Journal articles on the topic 'Cracks'
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1
Zhang, Yong Shen, and Yan Ying Li. "Research on the Rigidity of Continuous Beam with Equal Span under the Temperature Load." Advanced Materials Research 255-260 (May 2011): 846–50. http://dx.doi.org/10.4028/www.scientific.net/amr.255-260.846.
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Cracks appeared in concrete structure is always concerned in construction engineering. As the cracks appear, the rigidity of structure will descend. So only the combination of slip theory and the non-slip theory could reflect the development of cracks in the course of analysis of cracks development. For axial tension and bending components, stiffness changes before and after cracking. The continuous beam with equal span is analyzed under the temperature load by the finite element method. As the cracks with different space appear, there is an abrupt bending moment with every crack. Different crack spacing, crack steep drop differently. So the wider the crack’s space is, the higher the abrupt bending moment is.
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Liu, Shan Lin, Lu Wang, and Zheng Wang. "Experimental Study on Evolution Process of Short Fatigue Crack in 2A12 Alloy under Complex Stress State." Key Engineering Materials 703 (August 2016): 202–6. http://dx.doi.org/10.4028/www.scientific.net/kem.703.202.
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The fatigue behavior of 2A12 Aluminum alloy was experimentally studied through different annular notched specimens under symmetrical triangle with the frequency of 0.5 Hz. The experimental result showed that the microstructure played an important role during the entire fatigue life of 2A12 Aluminum alloy. The short fatigue crack only initiated due largely to the second-phase particle such as the S phase (Al2CuMg), the θ phase (CuAl2) and especially the black impurity phases debonding from the basal body when the fatigue cycle was sufficient. The cracks propagated separately along the circumferential direction of the notch, crack coalescence and interaction of cracks were not common at early and middle stage of short crack’s fatigue life. Cracks tended to propagate along direction different from the original one after crack coalescence. Surface crack length at early and middle stage of short crack’s fatigue life were presented. These curves showed crack growth rate increased relatively as the reducing of notched radius or the increasing of nominal strain amplitude which implied that geometry and loading conditions were the factors of the crack propagation.
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Stenseng, Arne. "Cracks and Structural Redundancy." Marine Technology and SNAME News 33, no. 04 (October 1, 1996): 290–98. http://dx.doi.org/10.5957/mt1.1996.33.4.290.
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This paper proposes a way to use finite element models to determine the effect of fatigue cracks in ship structures. Cracks of different lengths are modeled and the maximum nodal stress at the crack tip is used to estimate the stress intensity level. The calculated stress intensity factor is substituted into fracture mechanics equations to calculate the rate of crack growth and the critical crack length. The main advantage to calculating the stress intensity factor from an appropriate finite element model is that load redistribution effects are included. Since the ship structure is redundant, load shedding and multiple load paths can significantly reduce the propagation rate and thereby improve the safety of the structure. Including the crack in the finite element model also makes it possible to study the crack's impact on the stress levels in surrounding structure. The method is independent of the cause of structural failure, hence this kind of analysis can be used to investigate the effects of cracks created by fatigue, collision, or grounding damage.
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Cui, Wei, Zhongmin Xiao, Jie Yang, Mi Tian, Qiang Zhang, and Ziming Feng. "Multi-Crack Dynamic Interaction Effect on Oil and Gas Pipeline Weld Joints Based on VCCT." Energies 15, no. 8 (April 12, 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.
5
Jin, Man, and Wen Kui Zheng. "Cloud-Based Recognition Technology for Building Crack." Applied Mechanics and Materials 687-691 (November 2014): 3743–46. http://dx.doi.org/10.4028/www.scientific.net/amm.687-691.3743.
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Problem of identifying building crack is studied to provide technical support for the construction quality. In the building, building crackis an important factor affecting the construction quality. This paper presents a building crack recognition method based on cloud computing. Cloud model is established to pretreat the acquired building image, so as to improve image quality, and perform construction cracks identificationaccording to the processed image. Experimental results show that the improved algorithm for cracks construction identification can improve the recognition accuracy.
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Jin, Man, and Wen Kui Zheng. "Cloud-Based Recognition Technology for Building Crack." Applied Mechanics and Materials 644-650 (September 2014): 4178–81. http://dx.doi.org/10.4028/www.scientific.net/amm.644-650.4178.
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Problem of identifying building crack is studied to provide technical support for the construction quality. In the building, building crackis an important factor affecting the construction quality. This paper presents a building crack recognition method based on cloud computing. Cloud model is established to pretreat the acquired building image, so as to improve image quality, and perform construction cracks identificationaccording to the processed image. Experimental results show that the improved algorithm for cracks construction identification can improve the recognition accuracy.
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Saravani, M., and M. Azizi. "The Investigation of Crack's Parameters on the V-Notch Using Photoelasticity Method." ISRN Mechanical Engineering 2011 (April 14, 2011): 1–6. http://dx.doi.org/10.5402/2011/657819.
