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1
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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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.
3
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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McEvily, A. J. "Recent Advances in Fatigue Crack Growth." Key Engineering Materials 510-511 (May 2012): 15–21. http://dx.doi.org/10.4028/www.scientific.net/kem.510-511.15.
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Many of the recent advances in the understanding of the fatigue crack growth process have resulted from an improved realization of the importance of fatigue crack closure in the crack growth process. Two basic crack closure processes have been identified. One of which is known as plasticity-induced fatigue crack closure (PIFCC), and the other is roughness-induced fatigue crack closure (RIFCC). Both forms occur in all alloys, but PIFCC is a surface-related process which is dominant in aluminum alloys such as 2024-T3, whereas RIFCC is dominant in most steels and titanium alloys. A proposed basic equation governing fatigue crack growth is (1) where where Kmax is the maximum stress intensity factor in a loading cycle and Kop is the stress intensity factor at the crack opening level. is the range of the stress intensity factor at the threshold level which is taken to correspond to a crack growth rate of 10-11 m/cycle. The material constant A has units of (MPa)-2, and therefore Eq. 1 is dimensionally correct. Eq.1 has been successfully used in the analysis of both long and short cracks, but in the latter case modification is needed to account for elastic-plastic behavior, the development of crack closure, and the Kitagawa effect which shows that the fatigue strength rather than the threshold level is the controlling factor determining the rate of fatigue crack growth in the very short fatigue crack growth range. Eq. 1 is used to show that The non-propagating cracks observed by Frost and Dugdale resulted from crack closure. The behavior of cracks as short as 10 microns in length can be predicted. Fatigue notch sensitivity is related to crack closure. Very high cycle fatigue (VHCF) behavior is also associated with fatigue crack closure.
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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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Han, Zhichao, Caifu Qian, and Huifang Li. "Study of the Shielding Interactions between Double Cracks on Crack Growth Behaviors under Fatigue Loading." Metals 10, no. 2 (January 31, 2020): 202. http://dx.doi.org/10.3390/met10020202.
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In this paper, the interactions between double cracks with a co-bisector-line were investigated theoretically and experimentally. Fatigue crack growth tests of specimens with a single crack or double cracks were carried out to measure the crack growth rates, and finite element calculations were performed to obtain the stress intensity factors at crack tips. It was found that when the double cracks are in co-bisector-line, they present shielding interactions which reduce the stress intensity factors at crack tips as well as the crack growth rates. By modifying the stress intensity factors and the Paris equation considering the shielding interactions, a new simplification method was proposed to simplify the double cracks into a single crack with the same crack growth rates.
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Prakash, R. V. "Fatigue crack growth at stress concentrators under spectrum loading." Journal of Strain Analysis for Engineering Design 40, no. 2 (February 1, 2005): 117–27. http://dx.doi.org/10.1243/030932405x7764.
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Fatigue cracks initiate at stress raisers such as notches, discontinuities, and surface defects. Many of the field failures that indicate the presence of a fatigue crack at failure can be traced to crack initiation from one or more crack initiation sites and merger of cracks over a period of service. Substantial service life is spent in the growth of small cracks from an initial size of few micrometres before they coalesce and grow to critical dimensions that cause fracture. This paper summarizes research that was carried out in order to understand the kinetics of crack growth of small cracks at notches under simulated FALSTAFF service loading. This paper also presents a method used to understand crack growth kinetics in a pin-loaded lug joint through a crack-front-mapping technique.
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Kutsenko, O. G., L. V. Kharytonova, and R. M. Krush. "Regularities of flat cracks growth in plates." Bulletin of Taras Shevchenko National University of Kyiv. Series: Physics and Mathematics, no. 2 (2023): 124–27. http://dx.doi.org/10.17721/1812-5409.2023/2.19.
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The general regularities of the influence of the geometric parameters of a fatigue crack on the direction of its growth in elastic plates under uniaxial tension were studied. Straight cracks, cracks in the form of a full cosine period, cracks in the form of a circle arc and kinked cracks were considered in a broad range of their geometric parameters variations. The direction of crack growth was determined in accordance with the criteria of maximum tangential (circumferential) stresses. The stress intensity factor of mode I and mode II of fracture were determined numerically using the finite element method. The obtained results made it possible to conclude that in the case of smooth crack faces, the direction of its growth primarily depends on the angle between the tangent at the crack tip and the direction of tension. It was established that the presence of a corner point of the faces near crack tip significantly affects the direction of crack growth in the case of small angles, between the tangent and the direction of tension. For such cases, numerically, it was not possible to achieve a continuous limiting transition in the results when the corner point approaches the tip. This circumstance complicates the issue of choosing the size of the initial crack growth step.
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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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Lukaszewicz, Mikolaj, Shen Gi Zhou, and Alan Turnbull. "Novel Concepts on the Growth of Corrosion Fatigue Small and Short Cracks." Solid State Phenomena 227 (January 2015): 3–6. http://dx.doi.org/10.4028/www.scientific.net/ssp.227.3.
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Corrosion fatigue small, short and long crack growth rates have been determined for a 12Cr steam turbine steel in aerated 300 ppb Cl- + 300 ppb SO42- solution and in air at 90 °C. The crack growth rate for short and long cracks was monitored by direct current potential drop (DCPD) and for the small cracks by combining high resolution optical microscopy and DCPD. Comparison of the fatigue growth rate demonstrated that in solution the short crack growth rate was remarkably enhanced in comparison to long cracks, when the crack size is smaller than 250 μm. This enhancement was attributed to the electrochemical crack size effect associated with greater anodic polarisation of the short crack in such low conductivity solution. However, such enhanced growth was not observed for small cracks, which was rationalised on the basis of additional contribution of current from the pit limiting crack-tip polarisation.
