Academic literature on the topic 'Front wall crack'
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Journal articles on the topic "Front wall crack"
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Pyskunov, Serhii, Oleksii Shkryl, and Yurii Maksymiuk. "Determination of crack resistance of a tank with elliptical crack." Strength of Materials and Theory of Structures, no. 106 (May 24, 2021): 14–21. http://dx.doi.org/10.32347/2410-2547.2021.106.14-21.
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The occurrence of crack-like defects is a common phenomenon in the operation of vertical steel tanks (VST). Such defects can occur both at the beginning of the operation of the tanks, which may be associated with a violation of the manufacture conditions or the installation procedures of the tank elements and during operation. Over time, such defects increase significantly and turn into cracks. Existing regulations prohibit the operation of VST with cracks. At the same time, the organization that operates the tank does not always have the opportunity to perform repairs immediately. There are cases of trouble-free operation of tanks with non-through surface cracks at the stage of sustainable growth, which are confirmed by model calculations are known from practical experience. The analysis of crack resistance of the VST-5000 tank with a semi-elliptical crack under the action of hydrostatic pressure is carried out in the work. The level of filling the tank with petroleum products is 95% of its height. The semi-elliptical crack is located on outside surface of the wall panel in lower row of cladding. Determination of crack resistance of a tank with a crack is performed on the basis of stress intensity factors (SIF). Direct and energy methods were used to SIF calculation. Determination of the stress-strain state is performed on the basis of the semi-analytical finite element method (SFEM). The SIF distribution along the crack front obtained using SFEM by both direct and energy methods almost coincides and agrees well with the values of SIF calculated by the direct method when using three-dimensional FEM. The obtained values of SIF differ along the crack front by 50%: the minimum value of SIF acquires at the point of the front, which is located on the outer surface of the tank, the maximum one - at the point of the front inside the wall that is furthest from the outer surface. The obtained results show the quite uneven SIF distribution along the crack front, so that the calculation of such problems requires the spatial setting of problem.
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Qian, X., Robert H. Dodds, and Y. S. Choo. "Mode Mixity for Circular Hollow Section X Joints With Weld Toe Cracks." Journal of Offshore Mechanics and Arctic Engineering 127, no. 3 (January 26, 2005): 269–79. http://dx.doi.org/10.1115/1.1951771.
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This paper describes the mode mixity of stress-intensity factors for surface cracks at weld toes located at the saddle point in circular hollow section X joints. The remote loading applies a uniform tensile stress at the end of the brace along its axis. The three-dimensional finite element models employ mesh tieing between a topologically continuous, global mesh and a separate, local crack-front mesh. Analyses of a simple plate model that approximates key features of toe cracks at the brace-chord intersection verify the negligible effects of the recommended mesh-tieing scheme on stress intensity factors. The linear-elastic analyses compute the mixed-mode stress intensity factors along the crack front using an interaction-integral approach. The mixed-mode stress intensity factors indicate that the crack front experiences predominantly mode I loading, with KIII→0 near the deepest point on the front (ϕ=π∕2). The total crack driving force, described by the J integral, reaches a maximum value at the deepest point of the crack for the crack aspect ratio a∕c=0.25 considered here. The mode-mixity angle, ψ=tan−1(KII∕KI), at ϕ=π∕2 is compared for a range of practical X-joint configurations and crack-depth ratios. The present study demonstrates that the mode-mixity angle ψ increases with increasing brace-to-chord diameter ratio (β) and decreasing chord radius to wall thickness ratio (γ). Values of the nondimensional stress intensity factors (FI=KI∕σ¯brπa and FII=KII∕σ¯brπa), however, show an opposite trend, with higher crack driving forces for small β and large γ ratios. The variations in the brace-to-chord wall thickness ratio (τ) and the crack depth ratio (a∕t0) do not generate significant effects on the mode mixity.
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Perl, M., and B. Ostraich. "The Effect of Autofrettage on Uniform Arrays of Three-Dimensional Unequal-Depth Cracks in a Thick-Walled Cylindrical Vessel." Journal of Pressure Vessel Technology 127, no. 4 (May 4, 2004): 423–29. http://dx.doi.org/10.1115/1.2043210.