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V-notches are the most possible case for initiation of cracks in engineering structure. Cracks on the notch tip can be characterized by opening angle, tip radius, and depth of the V-notch. In this study, the effects of V-notch's opening angle on stress intensity factor and on -stress of the crack have been investigated in detail. Our calculation has been performed in a number of opening angles and various crack lengths in mode I loading using photoelasticity method. We show that as opening angle grows at constant crack's length, SIF and -stress decrease. Furthermore, as the crack's length increases, the V-notch effect diminishes and the crack behavior can be considered as a single-edge crack specimen. Finally, the obtained results were found to be in good agreement with outcome of numerical finite element analysis.
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Liu, Yan, Hong Zhou, Jing Yan Cheng, and Lu Quan Ren. "Influence of Processing Methods on Number and Form of Cracks of Bionic Units on Vermicular Cast Iron." Advanced Materials Research 499 (April 2012): 350–54. http://dx.doi.org/10.4028/www.scientific.net/amr.499.350.
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This paper focuses on the influence of processing methods on the cracks’ number and form of bionic units on the vermicular cast iron. The results show that there have already been cracks on the bionic units’ surface, and the crack number increases with the thermal cycles. The crack’s form on bionic units processed in air is tree-like structure, and that of bionic units processed in water is network structure. The twice laser process and the electro-pulsing treatment can effectively reduce the crack number of the bionic units processed in water, without changing the form.
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Chekunaev, Nikolay I. "Steady-State Crack Propagation in Stressed Elastic Solid." Key Engineering Materials 462-463 (January 2011): 495–500. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.495.
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A crack, symmetrically propagating in elastic material, was considered as superposition of surface Rayleigh waves. The self-similar growth of face loaded crack was considered in detail. Exact expressions of deformation and stress fields in the crack’s surrounding were found and asymptotic behavior of stress near cracks’ tips was also obtained. A condition that determines the crack’s velocity of self-similar propagation was found.
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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, no. 4 (October 1, 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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Morris, W. L., and M. R. James. "Small Cracks and the Transition to Long Cracks." MRS Bulletin 14, no. 8 (August 1989): 18–24. http://dx.doi.org/10.1557/s0883769400061923.
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The propagation of small fatigue cracks differs considerably from that of long cracks in the same material. Small cracks tend to grow more rapidly than would be expected from long-crack data. Following Suresh and Ritchie, cracks are small when (1) their length is small compared to the scale of local plasticity (a linear elastic fracture mechanics, LEFM, limitation); (2) their length is small compared to microstructural dimensions (a continuum mechanics limitation); or (3) they are merely physically small. The importance of understanding the anomalously rapid growth of small cracks has been the subject of recent reviews and two specialized conferences. The impact of small cracks on component design is to force the design of highly conservative structures.Many investigators have tried to correct LEFM to account for crack shortness. Since the early work of Kitagawa and Takahashi and Smith showing the limitations of LEFM, many procedures to modify, correct, or replace LEFM have been proposed to predict short-crack growth rates. These include mechanisms based on crack closure stress and crack deflection, elastic-plastic approaches such as theJintegral, or simply semi-empirical approaches. These methods have been reasonably successful when the crack length is a few times that of the relevant micro-structural size.
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Cui, Jintai, Huifang Li, Zhiwei Wu, and Caifu Qian. "Calculation of Stress Intensity Factor for Annular Double Cracks on Inner Surface of Pipeline." Coatings 14, no. 6 (June 12, 2024): 744. http://dx.doi.org/10.3390/coatings14060744.
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Cracks in engineered pipelines often appear in the form of multiple cracks or crack clusters with interactions between them. It is important to study the interaction between cracks if the pipeline crack cluster is to be evaluated in terms of equivalence and safety assessment. In this paper, based on FRANC3D crack analysis software, the interaction between circumferential parallel double cracks on the inner surface of pipelines was investigated, the factors affecting the interaction were examined, and the empirical equations for calculating the stress intensity factor (SIF) of double cracks was proposed. The results show that if there is no bias between the double cracks, the crack leading edge is shielded, but if there is offset between the double cracks, the crack leading edge is subjected to different interactions at different locations. The distal end of the cracks is generally strengthened, while the proximal end of the cracks is probably more shielded. The interaction effects between cracks are dependent on their relative positions rather than the pipe size or concerned crack size. According to the numerical simulation, boundaries for shielding or enhancing interactions were obtained, and the stress intensity factor calculation equations were fitted.
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Han, Zhichao, Caifu Qian, and Huifang Li. "Investigation of the Enhancement Interactions between Double Parallel Cracks on Fatigue Growth Behaviors." Materials 13, no. 13 (July 1, 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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Liu, Taoying, Ping Cao, and Hang Lin. "Evolution Procedure of Multiple Rock Cracks under Seepage Pressure." Mathematical Problems in Engineering 2013 (2013): 1–11. http://dx.doi.org/10.1155/2013/738013.
