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Mohammed, Mohammed Ameen, Zheng Han, and Yange Li. "Exploring the Detection Accuracy of Concrete Cracks Using Various CNN Models." Advances in Materials Science and Engineering 2021 (September 9, 2021): 1–11. http://dx.doi.org/10.1155/2021/9923704.
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Automatic crack detection with the least amount of workforce has become a crucial task in the inspection and evaluation of the performances of concrete structure in civil engineering. Recently, although many concrete crack detection models based on convolutional neural networks (CNNs) have been developed, the accuracy of the proposed models varies. Up-to-date, the issue regarding the convolutional neural network architecture with best performance for detecting concrete cracks is still debated in many previous studies. In this paper, we choose three established open-source CNN models (Model1, Model2, and Model3) which have been well-illustrated and verified in previous studies and test them for the purpose of crack detection of concrete structures. The chosen three models are trained using a concrete crack dataset containing 40,000 images those with 227 × 227-pixel in size. The performance of three different convolutional neural network (CNN) models was then evaluated. The comprehensive comparison result indicates that Model2 which used batch normalization is capable of the best performance amongst the three models as selected for concrete cracks detection, with recording the highest classification accuracy and low loss. In a conclusion, we recommend Model2 for a concrete crack detection task.
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Hu, Guo X., Bao L. Hu, Zhong Yang, Li Huang, and Ping Li. "Pavement Crack Detection Method Based on Deep Learning Models." Wireless Communications and Mobile Computing 2021 (May 15, 2021): 1–13. http://dx.doi.org/10.1155/2021/5573590.
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Severe weather and long-term driving of vehicles lead to various cracks on asphalt pavement. If these cracks cannot be found and repaired in time, it will have a negative impact on the safe driving of vehicles. Traditional artificial detection has some problems, such as low efficiency and missing detection. The detection model based on machine learning needs artificial design of pavement crack characteristics. According to the pavement distress identification manual proposed by the Federal Highway Administration (FHWA), these categories have three different types of cracks, such as fatigue, longitudinal crack, and transverse cracks. In the face of many types of pavement cracks, it is difficult to design a general feature extraction model to extract pavement crack features, which leads to the poor effect of the automatic detection model based on machine learning. Object detection based on the deep learning model has achieved good results in many fields. As a result, those models have become possible for pavement crack detection. This paper discusses the latest YOLOv5 series detection model for pavement crack detection and is to find out an effective training and detection method. Firstly, the 3001 asphalt crack pavement images with the original size of 2976 × 3978 pixels are collected using a digital camera and are randomly divided into three types according to the severity levels of low, medium, and high. Then, for the dataset of crack pavement, YOLOv5 series models are used for training and testing. The experimental results show that the detection accuracy of the YOLOv5l model is the highest, reaching 88.1%, and the detection time of the YOLOv5s model is the shortest, only 11.1 ms for each image.
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Burchill, Madeleine, Simon Barter, Lok Hin Chan, and Michael Jones. "Microstructurally small fatigue crack growth rates in aluminium alloys for developing improved predictive models." MATEC Web of Conferences 165 (2018): 13004. http://dx.doi.org/10.1051/matecconf/201816513004.
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The fatigue or durability life of a few critical structural metallic components often sets the safe and/or economic useful life of a military airframe. In the case of aluminium airframe components, growth rates, at or soon after fatigue crack nucleation are being driven by near threshold local cyclic stress intensities and thus are very low. Standard crack growth rate data is usually generated from large cracks, and therefore do not represent the growth of small cracks (typically <1mm). Discussed here is an innovative test and analysis technique to measure the growth rates of small cracks growing as the result of stress intensities just above the cyclic growth threshold. Using post-test quantitative fractographic examination of fatigue crack surfaces from a series of 7XXX test coupons, crack growth rates and observations of related growth phenomenon in the threshold region have been made. To better predict small crack growth rates under a range of aircraft loading spectra a method by which standard material data models could be adapted is proposed. Early results suggest that for small cracks this method could be useful in informing engineers on the relative severity of various spectra and leading to more accurate predictions of small crack growth rates which can dominate the fatigue life of airframe components.
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Cui, Jin, and Le Le Zhang. "Shakedown and Limit Analysis of Crack Structure Based on Simple Models." Advanced Materials Research 487 (March 2012): 216–20. http://dx.doi.org/10.4028/www.scientific.net/amr.487.216.
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For the loading capability of structures with cracks, the simply calculational models of structures with triangular and rectangular crack have been established, under considering the local rounded area of the crack tip in this paper. The calculation of limit/shakedown domains has been successfully done based on the method of interior point. The influence of some factors such as crack shape and tip size on the loading limit and shakedown of structure has been analyzed and compared, and the results are the trial foundation of intensive study about crack structures.
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De Iorio, Antonio, Marzio Grasso, George Kotsikos, F. Penta, and G. P. Pucillo. "Development of Predictive Models for Fatigue Crack Growth in Rails." Key Engineering Materials 488-489 (September 2011): 13–16. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.13.
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Fatigue failures of rails often occur at the rail foot, since the geometry of this zone gives rise to stress concentrations under service loads or defects during rail manufacture and installation. In this paper, the fatigue behavior of cracks at the web/foot region of a rail is analyzed numerically. Analytical models in the literature for a semi-elliptical surface crack in a finite plate assume that the geometry of the front remains semi-elliptical during the whole propagation phase and the ellipse axes do not undergo translations or rotations. Fatigue tests show that this is not the case for such cracks in rails. A predictive model for crack growth has been developed by assuming an initial small crack at one probable initiation point between the web and foot of the rail in reference to a service condition loading. SIF values have been estimated by means of the finite element method and the plastic radius correction. The results attained were compared with crack growth experimental data.
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Gardner, G. C., and R. J. Tyrrell. "The Flow Resistance of Experimental Models of Naturally Occurring Cracks." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 200, no. 4 (July 1986): 245–50. http://dx.doi.org/10.1243/pime_proc_1986_200_125_02.
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Naturally occurring cracks have rough surfaces which mate in such a fashion as to close the crack completely when the surfaces are pressed together. Experimental work shows that friction factors are given by a Nikuradse type of equation when the crack surfaces are widely spaced. The equation remains applicable as the crack closes until roughness elements from opposing surfaces start to overlap and then an upper limit is achieved. Further reduction in the crack wall separation causes a reduction in the friction factor, which may fall to the level applicable to a smooth-walled tortuous channel. These observations are in accord with theoretical concepts.
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Xu, Denghui, Tongcheng Han, Shengbiao Liu, and Li-Yun Fu. "Effects of randomly orienting penny-shaped cracks on the elastic properties of transversely isotropic rocks." GEOPHYSICS 85, no. 6 (October 21, 2020): MR325—MR340. http://dx.doi.org/10.1190/geo2019-0678.1.