11
Cui, Zhendong, and Weige Han. "In SituScanning Electron Microscope (SEM) Observations of Damage and Crack Growth of Shale." Microscopy and Microanalysis 24, no. 2 (April 2018): 107–15. http://dx.doi.org/10.1017/s1431927618000211.
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AbstractTo better understand the formation and evolution of hierarchical crack networks in shales, observations of microscopic damage, and crack growth were conducted using anin situtensile apparatus inside a scanning electron microscope. An arched specimen with an artificial notch incised into the curved edge was shown to afford effective observation of the damage and crack growth process that occurs during the brittle fracturing of shale. Because this arched specimen design can induce a squeezing effect, reducing the tensile stress concentration at the crack tip, and preventing the brittle shale from unstable fracturing to some extent. Both induced and natural pores and cracks were observed at different scales around the main crack path or on fractured surfaces. Observations indicate that the crack initiation zone develops around the crack tip where tensile stresses are concentrated and micro/nanoscale cracks nucleate. Crack advancement generally occurs by the continuous generation and coalescence of damage zones having intermittent en echelon microscopic cracks located ahead of the crack tips. Mineral anisotropy and pressure build-up around crack tips causes crack kinking, deflection, and branching. Crack growth is often accompanied by the cessation or closure of former branch cracks due to elastic recovery and induced compressive stress. The branching and interactions of cracks form a three-dimensional hierarchical network that includes induced branch cracks having similar paths, as well as natural structures such as nanopores, bedding planes, and microscopic cracks.
12
Zhang, Jian Yu, Rui Bao, Li Bin Zhao, Li Ping Long, and Bin Jun Fei. "Crack Growth Life Estimating for MSD Panel." Advanced Materials Research 33-37 (March 2008): 175–80. http://dx.doi.org/10.4028/www.scientific.net/amr.33-37.175.
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The problem of multiple site damage (MSD) has got more attention in ageing structures. Cumulative effects of interacting cracks may significantly degrade the damage tolerance capacity of structures. Cracks caused by MSD are extremely difficult to detect and greatly reduce the residual strength, fatigue life and overall structural integrity of aircraft panels. This paper presents a simple numerical method, which use the principles of fracture mechanics and the computation results, to predict the fatigue crack growth life of MSD structure. Comparing with calculating crack growth life cycle by cycle, this method will save much time. To verify the validity of the proposed method, experiment was conducted and reported with simulation specimen of representative MSD structure with 5 details. The comparison between the calculated a-N curves and the crack growth lives and the test results shows that the prediction result with this fast method is acceptable. A discussion was carried out by numerical analysis; in with typical MSD structures with different initial crack length were adopted. Crack interaction effect was found obviously, but it occurred mainly in the last part of the crack growth lives. The relative size of MSD cracks depends significantly on the distribution of the initial cracks.
13
Hashmi, Mudassar Hussain, Seyed Saeid Rahimian Koloor, Mohd Foad Abdul-Hamid, and Mohd Nasir Tamin. "Fractal Analysis for Fatigue Crack Growth Rate Response of Engineering Structures with Complex Geometry." Fractal and Fractional 6, no. 11 (November 1, 2022): 635. http://dx.doi.org/10.3390/fractalfract6110635.
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A growing fatigue crack in metallic materials and structures exhibits multifractal features that inherit signatures of the crack growth rate behavior of the material. This study exploits the recently established multifractal fatigue crack growth model to quantify the characteristic fatigue crack growth rate response of the AISI 410 martensitic stainless steel using an L-shaped bell crank structure. The objective is to demonstrate that the fatigue crack growth rate response of the material could be established by quantifying the fractality of the growing crack. The fractal approach avoids the need of the crack geometry factor when calculating the crack tip driving force. The fractal analysis of the crack image employs the box-counting algorithm to determine the fractal dimension along the edge of the crack length. The analysis is confined to the power law crack growth rate stage (Paris crack growth regime). Results show that the fatigue crack growth path in the bell crank structure is dictated by the Mode I (opening) component of the crack loading. The distribution of fractal-based fatigue crack growth rate data is within the 99% confidence limit of the median crack growth response by the Paris equation. Thus, the model could be employed for prediction of the fatigue crack growth response of engineering structures where the crack geometry factor is not readily available.
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Law, M., Valerie Linton, and Erwin Gamboa. "Fatigue Crack Growth Comparison between Sleeved and Non-Sleeved Pipeline." Advanced Materials Research 41-42 (April 2008): 105–12. http://dx.doi.org/10.4028/www.scientific.net/amr.41-42.105.
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A section of gas pipeline containing dormant stress corrosion cracks was removed from service and pressure cycled, and the crack growth from fatigue was measured. Crack growth was able to be conservatively calculated by BS7910. Parts of the pipeline section had composite repair sleeves placed over it in order to compare fatigue crack growth of sleeved and unsleeved cracks. Sleeved cracks consistently showed less crack growth than unsleeved cracks; this is believed to be due to reduced hoop stresses in the pipe under the composite repair sleeve and reduced crack opening. A simple model of the sleeve repair was developed which was consistent with the measured strains in the pipe. The application pressure of the sleeve repair affects the amount of stress reduction in the pipe and the amount of crack growth experienced. Two possible methods of repair of SCC affected pipelines were validated by this work.
15
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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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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Knorr, Alain Franz, and Michael Marx. "Microstructural Barriers against Fatigue Crack Growth." Materials Science Forum 783-786 (May 2014): 2339–46. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.2339.