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The distribution of the mode I stress intensity factor (SIF), resulting from autofrettage, along the fronts of radial, semi-elliptical surface cracks pertaining to large uniform arrays of unequal-depth cracks emanating at the bore of an overstrained thick-walled cylinder is studied. The three-dimensional analysis is based on the “two-crack depth level model” previously proposed and is performed via the finite element method employing singular elements along the crack front. The autofrettage residual stress field is simulated using an equivalent thermal load. The distribution of KIA, the stress intensity factor due to autofrettage, for numerous uneven array configurations bearing n=n1+n2=8-128 cracks, a wide range of crack depth-to-wall thickness ratios, a1∕t=0.01-0.4, and various crack ellipticities, a1∕c1=0.3-1.5, are evaluated for a cylinder of radii ratio Ro∕Ri=2. The results clearly indicate that unevenness, as reflected in KIA distribution, depends on all three parameters (i.e., the number of cracks in the array, cracks’ depth, and cracks’ ellipticity). The “interaction range” for the different combinations of crack arrays and crack depths is then evaluated. The range of influence between adjacent cracks on the maximal SIF, KAmax, is found to be dependent on the density of the array, as reflected in the intercrack aspect ratio, as well as on the cracks’ ellipticity.
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Perl, M., and B. Ostraich. "Analysis of Uniform Arrays of Three-Dimensional Unequal-Depth Cracks in a Thick-Walled Cylindrical Pressure Vessel." Journal of Pressure Vessel Technology 125, no. 4 (November 1, 2003): 425–31. http://dx.doi.org/10.1115/1.1613946.
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The effect of crack depth unevenness on the mode I stress intensity factor (SIF) distributions along the fronts of semi-elliptical surface cracks is studied. These three-dimensional radial cracks pertain to large uniform arrays of unequal-depth cracks emanating from the bore of a pressurized thick-walled cylinder. The analysis is based on the “two crack depth level model,” previously proposed, and is performed via the finite element (FE) method employing singular elements along the crack front. The distribution of KIP-the stress intensity factor due to pressurization, for numerous uneven array configurations bearing n=n1+n2=8 to 128 cracks, a wide range of crack depth to wall thickness ratios, a1/t=0.01 to 0.4, and various crack ellipticities, a1/c1=0.3 to 1.5, are evaluated for a cylinder of radii ratio Ro/Ri=2. To increase the accuracy of the evaluated SIFs an existing improved version of the displacement extrapolation method is used. The results clearly indicate that unevenness, as reflected in KIP distributions, depends on both the number of cracks in the array as well as on the cracks’ depths and ellipticities. The “interaction range” for the various configurations of uneven crack arrays is evaluated. The range of influence between adjacent cracks on the maximal SIF, KPmax, is found to be dependent on the density of the array, as reflected in the inter-crack aspect-ratio, as well as on the cracks’ elipticity.
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Perl, M., and B. Ostraich. "The Combined Effect of Pressure and Autofrettage on Uniform Arrays of Three-Dimensional Unequal-Depth Cracks in Gun Barrels." Journal of Pressure Vessel Technology 127, no. 4 (October 31, 2005): 464–70. http://dx.doi.org/10.1115/1.1806445.
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Due to the repeated firing of the gun, large uniform arrays of unequal-depth fatigue cracks develop from the inner surface of the barrel. The combined effect of pressure and autofrettage on the mode I stress intensity factor (SIF) distribution along the fronts of these three-dimensional, semi-elliptical, surface cracks is herein studied. Crack depth inequality is modeled using the “two-crack depth level model” previously proposed. The analysis is performed via the finite element (FE) method employing singular elements along the crack front. The autofrettage residual stress field is simulated using an equivalent thermal load. The distribution of the combined stress intensity factor due to pressurization and full autofrettage KIN=KIP+KIA, for numerous array configurations is evaluated for a barrel of outer to inner radii ratio of Ro/Ri=2. These configurations bear n=n1+n2=8 to 128 cracks, a wide range of crack depth to wall thickness ratios, a1/t=0.01 to 0.40, and various crack depth to half-length ratios (ellipticities) a1/c1=0.30 to 1.50. The results for KIN distributions clearly indicate that the level of effect of crack depth inequality depends on all three parameters: crack number in the array, crack depth and crack ellipticity. Furthermore, the results indicate that adjacent unequal-depth cracks influence each other only within a limited range of their depths, i.e., the “interaction range”. The range of influence between adjacent cracks on the maximal SIF KNmax depends on crack ellipticity and is found to be inversely proportional to the crack density of the array. The results re-emphasize the favorable effect the residual stress field has on the fracture endurance and the fatigue life of gun barrels bearing uniform arrays of three-dimensional unequal-depth cracks at their inner surface. This favorable effect is governed by the ratio of the gun’s material yield stress to its internal pressure—ψ=σ0/p. The higher ψ is, the more effective autofrettage becomes.
