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Yongdian Han - One of the best experts on this subject based on the ideXlab platform.
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theoretical and numerical analysis of the creep crack initiation time considering the constraint effects for pressurized pipelines with axial Surface Cracks
International Journal of Mechanical Sciences, 2018Co-Authors: Yongdian HanAbstract:Abstract A theoretical approach and numerical simulation were conducted to investigate the creep crack initiation (CCI) time and the effect of constraints induced by the geometrical sizes of pipelines with axial Surface Cracks. The theoretical enhancement model of the C*–Q* approach under the transient creep condition, which considers the load-independent constraint parameter Q*, was proposed to predict the CCI time around the crack front. The results revealed that the distribution regulation of Q* along the crack front for circumferential internal Surface Cracks and external Surface Cracks was similar. The maximum constraint level occurred near the deepest crack front part for Cracks with small a/c (a/c 0.4). The constraint values at the same position (2Φ/π) increased with the increasing of the crack depth when a/c kept constant. In addition, the axial internal Surface Cracks of pipelines were proved more dangerous than the external Surface Cracks with the same geometrical size. Furthermore, the CCI times were decided by the peak values of constraint, or the CCI firstly occurred at the position where the constraint level was maximum. Additionally, the variation of hydrostatic stresses and triaxiality considering the constraint was discussed. The suitability of the analytical C*–Q* approach was verified to predict CCI. The comparison of CCI times between the analytical approach and the BS 7910 as well as the FE results demonstrated that the solutions under stress intensity factor—Riedel–Rice (K-RR) control (initially by K, then by transient creep stress or Riedel–Rice conditions) were more accurate when internal pressure P 15 MPa.
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numerical analysis of the creep crack constraint effects and the creep crack initiation for pressurized pipelines with circumferential Surface Cracks
Advances in Engineering Software, 2018Co-Authors: Hongyang Jing, Lei Zhao, Yongdian HanAbstract:Abstract The creep crack constraint effects using a load-independent creep constraint parameter Q* and the creep crack initiation (CCI) times were characterized by 3D finite element method for pipelines with circumferential Surface Cracks of different geometrical sizes. The results revealed that the distribution regulation of Q* along the crack front for circumferential internal Surface Cracks and external Surface Cracks was similar. The maximum constraint level occurred near the deepest crack front part for Cracks with smaller a/c, while it occurred near the free Surface for Cracks with larger a/c. The constraint values at the same position (2Φ/π) increased with the increasing of the crack depth when a/c kept constant. The circumferential internal Surface Cracks of pipelines were proved more dangerous than the external Surface Cracks with the same geometrical size. Furthermore, the CCI times were decided by the peak values of constraint, or the CCI firstly occurred at the position where the constraint level was maximum. In addition, the empirical relationships between the CCI times and crack sizes were fitted, which was also verified effectively.
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characterization of creep crack tip constraint levels for pressurized pipelines with axial Surface Cracks
Advances in Engineering Software, 2017Co-Authors: Xingfu Zhang, Lei Zhao, Yongdian Han, Hongyang JingAbstract:Abstract Through extensive 3D finite element analyzes, the creep crack-tip constraint levels were characterized using a load-independent creep constraint parameter Q* for pipelines with axial Surface Cracks of different geometrical sizes, which involved in various crack depths and crack shapes. The Q* distribution along the crack front for axial internal Surface Cracks and axial external Surface Cracks exhibited the same distribution tendency. However, the constraint level of internal Surface Cracks was higher than external Surface Cracks. In addition, the constraint level was improved as the crack depth became deep; in contrast, the constraint level showed a reduction tendency as the crack shape ratio a/c increased from 0.2 to 1.0. The highest constraint levels for the axial Surfaces Cracks in pipelines approached to that of single-edge notched tension specimen. Finally, two empirical equations for estimating the constraint level were established as a function of crack depth ratio and crack shape ratio for axial Surface Cracks in pipelines.
M Freitas - One of the best experts on this subject based on the ideXlab platform.