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Fatigue induced fracture is the number one reason for failure of technical systems. However, in the stage of small crack growth grain or phase boundaries lead to a fluctuating crack propagation rate near the obstacle. Sometimes the cracks stop completely for a large number of cycles resulting in an additional number of life time cycles. However, so far it is not clear, what actually determines the resistance of a grain boundary against fatigue cracks. Therefore we developed a systematic experimental technique based on in-situ imaging in the scanning electron microscope and focused ion beam (FIB) crack initiation which gives detailed information on the interaction of short fatigue cracks with microstructural elements. We investigated the mechanisms of crack transmission in the neighbouring grain on the microscopic scale and identified different useful aspects of the interaction between microcracks and microstructural barriers. The 3D-tomographs revealed by serial sectioning an FIB give information about the transition process from one grain to the neighbouring one. The result is a purely geometrical consideration leading to a quantitative description of the blocking effect of grain boundaries on short fatigue crack growth. The results include useful aspects for fatigue life calculation and to make materials more fatigue resistant.
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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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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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Tumanov, N. V. "Steady fatigue crack growth: micromechanism and mathematical modeling." Industrial laboratory. Diagnostics of materials 84, no. 11 (December 3, 2018): 52–69. http://dx.doi.org/10.26896/1028-6861-2018-84-11-52-69.
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A universal energy-intensive micromechanism of periodic splitting-rupture (PSR) is revealed which proceeds at the front of the fatigue cracks in metallic materials, providing their steady growth, forming T-shaped crack tip and striated microrelief of the fracture surface. The PSR micromechanism is caused by a critical (prior to fracture) fragmentated structure formed in the area of the crack front where the material is subjected to multiple and increasing plastic deformation. This universal prefracture structure is a final stage of the evolution of the deformational structures emerged in front of the fatigue crack at the stage of stable crack growth in metallic materials with different initial structural states. This is responsible for universality of PSR micromechanism and fatigue striations. Fatigue striations are the traces of extending crack front with T-shaped tip formed during brittle transverse microsplitting along the overstressed boundaries of critical fragmentated structure. Based on 3D finite element modeling of the stress-strain state in front of the cracks with T-shaped tip, it is established that the value and the location of maximum of normalized in-plain stresses (acting in front of crack tip in the plane of crack along the normal to its front) are close or coincide for the cracks of different configuration and different types of tensile load under condition that splitting in the T-shaped crack tip is considerably less than the crack length. Taking into account the PSR micromechanism and asymptotic stress distribution in front of T-shaped crack tip the physically based mathematical model for steady fatigue crack growth is developed along with the techniques for prediction of steady fatigue crack growth in full-scale components under simple and complex loading cycles.
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KAMIL, KUSNO, MASAHIRO GOTO, SEUNG-ZEON HAN, KWANGJUN EUH, NORIO KAWAGOISHI, and SANGSHIK KIM. "SMALL CRACK GROWTH BEHAVIOR AND EVALUATION OF GROWTH RATE OF COPPER PROCESSED BY EQUAL CHANNEL ANGULAR PRESSING." International Journal of Modern Physics: Conference Series 06 (January 2012): 245–50. http://dx.doi.org/10.1142/s201019451200325x.
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Ultrafine grained copper processed by 4 cycles of equal angular pressing was fatigued to study the growth behavior of a small crack. After the crack initiation, the behavior of a major crack was monitored through plastic replication technique, showing that the crack growth rate is proportional to the crack length regardless of stress amplitudes. The crack growth rate of major cracks was evaluated by a term σanl, not by the stress intensity factor range, ΔK. Analysis on fracture surfaces by scanning electron microscopy showed a planar followed by a striated surface. The formation mechanism of fracture surface morphologies was discussed by considering the average grain size and the reversible plastic zone size at a crack tip.
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JONES, R., L. MOLENT, and S. PITT. "Crack growth of physically small cracks." International Journal of Fatigue 29, no. 9-11 (September 2007): 1658–67. http://dx.doi.org/10.1016/j.ijfatigue.2007.01.031.
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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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Qian, Cai-Fu, Ming-O. Wang, Bao-Juan Wu, Shu-Ho Dai, and J. C. M. Li. "Mixed-Mode Fatigue Crack Growth in Stainless Steels Under Biaxial Loading." Journal of Engineering Materials and Technology 118, no. 3 (July 1, 1996): 349–55. http://dx.doi.org/10.1115/1.2806817.
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Mixed-Mode fatigue crack propagation tests were carried out in stainless-steel cruciform specimens in which a center initial crack oriented at 45 deg was loaded biaxially. When the loadings were in-phase, the crack was deflected with the initial crack growth angles less than 50 deg and when they were out-of-phase, it was branched with the initial crack growth angles larger than 50 deg. In all the cases, the deflected or branched cracks propagated in Mode I, namely ΔKII was almost always zero along the crack paths. The relationship between deflected or branched cracks during propagation was also analyzed.
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Potirniche, G. P., M. F. Horstemeyer, P. M. Gullett, and B. Jelinek. "Atomistic modelling of fatigue crack growth and dislocation structuring in FCC crystals." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 462, no. 2076 (July 5, 2006): 3707–31. http://dx.doi.org/10.1098/rspa.2006.1746.