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Zhang, Quan, Bingxiang Huang, Manchao He, and Shan Guo. "A Numerical Investigation on the Hydraulic Fracturing Effect of Water Inrush during Tunnel Excavation." Geofluids 2020 (December 4, 2020): 1–15. http://dx.doi.org/10.1155/2020/6196327.
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When a high-pressure water source is located near a tunnel under excavation, water inrush is commonly associated with a hydraulic fracturing effect. To study the hydraulic fracturing effect of water inrush (HFEWI), flow-rock failure process analysis (F-RFPA2D) was adopted to simulate the water inrush process. The simulated results indicated that a stress disturbance area formed in front of the excavation face and that a hydraulic fracture zone formed in front of the karst cavity. Similarly, stress concentrations formed in front of the excavation face and the karst cavity. The hydraulic fracturing effect was characterized by stress concentration, and the local hydraulic crack propagation was the result of stress concentration. In addition, a pore pressure gradient formed in the crack-free area of the surrounding rock, and the occurrence of hydraulic cracking was the root cause of the significant change in water flow. When the hydraulic cracks initially formed and expanded, the zone of crack activity was large. As the cracks continued to expand, the range of activity decreased and finally concentrated directly in front of the excavation face. Additionally, the shapes of the water inrush channel obtained by the experimentation and numerical simulation were basically the same: semielliptical. During the evolution of hydraulic crack initiation, expansion, and penetration, the bottom of the excavated borehole was initially dry and then experienced seepage and water inrush. Finally, the minimum safe thickness of the rock wall was calculated to provide a safety guideline for this type of water inrush.
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Levy, C., M. Perl, and N. Kokkavessis. "Three-Dimensional Interaction Effects in an Internally Multicracked Pressurized Thick-Walled Cylinder—Part II: Longitudinal Coplanar Crack Arrays." Journal of Pressure Vessel Technology 118, no. 3 (August 1, 1996): 364–68. http://dx.doi.org/10.1115/1.2842201.
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In the first part of this paper, the interaction effects among many radial, internal, semi-circular, and semi-elliptical cracks in a pressurized, thick-walled vessel were quantified. In the present paper, the mode I stress intensity factor (SIF) distribution for numerous longitudinal coplanar, internal, semi-circular, and semi-elliptical arrays of surface cracks in an infinite, pressurized, thick-walled cylinder are evaluated. The 3-D analysis is performed by the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. The effects of dense and sparse interacting longitudinal coplanar crack arrays on the SIFs are studied for a wide range of crack depth to wall thickness ratios, a/t, from 0.05 to 0.6; and, for various ellipticities of the crack, i.e., the ratio of the crack depth to semi-crack length, a/c, from 0.2 to 2.0. An analysis is performed to determine the influence of the three major parameters—crack density, crack ellipticity, and crack depth—on the interaction effects between adjacent cracks. The results clearly indicate that crack density, and, in some cases, ellipticity have opposing effects on the SIF of longitudinal crack arrays as compared to radial crack arrays. As a result of these contrasting behaviors, thick-walled cylinders having combined longitudinal and radial crack arrays would need further study.
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Jin, You-lin, Song-lin Du, and Chao-jie Zhang. "Influence mechanism of large inclusion on wheel fatigue crack." Metallurgical Research & Technology 118, no. 5 (2021): 508. http://dx.doi.org/10.1051/metal/2021068.