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In practical geotechnical engineering, most of rock masses with multiple cracks exist in water environment. Under such circumstance, these adjacent cracks could interact with each other. Moreover, the seepage pressure, produced by the high water pressure, can change cracks’ status and have an impact on the stress state of fragile rocks. According to the theory of fracture mechanics, this paper discusses the law of crack initiation and the evolution law of stress intensity factor at the tip of a wing crack caused by compression-shear stress and seepage pressure. Subsequently, considering the interaction of the wing cracks and the additional stress caused by rock bridge damage, this paper proposes the intensity factor evolution equation under the combined action of compression-shear stress and seepage pressure. In addition, this paper analyzes the propagation of cracks under different seepage pressure which reveals that the existence of seepage pressure facilitates the wing crack’s growth. The result indicates that the high seepage pressure converts wing crack growth from stable form to unstable form. Meanwhile, based on the criterion and mechanism for crack initiation and propagation, this paper puts forward the mechanical model for different fracture transfixion failure modes of the crag bridge under the combined action of seepage pressure and compression-shear stress. At the last part, this paper, through investigating the flexibility tensor of the rock mass’s initial damage and its damage evolution in terms of jointed rock mass's damage mechanics, deduces the damage evolution equation for the rock mass with multiple cracks under the combined action of compression-shear stress and seepage pressure. The achievement of this investigation provides a reliable theoretical principle for quantitative research of the fractured rock mass failure under seepage pressure.
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Guan, Lu. "Analytical Solution for the Circular Orifice Problem with Four-Cracks." Applied Mechanics and Materials 778 (July 2015): 10–17. http://dx.doi.org/10.4028/www.scientific.net/amm.778.10.
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Using the method of complex analysis, the paper investigates the plane elasticity problem of circular orifices with four-cracks through conformal mapping, and provides an exact analytical solution for the crack-tip stress intensity factor (SIF). From this we have simulated circular orifices with three-cracks, symmetrical four-cracks, asymmetrical collinear double-cracks, and symmetrical collinear double-cracks; as well as the crack problems of asymmetrical cross-shaped cracks, symmetrical cross-shaped cracks, and T-shaped cracks.
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Le, Chengjun, Xuhua Ren, Haijun Wang, and Shuyang Yu. "Experimental and Numerical Study on the Failure Characteristics of Brittle Solids with a Circular Hole and Internal Cracks." Materials 15, no. 4 (February 14, 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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Shen, Jane-Sang, Julie P. Harmon, and Sanboh Lee. "Thermally-induced Crack Healing in Poly(Methyl Methacrylate)." Journal of Materials Research 17, no. 6 (June 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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Kamaya, Masayuki. "Evaluation of Fatigue Crack Growth of Interacting Surface Cracks." Advanced Materials Research 33-37 (March 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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Wang, Jianming, Zhonghui Chen, and Lingfan Zhang. "Unloading-Induced Crack Propagation of Two Collinear Unequal Length Flaws in Brittle Rocks." Geofluids 2020 (June 5, 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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Wang, Yingying, Cong Wang, Guoheng Liu, Chong Zhang, and Jianchang Li. "An Assessment Method of Sealing Performance and Stress Intensity Factors at Crack Tip of Subsea Connector Metal Sealing Rings." Energies 15, no. 13 (June 26, 2022): 4680. http://dx.doi.org/10.3390/en15134680.
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Subsea connectors are of a critical part for the sealing of subsea production systems. The working environment makes cracks initiate easily on subsea connector sealing rings. In order to ensure the safety and reliability of the sealing rings, it is necessary to study the crack’s influence on them. In this study, the main parameters that may influence stress intensity factors at crack tip are discussed. The sealing requirements of the subsea connector metal sealing rings were conducted. A finite element model was established to obtain the maximum equivalent stress and maximum equivalent plastic strain of crack-free sealing ring. Meanwhile, the influence of crack depths, crack positions, and crack angles on the sealing performance in preload and operating states was simulated through changing XFEM crack’s parameters in ABAQUS software, as well as their influence on stress intensity factors at the crack tip. The research shows that although the cracks have little effect on the sealing performance of sealing rings in the early stage, the stress intensity factors increase with the crack depths. Long-term use leads to crack propagation, structure breakage, and sealing failure. The research results are of some reference value for improving the safety and reliability of subsea connectors in practical engineering applications.
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Ren, Xu Dong, T. Zhang, Yong Kang Zhang, Da Wei Jiang, and Kang Min Chen. "Analysis of 7050 Aluminum Alloy Crack Growth by Laser Shock Processing." Advanced Materials Research 97-101 (March 2010): 3852–56. http://dx.doi.org/10.4028/www.scientific.net/amr.97-101.3852.
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Cracks were prefabricated on compact tension specimen of 7050 Aluminum alloy, which was laser shock processing(LSP) once and three times. The whole crack initiation process, distribution and size evolution on aluminum alloy was studied with replica technique and through optical microscope. It was found that without LSP, small cracks initiated at the grain boundary and grew quickly. The cracks continued growing in depth. The growth of short cracks had the trend of stop-and-go oscillation, the crack data were relatively scattered, and short cracks had short average length and grew earlier. After LSP, surface residual compressive stress restrained to the trend of crack origins where crack origins would form most easily; after origination, cracks initiated towards the processed region, but stop temporarily if encountering great resistance, and might generate additional crack origins; Moreover, the higher the level of stress created by LSP was, the fewer cracks initiated.
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MOHAMED, Hassan Idow, and Mustafa ALAS. "The Classification of Asphalt Pavement Crack Images Based on Beamlet Transform." Eurasia Proceedings of Science Technology Engineering and Mathematics 26 (December 30, 2023): 532–40. http://dx.doi.org/10.55549/epstem.1411085.
