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E Smith - One of the best experts on this subject based on the ideXlab platform.
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The effective tensile Failure Stress of an uncracked brittle structure: Failure at a blunt Stress concentration
Journal of Materials Science, 1998Co-Authors: E SmithAbstract:The paper proceeds from the basis that the dominant source of the geometry dependence of the effective tensile Failure Stress of an uncracked brittle structure is deterministic and is related to the formation of a damage zone at a free surface. The damage is represented by a cohesive zone, and Failure, i.e. the attainment of maximum load, is associated with the attainment of an elastically calculated effective tensile Failure Stress. With regard to Failure arising as a result of the formation of a damage zone at the surface of a blunt Stress concentration, the paper predicts the extent to which the effective tensile Failure Stress increases with increasing severity of the Stress concentration, i.e. as the root radius decreases.
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The small flaw tolerance of a brittle structure
Journal of Materials Science, 1998Co-Authors: E SmithAbstract:On the basis that the dominant source of the maximum load-size effect for an uncracked brittle structure is deterministic, it can be associated with the formation of a damage (fracture process) zone at a free surface. By modelling this damage in terms of the cohesive zone description, and associating the maximum load with the attainment (at the free surface) of an elastically calculated effective tensile Failure Stress, earlier work has shown that the effective Stress is critically dependent on the applied loading-included Stress gradient beneath the surface, with the effective Failure Stress increasing with the steepness of the Stress gradient. The earlier considerations have been extended in the present work to assess the effect of a small surface flaw (crack) on the effective Failure Stress, and to show how the small flaw tolerance, as manifested by the reduction in effective Failure Stress, depends on the Stress gradient, flaw depth and material fracture parameters. © 1998 Kluwer Academic Publishers
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The maximum load size effect for uncracked brittle structures
Journal of Materials Science, 1997Co-Authors: E SmithAbstract:The paper proceeds from the basis that the dominant source of the maximum load size effect for uncracked brittle structures is deterministic, and is related to the formation of a damage (fracture process) zone at a free surface. By modelling this damage behaviour in terms of the cohesive zone description, and by associating the maximum load with the attainment of an elastically calculated effective tensile Failure Stress, the paper projects the view that the effective Stress is critically dependent on the applied loading induced Stress gradient beneath the surface of a structure. The effective tensile Failure Stress increases with the steepness of the Stress gradient, and we therefore have a ready explanation as to why the effective tensile Failure Stress for an uncracked bend beam increses as the beam depth decreases.
J.w Chung - One of the best experts on this subject based on the ideXlab platform.
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Effects of network morphology on the Failure Stress of highly porous media
Physical Review B, 2002Co-Authors: J.w Chung, J.t.m. De HossonAbstract:In this study four types of morphologies are generated to illustrate the importance of the details of the network structure in relation to its mechanical strength while keeping the density fixed. By varying the disorder parameter in a dynamical system of weakly interacting void-volume spheres, it is possible to generate various correlated node distributions. A network of springs is constructed from the correlated node distribution, which can be sued to examine the Failure characteristics of materials that are not governed by systems commonly derived from regular spring networks. The structures of the various morphologies are characterized by the normalized radial distribution of the nodes. Within a single phase the correlation length is the predominant parameter that determines the Failure Stress of the network.
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Scaling of the Failure Stress of homophase and heterophase three-dimensional spring networks
Physical Review B, 2002Co-Authors: J.w Chung, De Jeff Hosson, Van Der Erik GiessenAbstract:This paper concentrates on the scaling of the Failure Stress of a three-dimensional spring network as a function of its volume. In particular, the influences of the geometry and the local structure are examined. Both homophase disordered three-dimensional structures and composite systems are studied, containing a more or less ordered slab. The structures are generated by starting with a node distribution. A molecular-dynamicsbased algorithm uses void volume spheres, which all have Lennard-Jones interacting outer surfaces. The generated distributions of nodes form the basis of a procedure to interconnect the nodes with springs. In the calculation of the Failure Stress the total elastic energy is described by two-body central force, three-body bond bending, and four-body torsion contributions. The areas under uniaxial compression are varied in the range of 0.64 ‐5.76 mm 2 , and the height h ranges between 0.80 and 6.4 mm. It is found that the Failure Stress at constant base area could be described by s fail}@log(h/j)# 21/m , where j represents the correlation length within the sample the ~logarithm is to the base e!. The values of m are effective values. Only within the same kind of Failure mechanism and microstructure does the exponent m become more or less universal. Actually, the modulus m appears to depend on the system size, but in all cases thin samples are stronger than thick samples under uniaxial compression, and the Failure Stress increases with increasing coordination number. The Failure Stress of heterophase materials differs considerably in our calculations from that of homophase materials. The composite materials exhibit an increase in strength by a factor of 4, in comparison to the disordered structures of the same size. The actual Failure Stress of the composite material depends critically on the layering effect of the disordered region near the ordered phase.
