced by the crack surface roughness was taken into consideration by using the contact between these crack surfaces. The effects of variable amplitude loading on the performance of short cracks are demonstrated with factors such as grain orientation and misorientation, crack length and the friction efficient between the contacted crack surfaces. Through the two indicators, crack tip opening displacement represented by "CTOD and "CTSD and the plastic strain range of crack tip, the characteristics of short cracks affected by loading blocks are discussed in detail. It is shown from the numerical results that the significance of the design of loading blocks in the fatigue experiments is evident and the performance of short cracks from the variable amplitude loading is more effective due to the closer to practice.
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Lukaszewicz, Mikolaj, Shen Gi Zhou i Alan Turnbull. "Novel Concepts on the Growth of Corrosion Fatigue Small and Short Cracks". Solid State Phenomena 227 (styczeń 2015): 3–6. http://dx.doi.org/10.4028/www.scientific.net/ssp.227.3.
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Corrosion fatigue small, short and long crack growth rates have been determined for a 12Cr steam turbine steel in aerated 300 ppb Cl- + 300 ppb SO42- solution and in air at 90 °C. The crack growth rate for short and long cracks was monitored by direct current potential drop (DCPD) and for the small cracks by combining high resolution optical microscopy and DCPD. Comparison of the fatigue growth rate demonstrated that in solution the short crack growth rate was remarkably enhanced in comparison to long cracks, when the crack size is smaller than 250 μm. This enhancement was attributed to the electrochemical crack size effect associated with greater anodic polarisation of the short crack in such low conductivity solution. However, such enhanced growth was not observed for small cracks, which was rationalised on the basis of additional contribution of current from the pit limiting crack-tip polarisation.
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Chen, Qingfeng, Min Huang i Jingmin Duan. "Experimental Study on the Crack Initiation and Propagation of Unequal Cracks in Rock-Like Materials". Advances in Materials Science and Engineering 2022 (18.10.2022): 1–15. http://dx.doi.org/10.1155/2022/7697952.
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The crack in the rock is a system that coexists with multiscale and interaction cracks, and it is necessary to evaluate the deformation, stability, and strength of rock mass in many engineering projects and the failure of rock are related to the distribution of cracks in the rock. Cracks of different lengths were set in rock-like materials, and uniaxial loading experiments were carried out under 30 test conditions by changing the length of the rock bridge and the short crack as well as the crack angle. During the experiment, a high-speed camera system was used to record the failure process of the specimens. The following conclusions were obtained: when the crack angle is in the range of 30°to 60° with the loading direction, the shorter cracks are more likely to propagate and coalesce. Most of the specimens initiate cracking from the outer tip of the longer crack and the key point of crack instability is the outer tip of the longer crack. The coalescence mode of the cracks is mainly related to the length of the rock bridge length and the crack angle.
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Xiong, Libo, Chunrong Hua, Funing Yang, Dawei Dong i Huajiang Ouyang. "Dynamic Characteristics Analysis of a Coupled Multi-crack Rotor System". Journal of Physics: Conference Series 2184, nr 1 (1.03.2022): 012040. http://dx.doi.org/10.1088/1742-6596/2184/1/012040.
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Abstract This paper establishes a coupled model for multi-crack rotor using Timoshenko beam element with six degrees of freedom, and derives the stiffness matrix in the equations of motion accounting for the coupling between multiple cracks (the interaction between cracks). Then the effects of crack orientation angles (the relative angle between cracks, γ) on dynamic characteristics of the coupled multi- crack rotor near 1/3 and 1/2 subcritical speeds are analysed. The coupling between cracks induces more complex nonlinear dynamic characteristics such as large magnitudes of the super-harmonic components, which can be used as the indicators of early crack and for multi-crack identification. This work has a promotive significance for the application of the model-based method in the field of multi-crack detection of actual rotors.
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Dubourg, M. C., i B. Villechaise. "Analysis of Multiple Fatigue Cracks—Part I: Theory". Journal of Tribology 114, nr 3 (1.07.1992): 455–61. http://dx.doi.org/10.1115/1.2920905.