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Fractured reservoirs, as one kind of unconventional reservoirs, have great potential for oil and gas development, and their accurate characterization requires the development of rock-physics models that better simulate real fractured rocks. However, current models focus mainly on the elastic properties of rocks with aligned cracks, while the effects of randomly orienting cracks in transversely isotropic (TI) rocks are poorly studied even though such conditions are frequently encountered in the earth. To address this problem, we have derived models for the elastic properties of rocks with a TI background permeated by 3D inclined cracks and randomly orienting cracks. Then, based on the developed models, we comprehensively study the effects of the two inclination angles (i.e., the dip angle between the cracks and the isotropic plane and the rotation angle between the cracks and the plane normal to the isotropic plane, respectively) of 3D inclined cracks on the elastic properties of TI rocks. We determine that the two angles have significant influences on the elastic coefficients and hence the elastic velocities, and that their influences on the elastic properties are varying in different directions. We further investigate the effects of crack density and aspect ratio of randomly orienting cracks on the elastic properties of the fractured rocks with a TI background. The results show that the increasing crack density and crack aspect ratio reduce the elastic coefficients and velocities for rocks with randomly orienting cracks, in which the relations between compressional-wave velocities and the crack properties (i.e., crack density and crack aspect ratio) are obtained to aid the interpretation of the acquired acoustic exploration data. The proposed new models can greatly improve the modeling capability for the elastic properties of rocks with a TI background permeated by inclined and randomly orienting cracks.
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Langer, J. S. "Models of crack propagation." Physical Review A 46, no. 6 (September 1, 1992): 3123–31. http://dx.doi.org/10.1103/physreva.46.3123.
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Khalkar, V., and S. Ramachandran. "The effect of crack geometry on non-destructive fault detection of EN 8 and EN 47 cracked cantilever beam." Noise & Vibration Worldwide 50, no. 3 (March 2019): 92–100. http://dx.doi.org/10.1177/0957456519834537.
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Since long it has been observed that the size of the crack in structures increases with time, and finally, it may lead to its catastrophic failure. Hence, it is crucial to do the vibration study of cracked structures with regard to vibration-based crack detection and the classification of cracks. So far, vibration-based non-destructive testing method is applied to many spring steel cracked cantilever beams for its possible crack detection. However, the effect of various kinds of practical cracks, that is, V-shaped and U-shaped, on the applicability of these methods has been overlooked. To investigate this issue, artificially cracks are made on the cantilever beam. By free vibration analysis, the effect of crack geometry, crack depth, and crack location on natural frequency is investigated. The natural frequency results obtained from V-shaped and U-shaped models for the same crack configurations are compared with each other and it is revealed that the results are not much sensitive for the change of crack geometry. Hence, it is clear that free vibration-based crack detection method approximately predicts the crack parameters, that is, crack location and crack depth, in structures irrespective of the crack geometry. It is also found that for the same configuration, results of natural frequency are comparatively on the lower side for U-shaped crack models than V-shaped crack models. In this study, the natural frequency of each cracked case is computed by a theoretical method and numerical method and shows good agreement. Finally, it is also observed that structural integrity of a cracked cantilever beam is a function of crack location.
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McClung, R. C. "A Simple Model for Fatigue Crack Growth Near Stress Concentrations." Journal of Pressure Vessel Technology 113, no. 4 (November 1, 1991): 542–48. http://dx.doi.org/10.1115/1.2928793.
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Fatigue crack growth rates are often difficult to predict for short cracks growing near stress concentrations. This paper presents a simple model to predict those growth rates which incorporates the phenomenon of crack closure. Crack opening stresses are shown to change significantly as cracks grow away from notches, and the simple model is designed to describe those changes. The effective stress range ratio, U, is assumed to be dependent on the local stress at the crack tip location in a corresponding uncracked body. The value of U changes with the normalized maximum stress in unnotched bodies, and this dependence can be quantified with elastic-plastic finite element models or simpler modified-Dugdale crack analyses. The local stress distribution is estimated with a Neuber analysis. A semi-empirical stress intensity factor solution is constructed and calibrated with known exact solutions. The crack growth rate is then calculated with the modified Paris law, taking crack growth constants from long crack data. The model is illustrated with a specific case study, the growth of cracks from center notches in an SAE 1026 steel. Experimental crack growth data for notches of different sizes and shapes compare favorably with the calculations. The scheme is contrasted with previous models for notch fatigue cracks. The implications of the simple model for other fatigue design problems are explored, highlighting the simplicity and generality of the model.
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Ass’ad, Jamal M., Robert H. Tatham, and John A. McDonald. "A physical model study of microcrack‐induced anisotropy." GEOPHYSICS 57, no. 12 (December 1992): 1562–70. http://dx.doi.org/10.1190/1.1443224.
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A laboratory study of the effects of oriented pennyshaped inclusions embedded in a solid matrix on the propagation of seismic shear waves shows good agreement with theoretical predictions for some polarizations and poor agreement for polarizations at large crack densities. The models are constructed of solid matrix of epoxy resin with inclusions of thin rubber discs of approximately equal cross-sectional areas. The theoretical basis for these experiments is the theory of Hudson, in which the wavelength is greater than the dimensions of the individual cracks and their separation distance, and the cracks are in dilute concentration. By a pulse transmission method, seismograms were gathered in models free of inclusions and models with inclusions. Seismic measurements of velocity anisotropy, for variations in both a polarization and propagation direction, were performed on physical models with inclusions (cracks) representing five different crack densities (1, 3, 5, 7, and 10 percent). Variations in velocity anisotropy at different crack densities have been evaluated by using Thomsen’s parameter (γ) which relates velocities to their elastic constants, [Formula: see text]. Comparisons between experimental and theoretical results indicate that with the waves polarized parallel to the aligned inclusions, [Formula: see text] agree well with the theoretical model. However, shear waves for the same propagation direction but polarized perpendicular to the plane containing the inclusions [Formula: see text] produced results that agree well with the theory for crack densities up to 7 percent, but disagree for higher crack densities. The deviation of γ at 10 percent crack density suggests that crack‐crack interaction and their coalescence may be observable and could lead to seismic techniques to differentiate between microcracks and larger macrocracks.
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Зернин, Михаил, and Mikhail Zernin. "MODELS OF PHYSICALLY SHORT AND MACROSCOPIC CRACK DEVELOPMENT AND THEIR APPLICATION FOR TIN BASED BABBIT." Bulletin of Bryansk state technical university 2019, no. 5 (June 4, 2019): 4–14. http://dx.doi.org/10.30987/article_5cda64cc1934b2.58791459.
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The stages of fatigue crack development are analyzed. The well-known models of physically short cracks and generalized models describing some stages are shown. A perspectivity of a statistical generalized model offered is shown. The parameters obtained of a cyclic crack resistance of tin-based babbit are presented.