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Pavement cracking is a common road infrastructure issue which significantly affects road performance, safety and longevity. This article employed a Beamlet Transform algorithm to detect and classify different types of flexible asphalt concrete pavement cracks. Additionally, a dedicated crack segmentation network was employed for precise segmentation of pavement crack. This approach incorporates advancements that has improve precision in crack classification and segmentation. Based on the results of the beamlet transform, significant improvements in the gray scale representation of crack, enhanced crack detection, reduced noise in crack images and a more precise measurement of cracks length were achieved. Computations were performed to determine the length of linear cracks and the area of block cracks. A total of 1000 pavement images were used for training and testing the accuracy of asphalt pavement crack detection and classification models. The research results showed that block cracking, alligator cracking, transverse cracking, and longitudinal cracking can all be recognized with a remarkable accuracy. Alligator cracks and block cracks achieved detection rates more than 90%, while detection rates for the longitudinal and transverse cracks reached more than 95% accuracy.
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Gao, Ruipeng, Mengmeng Liu, Bing Wang, Yiran Wang, and Wei Shao. "Influence of Stress Intensity Factor on Rail Fatigue Crack Propagation by Finite Element Method." Materials 14, no. 19 (September 30, 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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NEAMAH, HAYDER FANOOS. "ANALYSIS OF APPROXIMATED CURVED CRACKS IN HOMOGENEOUS AND GRADED MATERIALS." Journal of Engineering 15, no. 2 (June 1, 2009): 3777–92. http://dx.doi.org/10.31026/j.eng.2009.02.18.
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In this paper two stages of analysis are studied. In stage I, the influence of crack shape on thecrack-tip stresses, critical loads and subsequent propagation direction is investigated via a simpleanalytical model for cracks in homogeneous materials. This model is verified through finite elementsimulations using ANSYS. It is demonstrated that accurate predictions of mechanical energy releaserate and crack deflection angle may be obtained from a smaller number of crack shape parameters.In stage II, this concept is extended to curved cracks in functionally graded materials (FGMs).It iscommon that analytical and computational models of fracture in FGMs have focused almostextensively on straight cracks. If it can be demonstrated that straight cracks give an adequateapproximation of curved cracks in graded materials, then the existing solutions for straight cracksprovide a sufficient foundation for fracture analysis of FGMs. On the other hand, if straight cracksdo not adequately approximate curved cracks in FGMs, then the development of solutions for nonstraight cracks in graded materials is priority. Three cracks shapes approximations are performed tocompare with the actual crack in isotropic and graded materials. The crack propagation and the SIFswere simulated using finite element method. It was concluded that piecewise linear crack shapesprovide a significantly better approximation than straight crack shapes. Accordingly, analyticalsolutions for piecewise linear cracks in graded materials would be very useful, and should be afocus of future work in this area.
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Wang, Qiannan, Guoshuai Zhang, Yunyun Tong, and Chunping Gu. "A Numerical Study on Chloride Diffusion in Cracked Concrete." Crystals 11, no. 7 (June 25, 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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Huang, Y., N. Y. Li, H. W. Zhang, and K. C. Hwang. "Interactive Growth of Multiple Fiber-Bridged Matrix Cracks in Unidirectional Composites." Journal of Engineering Materials and Technology 118, no. 3 (July 1, 1996): 295–301. http://dx.doi.org/10.1115/1.2806809.
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A model is developed for monotonic and cyclic fiber sliding in a fiber-reinforced composite containing multiple cracks. The model is used to study the fatigue growth of multiple cracks in a matrix reinforced with aligned, continuous fibers, where cracks are bridged by frictionally constrained fibers. It is established that the crack tip stress intensity factor is significantly reduced in multiple cracking due to interactions among cracks and among slip zones. The fatigue crack does not grow as fast as that for a single bridged crack or for multiple nonbridged cracks, thus the approach to steady-state crack growth is significantly delayed.
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Wang, Chaolin, Yu Zhao, Yanlin Zhao, and 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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Kuo, C. H., L. M. Keer, and M. P. Bujold. "Effects of Multiple Cracking on Crack Growth and Coalescence in Contact Fatigue." Journal of Tribology 119, no. 3 (July 1, 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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Ezumie, Tsutomu, and Kenya Ueno. "Interference Effect of Interaction Cracks Investigated by Photoelastic and Caustics Methods." Key Engineering Materials 297-300 (November 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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Xu, Yan Hai. "Study on Crack Retardation with the Consideration of Crack Surface Roughness by FEM." Advanced Materials Research 97-101 (March 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.
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Jin, Huijin, Bing Cui, and Ling Mao. "Fatigue Growth Behaviour of Two Interacting Cracks with Different Crack Offset." Materials 12, no. 21 (October 28, 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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Takahashi, Akiyuki, Ayaka Suzuki, and Masanori Kikuchi. "Fatigue Crack Growth Simulation Using S-Version FEM: Application to Interacting Subsurface Cracks." Key Engineering Materials 741 (June 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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Chekunaev, Nikolay I., and Anatoly M. Kaplan. "Acceleration, Retardation and Crack Arrest in Stressed Heterogeneous Structures." Key Engineering Materials 462-463 (January 2011): 506–11. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.506.