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This paper analyzes the effects of multiple cracks situated in the contact zone vicinity of an elastic isotropic component, modeled as a half-plane. Friction between the crack faces is taken into account using Coulomb’s law. Straight arbitrarily oriented cracks are considered. Any contact condition can be modeled between the crack faces as well as any loading condition over the half-plane surface, including complete loading cycles. The method has been tested for up to 5 cracks and shows no limitation in crack number. Further, the method is general as no prior assumptions concerning the state of the crack, i.e., the slip-stick-open configurations along the crack are required. The stress intensity factors (SIFs) calculated for two crack configuration are compared with those obtained for single cracks.
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Prakash, R. V. "Fatigue crack growth at stress concentrators under spectrum loading". Journal of Strain Analysis for Engineering Design 40, nr 2 (1.02.2005): 117–27. http://dx.doi.org/10.1243/030932405x7764.
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Fatigue cracks initiate at stress raisers such as notches, discontinuities, and surface defects. Many of the field failures that indicate the presence of a fatigue crack at failure can be traced to crack initiation from one or more crack initiation sites and merger of cracks over a period of service. Substantial service life is spent in the growth of small cracks from an initial size of few micrometres before they coalesce and grow to critical dimensions that cause fracture. This paper summarizes research that was carried out in order to understand the kinetics of crack growth of small cracks at notches under simulated FALSTAFF service loading. This paper also presents a method used to understand crack growth kinetics in a pin-loaded lug joint through a crack-front-mapping technique.
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Bower, A. F. "The Influence of Crack Face Friction and Trapped Fluid on Surface Initiated Rolling Contact Fatigue Cracks". Journal of Tribology 110, nr 4 (1.10.1988): 704–11. http://dx.doi.org/10.1115/1.3261717.
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A two-dimensional model of a surface initiated rolling contact fatigue crack has been developed. The model takes into account the effects of frictional locking between the faces of the crack, and the influence of fluid pressure acting on the crack faces. The model has been used to investigate three possible mechanisms for propagating the cracks: mode II crack growth due to the cyclic shear stresses caused by repeated rolling contact; crack growth due to fluid forced into the crack by the load; and crack growth due to fluid trapped inside the crack. The predictions of the theory are compared with the behaviour of contact fatigue cracks.
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Swapnil Vilas Patil, Mr, Prof Mangesh M. Ghonge i . "Design and Development of Street Crack Detection". International Journal of Engineering & Technology 7, nr 3.8 (7.07.2018): 82. http://dx.doi.org/10.14419/ijet.v7i3.8.15226.
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Automated detection of street cracks is a crucial project. In transportation preservation for driving safety assurance and detection a crack manually is an exceptionally tangled and time excessive method. So with the advance of science and generation, automated structures with intelligence have been accustomed examine cracks instead of people. For crack detection and characterization image processing is used widely. But because of the inhomogeneity along the cracks, the inference of noise with the same texture and complexity of cracks, image processing remain challenging. In this paper, we focused on the system performance and the additional features. System which has crack detection accuracy issue, false detection of crack issue, efficiency issue are solved in this system. For better accuracy in detecting crack and increasing the performance of the system we used the random forest algorithm. This system help to detect and characterized the crack and it find out crack from noise also i.e. it neglect the noise better than existing system. Similarly, proposed method find out the length of the crack width and depth of the crack from image with the help of ground truth image.
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Yang, Bin, Hua Tan, Jia Xi Deng i Chan Pang. "Influences on the Axle Load Stress of the Cement-Concrete Pavement Structure Caused by the Crack or Cutting Crack of the Semi-Rigid Base". Advanced Materials Research 857 (grudzień 2013): 200–203. http://dx.doi.org/10.4028/www.scientific.net/amr.857.200.
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Some horizontal cracks will appear during the strength formation of the semi-rigid base, for the influences of dry shrinkage and temperature shrinkage exist, so the engineers often adopt the manual method of equidistant cutting crack to avoid the irregular cracks. In order to analyse the influences on the axle load stress of the cement-concrete pavement slab which caused by the width and position of the base cracks or cutting cracks, the 3D FEM was used to study them under the different working conditions considering the crack, width and position. By the above research, the results show the existing cracks affect the integrity and continuity of the pavement structure; The crack width has no large influence on the stress of the pavement slab, while the base stress decreases apparently with the increasing width, and it becomes stable finally; The stress of the pavement slab is maximum when the crack or cutting crack is located in the middle, while it's small when the crack or cutting crack is located in the one fourth of the pavement slab.