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Fatigue damage in face-centred cubic crystals by dislocation substructuring and crack growth was computationally simulated at the atomic scale. Single-crystal copper specimens with approximately 200 000 atoms and an initial crack were subjected to fatigue loading with a constant strain amplitude of ϵ max =0.01 and a load ratio of R = ϵ min / ϵ max =0.75. Cyclic plastic deformation around the crack tip is the main influencing factor for the propagation mechanisms of nanocracks. The main crack-propagation mechanisms occurred either by void nucleation in the high-density region near the crack tip or by fatigue cleavage of the atomic bonds in the crack plane. Fatigue crack growth at grain boundaries was also studied. For high misorientation angle grain boundaries, the crack path deviated while moving from one grain to another. For low crystal misorientations, the crack did not experience any significant out-of-plane deviation. For a large crystal misorientation, voids were observed to nucleate at grain boundaries in front of the crack tip and link back with the main crack. During fatigue loading, dislocation substructures were observed to develop throughout the atomic lattices. Fatigue crack growth rates for nanocracks were computed and compared with growth rates published in the literature for microstructurally small cracks (micron range) and long cracks (millimetre range). The computed growth rates for nanocracks were comparable with those for small cracks at the same stress intensity ranges and they propagated below the threshold for long cracks.
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Bower, A. F. "The Influence of Crack Face Friction and Trapped Fluid on Surface Initiated Rolling Contact Fatigue Cracks." Journal of Tribology 110, no. 4 (October 1, 1988): 704–11. http://dx.doi.org/10.1115/1.3261717.
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A two-dimensional model of a surface initiated rolling contact fatigue crack has been developed. The model takes into account the effects of frictional locking between the faces of the crack, and the influence of fluid pressure acting on the crack faces. The model has been used to investigate three possible mechanisms for propagating the cracks: mode II crack growth due to the cyclic shear stresses caused by repeated rolling contact; crack growth due to fluid forced into the crack by the load; and crack growth due to fluid trapped inside the crack. The predictions of the theory are compared with the behaviour of contact fatigue cracks.
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Ortiz, K., and A. S. Kiremidjian. "A Stochastic Model for Fatigue Crack Growth Rate Data." Journal of Engineering for Industry 109, no. 1 (February 1, 1987): 13–18. http://dx.doi.org/10.1115/1.3187085.
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This paper summarizes a new approach to the probabilistic modeling of fatigue crack growth. The material’s resistance to fatigue crack growth is modeled as a stochastic process, which varies randomly along the crack path. Model parameters are determined through time analysis of fatigue crack growth rate data. Predictions of the statistics of crack growth are excellent, especially for small cracks.
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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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Kikuchi, Masanori, Yoshitaka Wada, and Yu Long Li. "Evaluation of Interaction Effect of Two Surface Cracks by Fatigue." Key Engineering Materials 417-418 (October 2009): 97–100. http://dx.doi.org/10.4028/www.scientific.net/kem.417-418.97.
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Fatigue crack growth under mixed mode loading conditions is simulated using S-version FEM. By using S-FEM technique, only local mesh should be re-meshed for new crack configuration, and it becomes easy to simulate crack growth. By combining with auto-meshing technique, local mesh easily re-meshed and curved crack path is modeled easily. Fully automatic crack growth simulation system in 3-dimensional problem is developed. Using this system, several kinds of plural surface cracks problems are simulated. It is shown that intereaction effect between two surface cracks appear in complicated manner depending on intial distances between two cracks.
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Schneider, Jens, and Jonas Hilcken. "Cyclical fatigue of annealed and of thermally tempered soda-lime-silica glass." MATEC Web of Conferences 165 (2018): 18003. http://dx.doi.org/10.1051/matecconf/201816518003.
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We present experimental and theoretical investigations on the cyclic fatigue of annealed and of thermally tempered soda-lime-silica glass. Static fatigue due to subcritical crack growth at micro cracks significantly decreases the macroscopic strength of soda-lime-silica glass and causes a time-dependent strength reduction. A subsequent thermal tempering process is typically used to induce residual surface compression stresses, which inhibit the crack growth of surface cracks, and corresponding bulk tension stresses. From the experimental results we show that the existing models for static fatigue used in linear elastic fracture mechanics can be used for the lifetime prediction of cyclically loaded annealed glass and thermally tempered glass, although the (static) crack growth exponent slightly decreases in cyclic loading. The equivalent duration of tensile stress at the crack tip of a micro crack governs the crack growths and not the number of cycles. The threshold for subcritical crack growth determined from the cyclic experiments was found to be in good agreement with data from literature. But unlike in strength tests with singular and quasi-static re-loading, it could be found that periodic loading with load free intervals does not lead to a strength increase by crack healing effects. Based on the results, an engineering design concept for cyclically loaded glass is presented.
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Turnbull, Alan. "Corrosion pitting and environmentally assisted small crack growth." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2169 (September 8, 2014): 20140254. http://dx.doi.org/10.1098/rspa.2014.0254.
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In many applications, corrosion pits act as precursors to cracking, but qualitative and quantitative prediction of damage evolution has been hampered by lack of insights into the process by which a crack develops from a pit. An overview is given of recent breakthroughs in characterization and understanding of the pit-to-crack transition using advanced three-dimensional imaging techniques such as X-ray computed tomography and focused ion beam machining with scanning electron microscopy. These techniques provided novel insights with respect to the location of crack development from a pit, supported by finite-element analysis. This inspired a new concept for the role of pitting in stress corrosion cracking based on the growing pit inducing local dynamic plastic strain, a critical factor in the development of stress corrosion cracks. Challenges in quantifying the subsequent growth rate of the emerging small cracks are then outlined with the potential drop technique being the most viable. A comparison is made with the growth rate for short cracks (through-thickness crack in fracture mechanics specimen) and long cracks and an electrochemical crack size effect invoked to rationalize the data.