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Hamiltonian of the solid body with a crack inside in field of tensile stresses was derived. Hamiltonian equations describe process of crack propagation. A crack propagation was considered in heterogeneous material when in ground matrix present inclusions with work-of-fracture per unit surface significantly greater than in the matrix. Condition of cracks arrest in such system was found and length of path, passed until crack’s stop, was calculated.
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Segarra, M. S., Y. Shimada, A. Sadr, Y. Sumi, and J. Tagami. "Three-Dimensional Analysis of Enamel Crack Behavior Using Optical Coherence Tomography." Journal of Dental Research 96, no. 3 (November 25, 2016): 308–14. http://dx.doi.org/10.1177/0022034516680156.
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The aim of this study was to nondestructively analyze enamel crack behavior on different areas of teeth using 3D swept source-optical coherence tomography (SS-OCT). Ten freshly extracted human teeth of each type on each arch ( n = 80 teeth) were inspected for enamel crack patterns on functional, contact and nonfunctional, or noncontact areas using 3D SS-OCT. The predominant crack pattern for each location on each specimen was noted and analyzed. The OCT observations were validated by direct observations of sectioned specimens under confocal laser scanning microscopy (CLSM). Cracks appeared as bright lines with SS-OCT, with 3 crack patterns identified: Type I – superficial horizontal cracks; Type II – vertically (occluso-gingival) oriented cracks; and Type III – hybrid or complicated cracks, a combination of a Type I and Type III cracks, which may or may not be confluent with each other. Type II cracks were predominant on noncontacting surfaces of incisors and canines and nonfunctional cusps of posterior teeth. Type I and III cracks were predominant on the contacting surfaces of incisors, cusps of canines, and functional cusps of posterior teeth. Cracks originating from the dental-enamel junction and enamel tufts, crack deflections, and the initiation of new cracks within the enamel (internal cracks) were observed as bright areas. CLSM observations corroborated the SS-OCT findings. We found that crack pattern, tooth type, and the location of the crack on the tooth exhibited a strong correlation. We show that the use of 3D SS-OCT permits for the nondestructive 3D imaging and analysis of enamel crack behavior in whole human teeth in vitro. 3D SS-OCT possesses potential for use in clinical studies for the analysis of enamel crack behavior.
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Yuan, Duan Cai, Guo Jin Tang, Yong Jun Lei, and Shang Yang Meng. "Analysis of the Surface Cracks of Long Range Storage Solid Motor Grain." Key Engineering Materials 324-325 (November 2006): 93–96. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.93.
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The surface cracks are easy to occur in the solid missile motor grain. The solid missile motor grain with cracks is very dangerous when it is lunched, because the surface cracks might be propagation unstable when the internal pressure enters the surface cracks cavity. In order to analyze the surface crack of solid motor grain, with accelerated aging test, the variation law of mechanics properties of propellant in the storage period is obtained. Under internal pressure and axial acceleration loading, the three-dimension finite element models of the motor grain are established, three-dimension singular crack elements at the tips of surface cracks are established to simulate the cracks propagation. Along with the surface crack propagation, the stress intensity factors of the crack tips in different storage period are calculated to prejudge its stability respectively. The method and conclusions are available for using solid missile motor grain with surface cracks.
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Goehring, Lucas. "Evolving fracture patterns: columnar joints, mud cracks and polygonal terrain." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, no. 2004 (December 13, 2013): 20120353. http://dx.doi.org/10.1098/rsta.2012.0353.
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When cracks form in a thin contracting layer, they sequentially break the layer into smaller and smaller pieces. A rectilinear crack pattern encodes information about the order of crack formation, as later cracks tend to intersect with earlier cracks at right angles. In a hexagonal pattern, in contrast, the angles between all cracks at a vertex are near 120°. Hexagonal crack patterns are typically seen when a crack network opens and heals repeatedly, in a thin layer, or advances by many intermittent steps into a thick layer. Here, it is shown how both types of pattern can arise from identical forces, and how a rectilinear crack pattern can evolve towards a hexagonal one. Such an evolution is expected when cracks undergo many opening cycles, where the cracks in any cycle are guided by the positions of cracks in the previous cycle but when they can slightly vary their position and order of opening. The general features of this evolution are outlined and compared with a review of the specific patterns of contraction cracks in dried mud, polygonal terrain, columnar joints and eroding gypsum–sand cements.
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Kim, Hyunjun, Eunjong Ahn, Myoungsu Shin, and Sung-Han Sim. "Crack and Noncrack Classification from Concrete Surface Images Using Machine Learning." Structural Health Monitoring 18, no. 3 (April 23, 2018): 725–38. http://dx.doi.org/10.1177/1475921718768747.
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In concrete structures, surface cracks are important indicators of structural durability and serviceability. Generally, concrete cracks are visually monitored by inspectors who record crack information such as the existence, location, and width. Manual visual inspection is often considered ineffective in terms of cost, safety, assessment accuracy, and reliability. Digital image processing has been introduced to more accurately obtain crack information from images. A critical challenge is to automatically identify cracks from an image containing actual cracks and crack-like noise patterns (e.g. dark shadows, stains, lumps, and holes), which are often seen in concrete structures. This article presents a methodology for identifying concrete cracks using machine learning. The method helps in determining the existence and location of cracks from surface images. The proposed approach is particularly designed for classifying cracks and noncrack noise patterns that are otherwise difficult to distinguish using existing image processing algorithms. In the training stage of the proposed approach, image binarization is used to extract crack candidate regions; subsequently, classification models are constructed based on speeded-up robust features and convolutional neural network. The obtained crack identification methods are quantitatively and qualitatively compared using new concrete surface images containing cracks and noncracks.