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Fang, Zhi Hua, and Xiang Yang Liu. "The Vibration Modal Displacement Component Method of Identifying the Crack Damage from Simple Supported Beam." Advanced Materials Research 919-921 (April 2014): 355–58. http://dx.doi.org/10.4028/www.scientific.net/amr.919-921.355.
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Engineering structure often produces the crack in the use of a certain year, the crack will decline the stiffness of structure which affects the safety of the structure and the vibration characteristics of structure. A method of identifying the crack damage from beam by using the vibration modal displacement component to strutting the damage identification was put forward, the finite element models of beam which no crack, different position and different depth were established, the damage displacement modal parameters of beams pre and post were calculated, the change rule that the displacement modals variation of transverse component and displacement modals rate of change of axial displacement difference along with the different of the cracks depth and position was analyzed., The calculations showed that the sensitive to the crack position and depth along the crack direction displacement modal transverse component variation and change rate of the axial displacement difference can be used as the basis for crack damage identification of beam.
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Liu, Wen Lin, Ri Jie Yang, Zhi Tao Mu, Shu Yan Liu, and Da Zhao Yu. "Comparison of Crack Growth Models and Crack Closure Effect." Advanced Materials Research 311-313 (August 2011): 822–25. http://dx.doi.org/10.4028/www.scientific.net/amr.311-313.822.
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According to standard test method for fatigue crack growth rates of metallic materials, the crack growth rate of 30NCD16 at three stress ratio (R=0.1, 0.3 and 0.5) were measured. Based on linear elasticity fracture mechanics theory, the fatigue crack growth rate was studied through the nonlinear least squares fitting method. The Paris model parameters at steady growth region and near threshold growth region and NASGRO model parameters were obtained. The effective stress intensity factors versus curves at three stress ratios were determined by crack closure effect. The results show that the Paris equation can preferably describe relations at steady growth region. At this region the model parameter m lies 2.5-4. This result is consistent with the known statistical facts of most metallic materials. NASGRO equation can preferably describe relations from near threshold growth region to high values region. all the test data at three stress ratio was able to correlate and . Crack closure was the major factor in correlating stress ratio and crack growth rate, the degree of crack closure weaken with increasing stress ratio.
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Akramin, M. R. M., M. S. Marizi, M. N. M. Husnain, and M. Shamil Shaari. "Analysis of Surface Crack using Various Crack Growth Models." Journal of Physics: Conference Series 1529 (April 2020): 042074. http://dx.doi.org/10.1088/1742-6596/1529/4/042074.
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Cobb, A. C., J. E. Michaels, and T. E. Michaels. "An integrated approach to local ultrasonic monitoring of fastener hole fatigue cracks." Aeronautical Journal 113, no. 1150 (December 2009): 775–88. http://dx.doi.org/10.1017/s0001924000003432.
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Abstract Ultrasonic nondestructive evaluation methods are routinely used to detect and size fatigue cracks near fastener holes in aircraft structures as a part of scheduled maintenance. In contrast, statistical crack propagation models provide an estimate of the expected fatigue life assuming a known crack size and future fatigue loadings. Here an integrated approach for in situ diagnosis and prognosis of fastener hole fatigue cracks is proposed and implemented that incorporates both ultrasonic monitoring and crack growth laws. The sensing method is an ultrasonic angle beam technique, and cracks are automatically detected from the ultrasonic response. An extended Kalman filter is applied to combine ultrasonically estimated crack sizes with a crack growth law, effectively using the time history of the ultrasonic results rather than only the most recent measurement. A natural extension of this method is fatigue life prognosis. Results from fatigue tests on 7075-T651 aluminium coupons show improved crack size estimates as compared to those obtained from ultrasonic measurements alone, and also demonstrate the capability of predicting the remaining life. This approach for fatigue crack detection, sizing and prognosis is an example of a general strategy for in situ monitoring of structural damage whereby improved results are achieved from the integration of noisy measurements with imperfect crack growth models.
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Okodi, Allan, Yong Li, Roger Cheng, Muntaseer Kainat, Nader Yoosef-Ghodsi, and Samer Adeeb. "Crack Propagation and Burst Pressure of Pipeline with Restrained and Unrestrained Concentric Dent-Crack Defects Using Extended Finite Element Method." Applied Sciences 10, no. 21 (October 27, 2020): 7554. http://dx.doi.org/10.3390/app10217554.
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Mechanical damage in form of dents, cracks, gouges, and scratches are common in pipelines. Sometimes, these damages form in proximity of each other and act as one defect in the pipe wall. The combined defects have been found to be more injurious than individual defects. One of the combined defects in pipeline comprises of a crack in a dent, also known as dent-crack defect. This paper discusses the development of finite element models using extended finite element criterion (XFEM) in Abaqus to predict burst pressure of specimens of API X70 pipeline with restrained and unrestrained concentric dent-crack defects. The models are calibrated and validated using results of full-scale burst tests. The effects of crack length, crack depth, dent depth, and denting pressure on burst pressure are investigated. The results show that restrained dent-crack defects with shallow cracks (depth less than 50% wall thickness) inside dents do not affect pipeline operations at maximum allowable operating pressure if crack lengths are less than 200 mm. Releasing restrained dent-cracks when the pressure is at maximum allowable operating pressure can cause propagation of deep cracks (depth of 50% wall thickness or more) longer than 60 mm. However, only very long cracks (200 mm and higher) propagate to burst the pipe. Cracks of depth less than 20% of wall thickness inside dents formed at zero pressure are not propagated by the maximum allowable operating pressure. Dent-crack defects having dents of depth less than 2% outside diameter of pipe behave as plain cracks if the dents are formed at zero denting pressure but are more injurious than plain cracks if the dents are formed in pressurized pipes.
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Ricoeur, Andreas. "Electrostatic Tractions at Crack Faces Taking into Account Full Piezoelectric Field Coupling." Key Engineering Materials 452-453 (November 2010): 681–84. http://dx.doi.org/10.4028/www.scientific.net/kem.452-453.681.
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Cracks in piezoelectric solids have been subject to fracture mechanical investigations for more than 30 years. In the early years of research, boundary conditions at crack faces have been adopted from pure mechanical systems assuming traction free boundaries. From the electrostatic point of view, cracks have been assumed to be either free of surface charge or fully permeable. Later, limited permeable crack boundary conditions have become popular among the community, however still assuming traction-free crack faces. Recently, the theoretical framework has been extended including electrostatically induced mechanical tractions into crack models yielding a significant crack closure effect. However, these models are still simple neglecting e.g. piezoelectric field coupling. As one consequence, the tractions do not depend on the direction of the electric field with respect to the direction of material polarization. Here, an extended model is presented, entirely accounting for the piezoelectric coupling effect. In this case, the crack closure effect depends on the electric field direction. Additionally, the model yields a new shear effect.
