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1
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.
Full textAbstract:
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.
2
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.
3
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.
7
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.
9
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.
10
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.
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Perl, M., C. Levy, and V. Rallabhandy. "The Influence of the Bauschinger Effect on 3D Stress Intensity Factors for Internal Radial Cracks in a Fully or Partially Autofrettaged Gun Barrel." Journal of Pressure Vessel Technology 128, no. 2 (November 30, 2005): 233–39. http://dx.doi.org/10.1115/1.2172622.
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The influence of the Bauschinger effect (BE) on the three-dimensional, mode I, stress intensity factor (SIF) distributions for arrays of radial, internal, surface cracks emanating from the bore of a fully or partially autofrettaged thick-walled cylinder is investigated. A thorough comparison between the prevailing SIFs for a “realistic” (Bauschinger effect dependent autofrettage (BEDA)) and those for an “ideal” (Bauschinger effect independent autofrettage (BEIA)) is done. The three-dimensional (3D) analysis is performed via the finite element method and the submodeling technique, employing singular elements along the crack front. Both autofrettage residual stress fields, BEDA and BEIA, are simulated using an equivalent temperature field. More than 300 different crack configurations are analyzed. SIFs for numerous crack arrays (n=1-64 cracks), a wide range of crack depth to wall thickness ratios (a∕t=0.01-0.2), various ellipticities (a∕c=0.5-1.5), and different levels of autofrettage (ε=30-100%) are evaluated. The Bauschinger Effect is found to considerably lower the beneficial stress intensity factor due to autofrettage, KIA, by up to 56%, as compared to the case of ideal autofrettage. The reduction in KIA varies along the crack front with a maximum at the point of intersection between the crack plane and the inner surface of the cylinder, decreasing monotonically toward the deepest point of the crack. The detrimental influence of the BE increases as the number of cracks in the array increases and as crack depth decreases. For a partially autofrettaged cylinder, as the level of overstrain becomes smaller the influence of the BE is considerably reduced. As a result, the SIFs due to 100% BEDA differ by <10% as compared to 60% BEDA, and on the average the difference is only about 2–4%.
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Perl, M., and A. Nachum. "3-D Stress Intensity Factors for Internal Cracks in an Overstrained Cylindrical Pressure Vessel—Part I: The Effect of Autofrettage Level." Journal of Pressure Vessel Technology 122, no. 4 (July 21, 2000): 421–26. http://dx.doi.org/10.1115/1.1310162.
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Three-dimensional, mode I, stress intensity factor (SIF) distributions for arrays of internal surface cracks emanating from the bore of an autofrettaged thick-walled cylinder are evaluated in Part I of this paper. The 3-D analysis is performed via the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. The autofrettage residual stress field is simulated using an equivalent temperature field. More than 200 different crack configurations were analyzed. SIFs for numerous crack arrays (n=1–180 cracks), a wide range of crack-depth-to-wall-thickness ratios a/t=0.05-0.6, various ellipticities a/c=0.2-1.5, and different levels of autofrettage (e=10–100 percent) were evaluated. The results clearly indicate the importance of autofrettage in reducing the effective stress intensity factor, and thus, slowing the crack growth rate. The sensitivity of this favorable effect to the number of cracks in the array as well as to the level of autofrettage are also discussed. The combined effect of pressure and autofrettage is discussed in detail in Part II of this paper. [S0094-9930(00)00604-1]
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Perl, M., C. Levy, and J. Wang. "Interaction Effects in Combined Arrays of Radial and Longitudinal Semi-Elliptical Surface Cracks in Pressurized Thick-Walled Cylinder." Journal of Pressure Vessel Technology 119, no. 2 (May 1, 1997): 167–74. http://dx.doi.org/10.1115/1.2842279.
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In two previous papers, the interaction effects for two separate cases of large arrays of semi-elliptical, internal, surface cracks in a thick-walled, cylindrical pressure vessel were studied. First, arrays of radial cracks were considered followed by the study of longitudinal-coplanar crack arrays. Circumferential crack density and longitudinal crack spacing were found to have opposing effects on the prevailing stress intensity factors (SIFs). Consequently, in the present paper, combined arrays of both radial and longitudinal cracks are considered, and their interaction effects are studied. The mode I stress intensity factor (SIF) distribution for numerous configurations of combined semi-circular and semi-elliptical crack arrays 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 crack density in the circumferential direction and of relative spacing in the longitudinal direction on the SIFs are studied for combined arrays of up to 32 circumferentially equispaced, radial cracks and having longitudinal relative spacing of 2c/d of 0.25 to 0.99; for a wide range of crack depth to wall thickness ratios, a/t, from 0.05 to 0.4; and for various ellipticities of the crack, i.e., the ratio of crack depth to semicrack length, a/c, from 0.2 to 1.5. The results clearly indicate that the SIFs are considerably affected by the interaction among the cracks, and that the SIF values depend upon the circumferential density and longitudinal spacing, the crack depth and ellipticity, as well as the three-dimensional nature of the problem.
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Kikuchi, M., H. Miyamoto, and S. Sugawara. "Evaluation of the J-Integral of a Crack in a Pressure Vessel Under Thermal Transient Loadings." Journal of Pressure Vessel Technology 108, no. 3 (August 1, 1986): 312–19. http://dx.doi.org/10.1115/1.3264791.
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To assure the safe design of reactor vessels, the parameters of the fracture mechanics are evaluated for an assumed crack subjected to internal pressure and thermal loading. Several kinds of cracks are assumed to exist in the pressure vessel and two and three-dimensional finite element analyses are carried out. As the parameters of fracture, the J-integral and extended ones for a thermal field and a multi-phase material are used. The effect of the cladding on the J values is evaluated and discussed. It is shown that the contraction of the vessel wall, due to the decrease of the temperature at the inner surface, strongly affects the J value. Though three-dimensional analyses, the shape of the growing surface crack is estimated from the distribution of the J values along the crack front.
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Perl, M., C. Levy, and J. Bu. "Three-Dimensional Analysis of a Semi-Elliptical Crack Emanating From an Erosion at the Bore of an Autofrettaged Pressurized Cylinder." Journal of Pressure Vessel Technology 121, no. 2 (May 1, 1999): 209–15. http://dx.doi.org/10.1115/1.2883688.
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The effect of various erosion configurations on the mode I stress intensity factor (SIF) distribution along the front of a semi-elliptical crack, emanating from the deepest line of the erosion surface (DLES) at the bore of an autofrettaged, pressurized thick-walled cylinder of outer to inner radius ratio, Ro/Ri = 2, is investigated. The three-dimensional (3-D) linear elastic problem is solved via the finite element (FE) method using the ANSYS 5.2 standard code. Hill’s autofrettage residual stress field is simulated by an equivalent thermal load and the SIFs are determined by the nodal displacement method. SIF distribution along the front of semi-elliptical cracks of various crack depths to wall thickness ratios, a/t = 0.05 to 0.25, and ellipticities, a/c, ranging from 0.5 to 1.5, emanating from the DLES, are determined. Three groups of erosion geometries are considered: (a) arc erosions of constant relative depth, d/t, equal to 5 percent and with relative radii of curvature, r′/t, between 5 and 30 percent; (b) semi-elliptic erosions of constant relative depth, d/t, of 5 percent with erosion ellipticity, d/h, varying from 0.3 to 2.0; and (c) semi-circular erosions of relative depth, d/t, between 1 and 10 percent of the wall thickness. The effective SIF along the crack front results from the superposition of KIP—the SIF due to pressurization, and KIA—the negative SIF due to the autofrettage residual stress field. KIP is highly dependent on the stress concentration ahead of the DLES which directly relates to the erosion geometry. The absolute value of KIA is just slightly reduced by the presence of the erosion. Its change solely depends on, and is directly proportional to, the erosion depth. Thus, while deep cracks are almost unaffected by the erosion, the effective SIF for relatively short cracks is found to be significantly enhanced by its presence and might result in a shortening of the vessel’s fatigue life by up to an order of magnitude. Also, it is shown that 2-D analysis may lead to a nonconservative estimate of the vessel’s fatigue life.