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de Salles, Lucio Salles, Lev Khazanovich, and José Tadeu Balbo. "Non-Destructive Evaluation of Crack Initiation and Propagation in Continuously Reinforced Concrete Pavements." Transportation Research Record: Journal of the Transportation Research Board 2673, no. 3 (March 2019): 375–85. http://dx.doi.org/10.1177/0361198119833672.
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Transverse crack pattern significantly affects performance of continuously reinforced concrete pavement (CRCP). However, field and modeled crack spacing are based on visual surveys of fully developed transverse cracks visible on the slab surface. Because of the difficulties in detecting incipient cracks in concrete slabs, the effect that such cracks may have on CRCP performance is not currently considered. To address this issue, this paper presents a non-destructive evaluation methodology based on an ultrasonic linear-array system for detection of incipient cracks in CRCP slabs. Two ultrasonic signal-processing techniques were used. First, the Hilbert Transform Indicator was used to identify the presence of damage in the concrete slab indicating potential crack locations. Then ultrasonic image reconstructions of these locations were used to further evaluate crack presence. The methodology was applied to four sections of an experimental short CRCP composed of 50-m long slabs – short in comparison to traditional CRCP. The locations of 58 potential incipient cracks were identified updating the short CRCP crack spacing; 10 of these incipient cracks were confirmed as surface-visible cracks in later visual surveys. Additionally, the methodology shows potential to detect undesired crack patterns such as cluster and Y-cracking before the cracks emerge on the slab surface.
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Tan, Dong Lian, and Wen Hua Yan. "Existing Concrete Girder Bridges' Bending Stiffness Assessment Based on Crack Characteristics Parameters." Applied Mechanics and Materials 226-228 (November 2012): 1581–85. http://dx.doi.org/10.4028/www.scientific.net/amm.226-228.1581.
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A lot of existing reinforced concrete girder bridges appeared cracks in the service phase. Because of the beam's cracks existing, the sectional bending stiffness of the beam decreased. It would reduce the structure's bearing capacity, so the bridges' structure performance urgently needs to be assessed by effective methods, so as to study further measures. In this paper, based on the indoor model test results of four pieces of model beams, regression analysis of the crack characteristics parameters and test's load-displacement curves has been carried out. The relationship between crack characteristics parameters and girder bridge's bending stiffness has been established. The qualitative assessment of structure crack's appearance inspection is transmitted to quantitative assessment, so it will make the assessment more objective and scientific.
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Chandran, A., and M. Neelamegam. "Flexural Behaviour Of Strengthened RC Beams With Multi-Directional Basalt Fibre - Reinforced Polymer Composites." Archives of Civil Engineering 61, no. 1 (March 1, 2015): 45–58. http://dx.doi.org/10.1515/ace-2015-0003.
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AbstractThe paper describes an experimental behaviour of the basalt fibre reinforced polymer composite by external strengthening to the concrete beams. The BFRP composite is wrapped at the bottom face of R.C beam as one layer, two layers, three layers and four layers. The different characteristics - are studied in - first crack load, ultimate load, tensile and compressive strain, cracks propagation, crack spacing and number of cracks etc. To - investigate, total of five beams size 100mm× 160mm×1700mm were cast. One beam is taken as control and others are strengthened with BFRP composite with layers. From this investigation, the first crack load is increased depending on the increment in layers from 6.79% to 47.98%. Similarly, the ultimate load carrying - capacity is increased from 5.66% to 20%. The crack’s spacing is also reduced with an increase in the number of layers
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Guo, Lei, Jinchao Yue, Pan Guo, and Xiaofeng Wang. "Multiple Reflective Cracks in Semirigid Base Asphalt Pavement under Traffic Load Using XFEM." Advances in Civil Engineering 2022 (May 26, 2022): 1–12. http://dx.doi.org/10.1155/2022/9405338.
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This paper built a three-dimensional layered structure model of semirigid base asphalt pavement with single and double transverse reflective cracks based on the Extended Finite Element Method and fatigue fracture theory. The effects of the number of cracks, crack spacing, and crack length on the stress intensity factors (KI, KII, and Keff) under moving vehicle loads were studied. The fracture life of the asphalt pavement structure was calculated based on the Pairs formula. The results demonstrate that reflective cracks in semirigid asphalt pavement are composite cracks of type I and type II under moving vehicle loads, and shear fracture is the main reason for the failure of the base. The damage to the pavement base will be accelerated with the increase in the number of cracks and the length of the cracks. As the distance between the two reflection fractures is closer, the interaction between the cracks has a superimposed enhancement effect on the crack propagation. Compared with the single nonpenetrating crack model, the fatigue life of the nonpenetrating reflective crack in the double crack pavement structure with a crack spacing of 30 cm is reduced by 46.87%. The research on the propagation mechanism of reflective cracks in this paper provides the essential theoretical and numerical basis for the design, construction, working condition evaluation, and maintenance of pavement structures.