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stress intensity factors for semi elliptical Surface Cracks in round bars under bending and torsion
International Journal of Fatigue, 1999Co-Authors: Manuel Da Fonte, M FreitasAbstract:Abstract Stress Intensity Factor calculations for semi-elliptical Surface Cracks in round bars subjected to bending and torsion using a three-dimensional finite element model are presented. The configuration of the semi-ellipse follows the equation b=(2s)/π, experimentally obtained, where b is the crack depth and 2s is the arc crack length. First, Stress Intensity Factors are obtained for bending loading (Mode I) and compared with available literature results in order to validate the proposed model. Second, Stress Intensity Factors under torsion (Mode III) are computed by employing a finite element model of the whole round bar, since such loading is non-symmetrical. Results showed that in torsion case the Mode III loading also induces a significant KII at the points where the crack front intercepts the free Surface of the round bar, whereas at the deepest point only KIII exits. The aims of this study have in view the determination of the crack growth rate in rotating load-transmission devices with this type of crack.
Xin Wang - One of the best experts on this subject based on the ideXlab platform.
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analysis of semi elliptical Surface Cracks in the interface of bimaterial plates under tension and bending
Theoretical and Applied Fracture Mechanics, 2018Co-Authors: Xu Chen, Dunji Yu, Xin WangAbstract:Abstract A semi-elliptical Surface crack widely exists in the multilayered electronic devices, fibre reinforced laminated composites and solder joints. To ensure the safety of these structural components, three-dimensional interface fracture mechanics analysis is required. In this study, three-dimensional finite element analyses have been conducted to calculate the fracture mechanics parameters, including the stress intensity factors (SIFs), the strain energy release rate G and two phase angles ψ and φ for semi-elliptical interface Surface Cracks in finite thickness plates. A wide range of crack aspect ratios and relative depths are considered. The SIF computations are presented along the front of a three-dimensional bimaterial interface Cracks with a/t values of 0.2, 0.4, 0.6 or 0.8 and a/c values of 0.2, 0.4, 0.6 or 1.0. In particular, far-field loads i.e., remote tension and bending, and various combinations of bimaterials are investigated. These fracture mechanics parameters’ solutions are suitable for fracture and fatigue life prediction for semi-elliptical bi-material interface Surface Cracks in engineering components.
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stress intensity factors for low aspect ratio semi elliptical Surface Cracks in finite thickness plates subjected to nonuniform stresses
Engineering Fracture Mechanics, 1995Co-Authors: Xin Wang, S B LambertAbstract:Abstract Three-dimensional finite element analyses have been conducted to calculate the stress intensity factors for low aspect ratio semi-elliptic Cracks. The stress intensity factors are presented for the deepest and Surface points on semi-elliptic Cracks with low aspect ratios of 0.05 and 0.1, and a/t values of 0.2, 0.4, 0.6 and 0.8. Uniform, linear, parabolic or cubic stress distributions were applied to the crack face. The results for uniform and linear stress distributions were combined with corresponding results for higher aspect ratio Surface Cracks and edge Cracks to derive the weight function over the entire range of 0 ⩽ a/c ⩽ 1 and 0 ⩽ a/t ⩽ 0.8. The weight function is then verified against finite element data for the parabolic or cubic stress distributions. Differences were less than 3% for the Surface point and 5% for the deepest point.
Peter J Budden - One of the best experts on this subject based on the ideXlab platform.
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limit load solutions of plates with extended Surface Cracks under combined biaxial forces and cross thickness bending
Journal of Strain Analysis for Engineering Design, 2014Co-Authors: Peter J BuddenAbstract:Lower bound limit load solutions for extended Surface Cracks in plates with free ends (pin-loaded) under combined biaxial positive/negative force/stress and positive/negative through-thickness bending are developed based on the lower bound limit load theorem and both Tresca and Mises criteria. An existing Mises limit load solution for extended Surface Cracks in plates with fixed ends under combined biaxial tension and positive moment is extended to general solutions for combined biaxial positive/negative force/stress and positive/negative through-thickness bending moment. Corresponding reference stress expressions are also derived and presented.