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Božić, Željko, Siegfried Schmauder, and Marijo Mlikota. "Fatigue Growth Models for Multiple Long Cracks in Plates under Cyclic Tension Based on ΔKI, ΔJ-Integral and ΔCTOD Parameter." Key Engineering Materials 488-489 (September 2011): 525–28. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.525.
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This paper presents the implementation of fatigue crack growth power law equations based on ΔK,ΔJ-integral andΔCTODfracture mechanics parameters determined in an FE analysis, to plates with multiple site damage (MSD). Results of fatigue tests with constant amplitude tensile loading carried out on mild steel plate specimens damaged with a single central crack and with three collinear cracks are presented. A relatively larger plastic zone occurred in the crack tip region at higher fatigue crack growth rate (FCGR), from 10-7to 10-6m/cycle. The crack growth models based on the elastic-plastic fracture mechanics (EPFM) parameters describe better fatigue crack growth in this range as compared to the liner elastic models.
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Robinson, Cristopher, Muhammad Arif Beg, Terry Dossey, and W. Ronald Hudson. "Distress Prediction Models for Rigid Pavements for Texas Pavement Management Information System." Transportation Research Record: Journal of the Transportation Research Board 1524, no. 1 (January 1996): 145–51. http://dx.doi.org/10.1177/0361198196152400117.
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The development of distress prediction models for nonoverlaid portland cement concrete (rigid) pavements in Texas for the Texas Department of Transportation's pavement management information system is described. The regression models presented quantitatively predict distress level versus pavement age and are based on pavement condition data maintained by the Center for Transportation Research at The University of Texas at Austin. Models are available for the following distress types in continuously reinforced concrete pavement (CRCP): punchouts, portland cement concrete patches, asphalt patches, serviceability loss as measured by loss of ride score, transverse crack spacing, and crack spalling. Preliminary models are available for the following distresses in jointed concrete pavement and jointed reinforced concrete pavement: patches, corner breaks, faulted joints and cracks, spalled joints and cracks, transverse crack spacing, and slabs with longitudinal cracks. A sigmoidal regression equation was used for all distress types. Modifying factors to CRCP models, which are intended to capture the effects of structural, environmental, and traffic loading variables, are included. The models for CRCP represent a significant improvement from preliminary estimates made in 1993. The improvements to the models were made possible primarily by data collection efforts undertaken in the summer of 1994.
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Hu, Zheyuan, Zheming Zhu, Ruoqi Feng, and Rong Hu. "Stress Intensity Factors for Cracked Finite Plates with Mixed Boundary Condition." ISRN Mechanical Engineering 2013 (October 8, 2013): 1–11. http://dx.doi.org/10.1155/2013/471458.
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The mixed boundary problems for finite plates with one crack or two collinear cracks are studied. Complex stress functions that satisfy the equilibrium equations and compatibility conditions in the cracked plate as well as the stress condition on crack surfaces are presented. Four models, that is, a square plate with one crack or with two collinear cracks and an airfoil-shaped plate with one crack or with two collinear cracks, are established. The unknown coefficients of the complex stress functions are determined by using boundary collocation method (BCM). The effects of crack orientation, crack distance, and boundary condition on SIFs are investigated by combining with BCM, and the corresponding photoelastic experiments are conducted. The test results generally agree with the BCM calculation results.
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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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SUGA, T., S. SCHMAUDER, and G. ELSSNER. "ON THE INTERFACE CRACK MODELS." Le Journal de Physique Colloques 49, no. C5 (October 1988): C5–539—C5–544. http://dx.doi.org/10.1051/jphyscol:1988565.
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Garajeu, Mihail, and Eugen Soós. "Cosserat Models Versus Crack Propagation." Mathematics and Mechanics of Solids 8, no. 2 (April 2003): 189–218. http://dx.doi.org/10.1177/108128603029769.
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Liu, Bang, Zheming Zhu, Ruifeng Liu, Lei Zhou, and Duanying Wan. "Study on the Fracture Behavior of Cracks Emanating from Tunnel Spandrel under Blasting Loads by Using TMCSC Specimens." Shock and Vibration 2019 (May 20, 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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Son, Nguyen Quoc, and Nguyen Truong Giang. "Standard gradient models and crack simulation." Vietnam Journal of Mechanics 33, no. 4 (December 12, 2011): 293–301. http://dx.doi.org/10.15625/0866-7136/33/4/261.
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The standard gradient models have been intensively studied in the literature, cf. Fremond (1985) or Gurtin (1991) for various applications in plasticity, damage mechanics and phase change analysis. The governing equations for a solid have been introduced essentially from an extended version of the virtual equation. It is shown here first that these equations can also be derived from the formalism of energy and dissipation potentials and appear as a generalized Biot equation for the solid. In this spirit, the governing equations for higher gradient models can be straightforwardly given. The interest of gradient models is then discussed in the context of damage mechanics and crack simulation. The phenomenon of strain localization in a time-dependent or time-independent process of damage is explored as a convenient numerical method to simulate the propagation of cracks, in relation with some recent works of theliterature, cf. Bourdin & Marigo [3], Lorentz & al [5], Henry & al [12].
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Hu, Jiang, and Suhua Wu. "Statistical modeling for deformation analysis of concrete arch dams with influential horizontal cracks." Structural Health Monitoring 18, no. 2 (March 10, 2018): 546–62. http://dx.doi.org/10.1177/1475921718760309.
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Several concrete dams all over the world exhibit severe cracks. It is very important to investigate the influence of cracks on the long-term behavior of dam structures to ensure safe operation. The interpretation of measured dam displacements is usually based on statistical hydrostatic-seasonal-time and hydrostatic-thermal-time models. The main purpose of this article is to present a statistical hydrostatic-thermal-crack-time model to interpret displacements of concrete arch dams with influential horizontal cracks. The hydrostatic-thermal-crack-time model is applied to analyze the Chencun dam, an arch–gravity dam with a large-scale horizontal crack on the downstream face. The crack stretches horizontally across most of the dam blocks. Its crack mouth opening displacement had been continually increasing even after reinforcement treatment, accompanied by abnormal deformation characteristics of the arch–cantilever system. A three-dimensional finite element model, containing the pre-existing crack using special gap elements, is built to reproduce the structural response, assess the contribution of the crack on the registered movements, and obtain the relationship between the crack mouth opening displacement and the dam crest displacement. Based on this, the hydrostatic-thermal-CMOD-time model considering crack mouth opening displacement is developed. Compared with the traditional models, the hydrostatic-thermal-crack-time model is expected to provide a better fit accuracy. The results also show that the crack and the corresponding reinforcement measure have a significant effect on the deformation behavior of the dam. This can provide some useful indications for concrete structures with similar problems.
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Lin, X. B., and R. A. Smith. "Direct simulation of fatigue crack growth for arbitrary-shaped defects in pressure vessels." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 213, no. 2 (February 1, 1998): 175–89. http://dx.doi.org/10.1243/0954406991522257.