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Wan, Duanying, Zheming Zhu, Changlin Zhou, Jianfei Li, Peng Ying, and Meng Wang. "Effect of Pre-Existing Symmetrical Cracks on Propagation Behaviors of a Blast-Induced Crack." Shock and Vibration 2020 (August 7, 2020): 1–16. http://dx.doi.org/10.1155/2020/5892324.
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Defects such as voids, pores, and joints will transform into big scale cracks in the rock of tunnel surrounding under dynamic load like blasting and earthquake. In this paper, three kinds of symmetrical cracks were chosen as an example, and experiments and numerical simulations were conducted to study the effect of symmetric cracks on a blast-induced crack. The relationship of main crack propagation characteristic and distribution of symmetrical cracks was investigated. Some circular specimens using two kinds of material, PMMA and sandstone, including a center hole charged with a detonator and pre-existing cracks were used in the experiments. The test system consisted of an oscilloscope and an ultradynamic strain amplifier and crack propagation gauges (CPGs) were employed in monitoring propagation velocity. AUTODYN code was applied in numerical simulation to investigate the propagation behavior of main crack between symmetrical cracks. Linear equation of state and a modified major principal stress failure criterion was utilized to describe the status of rock material. Based on experimental and numerical results, it can be concluded that (1) the pre-existing symmetrical cracks have arrest effect on main crack propagation, (2) compressive stress in y-direction plays very important roles in crack arrest, and (3) the spacing of parallel cracks has a great influence on crack propagation length and velocity.
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Kim, D. S., and K. H. Lo. "Crack Interaction Criteria in Pressure Vessels and Pipe." Journal of Offshore Mechanics and Arctic Engineering 117, no. 4 (November 1, 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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Behn, Chris, and M. Marder. "The transition from subsonic to supersonic cracks." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2038 (March 28, 2015): 20140122. http://dx.doi.org/10.1098/rsta.2014.0122.
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We present the full analytical solution for steady-state in-plane crack motion in a brittle triangular lattice. This allows quick numerical evaluation of solutions for very large systems, facilitating comparisons with continuum fracture theory. Cracks that propagate faster than the Rayleigh wave speed have been thought to be forbidden in the continuum theory, but clearly exist in lattice systems. Using our analytical methods, we examine in detail the motion of atoms around a crack tip as crack speed changes from subsonic to supersonic. Subsonic cracks feature displacement fields consistent with a stress intensity factor. For supersonic cracks, the stress intensity factor disappears. Subsonic cracks are characterized by small-amplitude, high-frequency oscillations in the vertical displacement of an atom along the crack line, while supersonic cracks have large-amplitude, low-frequency oscillations. Thus, while supersonic cracks are no less physical than subsonic cracks, the connection between microscopic and macroscopic behaviour must be made in a different way. This is one reason supersonic cracks in tension had been thought not to exist.
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Buffière, Jean Yves, Emilie Ferrié, Wolfgang Ludwig, and Anthony Gravouil. "Characterisation and Modelling of the Three Dimensional Propagation of Short Fatigue Cracks." Materials Science Forum 519-521 (July 2006): 997–1004. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.997.
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This paper reports recent results on the characterisation and modelling of the three dimensional (3D) propagation of small fatigue cracks using high resolution synchrotron X ray micro-tomography. Three dimensional images of the growth of small fatigue cracks initiated in two Al alloys on natural or artificial defects are shown. Because of the small size of the investigated samples (millimetric size), fatigue cracks grown in conventional Al alloys with a grain size around 100 micrometers can be considered as microstructurally short cracks. A strong interaction of these cracks with the grain boundaries in the bulk of the material is shown, resulting in a tortuous crack path. In ultra fine grain alloys, the crack shapes tend to be more regular and the observed cracks tend to grow like ”microstructurally long cracks” despite having a small physical size. Finite Element meshes of the cracks can be generated from the reconstructed tomographic 3D images. Local values of the stress intensity factor K along the experimental crack fronts are computed using the Extended Finite Element method and correlated with the crack growth rate.
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Han, Zhichao, Caifu Qian, Lanqing Tang, and Huifang Li. "Determination of the Enhancement or Shielding Interaction between Two Parallel Cracks under Fatigue Loading." Materials 12, no. 8 (April 24, 2019): 1331. http://dx.doi.org/10.3390/ma12081331.
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In this paper, the interactions between two parallel cracks are investigated experimentally and numerically. Finite element models have been established to obtain the stress intensity factors and stress distributions of the parallel cracks with different positions and sizes. Fatigue crack growth tests of 304 stainless steel specimens with the single crack and two parallel cracks have been conducted to confirm the numerical results. The numerical analysis results indicate that the interactions between the two parallel cracks have an enhancement or shielding effect on the stress intensity factors, depending on the relative positions of the cracks. The criterion diagram to determine the enhancement or shielding effect between two parallel cracks is obtained. The changes of the stress fields around the cracks have been studied to explain the mechanism of crack interactions.