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Jung, Ju-Yeong, Hyuk-Jin Yoon i Hyun-Woo Cho. "A Study on Crack Depth Measurement in Steel Structures Using Image-Based Intensity Differences". Advances in Civil Engineering 2018 (2018): 1–10. http://dx.doi.org/10.1155/2018/7530943.
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This paper seeks to propose an image-based noncontact testing method in crack depth measurement. To this end, it predicted the crack depth using the intensity values of cracks and verified its validity. To analyze the intensity values of cracks, eight stainless steel specimens with an increase in crack depths ranging from 0 to 17.5 mm at an average of 2.5 mm were fabricated, and a contrast index was attached to the center of the crack of the specimens painted with black matte spray for accurate analysis. Through various experiments, it was found that the intensity values of the cracks which decrease with the depth of the cracks were inductively formulated, and the average error was about 15% when the crack depth predicted by the empirical equation was compared with the actual crack depth. In addition, the validation of the intensity reduction equation obtained by the inductive method was verified, and it was confirmed that the crack depth can be predicted by the intensity value of the crack.
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Ezumie, Tsutomu, i Kenya Ueno. "Interference Effect of Interaction Cracks Investigated by Photoelastic and Caustics Methods". Key Engineering Materials 297-300 (listopad 2005): 1939–44. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.1939.
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The crack, which occurs because of fatigue, should often consider not only the single crack but also plural cracks occurring. In this paper, the material strength when two or more cracks occurred because of fatigue etc. was examined by calculating stress intensity factor K value by using caustics method and the photoelasticity. In general, plural cracks are known KI value decreases compared with the single crack. Therefore, the influence on K value was experimentally examined from the point of the distance between the cracks, the angle, and the crack length and the mode change. As a result, KI value influences destruction in plural in exist only mode I and the mixed mode of mode I and mode Ⅱ like this research cracks. When the crack length becomes long if the distance between the cracks narrows, the decrease of KI value grows. In addition, it has been understood that the decrease of KI value is influenced by a/w on the boundary of d/a=1 (the distance between the cracks is equal to the crack length).
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Zhu, Yong, Ray K. L. Su i Qi Cai Yu. "Initial Crack Propagation Directions of Branched Crack under Tension with Finite Element Analysis". Advanced Materials Research 168-170 (grudzień 2010): 2553–57. http://dx.doi.org/10.4028/www.scientific.net/amr.168-170.2553.
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The initial crack propagation directions of branched cracks under tension are investigated. In this study, the material is assumed to be brittle and deformed linear elastically. The elastic stress fields and stress intensity factors are obtained by using finite element analysis method. Various parameters which including the lengths, the directions and the locations of branched cracks are investigated to study their effects on the crack initiation angles. Three kinds of crack propagation criteria are employed to obtain the crack initiation angles. The effects of crack propagation directions due to the use of different crack initiation criteria are studied and discussed in details.
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Sun, Yazhen, Ting Yan, Changyu Wu, Xiaofang Sun, Jinchang Wang i Xuezhong Yuan. "Analysis of the Fatigue Crack Propagation Process of the Stress-Absorption Layer of Composite Pavement Based on Reliability". Applied Sciences 8, nr 11 (30.10.2018): 2093. http://dx.doi.org/10.3390/app8112093.
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The stress-absorption layer in cement concrete pavement delays the development of reflection cracks and is good at fatigue resistance. Laboratory investigations of the anti-crack performance of the high viscous asphalt sand stress-absorption layer (HVASAL) and rubber asphalt stress-absorption layer (RASAL) were carried out by force-controlled fatigue crack propagation tests, for which three types of overlay structures with three types of pre-crack (i.e., the middle crack, the side crack, and the 45° inclined crack) were designed. A probability model was established to describe the propagation of the fatigue cracks. The fatigue crack propagation, the fatigue life, the crack propagation rate, and the crack propagation mechanism of the three types of overlay structure were compared and analyzed. The results show that the stress-absorption layers have good anti-crack fatigue performance, and that the RASAL is better than the HVASAL. The crack propagation patterns of the three types of overlay structure were found. In the double logarithmic coordinate, the curves of the three types of cracks are straight lines with different intercepts and slopes. The probability model quantifies the relationship between the crack propagation rate and ∆K. The influences of the three types of crack on the fatigue properties of the asphalt overlays are different.