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An advanced technique has been developed by the authors to predict fatigue crack growth for longitudinal and circumferential planar defects with arbitrary shape in pressure vessels. This is based on the step-by-step integration of an experimental fatigue crack growth law at a set of points along the crack front, enabling the crack shape developed during the fatigue process to be predicted. The stress intensity factors along the crack front are calculated by a three-dimensional finite element method. Automatic regeneration of finite element models for propagating cracks designed for this technique makes the simulation technique highly efficient. In this paper, following a description of the principle of the technique, some typical crack geometries are investigated. These include external and internal surface longitudinal cracks, an embedded longitudinal crack, a twin crack configuration and two circumferential surface cracks. The results obtained are compared with both the widely used ASME XI and BSI PD6493 guidelines, and some discussion on the safe use of the two guidelines is made.
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Guzina, B. B., D. H. Timm, and V. R. Voller. "Crack spacing in strained films." Journal de Physique IV 120 (December 2004): 201–8. http://dx.doi.org/10.1051/jp4:2004120023.
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Consider a thin film resting on a relatively thick substrate. When the substrate is subjected to an axial strain transverse cracks, normal to the direction, of the applied strain may appear in the film. It is observed that, for a given strain, the spacing between such cracks is uniform, with a clearly identifiable characteristic length scale that can be used to provide bounds on the spacing. Further, as the strain is increased, there is a densification of the cracks up to a saturation limit. Beyond the saturation limit additional strain produces no further cracks and the characteristic crack length scale for the given system remains fixed. This paper presents analytical models that can be used to predict the characteristic length scale both at the saturation limit and during the densification process. The models are shown to be applicable across a wide range of length scales; with abilities to determine the crack space length scale in both asphalt pavements (~100m) subjected to a thermal loading and strained ceramic films (~100μm).
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Hoagland, R. G., M. S. Daw, and J. P. Hirth. "Some aspects of forces and fields in atomic models of crack tips." Journal of Materials Research 6, no. 12 (December 1991): 2565–77. http://dx.doi.org/10.1557/jmr.1991.2565.
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This paper examines the stresses and displacement gradients in atomistic models of cracks based on an EAM potential devised for aluminum. Methods for computing these quantities are described. Results are presented for two models differing in terms of the orientations of the crack relative to the crystal, a [100] (010) orientation that behaves in a brittle fashion and a [111] (110) orientation that emits partial dislocations prior to extending. Both models display lattice trapping. The stresses in the brittle crack model are compared with the linear elastic prediction and found to be in remarkably good agreement to within distances of about one lattice parameter of the crack tip and at the free surface where contributions from sources other than strain energy (e.g., surface tension) influence the results. Similar results are observed for the ductile model until dislocation emission occurs. The largest stresses that develop just prior to crack extension or dislocation emission are used to estimate the ratio of theoretical tensile strength to shear strength in this material. Eshelby's conservation integrals, F and M, are also computed. F is found to be essentially contour independent and in agreement with the linear elastic prediction in both models until dislocation emission occurs, at which point a large screening contribution arises from the emitted partials. The contour size dependence of M reveals some interesting features of the crack tip including a slight wobble of the crack tip inside its potential well with changing applied K and the existence of forces acting to move the crack faces apart as blunting occurs.
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Tong, Jie. "Three Stages of Fatigue Crack Growth in GFRP Composite Laminates." Journal of Engineering Materials and Technology 123, no. 1 (February 13, 2000): 139–43. http://dx.doi.org/10.1115/1.1286234.
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Multiple fatigue crack growth behavior has been studied in model transparent GFRP laminates. Detailed experimental observations have been made on the growth of individual fatigue cracks and on the evolution of cracks in off-axis layers in 0/90/±45S and ±45/90S laminates. Three stages of fatigue crack growth in the laminates have been identified: initiation, steady-state crack growth (SSCG), crack interaction and saturation. The results show that SSCG rate is essentially constant under constant load, independent of crack length and crack spacing. Finite element models have been developed and used to calculate the strain energy release rates associated with the off-axis matrix cracking. A correlation has been achieved between fatigue crack growth rates in off-axis layers and the total strain energy release rates.
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Zhang, Xue Yi, Guang Ping Zou, and Hong Liang Li. "Dynamic Stress Concentration of Circular Cavity and Double Linear Cracks in Elastic Medium." Key Engineering Materials 419-420 (October 2009): 825–28. http://dx.doi.org/10.4028/www.scientific.net/kem.419-420.825.
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Sacttering of SH-wave of combined deffectiveness which included single circular cavity and double linear cracks in elastic medium was investigated in detail. Analytic solution of this problem was obtained by Green’s Function method and idea of crack-division at actual position of crack at two times. There were two key steps of this method. First step was to employ a special Green’s Function which was a fundamental solution of displacement field for an elastic space with a cavity in it subjected to out-of-plane harmonic line source force at any point at first. The sceond step was crack-division which was artificially to produce a crack by apllying opposite shear stress caused by incident SH-wave. Distribution of dynamic stress concentration factor (DSCF) at edge of cavity was studied by numerical analysis. Distribution Curves of DSCF of three models were plotted by numerical method in polar coordinate system. Three models were one circular cavity and without crack, one circular cavity and single crack and single circular cavity double cracks. The results were compared and discussed in different incident angle of SH-wave.Conclusion was that the interaction among SH-wave, single cavity and double crack was obvious. Dynamic stress concentration factor varied with angle and distance between cavity and crack.
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Kelliher, Dennis S. "Calculating Energy Release Rate as a Function of Crack Length Using a Multiple-Step Crack Closure Technique in Tire Finite Element Models." Tire Science and Technology 46, no. 3 (July 1, 2018): 130–52. http://dx.doi.org/10.2346/tire.18.460302.
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ABSTRACT When performing predictive durability analyses on tires using finite element methods, it is generally recognized that energy release rate (ERR) is the best measure by which to characterize the fatigue behavior of rubber. By addressing actual cracks in a simulation geometry, ERR provides a more appropriate durability criterion than the strain energy density (SED) of geometries without cracks. If determined as a function of crack length and loading history, and augmented with material crack growth properties, ERR allows for a quantitative prediction of fatigue life. Complications arise, however, from extra steps required to implement the calculation of ERR within the analysis process. This article presents an overview and some details of a method to perform such analyses. The method involves a preprocessing step that automates the creation of a ribbon crack within an axisymmetric-geometry finite element model at a predetermined location. After inflating and expanding to three dimensions to fully load the tire against a surface, full ribbon sections of the crack are then incrementally closed through multiple solution steps, finally achieving complete closure. A postprocessing step is developed to determine ERR as a function of crack length from this enforced crack closure technique. This includes an innovative approach to calculating ERR as the crack length approaches zero.
