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  • 1
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Fracture analysis of civil engineering structures often requires appropriate modeling of discrete cracks propagating in an inhomogeneous or nonlinear material. For example, quasi-brittle materials, such as concrete, are characterized by formation of cracks with fracture process zone under tension and plasticity under compression. Application of either finite element method (FEM) or boundary element method (BEM) to problems involving simultaneously discrete cracks and inhomogeneities or plastic deformations faces certain difficulties. Therefore, we propose the FEM-BEM superposition method, which removes the respective methods disadvantages while keeping their advantages. In the proposed method, the original problem involving both material inhomogeneity or plasticity and discrete cracks is decomposed into two subproblems. The inhomogeneity or inelastic deformation is represented in only one of the subproblems, while the cracks appear only in the other. The former subproblem is analyzed using FEM and the latter one by BEM, so as to utilize the advantages of the two methods. The solution of the original problem is then obtained by superposing the solutions of the two subproblems. In order to verify validity of the proposed method we present numerical results of several examples, including both linear-elastic and nonlinear fracture mechanics. The results are compared with available analytical solutions or with data computed by other numerical methods, showing both accuracy and computational superiority of the proposed method.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2009-03-13
    Description: The Mammoth Peak sheeted intrusive complex formed in the interior of a ~7–10 km deep magma chamber, specifically in the Half Dome granodiorite of the Tuolumne batholith, central Sierra Nevada, CA (USA). The sheets consist of fractionated melts with accumulated hornblende, biotite, magnetite, titanite, apatite, and zircon. The accumulation, especially of titanite, had a profound effect on minor and trace elements (Nb, Ta, Ti, REE, U, Th, P, Zr, Hf, etc.), increasing their contents up to five to six times. Our thermal–mechanical modeling using the finite element method shows that cooling-generated tensile stresses resulted in the inward propagation of two perpendicular sets of dilational cracks in the host granodiorite. We interpret the sheeted complex to have formed by a crack-seal mechanism in a high strength, crystal-rich mush, whereby outward younging pulses of fractionated magma were injected into these syn-magmatic cracks at the margin of an active magma chamber. Thermal–mechanical instabilities developed after the assembly of the sheeted complex, which was then overprinted by late ~NW–SE magmatic foliation. This case example provides a cautionary note regarding the interpretation that sheeted zones in large granitoid plutons imply a diking mechanism of growth because the sheeted/dike complexes in plutons (1) may display inverse growth directions from the growth of the overall intrusive sequence; (2) need not record initial chamber construction and instead may reflect late pulsing of magma within an already constructed magma chamber; (3) have an overprinting magmatic fabric indicating the continued presence of melt after construction of sheeted complexes and thus a prolonged thermal history as compared to dikes; and (4) because the scale of the observed sheeted complexes may be small (〈1%) in comparison to large homogenous parts of plutons, in which there is no evidence for sheeting or diking. Thus, where extensive dike complexes in plutons are absent, such as in much of the Tuolumne batholith, the application of an incremental diking model to explain chamber construction is at best speculative. ©2009 Springer-Verlag
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
    Topics: Geosciences
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  • 3
    Publication Date: 2012-04-01
    Description: A growing body of field evidence indicates that hypersolidus fabrics preserved in syntectonic plutons are likely to have formed in highly crystallized ‘rigid sponge’ magma. This paper demonstrates that such magma could be idealized as a rheological solid and that the development of non-coaxial fabrics in plutonic rocks can very conveniently be modeled in the framework of solid mechanics. Using the finite element method (FEM), we modeled two strain regimes of small magnitudes (plane-strain horizontal simple shear with the shear strain γ of up to 0.30 and plane-strain pure shear of up to 15% shortening) superposed onto vertically oriented and variously spaced elastic phenocrysts set in the viscoelastic matrix. In the simple shear regime, the phenocrysts slightly rotate toward the shear plane, while the principal strain directions in the matrix are instantaneously oriented at an angle of about 45° or less to the phenocryst fabric. Simple shear thus can only lead to the formation of oblique phenocryst and matrix fabrics. By contrast, the vertical phenocryst fabric is maintained in the pure shear regime, and a new horizontal fabric can develop almost instantaneously in the matrix even for small amounts of superposed shortening (5% shortening after 10 ky in our model). We conclude that such a mechanism can easily produce perpendicular hypersolidus fabrics in plutonic rocks and that only a very short time span (first thousands of years) is required to develop magmatic fabric in a pluton for ‘normal’ rates (10−15 to 10−13 s−1) of tectonic deformation. ©2011 Springer-Verlag
    Print ISSN: 1437-3254
    Electronic ISSN: 1437-3262
    Topics: Geosciences
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  • 4
    Publication Date: 2017-01-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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