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Pang, John Hock Lye, and You Xiang Chew. "Fatigue Crack Growth and Coalescence Algorithm Starting from Multiple Surface Cracks." Advanced Materials Research 891-892 (March 2014): 1003–8. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.1003.
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Fatigue crack growth and propagation analysis in welded joints have to deal with the complexity of modeling multiple weld toe surface cracks originating from weld toes. Fitness-For-Service (FFS) assessments for weld toe surface cracks employ a fracture mechanics and Paris Law approach to predict the fatigue crack propagation life of a semi-elliptical surface crack (SESC) to failure. A fatigue crack growth algorithm for assessing multiple surface crack growth, coalescence and propagation life was initially validated with previuously report crack growth data for a fillet shoulder specimen. Next a parametric study for single, double, and triple SESCs located along the weld toe line of a fillet weld was investigated with three starting crack depth sizes (0.1mm, 0.5mm, 1.0mm) coupled with three different crack aspect ratios (a/c = 1.0, a/c = 0.5 and 0.25) giving a total of 27 cases studied.
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Chan, K. S., J. Feiger, Y. D. Lee, R. John, and S. J. Hudak,. "Fatigue Crack Growth Thresholds of Deflected Mixed-Mode Cracks in PWA1484." Journal of Engineering Materials and Technology 127, no. 1 (January 1, 2005): 2–7. http://dx.doi.org/10.1115/1.1836765.
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The fatigue crack growth (FCG) behavior of PWA1484 single crystals was characterized in air under mixed-mode loading at 593°C as a function of crystallographic orientation using an asymmetric four-point bend test technique. Most mixed-mode fatigue cracks deflected from the symmetry plane and propagated as transprecipitate, noncrystallographic cracks, while self-similar fatigue crack growth occurred on the (111) planes in (111)/[011] and 111/[112]¯ oriented crystals. The local stress intensity factors and the crack paths of the deflected mixed-mode cracks were analyzed using the finite-element fracture mechanics code, FRANC2D/L. The results indicated that the deflected crack path was close to being normal to the maximum tensile stress direction where the Mode II component diminishes. Crystallographic analysis of the deflected crack paths revealed that the Mode I and the deflected mixed-mode cracks were usually of different crystallographic orientations and could exhibit different Mode I FCG thresholds when the crystallography of the crack paths differed substantially. These results were used to identify the driving force and conditions for cracking mode transition.
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Gall, Ken, Huseyin Sehitoglu, and Yavuz Kadioglu. "A Methodology for Predicting Variability in Microstructurally Short Fatigue Crack Growth Rates." Journal of Engineering Materials and Technology 119, no. 2 (April 1, 1997): 171–79. http://dx.doi.org/10.1115/1.2805990.
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A finite element model, which implements single crystal constitutive relationships, was used to simulate fatigue cracks growing at the microstructural level. Plastic deformation (slip) was allowed along two specified microscopic crystallographic planes. As the orientations of the slip systems were changed several crucial fatigue crack growth parameters, measured over all possible orientations, were found to vary: (1) crack tip forward slip band size, rp, 0.03 ≤ rp/(Kmax/λo)2 ≤ 0.31 where λo is the critical resolved shear stress on a slip system, (2) crack opening displacement, δ, 1.2 ≤ δ/(Kmax2/Emσo) ≤ 7.8 where Em and σo are the elastic modulus and yield stress of a polycrystalline material with many randomly oriented double slip crystals, and(3) crack closure level, Sopen/Smax, 0.02 ≤ Sopen/Smax ≤ 0.35. Corresponding to these differences in crack growth parameters, crack growth laws were used to estimate the expected changes in crack growth rates when microstructurally short cracks grow through grains with different crystallographic orientations. The resulting predictions form approximate upper and lower bounds on crack growth rates for microstructurally short cracks. For several different materials, the crack growth rate variability predictions were in the range 7 ≤ (da/dN)(max)/(da/dN)(min) ≤ 37, which is consistent with experimentally measured variations.
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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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He, Wen Tao, Jing Xi Liu, and De Xie. "Two-Dimensional Crack Growth Simulation under Mixed-Mode Loading." Applied Mechanics and Materials 577 (July 2014): 301–4. http://dx.doi.org/10.4028/www.scientific.net/amm.577.301.
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In this paper, an efficient simulation program (FCG-System) is proposed to simulate 2D fatigue crack growth under mixed-mode loading conditions. The simulation is basically an incremental crack extension procedure. An object-oriented modeling frame is proposed for simulating fatigue crack growth of complex structures. The modeling frame is developed in the context of the commercial FE code ABAQUS, utilizing Python language and ABAQUS Scripting Interface (ASI). The highly automatic finite element simulation method is not only used for a single crack tip, but also has been extended to the system of interactive multiple cracks. The robustness and the accuracy of the new simulation code will be shown by two examples, including single crack growth and multiple cracks growth. Those applications indicate that the implementation of the FCG-System, as proposed herein, can be a useful tool for this class of fatigue crack growth.
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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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McClung, R. C., and H. Sehitoglu. "Closure and Growth of Fatigue Cracks at Notches." Journal of Engineering Materials and Technology 114, no. 1 (January 1, 1992): 1–7. http://dx.doi.org/10.1115/1.2904135.