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In this paper, the formation mechanism of wheel rim crack and control technique was investigated. Feature of wheel rim crack and aggregated attachments on the inner wall of nozzle were examined through scanning electron microscope and energy dispersive spectrometer. Metal rheological test of round billet rolling was conducted to investigate the corresponding location of large inclusions in the round billet and in the wheel. It was found that the rim crack of wheels during service is caused by large inclusions that originated from the aggregated inclusions on the inner wall of the nozzle. According to Murakami’s modelling, the critical size of the inclusions that initiate cracks relates to the depth from the tread. The critical sizes of the inclusions for cracks initiation at 10 mm, 14 mm, 16 mm and 20 mm below the tread are about 0.1 mm, 0.2 mm, 0.5 mm and 1.5 mm, respectively. Process optimization was made with combination of a series methods. Dispersed annular venting stopper was adopted to block the aggregation and attachment of inclusions on the inner wall of nozzle. Current and frequency of electromagnetic stirring in mold were increased to restrain the impact depth of molten steel flow and inclusions. Cooling intensity of the secondary cooling was decreased to reduce the probability of inclusions captured at the solidification front. After optimization, the number of large inclusions was greatly reduced by more than 80%, and the number of inclusions larger than 1 mm is greatly reduced from 35% to 8%. The risk of wheel rim cracks occurrence could be reduced greatly.
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Zhao, Guang Hui, Hao Han Wang, Jian Shi, and Li Zhao. "Elastic-Plastic Fracture Mechanics Analyses of Surface Cracks in Drill String Subjected to Combined Loading." Key Engineering Materials 626 (August 2014): 62–67. http://dx.doi.org/10.4028/www.scientific.net/kem.626.62.
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The drill pipe near the surface stands the largest tension and torsion load for the full hole during drilling operation. And fatigue crack growth is always the major cause of failure of drill string. As an example, 5ʺ drill pipe that was near the well head of an ultra-deep straight well and made of 30CrMo, whose constitutional relation was fitted by experiment, was analyzed here. Simplifying the initial crack of the drill pipe as circumferential semi-elliptical surface crack, we simulated the elastic-plastic fracture feature of the drill string with surface crack, partly through-wall crack and fully through-wall crack under combined loading of axial force and torsion. Crack front geometry evolvement is simulated for the different stages of crack propagation. This work would provide a basis for the full-range analysis of fatigue crack growth.
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Perl, M., C. Levy, and J. Pierola. "Three-Dimensional Interaction Effects in an Internally Multicracked Pressurized Thick-Walled Cylinder— Part I: Radial Crack Arrays." Journal of Pressure Vessel Technology 118, no. 3 (August 1, 1996): 357–63. http://dx.doi.org/10.1115/1.2842200.
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Under certain conditions, numerous internal surface cracks develop in pressurized thick-walled cylinders, both in the radial and longitudinal directions. For fatigue life assessment of such vessels, the 3-D interaction effects among these cracks on the prevailing stress intensity factors (SIFs) need evaluation. In Part I of this paper, radial crack arrays are considered exclusively. The mode I SIF distribution for a wide range of semi-circular and semi-elliptical cracks are evaluated. The 3-D analysis is performed via the finite element method with the submodeling technique, employing singular elements along the crack front. SIFs are evaluated for arrays of up to n = 180 cracks; for a wide range of crack depth to wall thickness ratios, a/t, from 0.05 to 0.6; and, for various ellipticities of the crack, i.e., the ratio of crack depth to semicrack length, a/c, from 0.2 to 2. Using a least-squares fit, two simple expressions for the most critical (n = 2) SIFs are obtained for sparse and dense crack arrays. The formulas, which are functions of a/t and a/c, are of very good engineering accuracy. The results clearly indicate that the SIFs are considerably affected by the interaction among the cracks in the array as well as the three-dimensionality of the problem. In Part II of this paper, the interaction effects between longitudinal coplanar cracks will be analyzed.
Dissertations / Theses on the topic "Front wall crack"
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Šubrt, Stanislav. "Návrh přístroje pro analýzu vzniku a šíření trhlin." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231511.