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Sun, Yongyang, José M. Carcione, and Boris Gurevich. "Squirt-flow seismic dispersion models: a comparison." Geophysical Journal International 222, no. 3 (June 10, 2020): 2068–82. http://dx.doi.org/10.1093/gji/ggaa274.
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SUMMARY The anelastic properties of porous rocks depend on the pore characteristics, specifically, the pore aspect ratio and the pore fraction (related to the soft porosity). At high frequencies, there is no fluid pressure communication throughout the pore space and the rock becomes stiffer than at low frequencies, where the pore pressure is fully equilibrated. This causes a significant difference between the moduli at low and high frequencies, which is known as seismic dispersion and is commonly explained by the squirt-flow mechanism. In this paper, we consider and contrast three squirt-flow dispersion models: the modified Mavko–Jizba model, valid for a porous medium with arbitrary shapes of the pores and cracks, and two other models, based on idealized geometries of spheres and ellipsoids: the EIAS (equivalent inclusion-average stress) and CPEM (cracks and pores effective medium) models. We first perform analytical comparisons and then compute several numerical examples to demonstrate similarities and differences between the models. The analytical comparison shows that when the stiff pores are spherical and the crack density is small, the theoretical predictions of the three models are very close to each other. However, when the stiff pores are spheroids with an aspect ratio smaller than 1 (say, between 0.2 and 1), the predictions of inclusion based models are not valid at frequencies of ultrasonic measurements on rock samples. In contrast, the predictions of the modified Mavko–Jizba model are valid at ultrasonic frequencies of about 106 Hz, which is a typical frequency of laboratory measurements on core samples. We also introduce Zener-based bulk and shear dispersion indices, which are proportional to the difference between the high- and low-frequency stiffness moduli, and are a measure of the degree of anelasticity, closely related to the quality factors by view of the Kramers–Kronig relations. The results show that the three models yield similar moduli dispersion with very small differences when the crack density is relatively high. The indices versus crack density can be viewed as a template to obtain the crack properties from low- and high-frequency velocity measurements.
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Wijerathne, M. L. L., Muneo Hori, T. Okinaka, and Hide Sakaguchi. "Application of PDS-FEM for Simulating 3D Wing Crack Growth." Applied Mechanics and Materials 553 (May 2014): 725–30. http://dx.doi.org/10.4028/www.scientific.net/amm.553.725.
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3D wing crack growth is not a well understood phenomenon, although it is one of the key mechanisms of the failure of brittle materials under compression. Using PDS-FEM, we simulated the growth of 3D wing cracks emerging from pre-existing cracks in blocks of brittle linear elastic solids, under compression. The complex 3D wing crack profiles are reproduced with PDS-FEM, which uses non-overlapping shape functions of conjugate geometries to approximate functions and their derivatives. PDS-FEM provides numerically efficient failure treatment for modeling 3D cracks, making use of the numerous discontinuities in the approximated displacement field. Large scale models with several million elements are used to reproduce the experimentally observed details of wing crack profiles. The bending of crack surfaces at the tip of mode-I regions, extension of wing cracks and the growth of tensile openings or petal cracks at mode-III regions are reproduced, demonstrating the applicability of PDS-FEM for studying 3D wing crack growth phenomena.
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Khalkar, V., and S. Ramachandran. "The effect of crack geometry on stiffness of spring steel cantilever beam." Journal of Low Frequency Noise, Vibration and Active Control 37, no. 4 (April 4, 2018): 762–73. http://dx.doi.org/10.1177/1461348418765959.
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The survival of the crack in structures always keeps the structure away from performing well in applications due to significant changes in its dynamic response. It has been observed that in service the size of the crack in structures increases with time and finally it leads to its catastrophic failure. Hence it is crucial to do the vibration study of cracked beams in regard of free vibration-based crack detection and its crack classification. Until now the vibration-based nondestructive testing methods are applied to many spring steel cracked cantilever beams for its possible crack detection. However, the effect of various kinds of practical cracks, i.e. V-shaped, U-shaped and rectangular-shaped open cracks, on the applicability of these methods has been overlooked. In order to investigate this issue, artificially cracks are made on the cantilever beam. By free vibration analysis, the effect of crack geometry, crack depth, and crack location on the beam stiffness is investigated. In this study, the stiffness of each cracked case is computed by the deflection methods and vibration methods to ensure the strong validation. The stiffness results obtained from V-shaped, U-shaped and rectangular-shaped crack models for the same configuration are compared with each other and it is found that the results of the stiffness are comparatively more sensitive to U-shaped crack models. Through vibration study, it is found that spring steel structures are slightly sensitive to the change in crack geometries as long as the vibration characteristics are concerned. Hence, it is obvious that free vibration-based crack detection method can satisfactorily predict the location and depth of the crack in any spring steel structures irrespective of the crack geometries. Apart from this, it is also found that for the same configurations, EN 8 and EN 47 cracked cantilever beams give the identical structural integrity or structural stability property for all the cracked cases. Lastly, it is also found that as the crack depth increases by keeping the crack location constant, the stiffness of the beam decreases.
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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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Rabczuk, Timon. "Computational Methods for Fracture in Brittle and Quasi-Brittle Solids: State-of-the-Art Review and Future Perspectives." ISRN Applied Mathematics 2013 (March 20, 2013): 1–38. http://dx.doi.org/10.1155/2013/849231.
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An overview of computational methods to model fracture in brittle and quasi-brittle materials is given. The overview focuses on continuum models for fracture. First, numerical difficulties related to modelling fracture for quasi-brittle materials will be discussed. Different techniques to eliminate or circumvent those difficulties will be described subsequently. In that context, regularization techniques such as nonlocal models, gradient enhanced models, viscous models, cohesive zone models, and smeared crack models will be discussed. The main focus of this paper will be on computational methods for discrete fracture (discrete cracks). Element erosion technques, inter-element separation methods, the embedded finite element method (EFEM), the extended finite element method (XFEM), meshfree methods (MMs), boundary elements (BEMs), isogeometric analysis, and the variational approach to fracture will be reviewed elucidating advantages and drawbacks of each approach. As tracking the crack path is of major concern in computational methods that preserve crack path continuity, one section will discuss different crack tracking techniques. Finally, cracking criteria will be reviewed before the paper ends with future research perspectives.
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Lin, Jianjun, Huisu Chen, Zhong Lv, and Yujiang Wang. "Analytical solution on dosage of self-healing capsules in materials with two-dimensional multi-shaped crack patterns." Science and Engineering of Composite Materials 25, no. 6 (November 27, 2018): 1229–39. http://dx.doi.org/10.1515/secm-2017-0256.