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Failure Stress of a disordered three-dimensional spring network
Physical Review B, 2001Co-Authors: J.w Chung, De Jeff Hosson, Van Der Erik GiessenAbstract:This paper concentrates on the Failure Stress of a disordered three-dimensional spring network. In particular, we investigate the effects of several fracture criteria and of the connectivity at the nodes in the network. A node cannot be connected with another node if its relative distance is larger than a certain cutoff radius or a so-called connectivity threshold. In our modeling approach, the spring networks were loaded in compression and the network configuration with the lowest energy was calculated after each increment of force. Subsequently, the mechanical properties of the relaxed network structures were investigated using various fracture criteria. The largest threshold value of displacement was set to the commonly used criterion for brittle fracture, i.e., a fraction criterion of 1%, but also lower values (0.75%, 0.50%, and 0.25%) were examined. In addition, for each of these fracture criteria the Stress calculations were repeated with different connectivity thresholds. From this investigation it is concluded that it is not sufficient to examine only the fracture strain. In particular, the connectivity, i.e., the connectivity threshold ${C}_{0},$ which controls the spring entanglement between the nodes, has a substantial effect on the crack morphology. Larger ${C}_{0}'\mathrm{s}$ result in smaller fragments caused by crack branching.
Van Der Erik Giessen - One of the best experts on this subject based on the ideXlab platform.
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Scaling of the Failure Stress of homophase and heterophase three-dimensional spring networks
Physical Review B, 2002Co-Authors: J.w Chung, De Jeff Hosson, Van Der Erik GiessenAbstract:This paper concentrates on the scaling of the Failure Stress of a three-dimensional spring network as a function of its volume. In particular, the influences of the geometry and the local structure are examined. Both homophase disordered three-dimensional structures and composite systems are studied, containing a more or less ordered slab. The structures are generated by starting with a node distribution. A molecular-dynamicsbased algorithm uses void volume spheres, which all have Lennard-Jones interacting outer surfaces. The generated distributions of nodes form the basis of a procedure to interconnect the nodes with springs. In the calculation of the Failure Stress the total elastic energy is described by two-body central force, three-body bond bending, and four-body torsion contributions. The areas under uniaxial compression are varied in the range of 0.64 ‐5.76 mm 2 , and the height h ranges between 0.80 and 6.4 mm. It is found that the Failure Stress at constant base area could be described by s fail}@log(h/j)# 21/m , where j represents the correlation length within the sample the ~logarithm is to the base e!. The values of m are effective values. Only within the same kind of Failure mechanism and microstructure does the exponent m become more or less universal. Actually, the modulus m appears to depend on the system size, but in all cases thin samples are stronger than thick samples under uniaxial compression, and the Failure Stress increases with increasing coordination number. The Failure Stress of heterophase materials differs considerably in our calculations from that of homophase materials. The composite materials exhibit an increase in strength by a factor of 4, in comparison to the disordered structures of the same size. The actual Failure Stress of the composite material depends critically on the layering effect of the disordered region near the ordered phase.
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Failure Stress of a disordered three-dimensional spring network
Physical Review B, 2001Co-Authors: J.w Chung, De Jeff Hosson, Van Der Erik GiessenAbstract:This paper concentrates on the Failure Stress of a disordered three-dimensional spring network. In particular, we investigate the effects of several fracture criteria and of the connectivity at the nodes in the network. A node cannot be connected with another node if its relative distance is larger than a certain cutoff radius or a so-called connectivity threshold. In our modeling approach, the spring networks were loaded in compression and the network configuration with the lowest energy was calculated after each increment of force. Subsequently, the mechanical properties of the relaxed network structures were investigated using various fracture criteria. The largest threshold value of displacement was set to the commonly used criterion for brittle fracture, i.e., a fraction criterion of 1%, but also lower values (0.75%, 0.50%, and 0.25%) were examined. In addition, for each of these fracture criteria the Stress calculations were repeated with different connectivity thresholds. From this investigation it is concluded that it is not sufficient to examine only the fracture strain. In particular, the connectivity, i.e., the connectivity threshold ${C}_{0},$ which controls the spring entanglement between the nodes, has a substantial effect on the crack morphology. Larger ${C}_{0}'\mathrm{s}$ result in smaller fragments caused by crack branching.
Guangwei Zhang - One of the best experts on this subject based on the ideXlab platform.