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The main goal of this thesis is to get an insight into a field of non-destructive testing using potential drop techniques that have nowadays become the standard not only in the fatigue and loading tests but also in the industry. These methods can serve to non-destructively and continuously measure material specimens, thickness, corrosion losses, deformations, spectroscopy and detection and analysis of crack geometry. They can help to identify materials and measure material changes over time. The second part of this thesis deals with designing the aperture for detection of cracks in steam and product piping using potential drop technique modified by Ing. Ladislav Korec, CSc. Last part deals with extensive testing, experimenting and evaluation of the aperture.
Conference papers on the topic "Front wall crack"
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Shim, Do-Jun, David Rudland, and Jeong-Soon Park. "Surface to Through-Wall Crack Transition Model for Axial Cracks in Pipes." In ASME 2014 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/pvp2014-28048.
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Recent studies have shown that a subcritical surface crack, due to PWSCC, can transition to a through-wall crack with significant differences between the inner diameter and outer diameter crack lengths. This behavior has been observed for both circumferential and axial cracks. Recently, a surface to through-wall crack transition model has been developed for circumferential cracks using existing K and COD solutions for non-idealized circumferential through-wall cracks. In this paper, a similar crack transition model was developed for axial cracks. As a first step, a study was conducted to define the appropriate crack front shape for non-idealized axial through-wall cracks. Then, elastic finite element analyses were carried out to develop K and COD solutions using these crack front shapes. The newly developed solutions were utilized for the crack transition model. The present crack transition model includes a criterion for transitioning the final surface crack to the initial non-idealized TWC. This criterion determines when the transition should occur (based on surface crack depth) and determines the two crack lengths (at ID and OD surfaces) of the initial non-idealized TWC. Furthermore non-idealized TWC growth can be conducted using the proposed model. Example results (crack length and COD) obtained from the proposed model were compared to those obtained from the natural crack growth simulations. Results presented in this paper demonstrated the applicability of the proposed model for simulating axial crack transition.
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Qian, Xudong, and Tieping Li. "Residual Stress Effects on the Crack-Front Constraints for Surface Cracks in Pipes." In ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/omae2010-20068.
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This paper investigates the effect of residual stresses on the linear-elastic KI-T fields along the front of circumferential surface cracks in pipelines. The numerical procedure simulates three typical patterns of residual stresses through a modified eigenstrain approach, which combines a thermal loading with a mechanical traction imposed on the heat-affected zone. The three residual stress profiles considered correspond to the high-heat input, the medium-heat input and the low heat input welding processes for circumferential butt welds in pipes outlined in BS 7910. The linear-elastic KI-T stresses, computed from the interaction-integral approach, characterize the constraints along the front of the circumferential flaw. The numerical investigation, covering a comprehensive matrix of geometric parameters, shows that different residual stress fields impose substantial effects on the KI-T stresses along the front of the surface crack in the wall of a pipeline. The deepest point along the crack-front often experiences low crack-front constraints characterized by the computed negative T-stresses for all three residual stress fields considered. The magnitudes of the KI-values and T-stresses show pronounced variations with the change in the ratio of the crack depth over the wall thickness of the pipe (a/t). The variation in the crack aspect ratio (the crack depth over the crack length, a/c) introduces marginal variation in the computed T stresses. The ratio of the outer diameter to the wall thickness of pipe imposes very little effect on the linear-elastic crack-front constraints for the geometric parameters considered.
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Liu, Jun, Bo Yan, and Naibin Jiang. "Computational Method for Crack-Opening-Area of Nuclear Pressure Pipe With Circumferential Through-Wall Crack." In 18th International Conference on Nuclear Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/icone18-29450.