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Tan, Choon-Lai, Anthony P. Parker, and Chantz W. V. Cassell. "Stress Intensity Factors for a Curved-Front Internal Crack in an Autofrettaged Tube With Bauschinger Effect." Journal of Pressure Vessel Technology 126, no. 2 (May 1, 2004): 229–33. http://dx.doi.org/10.1115/1.1689358.
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Pressure vessel steels exhibit the Bauschinger effect that significantly reduces post-autofrettage residual compressive hoop stresses in the near-bore region in comparison with ‘ideal’ (elastic-perfectly plastic) behavior. These reduced hoop stress profiles were calculated using Von Mises’ criterion via a nonlinear analysis for the case of open-end (engineering plane strain) autofrettage. These profiles were then used to obtain stress intensity factor solutions via the Boundary Integral Equation (BIE) method, commonly known as the Boundary Element Method (BEM). Results are presented for tubes of diameter ratio 2 and 2.5 with an internal semi-elliptical surface crack having a maximum depth/surface length ratio of 0.4 (i.e., an eccentricity of 0.8). Crack depths range from 20% to 80% of wall thickness and results are presented for seven locations on the crack front from maximum depth to free surface. For crack depths up to 20% of wall thickness there is a significant reduction in magnitude of autofrettage stress intensity factor due to Bauschinger effect. For typical overstrain levels this reduction is approximately 30% of “ideal” values. Such a reduction may, in turn, cause an order of magnitude reduction in the fatigue lifetime of the vessel.
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Pan, J. "Estimation of Energy Release Rates and Instability Analysis for a Pipe With a Circumferential Surface Crack Subjected to Bending." Journal of Pressure Vessel Technology 108, no. 1 (February 1, 1986): 33–40. http://dx.doi.org/10.1115/1.3264749.
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An estimation of the energy release rate J for a three-dimensional nonlinear elastic solid containing a two-dimensional plane crack is presented. Special attention is focused on a pipe with a circumferential surface crack subjected to bending. The present analysis gives an estimation of the distribution of J along the crack front of a circumferential surface crack. Fracture instability of the cracked solid is also discussed. Based on the deformation theory of plasticity and a postulated criterion for crack growth, wall-breakthrough instability of the circumferential surface crack is examined. The predictions of the present analysis are in agreement with experimental observations, and indicate that a longer circumferential surface flaw is more susceptible to radial instability. Implications of this study on “leak before break” conditions are also discussed.
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Her, Shiuh-Chuan, and Hao-Hi Chang. "STRESS INTENSITY FACTORS OF A SEMI-ELLIPTICAL CRACK IN A HOLLOW CYLINDER." Transactions of the Canadian Society for Mechanical Engineering 39, no. 3 (September 2015): 557–68. http://dx.doi.org/10.1139/tcsme-2015-0043.
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In this investigation, the weight function method was employed to calculate stress intensity factors for semi-elliptical surface crack in a hollow cylinder. A uniform stress and a linear stress distribution were used as the two references to determine the weight functions. These two factors were obtained by a three-dimensional finite element method which employed singular elements along the crack front and regular elements elsewhere. The weight functions were then applied to a wide range of semi-elliptical surface crack subjected to non-linear loadings. The results were validated against finite element data and compared with other analyses. In the parametric study, the effects of the ratio of the surface crack depth to length ranged from 0.2 to 1.0 and the ratio of the crack depth to the wall thickness ranged from 0.2 to 0.8 on stress intensity factors were investigated.
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Wei, Jifeng, Zhixin Du, Yonghui Zheng, and Oundavong Ounhueane. "Research on Damage Characteristics of Brick Masonry under Explosion Load." Shock and Vibration 2021 (August 26, 2021): 1–11. http://dx.doi.org/10.1155/2021/5519231.
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As the main structural component of partition wall or load-bearing wall, brick masonry has been widely used in construction engineering. However, brick and mortar are all brittle materials prone to crack. Nowadays, fireworks, gas stoves, high-pressure vessels, and other military explosives may explode to damage nearby structures. Many explosion casualties had shown that the load-bearing capacity of brick masonry decreased dramatically and cracks or fragments appeared. Previous studies mainly focused on noncontact explosion in which shock wave is the main damage element. In fact, the response and damage effect of brick masonry wall under contact explosion are more complex, which attracts more attention now. In order to explore the damage characteristics of brick masonry under explosion load, a series of simulations and verification experiments are conducted. RHT and MO granular material models are introduced to describe the behaviour of brick and masonry, respectively, in simulation. The combination effect of front compressive wave and back tensile wave are main factors influencing the breakage of masonry wall. The experimental results are well in accordance with the simulation results. The front cross section dimension of crater is closely related to the radius of spherical explosive charge. A power function predictive model is developed to express the relationship between the radius of hole and the radius of explosive. Furthermore, with increasing the quantity of explosive charge, the number and ejection velocity of fragments are all increased. The relationship between maximum ejection velocity and the quantity of explosive also can be expressed as a power function model.
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Kumar, V., M. D. German, and B. I. Schumacher. "Analysis of Elastic Surface Cracks in Cylinders Using the Line-Spring Model and Shell Finite Element Method." Journal of Pressure Vessel Technology 107, no. 4 (November 1, 1985): 403–11. http://dx.doi.org/10.1115/1.3264474.
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This paper presents elastic analysis of axial and circumferential semielliptical surface flaws in cylinders using the line-spring model of Rice and Levy [1-3] and a shell finite element method. Results for the stress intensity factor are obtained at various points along the crack front, and are compared in some cases against published literature solutions. A broad range of values for the cylinder radius-to-wall thickness ratio, flaw depth and aspect ratio are considered including surface flaws with very large aspect ratios. The critical values of aspect ratio at which the surface flaws can be treated as 2-dimensional cracks are determined. Effect flaw location (internal or external) and flaw shape (semielliptical, circular or rectangular) are also investigated. Finally, the significance of these results in the elastic-plastic fracture analysis procedures is discussed.
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Sung, Yu, Daniel J. Cantliffe, and Russell T. Nagata. "Structural Changes in Lettuce Seed during Germination Altered by Genotype, Seed Maturation Temperature, and Priming." HortScience 32, no. 3 (June 1997): 526E—527. http://dx.doi.org/10.21273/hortsci.32.3.526e.