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Coseismic Coulomb Stress changes caused by the Mw6.9 Yutian earthquake in 2014 and its correlation to the 2008 Mw7.2 Yutian earthquake
Journal of Asian Earth Sciences, 2015Co-Authors: Lianwang Chen, Shaofeng Liu, Shuxin Yang, Xingyue Yang, Guangwei ZhangAbstract:Abstract A three-dimensional viscoelastic finite element model of the Qinghai–Tibet Plateau and its adjacent regions was used to explore the relationship between the Mw7.2 Yutian earthquake in 2008 and the 2014 Mw6.9 Yutian earthquake. We further analyzed the Coulomb Failure Stress change caused by the Yutian Mw6.9 earthquake on faults surrounding the Bayan Har block and discussed the relationship between the Coulomb Stress change and aftershock distribution. The preliminary results showed that: (1) The Coulomb Failure Stress change caused by the Mw7.2 Yutian earthquake in 2008, which was projected on the slip direction of the 2014 Yutian Mw6.9 earthquake, exceeded the earthquake triggering threshold of 0.01 MPa, implying an apparent triggering effect. Specifically, the coseismic Coulomb Failure Stress changes were 0.0167 MPa and 0.0170 MPa when assuming apparent friction coefficients of 0.4 and 0.6, respectively. The Coulomb Failure Stress changes, including viscoelastic relaxation effects, were 0.0187 MPa and 0.0194 MPa respectively. Combined with the tectonic Stressing rate, the Mw6.9 Yutian earthquake in 2014 was advanced 21.4–24.9 years by the 2008 Mw7.2 Yutian earthquake; (2) The Stress changes derived from the viscoelastic relaxation effect were much less than that from the coseismic effect, which was possibly interpreted as the shorter elapsed time between the two earthquakes relative to the characteristic time; (3) The Coulomb Failure Stresses increased on the mid-northern segment of the Altyn Tagh fault, the middle segment of the Mani-Yushu fault and the western segment of the eastern Kunlun fault, which demonstrated increasing seismic potential. In particular, the Coulomb Failure Stress on the middle segment of the Altyn Tagh fault increased by 2.8 × 103 Pa, the most significant increase. In contrast, the Coulomb Failure Stress decreased on the western segment of the Mani-Yushu and Minjiang faults, with the western segment of the Mani-Yushu fault dropping by 3.6 × 103 Pa. The Coulomb Stress changes on most faults surrounding the Bayan Har block were calculated to have increased, while the Minjiang fault on the eastern boundary was inhabited due to the enhancement of coseismic compressive Stresses; (4) Combining the relocation of the aftershock sequence with the coseismic Failure Stress change, we concluded that the Mw6.9 Yutian main-shock triggered the aftershock sequences.
Charles Antle - One of the best experts on this subject based on the ideXlab platform.
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Statistical Distribution of Failure Stress Values from Superpave® Direct Tension Test
Transportation Research Record: Journal of the Transportation Research Board, 2002Co-Authors: Raj Dongré, Charles AntleAbstract:A statistically robust method was developed using the Weibull distribution to identify and eliminate outliers from the Failure Stress determinations. The method is applicable to any Failure Stress data set that follows the Weibull distribution; however, in this application, it was developed for the AASHTO standard test method for conducting the direct tension test (DTT). A large number of Stress-at-Failure measurements with the DTT were made in the course of instructing users of this device. These data, all for the same asphalt, provided the means for studying the nature of the distribution of the breaking strength of these asphalt specimens. The training database contains more than 900 data points. The current AASHTO practice of eliminating the lowest two Stress values was found to be reasonable. However, it is an arbitrary method that may lead to problems in the future. On the basis of the results of this study, the procedure is recommended for use and implementation in the next AASHTO version of the DTT standard.
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STATISTICAL DISTRIBUTION OF Failure Stress VALUES FROM SUPERPAVE (REGISTERED TRADEMARK) DIRECT TENSION TEST
Transportation Research Record, 2002Co-Authors: Raj Dongré, Charles AntleAbstract:A statistically robust method was developed using the Weibull distribution to identify and eliminate outliers from the Failure Stress determinations. The method is applicable to any Failure Stress data set that follows the Weibull distribution; however, in this application, it was developed for the AASHTO standard test method for conducting the direct tension test (DTT). A large number of Stress-at-Failure measurements with the DTT were made in the course of instructing users of this device. These data, all for the same asphalt, provided the means for studying the nature of the distribution of the breaking strength of these asphalt specimens. The training database contains more than 900 data points. The current AASHTO practice of eliminating the lowest two Stress values was found to be reasonable. However, it is an arbitrary method that may lead to problems in the future. On the basis of the results of this study, the procedure is recommended for use and implementation in the next AASHTO version of the DTT standard.