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The determination of crack-opening-area (COA) is very important in the application of LBB technique. A numerical method based on coupled finite element-meshless Galerkin method (FEM/EFG) is proposed to calculate the crack-opening-area of cracked pipes in nuclear power station. By means of the method by which the meshless nodes are used in the vicinity of crack front and the finite elements are applied in remained zone, the resolved domain is numerically discreted. This technique can speed up the set up of the numerical model and improve the computational precise. Based on the displacement field determined by the coupled FEM/EFG, a kind of surface integral method is used to accurately calculate the crack-opening-area. The correctness and validity of the presented method are demonstrated by comparing the COA results of centre-cracked panel under uniform load determined by the presented method with those from theoretic formula. Subsequently the numerical method for cracked panel is employed to calculate the crack-opening-area of nuclear pressure pipe. The numerical COA results are compared with those determined by engineering methods. It is shown that for thick-wall or middle-thick-wall pipes, the COA results obtained by the presented method are more conservative than those by the engineering methods, whereas for thin-wall pipes, the results by the later one are more conservative than those by the former.
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Huh, Nam-Su, Do-Jun Shim, Ji-Ho Kim, Gery M. Wilkowski, and Jun-Seok Yang. "Stress Intensity Factors of Slanted Through-Wall Cracks in Plate and Cylinder." In ASME 2007 Pressure Vessels and Piping Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/pvp2007-26209.
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For Leak-Before-Break (LBB) analysis of nuclear piping, a circumferential through-wall crack (TWC) with the crack front parallel to the cylinder radius is typically postulated, i.e., an idealized TWC. Such assumption simplifies the LBB analysis significantly. However, in reality, an internal surface crack grows through the wall thickness and penetrates through the wall thickness at the deepest point. Hence, a TWC with different crack lengths at inner and outer surfaces is formed. Such a TWC is referred to as a “slanted TWC” in the present study. Leak rates as well as SCC and fatigue crack growth rates of slanted TWC are expected to be quite different from those of postulated idealized TWC. In this context, characterization of the actual TWC shape during crack growth due to fatigue or stress corrosion cracking is essential for accurate LBB analysis. Based on detailed 3-dimensional (3-D) elastic finite element (FE) analyses, the present paper provides stress intensity factors (SIFs) for plates and cylinders with slanted TWCs. As for loading conditions, axial tension was considered for the plates, whereas axial tension and global bending were considered for the cylinders. In order to cover the practical range of crack sizes, the geometric variables affecting the SIF were systematically varied. Based on FE analysis results, SIFs along the crack front, including the inner and outer surface points, were provided. The SIFs of slanted TWC can be used to evaluate the fatigue crack growth of a TWC and to perform detailed LBB analysis considering a more realistic crack shape.
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Thorwald, Greg, and Pedro Vargas. "Cylinder Axial Crack Reference Stress Comparison Using Elastic-Plastic FEA 3D Crack Mesh J-Integral Values." In ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65760.
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The reference stress for axial (longitudinal) surface cracks in cylinders is compared using equations from the 2016 API 579-1/ASME FFS-1 and BS 7910:2013 engineering standards, and by using J-integral values from elastic-plastic Finite Element Analysis of three-dimensional crack meshes to compute crack front reference stress. The cylinder axial surface crack reference stress solutions from the two standards differ, and further examination and comparison is desired. To evaluate if a crack is unstable and may cause catastrophic structural failure, the Failure Assessment Diagram method provides an evaluation using two ratios: brittle fracture and plastic collapse. The FAD vertical axis gives the Kr stress intensity to toughness ratio, and the FAD horizontal axis gives the Lr reference stress to yield strength ratio. The details of the FAD method are described in both standards, along with stress intensity and reference stress solutions for various geometries and crack shapes. Since the cylinder axial surface crack reference stress solutions from API 579 and BS 7910 differ, J-integral values are used to compute reference stress trends that provide additional insight and reveal if there is agreement with one or the other or neither standard. Computing reference stress from crack front J-integral results is described in API 579 Annex 9G Section 9G.4. A 3D crack mesh is created for each crack and cylinder size. Along the crack front the focused mesh pattern uses initially coincident groups of nodes at each crack front position. The group of nodes at each location on the crack front are initially coincident and can separate to help model the blunting at the crack front as the loading increases and local plasticity occurs. Post processing calculations use the J-integral versus load trend and the material specific Kr at Lr = 1 ratio to determine the reference stress geometry factor. The reference stress is computed at each crack front node to find the maximum crack front reference stress value for comparison to the engineering standards’ reference stress solutions. A range of surface crack sizes in thin to thick wall cylinders with internal pressure are used to examine reference stress trends. Standard pipe sizes and typical pipeline steel material is used in the analysis. The difference in reference stress solutions was found during an engineering critical assessment, so the J-integral approach was used to improve the solution to reduce conservatism and allow the component to remain in service.