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Thermotolerance in lettuce seed at high temperature was investigated using primed and nonprimed seed or seeds matured at 20/10°C and 30/20°C. During seed germination at 36°C, the structural changes of the seed coverings in front of the radicle tip were observed in an anatomical study. In all seeds during imbibition, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition: the protein bodies in the vacuoles enlarged and were gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, then the radicle elongated toward this ruptured area. The findings suggested that the papery endosperm layer presented mechanical resistance to lettuce seed germination and the weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of `Dark Green Boston', `Everglades', and PI 251245 matured at 30/20°C had greater thermotolerance than those matured at 20/10°C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20°C were more easily disrupted and ruptured during early imbibition than seeds matured at 20/10°C, suggesting that these seeds could germinate quickly at supra-optimal temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, it was observed that genotype thermotolerance had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves.
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Chen, Qing Feng, Zhong Hui Chen, Ning Ma, Wei Zhang, and Hui Li. "The Zonal Disintegration Law within Coal in Front of Working Face in Deep Coal Mine." Applied Mechanics and Materials 353-356 (August 2013): 1082–89. http://dx.doi.org/10.4028/www.scientific.net/amm.353-356.1082.
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The mining coal in the front of long wall face consists of elastic zone, plastic zone and fracture zone. Based on the research of zonaldisintegration of surrounding rock mass in deep tunnel, the zonal disintegration phenomenon of deep coal mine was analyzed by using the theoretical analysis method. On the basis of the Griffith theory, the internal and external boundary formulas of fracture zone and the mechanical criteria of zonal disintegration were obtained. The research shows that the essence of zonal disintegration is the tensile failure and brittle tension crack failure under the abutment pressure, the main influence factors of the width variation of fracture zone are original rock stress and un-axial tensile strength of coal.
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Kaczmarek, Tomasz. "To break “the Black Wall”. The motif of fear in plays by Henri-René Lenormand." Acta Universitatis Lodziensis. Folia Litteraria Polonica 57, no. 2 (June 30, 2020): 27–38. http://dx.doi.org/10.18778/1505-9057.57.02.
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Henri-René Lenormand refreshed theatre, defining a new domain for it: the mysteries of the human soul. In all of his plays, he strived to explain the secret of internal life, as well as to solve the mystery that people are to themselves. Therefore, dramaturgy was for the author of La Folle du Ciel not only a means of literary expression, but also a kind of therapy, enabling him to combat his depression. In this article, three plays are discussed: Le Temps est un songe, Les Ratés, and Le Lâche, in which the French playwright diagnosed cases of melancholia by describing the psychotic world from the perspectives of the suffering protagonists. He presented them in closure, isolated from the rest of the world, suffocating in claustrophobic rooms under mansard roofs which symbolised their strained mental conditions. Apart from physical walls, in Lenormand’s works there is also the invisible to the eye yet pervasive “black wall”, in front of which a human being stands completely defenceless and mentally broken, trying to find in it even the slightest crack enabling them to escape the delusional world.
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Sung, Yu, Daniel J. Cantliffe, Russell T. Nagata, and Warley M. Nascimento. "Structural Changes in Lettuce Seed During Germination at High Temperature Altered by Genotype, Seed Maturation Temperature, and Seed Priming." Journal of the American Society for Horticultural Science 133, no. 2 (March 2008): 300–311. http://dx.doi.org/10.21273/jashs.133.2.300.
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To investigate thermotolerance in seeds of lettuce (Lactuca sativa L.), primed, nonprimed, or seeds matured at 20/10 and 30/20 °C (day/night on a 12-h photoperiod) were imbibed at 36 °C for various periods and then dissected. Structural changes in seed coverings in front of the radicle tip were observed during germination at high temperature. Thermotolerant genotypes, ‘Everglades’ and PI 251245, were compared with a thermosensitive cultivar, ‘Dark Green Boston’. In all seeds that germinated, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue (constriction of the endosperm membrane near the basal end of the seed) at the micropylar region and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition in these seeds; the protein bodies in the vacuoles enlarged and gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, and then the radicle elongated toward this ruptured area. The findings suggested that the endosperm layer presented mechanical resistance to germination in seeds that could not germinate at 36 °C. Weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of ‘Dark Green Boston’, ‘Everglades’, and PI 251245 matured at 30/20 °C had greater thermotolerance than those matured at 20/10 °C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20 °C were more readily disrupted and ruptured during imbibition than seeds matured at 20/10 °C, suggesting a reason why these seeds could germinate quickly at supraoptimal temperatures. Similar endosperm structural alterations also were observed in primed seeds. Priming led to rapid and uniform germination, circumventing the inhibitory effects of high temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, we observed that genotype, seed maturation temperature, or seed priming had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves leading to cell collapse.
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Khederzadeh, H., and K. Sennah. "Development of cost-effective PL-3 concrete bridge barrier reinforced with sand-coated glass fibre reinforced polymer (GFRP) bars: static load tests." Canadian Journal of Civil Engineering 41, no. 4 (April 2014): 368–79. http://dx.doi.org/10.1139/cjce-2013-0394.
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One of the main factors concerning durability and service life of steel-reinforced bridges is corrosion of steel bars especially when exposed to a harsh environment. The use of glass fibre reinforcing polymer (GFRP) bars as non-corrosive material has emerged as an innovative solution to corrosion related problems, reduce the maintenance cost, and increase the service life of bridge structures. A recent cost-effective design of PL-3 bridge barrier was developed at Ryerson University incorporating high-modulus GFRP bars with headed ends. This paper presents results of full-scale static tests to collapse performed on the developed PL-3 bridge barrier at interior and exterior locations to investigate the ultimate load carrying capacity to be compared with Canadian Highway Bridge Design Code (CHBDC). The experimental ultimate load carrying capacity of the barriers was observed to be far greater than CHBDC factored design transverse load. The failure pattern was initiated by a trapezoidal crack pattern at the front face of the barrier, followed by punching shear failure at the transverse load location. Based on the punching shear failure developed in the barrier wall and comparison with available punching shear equations in the literature, an empirical punching shear equation is proposed to determine the transverse load carrying capacity of PL-3 bridge barrier walls reinforced with GFRP bars.
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Yang, Hengze, Zhongping Guo, Daozhi Chen, Chao Wang, Fuyu Zhang, and Zhaowen Du. "Study on Reasonable Roadway Position of Working Face under Strip Coal Pillar in Rock Burst Mine." Shock and Vibration 2020 (November 2, 2020): 1–21. http://dx.doi.org/10.1155/2020/8832791.
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It is of great significance to study the reasonable position of mining roadway under strip coal pillar for increasing the stability of mining roadway, reducing the waste of resources, and realizing the safety production of working face. Based on the research background of the working face under the strip coal pillar in Jinqiao Coal Mine of Jining, Shandong Province, through theoretical analysis, similar material simulation experiment, and numerical simulation experiment, the stress distribution law, plastic failure range, and rationality of coal pillar setting in different width sections are systematically studied. Finally, the tailentry of working face is determined at the position of 5 m from the bottom of strip coal pillar to 1308 goaf. During the mining period of 1310 working face, the peak value of side abutment pressure is at the position of 3∼4 m; beyond 25 m in front of the coal wall, the deformation of the surrounding rock on the tailentry surface is small. After entering the advanced support section, the deformation of the two sides is mainly longitudinal crack expansion and local shallow small flakes; however, the roof is complete and stable. Therefore, the selection of tailentry location and coal pillar width has played a good role. The research results of this study can provide some reference for similar mine with similar geological and production technical conditions.