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The closure behavior of fatigue cracks growing out of notches is studied with an elastic-plastic finite element model. Crack opening stresses are shown to change significantly as the crack extends. Opening stresses are low at first and then gradually rise to stable values as the crack tip moves away from the notch field. These transient changes are not limited to the region of the original inelastic notch field. The rate of change of opening stresses with increasing crack length is a function of both nominal maximum stress and nominal stress ratio. Stable levels are reached more quickly at higher stress ratios and lower maximum stresses. These transient changes in Sopen have been emulated with a simple model which considers only changes in Sopen due to changes in the local stress field. The numerical results are quantitatively consistent with observed trends in experimental crack growth data, which show that accelerated crack growth can occur beyond the original notch plastic boundary. Finite element results and experimental data also both suggest that the accelerated short crack growth effect for cracks near notches is much less pronounced at higher stress ratios.
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Tomaru, Shuji, and Akiyuki Takahashi. "Three-dimensional fatigue crack growth simulation of embedded cracks using s-version FEM." International Journal of Structural Integrity 11, no. 4 (December 19, 2019): 547–55. http://dx.doi.org/10.1108/ijsi-10-2019-0107.
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Purpose Since the most of structures and structural components suffers from cyclic loadings, the study on the fatigue failure due to the crack growth has a great importance. The purpose of this paper is to present a three-dimensional fatigue crack growth simulation of embedded cracks using s-version finite element method (SFEM). Using the numerical results, the validity of the fitness-for-service (FFS) code evaluation method is verified. Design/methodology/approach In this paper, three-dimensional fatigue crack propagation analysis of embedded cracks is performed using the SFEM. SFEM is a numerical analysis method in which the shape of the structure is represented by a global mesh, and cracks are modeled by local meshes independently. The independent global and local meshes are superimposed to obtain the displacement solution of the problem simultaneously. Findings The fatigue crack growth of arbitrary shape of cracks is slow compared to that of the simplified circular crack and the crack approximated based on the FFS code of the Japan Society of Mechanical Engineers (JSME). The results tell us that the FFS code of JSME can provide a conservative evaluation of the fatigue crack growth and the residual life time. Originality/value This paper presents a three-dimensional fatigue crack growth simulation of embedded cracks using SFEM. Using this method, it is possible to apply mixed mode loads to complex shaped cracks that are closer to realistic conditions.
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Goto, Masahiro, Takaei Yamamoto, Junichi Kitamura, Seung Zeon Han, R. Takanami, Terutoshi Yakushiji, and J. H. Lee. "Growth Rate of Small Surface-Cracks in Age Hardening Cu-Ni-Si Alloy under Cyclic Stressing." Key Engineering Materials 827 (December 2019): 216–21. http://dx.doi.org/10.4028/www.scientific.net/kem.827.216.
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Stress-controlled fatigue tests were conducted on round-bar specimens to understand the fatigue behavior of precipitate-strengthened Cu–6Ni–1.5Si alloy. The cracks were initiated at the grain boundaries, followed by growth along the crystallographic slip planes in the adjacent grains. The crack growth data of plain specimens exhibited a large scatter, resulting in a difficulty of the measurement of crack growth rate. To evaluate the small-crack growth rate of the alloy, the plain specimens with a small blind hole as the crack starter were fatigued. The crack growth rate of small cracks from the hole was uniquely determined by a term σanl and the material constant, n, was 5.3. The term σanl with n = 5.3 was applied to the plain specimen, showing good applicability of the term to small cracks in the plain specimen.
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De Francisco, Unai, Felix Beckmann, Julian Moosmann, Nicolas O. Larrosa, and Matthew J. Peel. "3D characterisation of hydrogen environmentally assisted cracking during static loading of AA7449-T7651." International Journal of Fracture 232, no. 1 (October 28, 2021): 93–116. http://dx.doi.org/10.1007/s10704-021-00595-y.
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AbstractIn this investigation, synchrotron X-ray microtomography was used to perform 3D in situ observations of crack initiation and growth during hydrogen environmentally assisted cracking (HEAC) in tensile samples of AA7449-T7651. Two smooth tensile samples with a 1 mm diameter gauge section were held at a fixed displacement ($$\approx 30$$ ≈ 30 % of yield stress) in warm, moist air ($$\approx 76\,^\circ $$ ≈ 76 ∘ C, 73% relative humidity). The samples were then imaged repeatedly using X-ray tomography until they fractured completely. The tomograms showing the nucleation and evolution of intergranular cracks were correlated with electron microscopy fractographs. This enabled the identification of crack initiation sites and the characterisation of the crack growth behaviour relative to the microstructure. The samples were found to fracture within an environmental exposure time of 240 min. Some cracks in both samples nucleated within an exposure time of 80 min (33–40% of the total lifetime). Many cracks were found to nucleate both internally and at the sample surface. However, only superficial cracks contributed to the final fracture surface as they grew faster owing to the direct environmental exposure and the larger crack opening. HEAC occurred prominently via brittle intergranular cracking, and cracks were found to slow down when approaching grain boundary triple junctions. Additionally, crack shielding from nearby cracks and the presence of coarse Al–Cu–Fe particles at the grain boundaries were also found to temporarily reduce the crack growth rates. After prolonged crack growth, the HEAC cracks displayed ductile striations and transgranular fracture, revealing a change in the crack growth mechanism at higher stress intensity factors.
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Akama, Makoto. "Fatigue Crack Growth under Non-Proportional Mixed Mode Loading in Rail and Wheel Steel Part 1: Sequential Mode I and Mode II Loading." Applied Sciences 9, no. 10 (May 16, 2019): 2006. http://dx.doi.org/10.3390/app9102006.