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Rabczuk, T., B. Bezensek, and S. Bordas. "Application of Extended Element-Free Galerkin Method to Multiple Flaws Under Brittle Fracture Conditions." In ASME 2008 Pressure Vessels and Piping Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/pvp2008-61550.
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The extended element-free Galerkin (XEFG) method incorporates cracks through partition of unity enrichment of the standard basis functions. Discontinuous functions are added to capture the jump through the crack faces and near-front enrichment is added to capture the asymptotic behaviour in the vicinity of the crack fronts. Depending on the material behaviour, these functions can be of various type. The method can treat initiation, growth and coalescence of cracks seamlessly in both linear elastic and non-linear settings. The method is a powerful tool for modelling and studying crack paths, which are a central feature in the assessment of multiple flaws. The method is applied to the problem of multiple non-aligned flaws in a ferritic plate under cleavage failure. Fracture paths from two non-aligned notches in a plate are modelled. Based on the observations of crack paths the critical flaw alignment distance is established for non-aligned through-wall flaws.
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Bourga, Renaud, Bin Wang, Philippa Moore, and Yin Jin Janin. "The Effect of Crack Shape Idealisation on Leak-Before-Break Assessment." In ASME 2016 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/pvp2016-63877.
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Based on detailed 3D finite element (FE) analyses, idealized and non-idealized axial through-wall flaws were evaluated in a cylinder under internal pressure. The key parameters (Stress Intensity Factor, Reference stress, and Crack Opening Area) from widely accepted structural integrity assessment procedures (BS 7910 and API 579-1/ASME FFS-1) were explored and compared between idealized (perpendicular straight-sided flaw) and non-idealized geometry. The effect of crack shape on the evolution of stress intensity factors and crack opening areas along the crack front were also investigated. Non-idealized crack shapes have been modelled assuming a straight crack front with different internal and external crack lengths. The influence of crack shape has been evaluated by varying the crack front location and lengths ratios. The current findings highlight the significance of assessing a more realistic crack shape and should be considered in a leak-before-break (LBB) analysis. A non-idealized crack has a significantly smaller crack opening area than the equivalent idealized through-wall crack. Therefore the leakage rate at this stage of crack growth will be lower than predicted by standard solutions. Stress intensity factor solutions should also take the crack shape variation into account with regards to fatigue crack growth as a surface flaw propagates through-thickness.
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Telichev, Igor. "Failure Analysis of Impact Damaged Pressure Vessels and Pipelines." In 2008 7th International Pipeline Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/ipc2008-64332.
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The present paper is devoted to analysis of burst conditions of the pipeline-in-service and vessel under high pressure subjected to the debris impact due to accidental explosion. The central concern of this study is to determine the border between simple perforation and catastrophic fracture of impact damaged pressurized structure. Under certain conditions vessel perforation from the front side can lead to unstable, rapid crack growth (“unzipping”). The pressure vessel of the relatively small size can be damaged from the rear side as well. As a consequence, two main classes of catastrophic failure of such structures are likely to occur: structure fracture from the front side and failure from the rear side. Damage patterns and mechanisms leading to unstable crack growth are discussed. The impact holes in a wall of pressurized structure are considered as a crack-like defect. By the model suggested, the cracked area around the penetrated hole is simulated by two radial cracks emanating from the rim of a hole. So the diameter of the model hole is equal to the diameter of the front impact hole; the length of the crack is bounded by a damage zone, which is a zone of spall cracks adjacent to the perforated hole. In a gas-filled cylinder shell the stresses in the circumferential direction are twice the longitudinal stresses. Thus, in the process of fracturing the cracks tend to run longitudinally, perpendicular to the hoop stress. By this reason the hypothetical radial cracks are normal to the hoop stress. Nonlinear fracture mechanics techniques were used to analyze and predict whether a wall perforation will lead to mere leakage of gas, or whether an unstable crack will run and destroy the pressurized structure. The problem was solved by numerical method of singular integral equations in Chebyshev’s polynomials. A developed model was successfully applied to the simulation of experimental results.