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Qu, Honglue, Chenxu Wang, Gulan Zhang, Ying Liu, Hao Luo, and Qian Mei. "Seismic damage mechanism of bedrock and overburden layer slope reinforced by sheet pile wall." Journal of Geophysics and Engineering 16, no. 4 (July 15, 2019): 667–79. http://dx.doi.org/10.1093/jge/gxz032.
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Abstract Sheet pile walls, widely used in landslide control projects, have demonstrated excellent seismic performance during the great Wenchuan earthquake, as indicated by an investigation of retaining walls following earthquake damage. To further understand the mechanism of seismic damage based on the Hilbert–Huang transform method and marginal spectrum identification theory, a large-scale shaking table test of bedrock and overburden layer slope reinforced by sheet pile wall was carried out, and the mechanism of seismic damage was analysed. The results show that the change in marginal spectrum amplitude and characteristic frequency can clearly indicate the degree of seismic damage to the slope soil. First, the dynamic response of the slope soil near sheet pile wall is smaller than the response observed in soil farther from the wall, and the degree of seismic damage near the wall is relatively weaker than that farther away from the wall. Second, the energy of the seismic wave cannot be completely transferred behind the wall, and the strip cracks of soil behind the wall can be determined. Finally, the slope soil slides along a slip surface so that the front edge of the slope is squeezed due to the vertical tensile cracks at the rear edge. In addition, the results confirm the feasibility of the Hilbert–Huang transform method for studying the mechanism of the seismic damage to the structure-soil coupling system.
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Vajedian, Sanaz, Mahdi Motagh, Zahra Mousavi, Khalil Motaghi, Eric Fielding, Bahman Akbari, Hans-Ulrich Wetzel, and Aliakbar Darabi. "Coseismic Deformation Field of the Mw 7.3 12 November 2017 Sarpol-e Zahab (Iran) Earthquake: A Decoupling Horizon in the Northern Zagros Mountains Inferred from InSAR Observations." Remote Sensing 10, no. 10 (October 3, 2018): 1589. http://dx.doi.org/10.3390/rs10101589.
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The study of crustal deformation fields caused by earthquakes is important for a better understanding of seismic hazard and growth of geological structures in tectonically active areas. In this study, we present, using interferometric measurements constructed from Sentinel-1 Terrain Observation with Progressive Scan (TOPS) data and ALOS-2 ScanSAR, coseismic deformation and source model of the Mw 7.3, 12 November 2017 earthquake that hit northwest of the Zagros Mountains in the region between Iran–Iraq border. This was one of the strongest seismic events to hit this region in the past century, and it resulted in an uplift area of about 3500 km2 between the High Zagros Fault (HZF) and Mountain Front Fault (MFF) with a maximum amount of 70 cm south of Miringe fault. A subsidence over an area of 1200 km2 with a maximum amount of 35 cm occurred near Vanisar village at the hanging wall of the HZF. Bayesian inversion of interferometric synthetic aperture radar (InSAR) observations suggests a source model at a depth between 14 and 20 km that is consistent with the existence of a decoupling horizon southwest edge of the northern portion of the Zagros Mountains near the MFF. Moreover, we present evidence for a number of coseismically induced rockslides and landslides, the majority of them which occurred along or close to pre-existing faults, causing decorrelation in differential interferograms. Exploiting the offset-tracking technique, we estimated surface motion by up to 34 and 10 m in horizontal and vertical directions, respectively, due to lateral spreading on a big coseismic-induced landslide near Mela-Kabod. Field observations also revealed several zones of en echelon fractures and crack zones developed along a pre-existing fault passing through Qasr-e Shirin City, which exhibited secondary surface slip by up to 14 cm along its strike.
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Xia, Jing Liang, Zhuan Qin Wu, Ren Jie Shang, Bei Xing Li, Fang Xin Jiang, and Zhi Qiang Yin. "Investigation of Durability of Wall Materials Concrete Prepared with Fly Ash." Applied Mechanics and Materials 174-177 (May 2012): 657–61. http://dx.doi.org/10.4028/www.scientific.net/amm.174-177.657.
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Based on durability of fly ash concrete, the freezing and thawing, impermeability and cracking resistance of fly ash concrete were researched. The results show that the frost resistance of concrete was reduced, impermeability and crack resistance were improved with increasing the fly ash content.
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Santrač, Petar, Slobodan Grković, Danijel Kukaras, Neđo Đuric, and Mila Svilar. "Case Study—An Extreme Example of Soil–Structure Interaction and the Damage Caused by Works on Foundation Strengthening." Applied Sciences 11, no. 11 (June 3, 2021): 5201. http://dx.doi.org/10.3390/app11115201.
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This paper describes the works on foundation strengthening of the towers of the Cathedral of St. Theresa of Avila in Subotica and the damages caused by these works. Strengthening was performed by means of jacked-in piles and deep soil injection. The construction of the Cathedral began in 1773 and it lasted for several decades with frequent interruptions and changes to the project. The present appearance of the facade was created in 1912. According to historic data, several years after construction, the cracks appeared on the front facade. With time, these cracks became more pronounced, and in 2015, when the remediation project started, the total width of major cracks reached about 15 cm. The first contemporary attempt to repair the towers was made in 2017 by inserting piles beneath the foundations. These works were interrupted due to increased settlements and the appearance of new cracks. In the second attempt, the strengthening was performed by deep injection of soil with expansive resins. During these works, settlements and damages intensified even more, causing the works to be halted in 2018. Analysis of the whole structure and revaluation of all the results, obtained from continuous monitoring of settlements and crack widths from the previous period, led to the new remediation proposal. The imperative was to retain the original appearance of the Cathedral facades while performing the total reconstruction of the upper sections of the front facade. This implies that the overall weight of the reconstructed parts is to be decreased, while the strength is to be increased. Strong structural connections are planned, both among the two towers, and between the towers and the nave. These clear structural solutions will lead to reduced stresses within the existing brick walls, reduced contact soil pressures and ceasing of increased settlements and tilting of the Cathedral towers.
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Xiao, Li Guang, Chang Liu, and Shi Ting Zhang. "Influences of Polypropylene Fiber on Properties of Foam Concrete with Iron Tailings." Advanced Materials Research 1004-1005 (August 2014): 1575–78. http://dx.doi.org/10.4028/www.scientific.net/amr.1004-1005.1575.
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Iron tailings are mineral wastes obtained from industrial processing and magnetic separation of iron ore. Foam concrete with iron tailings can be made with iron tailings, cement, fly ash, silica fume, polypropylene fiber, superplasticizer, early strength agent, accelerating agent and foaming agent. The influences of polypropylene fiber on the crack resistance and frost resistance of foam concrete have been investigated in this study. Further, the microstructure of foam concrete was observed. This result demonstrates that polypropylene fiber has greatly increased the crack resistance and frost resistance of foam concrete. The pore structure of foam concrete is improved obviously by polypropylene fiber. Due to the uniformly distributed pores, high porosity and rather complete pore wall, the mechanical properties and thermal properties of foam concrete are excellent. The foam concrete with high-strength and excellent thermal insulation property develops a new route for the comprehensive utilization of iron tailings.
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Barthwal, Himanshu, and Mirko van der Baan. "Role of fracture opening in triggering microseismicity observed during hydraulic fracturing." GEOPHYSICS 84, no. 3 (May 1, 2019): KS105—KS118. http://dx.doi.org/10.1190/geo2018-0425.1.