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Fatigue tests were performed to estimate the coplanar and branch crack growth rates on rail and wheel steel under non-proportional mixed mode I/II loading cycles simulating the load on rolling contact fatigue cracks; sequential and overlapping mode I and II loadings were applied to single cracks in the specimens. Long coplanar cracks were produced under certain loading conditions. The fracture surfaces observed by scanning electron microscopy and the finite element analysis results suggested that the growth was driven mainly by in-plane shear mode (i.e., mode II) loading. Crack branching likely occurred when the degree of overlap between these mode cycles increased, indicating that such degree enhancement leads to a relative increase of the maximum tangential stress range, based on an elasto–plastic stress field along the branch direction, compared to the maximum shear stress. Moreover, the crack growth rate decreased when the material strength increased because this made the crack tip displacements smaller. The branch crack growth rates could not be represented by a single crack growth law since the plastic zone size ahead of the crack tip increased with the shear part of the loading due to the T-stress, resulting in higher growth rates.
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Shaari, Mohd Shamil, Sylvia Urai, Akiyuki Takahashi, and Mohd Akramin Mohd Romlay. "Predicting Fatigue Crack Growth Behavior of Coalesced Cracks Using the Global-Local Superimposed Technique." Frattura ed Integrità Strutturale 16, no. 62 (September 22, 2022): 150–67. http://dx.doi.org/10.3221/igf-esis.62.11.
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The S-version Finite Element Method (FEM) is known as a global-local superimposed approach that consists of two separate meshes referred to as global and local cracks. The relationship between the energy release rate and the Stress Intensity Factor (SIF) is evaluated to characterize the growth behavior of the fatigue cracks. The SIF is determined using the Virtual Crack Closure Method (VCCM). The cracks propagated in the direction of the loading before coalescing into a single crack. Each crack begins with a length of 10mm and a depth of 3mm. After the crack coalesces, the diameter of the surface crack before it breaks is 28mm, whereas the depth of the crack is 5.3mm. The V-shaped surface crack forms quickly after coalescence occurs and continues to propagate into a massive semi-elliptical surface crack before finally breaking. The result was validated and compared between S-version FEM and the analytical solution. The behavior of the fatigue crack growth shows a good agreement between both methods with small errors. The result indicates that the Root Mean Square Error (RMSE) values before coalescing are 0.1496 with 0.6, and after coalescing is 0.4, the RMSE value is 0.1665. Therefore, it can be stated that the S-version FEM approach can predict the growth of fatigue cracks.
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Ma, Wei. "Discontinuous Growth Mechanisms of Mode II Crack under High-Speed Impact Conditions." Advanced Materials Research 41-42 (April 2008): 169–73. http://dx.doi.org/10.4028/www.scientific.net/amr.41-42.169.
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A recoverable plate impact testing technology has been used for studying the growth mechanisms of mode II crack. The results show that interactions of microcracks ahead of a crack tip cause the crack growth unsteadily. Failure mode transitions of materials were observed. Based on the observations, a discontinuous crack growth model was established. Analysis shows that the shear crack grows unsteady as the growth speed is between the Rayleigh wave speed cR and the shear wave speed cs; however, when the growth speed approaches 2cs, the crack grows steadily. The transient microcrack growth makes the main crack speed to jump from subsonic to intersonic and the steady growth of all the sub-cracks leads the main crack to grow stably at an intersonic speed.
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Yarullin, Rustam, and Mikhail Yakovlev. "Fatigue growth rate of inclined surface cracks in aluminum and titanium alloys." Frattura ed Integrità Strutturale 16, no. 60 (March 25, 2022): 451–63. http://dx.doi.org/10.3221/igf-esis.60.31.
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In this paper the fatigue crack growth tests were carried out on surface-crack tension (SCT) specimens, made of 7050 and Ti6Al4V alloys, with initial semi-elliptical surface cracks. Pure Mode I conditions were realized on SCT specimens with crack plane located orthogonal to the loading direction, while Mixed-mode conditions were observed on SCT specimens with inclined crack. Optical microscope measurements and the crack mouth opening displacement (CMOD) method were respectively used to monitor crack length and calculate crack depth. Current crack shape during the tests was highlighted by alternation of loading spectrum with baseline load block and a marker load block. The stress strain field along the crack front of semi-elliptical cracks in the SCT specimens was assessed by Finite Element Method (FEM) analysis. The stress intensity factors (SIFs) were calculated along crack fronts and equivalent elastic SIF formulation was used for crack growth rate assessment under mixed mode conditions. As a result, the fracture resistance parameters of aluminum and titanium alloys were obtained for two crack propagation directions under Mode I and Mixed-mode loading. The benefits of using the computational and experimental results of SCT specimen for the assessment of the surface crack growth rate in aluminum and titanium alloys under Mixed-mode loading conditions were stated.
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Lin, X. B., and R. A. Smith. "Fatigue Growth Prediction of Internal Surface Cracks in Pressure Vessels." Journal of Pressure Vessel Technology 120, no. 1 (February 1, 1998): 17–23. http://dx.doi.org/10.1115/1.2841878.
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Fatigue crack growth was numerically simulated for various internal surface cracks with initially either semi-elliptical or irregular crack fronts. The simulation was directly based on a series of three-dimensional finite element analyses from which the stress intensity factors along the front of growing cracks were estimated. The fatigue crack growth law obtained from small laboratory specimens was incrementally integrated at a set of points along the crack front, and a new crack front was then re-established according to the local advances at this set of points by using a cubic spline curve. This method enabled the crack shape to be predicted without having to make the usual assumption of semi-elliptical shape. Fatigue analysis results are presented and discussed for fatigue shape developments and deviations from the semi-elliptical shape, aspect ratio changes, stress intensity factor variations during crack growth, and fatigue life predictions. Some of the results were also compared with those obtained by two simplified methods based on one and two degree-of-freedom models, respectively.