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AbstractThis article presents a numerical method for determining the dosage of pre-embedded capsules in self-healing materials with complex crack patterns. The crack distribution on the surface of materials is simplified into a two-dimensional (2D) multi-shaped geometrical structure composed of triangles, rhombuses, and hexagons with specified area fractions, and further decomposed into three separate mono-shaped crack systems. Then, the dosage of capsules required to heal the cracks in each mono-shaped crack system is computed. According to the area fraction of each mono-shaped polygon in the whole system, the integrated models of crack-hitting probability by the capsules and the capsule dosage for the multi-shaped crack system are derived. The analytical results reveal that the dosage of capsules significantly depends on the spatial distribution of the cracks and the ratio of the capsule length to the crack size. For a certain fixed crack pattern, the size and dosage of capsules will strongly affect crack healing efficiency.
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Qiu, Bao Xiang, Zeng Liang Gao, Li Juan Lu, Xiao Gui Wang, and Y. Y. Jiang. "Two Models for Predicting Fatigue Crack Growth." Advanced Materials Research 44-46 (June 2008): 917–24. http://dx.doi.org/10.4028/www.scientific.net/amr.44-46.917.
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In this investigation two fatigue crack growth models based on the different physical assumptions were systematically analyzed. One model makes use of the size of the stable damage distribution zone near crack as the major contributor to the fatigue crack growth. This model is based on the concept that a material point failures and a new crack will form when the fatigue damage value of the material point reach the critical damage. The other model supposes that fatigue growth can be described as a process with sequentially breaking small volume elements behind the crack tip. The fatigue crack growth can be regarded as successive crack re-initiation over a critical distance. The fatigue crack growth rate can be determined as the ratio of the critical distance to the average life within critical distance. Both models use macro parameter to describe the microscopic mechanism. An elastic-plastic finite element analysis (FEA) was used to obtain the detailed stress-strain history of the notched component with a detailed consideration of the cyclic plasticity of the material using a robust cyclic plasticity model. The fatigue damage distribution and the average damage within the critical distance near the crack tip can be obtained by combining the fatigue damage parameter with the stress strain distribution from the finite element analysis. These two models were evaluated using the experimental results obtained from the crack grow experiments on compact specimens made from 16MnR. The predicting results using these two models correlate well with the experimental data. The results show that two models can well describe the notch effect on the fatigue crack growth.
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Shen, Xin Pu, and Xiao Chun Wang. "Comparative Studies on Mixed Mode Cohesive Interface Cracks of Quasi-Brittle Materials." Applied Mechanics and Materials 584-586 (July 2014): 1780–88. http://dx.doi.org/10.4028/www.scientific.net/amm.584-586.1780.
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Concerning on the modelling of quasi-brittle fracture process zone at interface crack of quasi-brittle materials and structures, typical constitutive models of mixed mode interface cracks were compared. Numerical calculations of the constitutive behaviours of selected models were carried out at local level. Aiming at the simulation of quasi-brittle fracture of concrete-like materials and structures, the emphases of the qualitative comparisons of selected cohesive models are focused on: (1) the fundamental mixed mode fracture behaviours of selected interface crack models; (2) dilatancy properties of the selected models under mixed mode fracture loading conditions.
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Graciani, Enrique, Vladislav Mantič, and Federico París. "Effect of Friction on the Size of the Near-Tip Contact Zone in a Penny-Shaped Interface Crack." Key Engineering Materials 618 (July 2014): 179–201. http://dx.doi.org/10.4028/www.scientific.net/kem.618.179.
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Relations between different solutions of an interface crack in a neighborhood of the crack tip given by the open model, frictionless and frictional contact models of interface cracks are analyzed numerically for a penny-shaped interface crack subjected to remote tension. A new analytic expression for the size of the near-tip contact zone in presence of Coulomb friction between crack faces is proposed in the so-called case of the contact zone field embedded in the oscillatory field.
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Meng, Shang Yang, Jun Li Han, Chang Shun Liu, and Xiao Hong Yang. "Stability Analysis of Cracks in the Stress-Release Boot of Solid Rocket Motor Grain with J-Integral." Advanced Materials Research 328-330 (September 2011): 1210–15. http://dx.doi.org/10.4028/www.scientific.net/amr.328-330.1210.
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The stress-release boot is always used in the fore and rear of SRM grain to relief stress-strain concentration under thermal loading. Since the debonded crack in the stress-release boot may be propagation unstable when the internal pressure entered the debonded crack cavity, the SRM with debonded cracks is very dangerous when it is lunched. So the stability analysis of the debonded cracks is very important to evaluate the defect grain structure integrity. In order to investigate the stability of debonded cracks in the stress-release boot of SRM grain during ignition pressurization, three-dimension (3-D) viscoelastic finite element models of the SRM grain with debonded cracks are established. The 3-D singular crack elements at the tips of cracks are developed to simulate the stress-release boot debonded crack propagation. And all the singular crack elements are included in the 3-D J-integral loop surface to improve the calculation precision. Along with the debonded crack propagation, the 3-D J-integrals of the debonded crack tips are respectively calculated to prejudge its expanding trend. The results show that the most dangerous situation will occur in the fore stress-release boot debonded cracks during the rocket being launched.
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Li, Si Qi, and Yin Bai. "Overview of Numerical Simulation Model of Mesoscopic Concrete Crack." Applied Mechanics and Materials 744-746 (March 2015): 1443–47. http://dx.doi.org/10.4028/www.scientific.net/amm.744-746.1443.
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Through a number of literature analysis and research, this paper investigates the reviews and comparison under the meso model for numerical simulation of crack in a finite element model (FEM), including discrete fracture model, smeared crack model, fracture mechanics crack model,bond crack model. Studies show that: compared to other fracture models , smeared crack model by eliminating the need to change the unit type and re-division unit grid computing simple and widely used for treatment of concrete cracks in finite element method, the author cites a using smeared crack model example that are discussed in the paper.
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Mughrabi, Haël. "Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2038 (March 28, 2015): 20140132. http://dx.doi.org/10.1098/rsta.2014.0132.
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In this survey, the origin of fatigue crack initiation and damage evolution in different metallic materials is discussed with emphasis on the responsible microstructural mechanisms. After a historical introduction, the stages of cyclic deformation which precede the onset of fatigue damage are reviewed. Different types of cyclic slip irreversibilities in the bulk that eventually lead to the initiation of fatigue cracks are discussed. Examples of trans- and intercrystalline fatigue damage evolution in the low cycle, high cycle and ultrahigh cycle fatigue regimes in mono- and polycrystalline face-centred cubic and body-centred cubic metals and alloys and in different engineering materials are presented, and some microstructural models of fatigue crack initiation and early crack growth are discussed. The basic difficulties in defining the transition from the initiation to the growth of fatigue cracks are emphasized. In ultrahigh cycle fatigue at very low loading amplitudes, the initiation of fatigue cracks generally occupies a major fraction of fatigue life and is hence life controlling.
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Fang, Zhi Hua, and Xiang Yang Liu. "Research on Recognition Methods of Crack Damage from Beam Based on the Vibration Modal." Applied Mechanics and Materials 578-579 (July 2014): 1024–27. http://dx.doi.org/10.4028/www.scientific.net/amm.578-579.1024.