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Hydraulic fracturing in low-permeability hydrocarbon reservoirs creates/reactivates a fracture network leading to microseismic events. We have developed a simplified model of the evolution of the microseismic cloud based on the opening of a planar fracture cavity and its effect on elastic stresses and pore pressure diffusion during fluid injection in hydraulic fracturing treatments. Using a material balance equation, we compute the crack tip propagation over time assuming that the hydraulic fracture is shaped as a single penny-shaped cavity. Results indicate that in low-permeability formations, the crack tip propagates much faster than the pore pressure diffusion front thereby triggering the microseismic events farthest from the injection domain at any given time during fluid injection. We use the crack tip propagation to explain the triggering front observed in distance versus time plots of published microseismic data examples from hydraulic fracturing treatments of low-permeability hydrocarbon reservoirs. We conclude that attributing the location of the microseismic triggering front purely to pore pressure diffusion from the injection point may lead to incorrect estimates of the hydraulic diffusivity by multiple orders of magnitude for low-permeability formations. Moreover, the opening of the fracture cavity creates stress shadow zones perpendicular to the principal fracture walls in which microseismic triggering due to the elastic stress perturbations is suppressed. Microseismic triggering in this stress shadow region may be attributed mainly to pore pressure diffusion. We use the width, instead of the longest size, of the microseismic cloud to obtain an enhanced diffusivity measure, which may be useful for subsequent production simulations.
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Dong, Shaoyang, and Xiong (Bill) Yu. "Microstructure-Based Random Finite Element Method Simulation of Frost Heave: Theory and Implementation." Transportation Research Record: Journal of the Transportation Research Board 2672, no. 52 (October 4, 2018): 347–57. http://dx.doi.org/10.1177/0361198118798721.
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Frost heave can cause serious damage to civil infrastructure. For example, interactions of soil and water pipes under frozen conditions have been found to significantly accelerate pipe fracture. Frost heave may cause the retaining walls along highways to crack and even fail in cold climates. This paper describes a holistic model to simulate the temperature, stress, and deformation in frozen soil and implement a model to simulate frost heave and stress on water pipelines. The frozen soil behaviors are based on a microstructure-based random finite element model, which holistically describes the mechanical behaviors of soils subjected to freezing conditions. The new model is able to simulate bulk behaviors by considering the microstructure of soils. The soil is phase coded and therefore the simulation model only needs the corresponding parameters of individual phases. This significantly simplifies obtaining the necessary parameters for the model. The capability of the model in simulating the temperature distribution and volume change are first validated with laboratory scale experiments. Coupled thermal-mechanical processes are introduced to describe the soil responses subjected to sub-zero temperature on the ground surface. This subsequently changes the interaction modes between ground and water pipes and leads to increase of stresses on the water pipes. The effects of cracks along a water pipe further cause stress concentration, which jeopardizes the pipe’s performance and leads to failure. The combined effects of freezing ground and traffic load are further evaluated with the model.
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Izbitskaya, Y. S., S. V. Kaloshina, and D. G. Zolotozubov. "THE ANALYSIS OF DEFECTS AND REPAIR METHODS OF THE FRONT LAYER OF BRICKWORK OF MULTILAYER WALLS ON THE EXAMPLE OF A RESIDENTIAL BUILDING IN PERM." Construction and Geotechnics 10, no. 2 (December 15, 2019): 40–50. http://dx.doi.org/10.15593/2224-9826/2019.4.04.
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The article discusses the problem of defects in the front layer of brickwork of multilayer walls. At many facilities constructed using the technology of laminated masonry with brick facing, after several years of operation, defects such as vertical cracks in the masonry face layer and destruction of the bricks of the face layer begin to appear. These defects violate the aesthetic appearance of the building, reduce the thermal characteristics of the external walls, and, in some cases, can lead to the collapse of certain sections of the brick cladding layer. This problem is considered on the example of a 10-storey residential building with external multilayer walls, located in Perm. The building was commissioned in 2005, but already in 2010, many defects of the front layer of masonry were discovered. The article provides data obtained during surveys carried out in 2010 and 2019. The main defects of the external masonry verst are described, among which one can distinguish the destruction of the masonry face layer, vertical cracks, the absence of stitching along the supporting corner of the masonry, and the absence of expansion joints. The main causes of damage are associated with numerous deviations from the project. The results of calculating the outer verst of brickwork for eccentric compression are presented. As measures aimed at eliminating defects, the article describes possible methods of repairing the face masonry: the installation of vertical and horizontal expansion joints, longitudinal reinforcement and anchoring with BIT rods to prevent the development of vertical cracks and destruction of the masonry.
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Ouyang, Chen Bing, and Ying Chen. "The Critical Construction Techniques of Preventing Quality Defects of External Wall Insulation." Applied Mechanics and Materials 105-107 (September 2011): 1011–15. http://dx.doi.org/10.4028/www.scientific.net/amm.105-107.1011.
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Since China's enforcement of building energy saving standards, external insulation technology has been applied in a mount of buildings. However, four common defects of it, namely crack, shedding and hollow, leakage, frost and condensation, had gradually appeared. This study tries to find out the critical construction techniques of preventing these defects which are closely related to quality in order that engineers pay more attention to them during construction. Literature research and field investigation to engineers and technicians are adopted. Designed questionnaires, including 61 kinds of detailed defects causes and relevant preventive measures, are used in the survey. Through statistical analysis of survey data, the mesh, plastering mortar configuration, etc. 10 detailed causes are suggested as main defect reasons according to harm grade. Meanwhile, corresponding 15 highly effective construction technical countermeasures are put forward finally.
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Xiong, Xue Yu, and Zhao Yang Su. "Features and Current Damaged Situation of Hui-Style Architecture." Advanced Materials Research 838-841 (November 2013): 2905–9. http://dx.doi.org/10.4028/www.scientific.net/amr.838-841.2905.
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As the key element of Huizhou culture, Hui-style architecture is one of the masterpieces of Chinese ancient architectures. The Hui-style architecture was highly praised by architecture masters both at home and abroad because of its phenotypic features, such as black tiles, white wall, and horse-like wall; its decoration features, such as tile carving, wood carving, stone carving; and its living features, such as high house, deep well, large lobby. Since most of the Hui-style architectures were built long time ago, had not been repaired for many years, as well as influenced by different kinds of natural hazards, the Hui-style architectures were decayed, eaten by worms, or damaged by fire to different degree. Most of these architectures could not meet the living requirements nowadays with faint light, high humidity, poor sound insulation, badly cracks and corrosion of all kinds of wood components; and needed to be repaired and reinforced badly. Based on this situation, the author believes that the Hui-style architecture would be in its original appearance in front of the word in the near future if the scientific research and proper reinforcement measures were adopted for the reinforcement of the Hui-style architectures.
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Hinkel, Kenneth M. "Are Soil Tongues in Northeastern Indiana Periglacial Relics or Active Fingering Zones?" Quaternary Research 39, no. 1 (January 1993): 75–83. http://dx.doi.org/10.1006/qres.1993.1009.