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Luo, Yuan, Xiaofan Liu, Fanghuai Chen, Haiping Zhang, and Xinhui Xiao. "Numerical Simulation on Crack–Inclusion Interaction for Rib-to-Deck Welded Joints in Orthotropic Steel Deck." Metals 13, no. 8 (August 5, 2023): 1402. http://dx.doi.org/10.3390/met13081402.
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Weld defects such as porosity, inclusion, burn-through, and lack of penetration are difficult to detect and control effectively in an orthotropic steel deck (OSD), which will be a fatigue crack initiation site and lead to several fatigue cracking. The crack growth behavior in defective welded joints is different from that of defect-free joints. This study investigates crack–inclusion interaction for rib-to-deck welded joints in OSDs based on numerical simulation and linear elastic fracture mechanics (LEFM). A refined finite element model of a half U-rib with cracks and inclusions was established by using the FRANC3D-ABAQUS interactive technology. The full processes of the crack–inclusion interaction from approaching and penetrating were accurately simulated. Critical parameters, including the stress intensity factor (SIF), the shape factor, the growth rate, and the growth direction were analyzed. The stiff and soft inclusions amplify and shield the SIF of cracks when the crack grows to the local area of inclusions. During the entire process of crack growth, the soft and stiff inclusion accelerate and inhibit the crack growth, respectively. The stiff inclusion will lead to asymmetric growth of the crack shape, where the portion of the crack away from the inclusions has a higher growth rate. The soft and stiff inclusions will attract and repel the direction of crack growth at the proximal point, respectively.
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MATSUSAKO, HIRONORI, KOHJI KARIYA, NORIO KAWAGOISHI, QINGYUAN WANG, and MASAHIRO GOTO. "EFFECT OF TEXTURE ON FATIGUE PROPERTIES OF AGE-HARDENED Al ALLOYS UNDER ULTRASONIC LOADING." International Journal of Modern Physics: Conference Series 06 (January 2012): 294–99. http://dx.doi.org/10.1142/s2010194512003339.
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Effects of texture and loading frequency on the fatigue crack growth behavior of an extruded and a drawn Al alloys of 2017-T4 were investigated under ultrasonic loading frequency (20kHz) in the relative humidity of 25% and 85%, respectively. The extruded alloy has a marked texture of (111) orientation, but this specified orientation is not observed in the drawn alloy. Most of fatigue life was occupied by the growth life of small cracks in the both alloys regardless of humidity. In the low humidity, crack growth was retarded at about 0.3 mm in length in the both alloys. Although crack growth was accelerated by high humidity in the early growth process, there was no or little influence of humidity on the growth rate of cracks over about 0.3 mm in the both alloys. After the retardation of crack growth, fracture surfaces featured with many slip planes in the extruded alloy and many facets in the drawn one, respectively. The difference in growth mechanism between short cracks (<0.3 mm) and longer ones (>0.3 mm) was caused by the environment at crack tips due to high crack growth rate under ultrasonic loading, and that between the both alloys was related to the degree of texture.
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Guo, Hao, Guang Fu Li, Xun Cai, Jiasheng Bai, and Wu Yang. "Effect of Cyclic Loading on Crack Propagation of X-70 Pipeline Steel in Near-Neutral pH Solution." Key Engineering Materials 297-300 (November 2005): 2501–7. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2501.
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Crack propagation of X-70 pipeline steel in near-neutral pH solution was studied under different modes of cyclic loading. A revised equation of crack growth rate vs. Δ K was obtained. Average crack growth rate increased with cycles under conditions of different R values. Linear shape notch specimen made cracks much easier to initiate and propagate than V-shaped notch specimen did. For different R values, the curves of crack growth rate with cycles were similar, but the platform propagation period and quick propagation period were different obviously. Crack growth rate at both periods increased and thus failure time decreased markedly with decrease of R value. The propagation directions of cracks were different under different cyclic loading conditions. Under mode I (single tensile stress) cyclic loading, cracks were straight and perpendicular to the tensile stress axis, while under mixed-mode I/III (tensile/shear stress) cyclic loading, cracks were sinuous and did not propagate in the direction perpendicular to the main tensile stress axis.
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Lados, Diana A. "Fatigue Crack Propagation Mechanisms of Long and Small Cracks in Al-Si-Mg and Al-Mg Cast Alloys." Materials Science Forum 618-619 (April 2009): 563–74. http://dx.doi.org/10.4028/www.scientific.net/msf.618-619.563.
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Fatigue crack growth of long and small cracks was investigated for various Al-Si-Mg and Al-Mg cast alloys. Low residual stress was ensured during processing to concentrate on microstructural effects on crack growth. Compact tension and single edge tension specimens were fatigue crack growth tested at room temperature and stress ratio, R = 0.1. Microstructure related mechanisms were used to explain the near-threshold behaviour and crack growth response in Regions II and III for each material considering relevant microstructural features such as SDAS, grain size, and volume fraction and morphology of eutectic Si. Threshold behaviour of long cracks is attributed to closure-dependent mechanisms. In Regions II and III, the changes in crack growth mechanisms were explained through correlations between the extent of the plastic zone ahead of the crack tip and material-specific microstructural damage. Threshold behaviour of small cracks is explained through closure-independent mechanisms, specifically through the barrier effects of controlling microstructural characteristics specific to each material. Recommendations for integrating materials knowledge in structural design for fatigue performance are given.