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Perl, M., and V. Bernstein. "Three-Dimensional Stress Intensity Factors for Arrays of Radial Cracks Emanating From the Inner Surface of a Thick-Walled Spherical Pressure Vessel." In ASME 2008 9th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2008. http://dx.doi.org/10.1115/esda2008-59158.
Full textAbstract:
Some spherical pressure vessels are manufactured by methods such as the Integrated Hydro-Bulge Forming (IHBF) method, where the sphere is composed of a series of double curved petals welded along their meridional lines. Such vessels are susceptible to multiple radial cracking along the welds. For fatigue life assessment and fracture endurance of such vessels one needs to evaluate the Stress Intensity Factors SIF distribution along the fronts of these cracks. However, to date, only two-dimensional SIFs for one through the thickness crack in a thin spherical shells is available. In the present paper, mode I SIF distributions for a wide range of lunular and crescentic cracks are evaluated. The 3-D analysis is performed, via the FE method employing singular elements along the crack front, for three sphere geometries with outer to inner radius ratios of η = Ro/Ri = 1.1, 1.7, and 2.0. SIFs are evaluated for arrays containing n = 1–20 cracks,; for a wide range of crack depth to wall thickness ratio, a/t, from 0.025 to 0.8; and for various ellipticities of the crack, i.e., the ratio of crack depth to semi crack length, a/c, from 0.2 to 1.5. The obtained results clearly indicate that the SIFs are considerably affected by the three-dimensionality of the problem and by the geometrical parameters: the geometry of the sphere – η, the number of cracks in the array – n, the depth of the crack – a/t, and its ellipticity – a/c.
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Perl, M., and V. Berenshtein. "Three-Dimensional Stress Intensity Factors for Ring Cracks and Arrays of Coplanar Cracks Emanating From the Inner Surface of a Spherical Pressure Vessel." In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97006.
Full textAbstract:
Certain spherical pressure vessels are composed of two hemispheres joined together by a girth weld. These vessels are susceptible to multiple cracking along the weld resulting in one or more cracks developing from the inner surface of the vessel and creating either a ring (circumferential) crack, or an array of coplanar cracks on the equatorial-weld plane. In order to assess the fracture endurance and the fatigue life of such vessels it is necessary to evaluate the Stress Intensity Factors (SIF) distribution along the fronts of these cracks. However, to date, only two solutions for the SIF for an internal ring crack as well as two 3-D solutions for a single internal semi-elliptical crack prevailing in various spherical pressure vessels are available. In the present analysis, mode I SIF distributions for a wide range of ring, lunular, and crescentic cracks are evaluated. The 3-D analysis is performed, via the FE method employing singular elements along the crack front. SIFs for numerous ring cracks of different depths prevailing in thin, moderately thick, and thick spherical vessels are evaluated first. Subsequently, Three-dimensional Mode I SIF distributions along the crack fronts of a variety of lunular and crescentic crack array configurations are calculated for three spherical vessel geometries, with outer to inner radii ratios of R0/Ri = 1.01, 1.1, and 1.7 representing thin, moderately thick, and thick spherical vessels. SIFs are evaluated for arrays of density δ = 0 to 0.99; for a wide range of crack-depth to wall-thickness ratios, a/t, from 0.025 to 0.95; and for various lunular and crescentic cracks with ellipticities, i.e., the ratio of crack-depth to semi-length, a/c, from 0.2 to 1.5. The obtained results clearly indicate that the SIFs are considerably affected by the three-dimensionality of the problem and by the following parameters: the crack density of the array – δ, the relative crack depth – a/t, crack ellipticity – a/c, and the geometry of the spherical vessel – η. Furthermore, it is shown that in some cases the commonly accepted approach that the SIF for a ring crack of any given depth is the upper bound to the maximum SIF occurring in an array of coplanar cracks, of the same depth, is not universal.