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AbstractSoil tongues, or soil fingers, have been identified along the walls of an active gravel pit in northeastern Indiana. Locally enhanced pedogenesis, primarily carbonate leaching and clay illuviation, has resulted in wedge- and cone-shaped extensions of the B horizon into the underlying calcareous glaciofluvial sediments. Although previously described in the literature, the features at this site are considered unusual both for the numerous well-defined tongues and for the regularity of tongue spacing, which gives the illuviation front the appearance of a high-amplitude sinusoidal wave train. Depth to the illuviation front was measured at 0.25-m intervals along a 40-m exposure. Statistical tests indicate that the spatial pattern is nonrandom. The data were transformed using Fourier methods, and the resulting variance spectrum show a peak intensity at wavelengths bracketing 1.5 m. The results of these analyses suggest a surficial or near-surface topographic control. Climatic conditions following local glacier recession favored periglacial activity, and there is some evidence to suggest development of thermal contraction cracks and nonsorted or poorly sorted polygons 1.5 m in diameter. As an alternative hypothesis, laboratory experiments suggest that regularly spaced fingers can develop in homogeneous materials when instability occurs at the wetting front. In this case, soil tongues cannot be used as relict indicators of periglacial activity.
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Žiogas, Vigantas Antanas, Svajūnas Juočiūnas, and Giedrius Žiogas. "HYDROTECHNICAL CONCRETE WITH LOCAL AGGREGATES AND THEM USING FOR MONOLITHIC STRUCTURES." Engineering Structures and Technologies 1, no. 2 (June 30, 2009): 102–10. http://dx.doi.org/10.3846/skt.2009.13.
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The article discusses the technological peculiarities of construction monolithic hydrotechnical concrete structures, use of local aggregates for producing special concretes, methods of determining water impermeability of concretes as well as the evaluation of the methods mentioned above. The article presents the requirements for the granulometric composition of aggregate mixes for the production of flowing concrete mixes used for the construction of monolithic hydrotechnical structures. The possibilities and expediency of using local crushed gravel with increased amounts of weak particles for hydrotechnical structures are discussed. The mass loss of weak particles is slight compared with the whole mass of aggregates, and the total mass loss of crushed gravel it occurs due to micro-cracks present in particles. The frost resistance mark of crushed gravel and its suitability for hydrotechnical concretes should be determined by evaluating the amount of weak particles and their frost resistance. The article discusses concrete impermeability data received by means of two methods (according to LSTST 1974:2005 and LSTST EN 12390–8 requirements). Theoretical water penetration depths have been calculated. Determination of water impermeability according to LSTST 1974:2005 is recommended for C25/30 and lower compressive strength class concretes with W≤8. The LSTST EN 12390–8 water impermeability determina-tion method is recommended for C25/30 and higher compressive strength class concretes whose water impermea-bility mark is W≥8. For the construction of certain hydrotechnical structures water impermeable concretes whose water penetration depth should not exceed 20mm are recommended for use instead of the W6 and W8 concretes. Technological peculiarities and potential technological-organizational solutions for high walls of a water treatment plant have been discussed. The analysis of potential concreting methods of the reservoir’s high walls has been made as well as that of the key parameters of the continuous concreting process and their interaction. Dependences for the estimation of continuous concreting volumes and permissible concreted segment lengths have been proposed by evaluating the beginning of the intensive formation structure of concrete, number of layers in the height of the concreted wall and concreting intensity.
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Supponen, Lauri. "In A Deepening Light: Musica nova Helsinki 2017." Tempo 71, no. 281 (June 21, 2017): 96–98. http://dx.doi.org/10.1017/s0040298217000390.
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As the audience's rustling quietens along with the memories of everyday pulses, ethereal sounds appear. We are at Helsinki's iconic Rock Church, on the eighth night of the biennial Musica nova festival for contemporary music. The Helsinki Chamber Choir sound the first, lingering lines of György Ligeti's Lux Aeterna from the balcony, behind the audience. The peculiar acoustics give the illusion that the choir is hidden in between the crevasses and cracks of the stone wall in front. The listener is surrounded. Marvellously kept together by Nils Schweckendiek, the singers transform the colour of their voices into sine-tones and oboes in a strangely soothing way. This rendition now somewhat more present than the night before, when the choir echoed the same micropolyphonic lines across the aula of the Kiasma art museum. There the cool distance of the work really spoke in a mesmerising way, with an unreachable caress.
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Luo, Fu Qiang, Fu Shui Xu, Jing Bo Li, Bo Wen Zou, and Qing Ying Kang. "Simulation of the NOX Emissions for a CNG Direct-Injection Engine." Applied Mechanics and Materials 278-280 (January 2013): 319–22. http://dx.doi.org/10.4028/www.scientific.net/amm.278-280.319.
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The distribution of temperature and NOX concentration field under different crank angle of a CNG direct-injection engine converted from a four-valve gasoline vehicle engine are calculated by the computation model of the CNG direct-injection engine work process using CFD software. The results show that the temperature field spreads around the center of the spark plug in initial combustion period. The position of maximum temperature in combustion chamber moves from the spark plug to the wall and temperature tends to uniform distribution as the piston goes down along with the spread of flame front and the completion reaction after the flame. Temperature distribution is vital to the generation of NOX which changes along with high-temperature zone. The change principle of quantity of NOX in the cylinder is that at first, the quantity continues increasing, then declines, and finally remains stable. Besides this, the generation amount of NOX increase along with the speed.
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Calle, Klaas, and Nathan Van Den Bossche. "Sensitivity analysis of the hygrothermal behaviour of homogeneous masonry constructions: Interior insulation, rainwater infiltration and hydrophobic treatment." Journal of Building Physics 44, no. 6 (May 2021): 510–38. http://dx.doi.org/10.1177/17442591211009937.
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Historical masonry constructions are difficult to mimic in hygrothermal models. The material properties of the walls are often highly uncertain due to the natural origin of the aggregates and the various, manual production processes used through time. Therefore, sensitivity analyses based on probabilistic simulations are powerful tools to indicate the risks on damage in masonry constructions. Damage criteria for relevant pathologies such as frost damage, potential decay of wooden beam heads and mould growth at the interior surface are used. The assessment methods (Scatter plots, Classification trees and Sobol indices) are based on 1D Heat, Air and Moisture simulations, including realistic variations on climate parameters and wall properties. These methodologies are applied to probabilistic simulations in which a potential damage risk is expected in historic masonries. The application of interior insulation, the use of hydrophobic treatments, and the impact of potential water infiltrations through cracks are discussed. In most of these situations a high dependency of each of the damage criteria on the rain intensity, the trend of the moisture retention/liquid conductivity curve and the absorption coefficient is evident, but also additional insights are found. For example, the thermal impact of interior insulation is negligible compared to its reduction of the first phase drying potential towards the interior. For hydrophobic treatments, the risk for damage typically decreases, but in combination with a rain water infiltration rate above approximately 5% of the wind driven rain the risk on mould growth at the interior surface significantly increases.
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Ji, Zhe, Kang Cheng Lu, and Chao Chao Ma. "Classification, Causes of Tunnel Frost Damages in Cold Region and Several New Technologies to Prevent them." Applied Mechanics and Materials 170-173 (May 2012): 1504–10. http://dx.doi.org/10.4028/www.scientific.net/amm.170-173.1504.
