Walsh Joseph B.

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Walsh
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Joseph B.
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  • Preprint
    A new model for analyzing the effect of fractures on triaxial deformation
    ( 2006-03-20) Zhu, Wenlu ; Walsh, Joseph B.
    Rock is porous, with a connected network of cracks and pores. The static and dynamic behaviors of a rock sample under load depend on both the solid mineral matrix and the porous phase. In general, the configuration of the pore phase is complex; thus most studies on the effect of the porous phase on rock deformation are conducted numerically and theoretical analyses of the constitutive relations are scarce. We have studied rock deformation under axially-symmetric loading by analyzing a model where the pore phase is approximated by rough planes, randomly spaced and oriented, extending through the sample. The roughness is caused by asperities, all with the same tip radii, but having heights h with a probability density distribution given by the negative exponential e-h/λ where λ is a length parameter. Slip at contacts under local shear stress is resisted by simple Coulomb friction, with friction coefficient f. Both static and dynamic deformation were analyzed. The effect of porosity on deformation for both modes was found to be given by the non-dimensional parameter λαj, where αj is the total area of the fault planes per unit volume. We demonstrate that stress-induced microfracturing begins as randomly oriented microslip throughout the sample. As axial load increases, microslip occurs along preferred orientations and locations, which finally leads to deformation on a single fault. The model was found to fault under static loading conditions---the axial load at faulting and the angle of the “fracture” plane agree with values of those parameters given by Coulomb’s theory of fracture. Dynamic moduli and Poisson’s ratio are found to be virtually elastic and independent of the friction coefficient acting at contacts. The attenuation for uniaxial dynamic loading is a strong function of the friction coefficient and increases linearly with strain amplitude, in agreement with laboratory measurements.
  • Technical Report
    Strength of the ALVIN hulls
    (Woods Hole Oceanographic Institution, 1966-04) Walsh, Joseph B. ; Mavor, James W.
    Results are presented of pressure tests, measurements and analyses of the strength of the three pressure hulls constructed for the deep submergence vehicle ALVIN. Comparison of stress distribution as measured in various tests and predicted theoretically is made. Failure of the hull can occur by buckling or by yielding over an appreciable fraction of shell thickness or by yielding at a stress concentration. A DTMB analysis predicts collapse of the three hulls No. 1, 2, and 3 at 7040, 7160, and 6720 psi respectively. No. 1 hull has been tested to 4400 psi. From strain measurements, isolated yielding at the inside surface of hull No. 2 (presently in ALVIN) will occur at a pressure of 5800 psi. However, yielding through the entire section would not occur until near the predicted collapse pressure. The maximum Mises equivalent stress at the test pressure of 3300 psi is 62,000 psi. The comparable material yield strength 125,000 psi is used with hull No. 2. the strength of the plexiglas viewing ports, the electrical lead-throughs and the hull release mechanism are referenced but not discussed.
  • Article
    Sliding of a rough surface under oblique loading
    (American Geophysical Union, 2004-05-19) Walsh, Joseph B. ; Zhu, Wenlu
    Sliding of a rough surface having a range of asperity heights is a gradual process, starting at contacts under relatively low normal shear load and spreading until the surface slides as a unit. We analyze this process theoretically for asperities with spherical tips, with heights having a probability density distribution given by a negative exponential. The case where applied normal traction increases concurrently with applied shear is treated in detail, resulting in analytical expressions for the normal and shear displacements. These results are used to show limitations on constitutive behavior for more complex normal stress-shear stress histories.