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Structural crack damage will degrade its carrying capacity, and affect the security of the structure. Thus early detection of crack damage is a guarantee of the structure safety. Cracks can change the vibration characteristics of the structure, therefore we proposed a method of identifying the crack damage based on the vibration modal. Take both ends fixed beam as an example, through establish the finite element models of crack-free beam and the crack beam with different location and different depth, we calculate the displacement modal parameters of beam before and after the damage, analyze the variation law of displacement modal horizontal component of change and displacement modal Axial displacement difference rate of change varies with crack depth and location, results show that the variation of displacement modal horizontal component and the change rate of displacement modal Axial displacement difference along crack direction are sensitive to cracks location and depth, these can be used as a basis for identification of beam’s crack damage.
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Nair, Shantikumar V., and Tsung-Ju Gwo. "Role of Crack Wake Toughening on Elevated Temperature Crack Growth in a Fiber Reinforced Ceramic Composite." Journal of Engineering Materials and Technology 115, no. 3 (July 1, 1993): 273–80. http://dx.doi.org/10.1115/1.2904218.
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Theoretical models were developed to predict the nature of the elevated temperature failure behavior in composites containing bridged cracks both for the case where crack front creep is absent (brittle regime) and for the case where a frontal creep process zone is present (ductile regime). The nature of the thermally activated time-dependent bridging of matrix cracks was first briefly reviewed from an earlier study and then applied to the case where crack front creep was present. Stable crack growth was predicted both in the presence and absence of crack front creep after an initial delay period, or initiation, which depends on crack size and wake parameters, such as, fiber diameter, volume fraction and interface properties. The dependence of the initiation time and crack growth rates on flaw size and wake parameters as well as on composite microstructure was derived both for the presence and absence of crack front creep. The implications of the results for elevated temperature composite component design are discussed.
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Spagnol, Joseph, Helen Wu, and Chunhui Yang. "Application of Non-Symmetric Bending Principles on Modelling Fatigue Crack Behaviour and Vibration of a Cracked Rotor." Applied Sciences 10, no. 2 (January 20, 2020): 717. http://dx.doi.org/10.3390/app10020717.
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Many studies on cracked rotors developed crack breathing models that assume that the neutral axis of bending always remains horizontal for simplification. These models may generate significant discrepancies and thus there is a need to develop more sophisticated models to look into the shifting of the neutral axis for a cracked rotor. Herein, a case study on the shifting of the neutral axis for a cracked rotor is firstly performed by using a three-dimensional finite element model to confirm that the neutral axis becomes inclined as the cracked rotor rotates. In response to this finding, non-symmetric bending principles are used to develop a new crack breathing model which has the advantage of being able to numerically calculate the inclination angle of the neutral axis. When compared to an existing crack model in the literature that assumes that the neutral axis remains horizontal (HNA model), the proposed model is relatively less stiff in bending as a result of an overall lower area moment of inertia. Using the harmonic balance method, a two-dimensional finite element vibration model of a cracked rotor was devised by employing the proposed crack breathing model and the HNA model for validation. It can be found that the vibration amplitudes of the first three frequency components are similar between the two models for shallow cracks and significantly differed for deep cracks. This result highlights the potential of the proposed model for modelling and detecting mid-to-late-stage cracks in rotors.
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Bloom, J. M., S. R. Daniewicz, and J. L. Hechmer. "Plane Strain Crack Growth Models for Fatigue Crack Growth Life Predictions." Journal of Pressure Vessel Technology 118, no. 1 (February 1, 1996): 78–85. http://dx.doi.org/10.1115/1.2842167.
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Experimental data and analytical models have shown that a growing fatigue crack produces a plastic wake. This, in turn, leads to residual compressive stresses acting over the crack faces during the unloading portion of the fatigue cycle. This crack closure effect results in an applied stress intensity factor during unloading which is greater than that associated with the Kmin, thus producing a crack-driving force which is less than ΔK = Kmax − Kmin. Life predictions which do not account for this crack closure effect give inaccurate life estimates, especially for fully reversed loadings. This paper discusses the development of a crack closure expression for the 4- point bend specimen using numerical results obtained from a modified strip-yield model. Data from tests of eight 4-point bend specimens were used to estimate the specimen constraint factor (stress triaxiality effect). The constraint factor was then used in the estimation of the crack opening stresses for each of the bend tests. The numerically estimated crack opening stresses were used to develop an effective stress intensity factor range, ΔKeff The resulting crack growth rate data when plotted versus ΔKeff resulted in a material fatigue crack growth rate property curve independent of test specimen type, stress level, and R-ratio. Fatigue crack growth rate data from center-cracked panels using Newman's crack closure model, from compact specimens using Eason 's R-ratio expression, and from bend specimens using the model discussed in this paper are all shown to fall along the same straight line (on log-log paper) when plotted versus ΔKeff, even though crack closure differs for each specimen type.
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Torres, Roberto, Hiroyuki Kumagai, and Kimiko Taguchi. "Source models of long-period seismic events at Galeras volcano, Colombia." Geophysical Journal International 227, no. 3 (August 14, 2021): 2137–55. http://dx.doi.org/10.1093/gji/ggab325.
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SUMMARY Long-period (LP) seismic events have occurred repeatedly at Galeras volcano, Colombia, during the transition from effusive dome formation to explosive Vulcanian eruptions. Since 1989, two types of LP events have been observed there: one characterized by long-lasting, decaying harmonic oscillations (NLP events) and the other by non-harmonic oscillatory features (BLP events). NLP events are attributed to resonances of a dusty gas-filled crack in the magma plugging the eruptive conduit. Sixteen episodes of NLP events occurred at Galeras during 1992–2010, each characterized by systematic temporal variations in the frequencies and quality factors of NLP events. Our and previous estimates of crack model parameters during three of those NLP episodes indicate that the similar temporal variations in crack geometry and fluid properties can be explained by an increase in the ash content within the crack and a decrease in crack volume. We found that NLP events, associated with low SO2 fluxes, are anticorrelated with BLP events, which are accompanied by high SO2 emissions. From our observations and analytical results, we inferred that BLP events are generated by resonances of open cracks in the uppermost magma plug, corresponding to tuffisite veins, that efficiently transfer volcanic gases. After sufficient degassing and densification, the magma plug effectively seals the conduit. The growing overpressure in the deeper magma is then released through a shear fracture along the conduit margin. The intrusion of deeper, vesiculated magma into the shear fracture depressurizes and fragments the magma, producing a dusty gas and triggering the crack resonances that generate NLP events. Our results thus indicate that the evolution of the properties of the magma plug controls the occurrences of BLP and NLP events at Galeras. Although NLP events do not always precede explosive eruptions, they indicate that an important overpressure is building in the shallow conduit.