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global limit load solutions for plates with Surface Cracks under combined biaxial forces and cross thickness bending
International Journal of Pressure Vessels and Piping, 2011Co-Authors: Peter J BuddenAbstract:Abstract A global limit load solution for rectangular Surface Cracks in plates under combined end force and cross-thickness bending is derived, which allows any combination of positive/negative end force and positive/negative cross-thickness moment. The solution is based on the net-section plastic collapse concept and, therefore, gives limit load values based on the Tresca yielding criterion. Solutions for both cases with and without crack face contact are derived when whole or part of the crack is located in the compressive stress zone. From the solution, particular global limit load solutions for plates with extended Surface Cracks and through-thickness Cracks under the same loading conditions are obtained. The solution is consistent with the limit load solution for Surface Cracks in plates under combined tension and positive bending due to Goodall & Webster and Lei when both the applied end force and bending moment are positive. The solution reduces to the limit load solution for plain plates under combined end force and cross-thickness bending when the crack vanishes.
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effect of internal pressure on plastic loads of 90 elbows with circumferential part through Surface Cracks under in plane bending
Engineering Fracture Mechanics, 2010Co-Authors: Seok Pyo Hong, Yun-jae Kim, Jong Hyun Kim, Peter J BuddenAbstract:Abstract This paper quantifies the effect of internal pressure on plastic loads for elbows with circumferential through-wall and constant-depth part-through Surface Cracks under in-plane bending. Results are based on FE limit analyses using elastic–perfectly plastic materials and the non-linear geometry option. It is found that, for larger values of r / t , the pressure effect on plastic loads is more pronounced and plastic loads for combined loading cases could be much higher than those for pure bending cases. Full FE data of plastic loads are tabulated, and effects of crack geometries on interaction curves are discussed.
Ali Ayhan - One of the best experts on this subject based on the ideXlab platform.
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stress intensity factors and equations for tangential Surface Cracks in rotating hollow disks
Theoretical and Applied Fracture Mechanics, 2020Co-Authors: Ali AyhanAbstract:Abstract In this study, normalized mode-I stress intensity factors (SIFs) along fronts of three-dimensional tangential Surface Cracks contained in rotating hollow disks are presented. A wide range of Surface Cracks with different values of crack aspect ratio, crack depth and radial coordinate along with different geometric parameter settings of the disk are included in the study, yielding a large class of solutions that may be faced with in practical engineering applications. Equations are also developed to allow computations of SIFs for any values of the parameters defining the problem within their practical limits. The results show that for a given crack shape and normalized depth, normalized SIFs decrease with increasing radial coordinate of the crack and with increasing ratio of the inner and outer disk radii. It is also observed that normalized SIFs increase slightly with increasing normalized thickness of the disk for a given crack shape, location and depth. A stress-based procedure is also introduced and validated that can be used to determine the normalized SIFs for a crack located at a radial coordinate based on the normalized SIFs of another crack located at a different radial position.
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Surface Cracks in finite thickness plates under thermal and displacement controlled loads part 2 crack propagation
Engineering Fracture Mechanics, 2014Co-Authors: Mahmut Uslu, Oguzhan Demir, Ali AyhanAbstract:Abstract Surface Cracks in finite-thickness plates subjected to thermal or displacement-controlled loads are considered with a focus on crack propagation. Detailed crack propagation analyses are performed and the effect of loading type on crack propagation patterns and lives are systematically investigated. The results show that although there are some slight differences between the crack propagation patterns and lives for the uniform stress and displacement loading, there exist increasingly higher differences for the bending stress and displacement loads during crack growth. It is shown that propagation lives are higher in the case of displacement/thermal loading compared to those of mechanical/stress loads.
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stress intensity factors for three dimensional Surface Cracks using enriched finite elements
International Journal for Numerical Methods in Engineering, 2002Co-Authors: Ali Ayhan, H F NiedAbstract:The analysis of three-dimensional crack problems using enriched crack tip elements is examined in this paper. It is demonstrated that the enriched finite element approach is a very effective technique for obtaining stress intensity factors for general three-dimensional crack problems. The influence of compatibility, integration, element shape function order, and mesh refinement on solution convergence is investigated to ascertain the accuracy of the numerical results. It is shown that integration order has the greatest impact on solution accuracy. Sample results are presented for semi-circular Surface Cracks and compared with previously obtained solutions available in the literature. Good agreement is obtained between the different numerical solutions, except in the small zone near the free Surface where previously published results have often neglected the change in the stress singularity at the free Surface. The enriched crack tip element appears to be particularly effective in this region, since boundary conditions can be easily imposed on the stress intensity factors to accurately represent the correct free Surface condition. Copyright © 2002 John Wiley & Sons, Ltd.