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This paper classifies the tunnel frost damages and discusses their causes, especially the causes of lining structural damage for freezing and they are classified into two categories: the outer freezing damage and the inner freezing damage of lining. The analysis shows that the former has a little effect on the structure, but the latter has big threat. For the phenomenon that cracks frequently occur in the tunnel lining of cold regions, some measures to prevent cracks are presented, including reducing adverse constraints in the process of temperature change and preventing large temperature stress. In cold regions, it is unsuitable to adopt back paste-type water-stops to prevent the leakage from lining construction joints, and a good choice is to utilize the buried drainage water-stops. The ring drainage pipes directly connect with the central drainage pipe, and thermal insulating layer with belt shape is set along the ring drainage pipes in some sections where surrounding rock is water-rich and the middle and lower part of the ring drainage pipe are easily frozen. In sections with high potential freezing threat, an anti-freezing plan is offered that electric heating wires are installed behind the lining wall. The test shows that above techniques have good effects in cold region tunnels.
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Chepizhko, Oleksandr, Costanza Giampietro, Eleonora Mastrapasqua, Mehdi Nourazar, Miriam Ascagni, Michela Sugni, Umberto Fascio, et al. "Bursts of activity in collective cell migration." Proceedings of the National Academy of Sciences 113, no. 41 (September 28, 2016): 11408–13. http://dx.doi.org/10.1073/pnas.1600503113.
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Dense monolayers of living cells display intriguing relaxation dynamics, reminiscent of soft and glassy materials close to the jamming transition, and migrate collectively when space is available, as in wound healing or in cancer invasion. Here we show that collective cell migration occurs in bursts that are similar to those recorded in the propagation of cracks, fluid fronts in porous media, and ferromagnetic domain walls. In analogy with these systems, the distribution of activity bursts displays scaling laws that are universal in different cell types and for cells moving on different substrates. The main features of the invasion dynamics are quantitatively captured by a model of interacting active particles moving in a disordered landscape. Our results illustrate that collective motion of living cells is analogous to the corresponding dynamics in driven, but inanimate, systems.
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Subota, Іrіna, Larysa Spasonova, and Аnastasia Sholom. "Influence of forming pressure on frost resistance of ceramics." Technology audit and production reserves 2, no. 1(58) (April 30, 2021): 15–20. http://dx.doi.org/10.15587/2706-5448.2021.229172.
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The object of research is low-melting clays of the Kyiv region (Ukraine). The work is devoted to the study of obtaining ceramic materials resistant to low temperatures. Frost resistance is one of the most important characteristics for regions in which ceramic materials are used with frequent temperature transitions through 0 °C. The production of frost-resistant ceramic wall materials is determined by the type of raw materials and technological production parameters. The main technological methods for increasing frost resistance are: the use of less dispersed clays; batch homogenization; formation of raw material without textural defects and prevention of cracks during drying and firing. The work shows that the existing methods for increasing frost resistance can be implemented by reducing water absorption due to the creation of a microporous structure with predominantly closed pores by increased pressure of a semi-dry method of formation. An increase in the pressing pressure leads to an increase in the number of contacts of the molecules of the ceramic mass at the stage of formation. Due to this, the strength of the molded samples at a pressing pressure of more than 30 MPa is higher compared to samples molded by the plastic method. It was also found that an increase in the pressing pressure makes it possible to speed up the drying process of ceramic products, reducing energy consumption for their production. Due to an increase in the pressing pressure to 50 MPa, the strength of samples obtained by semi-dry pressing is 55.4 MPa, while for samples during plastic formation it is 22.9 MPa. Water absorption, on the contrary, for dry pressing is 9.3 %, while for plastic pressing it is 12.2 % at a firing temperature of 1000 °C. It is shown that increasing the pressing pressure is an effective way to improve the quality of ceramic materials based on local low-plasticity clay raw materials. Saving natural and energy resources, developing new sources of raw materials and comprehensive improvement of products with environmental friendliness of production remain important today.
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Ozgen Karacan, C., Abraham S. Grader, and Phillip M. Halleck. "Mapping of Permeability Damage Around Perforation Tunnels." Journal of Energy Resources Technology 123, no. 3 (May 10, 2001): 205–13. http://dx.doi.org/10.1115/1.1386389.
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We have investigated porosity and permeability damage around perforations using a combination of transient analysis and X-ray CT. The method applied allowed us to perform the entire experiments on samples under simulated in-situ stress conditions and to map variations in permeability along the length of the core as well as with radial distance from the perforation. Berea (10.2-cm (4-in.) dia) cores saturated with low-viscosity silicone oil were perforated using conventional-shaped charges (6-g HMX) and API RP43 procedures by using 6.88-MPa (1000-psi) effective stress and 5.16-MPa (750-psi) and 2.61-MPa (350-psi) underbalance. Low-permeability Torrey Buff Sandstone was also perforated using 5.16-MPa (750-psi) underbalance. After sufficiently flowing the perforations, higher-viscosity silicone oil was injected. The movement of fluids was tracked using X-ray CT to measure the local velocity of the viscous fluid front at different locations along the perforation. Results of these tests were compared in terms of permeability and porosity damage. Quantitative analysis on Berea cores show, for the specific charge and test conditions used, that damage extends approximately 2 cm (0.78 in.) from the center of the perforation. Comparison of tests performed with 2.41-MPa (350-psi) and 5.16-MPa (750-psi) underbalance show a clear increase in permeability near the tunnel wall at the higher underbalance. A zone of somewhat-reduced permeability exists at approximately 1.7 cm from the perforation center in the latter case. Porosity profiles calculated show that porosity is almost uniform out from the tunnel and there is no compacted zone near the tunnel wall in liquid-saturated cores. However, there is a high-porosity zone from the tunnel wall out about 2 mm. This may be due to a region of circumferential partings and small cracks that lead to high porosity or due to the possible artifacts discussed in the paper. Qualitative results have also been obtained for a tight sandstone for which underbalance was insufficient to remove debris from the perforation tunnel. CT images reveal that the plugged tunnel acts as a conduit for fluid flow, showing that the plugging material has significantly higher permeability than the surrounding rock.
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Yasrifullah, Achmad, and Adriani Adriani. "THE DESIGN OF THE CONSTRUCTION OF RETAINING WALLS ON THE RIVER SLOPES OF KUIN." CERUCUK 4, no. 1 (June 7, 2021): 83. http://dx.doi.org/10.20527/crc.v4i1.3580.
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North Kuin Street, North Kuin, North Banjarmasin Subdistrict, South Kalimantan Sub-district is right on the outskirts of Kuin River. Precisely the road that is in front of the Sultan Suriansyah Mosque, where the road has experienced cracks that can potentially occur landslides. In the event of an avalanche, it will result in obstructed traffic activities on the road which also affect the economy of the surrounding community. So from that the soil retaining wall is needed to maintain the stability of the land on the outskirts of the Kuin River so that landslides do not occur.This design begins with identifying problems that occur. Next is data collection of investigations in the field and laboratory. Then the data obtained are analyzed and interpreted and then visualized in the form of stratigraphy by plotting the type of soil by the results of sondir and boring that have been interpreted. After that, check the initial condition of the slope so that the shape of the avalanche can be identified. Then proceed with calculating the forces acting on the retaining wall due to traffic loads and other loads above it to obtain carrying capacity from the ground. Then proceed with modeling and analysis using Geo Studio 2012 software to see the value of SF (safety factor). At the end of the calculation the volume and price of the work unit are calculated to obtain the amount of the budget plan (RAB). From the results of the analysis of the design of anchor plaster, it was obtained a box profile of FSP VIL steel plaster with a total length of 28 m plaster. At stake uses a steel pipe with a diameter of 91.44 cm which is set at a depth of 28 m. For slope stability with pile reinforcement obtained SF = 1.835> 1.5, it can be said to be safe. Based on the calculation of the volume and price of the work unit, this design requires a cost of Rp. 7,340,166,486, -
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SUTO, Masashi, Hidehiko OGATA, Akio ISHIGAMI, and Toshikazu KANETA. "THE APPLICABILITY OF GROUTING METHOD FOR CRACKS OF RC OPEN CHANNEL SIDE WALL CAUSED BY FROST DAMAGE DETERIORATION AND THE EVALUATION OF FILLING RANGE USING ULTRASONIC METHOD." Cement Science and Concrete Technology 66, no. 1 (2012): 295–302. http://dx.doi.org/10.14250/cement.66.295.