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Zhao, Shijun, Qing Zhang, and Limin Liu. "Crack Initiation, Propagation, and Coalescence Experiments in Sandstone Brazilian Disks Containing Pre-Existing Flaws." Advances in Civil Engineering 2019 (January 22, 2019): 1–11. http://dx.doi.org/10.1155/2019/9816067.
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This study aims to investigate the fracture behaviors of cracks and crack systems in Brazilian disk (BD) sandstone specimens under compressive line loading. We conduct a series of rock fracture experiments to investigate crack initiation, propagation, and coalescence in samples with one or more pre-existing flaws under radial compressive stress. The displacements and failure loads of the tested specimens are measured. Experimental results show that there are two main types of cracks growing from the pre-existing flaws: wing cracks and secondary cracks. Both initiate mostly from the tips of the pre-existing flaws and propagate in a stable manner. The results reveal that wing cracks appear first and propagate toward the loading direction. Secondary cracks can form in some multiple pre-cracked cases after wing cracks are already present. We also provide a characterization of the observed crack propagation paths and patterns and discuss the influence of pre-existing crack or crack systems. The results help in investigating the failure mechanisms and mechanical properties of rock or rock-like materials.
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Zhang, Hou Quan, Xing Gen Huang, Li Bing Xue, and Yan Feng Zhang. "Producing Mechanism and Distribution Laws of Remote Cracks for Geotechnical Engineering Structure." Applied Mechanics and Materials 50-51 (February 2011): 869–74. http://dx.doi.org/10.4028/www.scientific.net/amm.50-51.869.
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The purpose of this paper is to investigate producing mechanism and distribution laws of remote cracks for geotechnical engineering structure. The fracture modes of geotechnical material containing a hole with different lateral confining pressure coefficients of 0, 0.05, 0.1, 0.15, 0.25, 0.33, 0.75 and 1 were numerically simulated using RFPA2D (rock failure process analysis) code. The results indicate that under a certain confining pressure, three types of cracks, i.e., primary crack, remote crack and shear crack, can be observed simultaneously in the same sample. When the lateral pressure coefficient is satisfied that 0<k<0.33, the remote cracks in en echelon forms occur in the remote region from the hole. The minimum distance of remote crack from the hole boundary is more than 0.5r (“r” denotes the radius of hole). Remote cracks are resulted by the connection of many micro vertical tensile cracks. The distribution laws of remote cracks are followed by the modulus r (i=1, 2, 3, 4). A primary tensile crack is one necessary condition for the occurrence of remote cracks for circular geotechnical engineering structure.
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Ko, Tae Young, and Sean Seungwon Lee. "Characteristics of Crack Growth in Rock-Like Materials under Monotonic and Cyclic Loading Conditions." Applied Sciences 10, no. 2 (January 20, 2020): 719. http://dx.doi.org/10.3390/app10020719.
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Experiments with gypsum as a model rock material were conducted to investigate the characteristics of crack growth under monotonic and cyclic loading. The specimens had two pre-existing flaws that were placed at different inclination angle, spacing and continuity. Tensile or wing cracks and secondary or shear cracks were observed in both the monotonic and cyclic tests. Wing cracks or tensile cracks initiated at (or near) the tips of flaws and grew parallel to the loading direction. Secondary or shear cracks occurred after initiation of the wing crack and culminated in a final failure. Secondary cracks started at the tips of flaws and propagated in the colinear direction of flaws or perpendicular to loading. Six types of coalescence were observed. Both the monotonic and cyclic tests showed almost identical coalescence types. Coalescence occurred due to the internal shear cracks in specimens containing colinear flaws, while it occurred through combinations of internal shear cracks, internal wing cracks and tension cracks in specimens with non-colinear flaws. Fatigue cracks occurred in tests under cyclic loads. Finally, the subcritical crack growth parameters under monotonic and cyclic loading were determined. Although there were variations in the parameters, the parameter “n” showed similar values.
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Rahman, Khairulanwar Ab, and Khairul Nizam Tahar. "Possibility the use of UAV platform for building’s crack length measurement." IOP Conference Series: Earth and Environmental Science 1051, no. 1 (July 1, 2022): 012006. http://dx.doi.org/10.1088/1755-1315/1051/1/012006.
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Abstract This study uses Unmanned Aerial Vehicle (UAV) as a platform to inspect and monitor a building. It focuses on the inspection of defects in buildings, especially cracks. The aim of this study is to investigate cracks on a building by using UAV photogrammetry. The building was used as an object for this study because there are demands from the building maintenance team to assess cracks on the building in an effective way, where it can help to provide reliable crack information. The selected building for this study was an old apartment building with cracks, making it appropriate for this study. There were several steps and procedure used to capture the image of cracks on the building. From the image captured by using UAV, measurement of the cracks can be identified by using a software. There were also different approaches for the output. First is the 3D model of the building and second is the measurement of cracks. The 3D model of the building was created by using Agisoft Photoscan software for the purpose of getting the overview of building dimension. The measurement of cracks was processed by using PhotoModeler software. The accuracy achieved for this study was ±0.8cm. The result showed that UAV photogrammetry can help the current surveying work, especially on building maintenance. Besides, it can capture the crack’s images from certain altitude. The authors used UAV for smart building monitoring assessment, which was less considered in the past.