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Obodovich, O. M., O. M. Nedbailo, O. G. Chernyshyn, and A. E. Nedbailo. "Intensification of loosening of asbestos fibers by means of hydromechanical processing." Кераміка: наука і життя, no. 1(50) (March 17, 2021): 26–29. http://dx.doi.org/10.26909/csl.1.2021.4.
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Acceptance of high-quality aqueous suspensions based on chrysotile asbestos is an urgent technical task in a number of industries. Asbestos-cement mortar is used as an asbestos-cement crust for insulation of walls and other building surfaces, due to this composition of the treated surfaces perfectly retain heat, resistant to moisture, and most importantly - asbestos fibers contribute to the smoothness of the surface and crack is not formed. No less popular is the use of asbestos-cement mortar with a high content of asbestos in the insulation of ventilation ducts and pipelines. This composition of asbestos-cement mortar is used to strengthen the joints of asbestos-cement pipes, as well as as a filler in the laying of cast iron pipes to give the joints additional elasticity.
Asbestos-cement mortar has plasticity, resistance to stretching and reinforcement of asbestos, as well as strength and versatility in the use of cement. Due to these properties, asbestos and cement perfectly adhere to each other to obtain a durable, strong, frost-resistant, virtually waterproof and fire-resistant building material.
The result of the microscopic examination is reason to believe that from the technological process of production of slate can be removed electromechanical mixer for the preparation of a solution of asbestos + water + portland cement. In this case, given the fact of continued loosening of asbestos in the preparation of the mold mixture of asbestos + water + portland cement, it will be sufficient to ensure the degree of loosening of asbestos in the ripper at the minimum required level (for example, not more than 85%). It is assumed to obtain a mold mixture with a high degree of homogeneity of the components with reduced costs of Portland cement due to its physico-chemical activation by hydraulic fluxes.
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Kamau, Kevin K., Gabriel Magoma, Allan Ole Kwallah, Charles K. Syengo, and Matilu Mwau. "Seroprevalence of chikungunya fever virus and O’nyong Nyong fever virus among febrile patients visiting selected hospitals in 2011-2012 Trans Nzoia County, Kenya." International Journal of Research in Medical Sciences 6, no. 6 (May 25, 2018): 1913. http://dx.doi.org/10.18203/2320-6012.ijrms20182271.
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Background: Chikungunya virus (CHIKV) is an alphavirus in the Semliki Forest complex, and is most closely related to O’Nyong Nyong virus (ONNV). CHIKV and ONNV are mosquito-borne alphaviruses endemic in East Africa that cause acute febrile illness and arthralgia. The objectives of this study were to measure seroprevalence of CHIKV and ONNV in selected health facilities in Western Kenya and link it to demographics and other risk factors.Methods: The study design was cross sectional in selected health facilities. We tested for anti-CHIKV antibodies using In-house Indirect IgG Enzyme Linked Immunosorbent Assay (ELISA) and In-house IgM Capture ELISA and confirmed with Focus Reduction Neutralization Test (FRNT) for specific alphavirus neutralizing antibodies against CHIKV or ONNV. Mean, median and standard deviation were used to summarize the data. Comparisons of means and medians were done using Student’s t test. Prevalence rates were determined using descriptive statistics (e.g. proportions, rates).Results: From the 382 samples that were successfully collected, 114 (29.84%) had anti-CHIKV antibodies by the ELISA test. Of these, 27 (7.1%) had CHIKV-specific neutralizing antibodies and 5 (1.3%) had ONNV-specific neutralizing antibodies. Age was significantly associated with seropositivity (OR=1.03; P=0.015, 95% C.I 1.01-1.06). Males were less likely to be seropositive (OR=0.67; P=0.358, 95% C.I 0.27-1.52). Risk factors associated with seropositivity included collecting firewood (OR=2.73 95% 1.13- 6.41) and walls with holes and cracks (OR=0.23 95% C.I 0.04 -0.86).Conclusions: Both CHIKV and ONNV infections were confirmed in the participants’ more so in women and adults, demonstrating undocumented and ongoing transmission in Western Kenya. In 2011 and 2012 CHIKV and ONNV contributed 8.4% of fevers presented in the three selected health facilities in Western Kenya.
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Mou, Jianye, D. Zhu, and A. D. D. Hill. "Acid-Etched Channels in Heterogeneous Carbonates—a Newly Discovered Mechanism for Creating Acid-Fracture Conductivity." SPE Journal 15, no. 02 (December 17, 2009): 404–16. http://dx.doi.org/10.2118/119619-pa.
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Summary In the acid-fracturing process, the fracture conductivity created by acid etching of the fracture walls is because of the surface roughness created by the acid's nonuniform dissolution of the fracture surfaces. The acid-fracture conductivity is dependent on surface etching patterns, which are determined by permeability and mineralogy distributions. That is, the spatial distribution of fracture roughness affects the fracture conductivity, which cannot be considered in laboratory measurements of acid-fracture conductivity, which use core samples that are too small to observe such macroscale heterogeneities, or in typical acid-fracture simulators, in which the gridblock size is much larger than the scale of local heterogeneities. An accurate prediction of acid-fracture conductivity necessitates the detailed description of the acid etching profiles on the fracture surfaces, which depend on acid transport in the fracture, leakoff because of local permeability, and acid/rock reactions. In this paper, we developed a 3D intermediate-scale acid-fracture model with gridblock sizes small enough (gridblock sizes comparable to the core-sample size in experiments) and total dimensions large enough (the total dimensions comparable to a gridblock size in an acid-fracture simulator) to capture local and macroscale heterogeneity characteristics. The model predicts the pressure field, the flow field, acid concentration profiles, and fracture-surface profiles as functions of acid injection volume. In the model, we use a front-fixing method (Crank 1984) to handle the irregular, moving boundaries in numerical simulation. Spatially correlated permeability and mineralogy distributions were generated by using a semivariogram model. The model was validated by comparing simulation results with experimental results from an acid-fracture conductivity cell. With the model, by extensive numerical simulation, we analyzed the relationship among fracture-surface-etching patterns, conductivities, and the distributions of permeability and mineralogy. We also illustrated the formation characteristics necessary for acid to create channel-caused high acid-fracture conductivity. We found that a fracture segment with channels extending from the inlet to the outlet of the segment has high conductivity because fluid flow in deep channels causes a very small pressure drop. Such long and highly conductive channels can be created by acids if the formation has heterogeneities in either permeability or mineralogy or both, with high correlation length in the main flow direction, which is the case in laminated formations.