Relation Between Macroscopic Shear Moduli and Micromechanical Shear Stress Concentrations of Multicomponent Materials

1967 ◽  
Vol 50 (6) ◽  
pp. 331-332 ◽  
Author(s):  
D. P. H. HASSELMAN
1973 ◽  
Vol 8 (2) ◽  
pp. 134-139 ◽  
Author(s):  
R D Adams ◽  
N A Peppiatt

Poisson's ratio strains in the adherends of a simple adhesive lap joint induce transverse stresses both in the adhesive and in the adherends. Two simultaneous second-order partial-differential equations were set up to describe the normal stresses along and across an adherend and were solved both by an approximate analytical method and a finite-difference technique: the two solutions agreed closely. The adhesive shear stresses can then be obtained by differentiating these solutions. The transverse shear stress has a maximum value for metals of about one-third of the maximum longitudinal shear stress, and this occurs at the corners of the lap, thus making the corners the most highly stressed parts of the adhesive. Bonding adherends of dissimilar stiffness was shown to produce greater stress concentrations in the adhesive than when similar adherends are used.


2020 ◽  
Vol 25 (10) ◽  
pp. 1904-1923
Author(s):  
Youxue Ban ◽  
Changwen Mi

For a solid surface or interface that is subjected to transverse loading, the influence of its flexural resistibility to bending deformation becomes significant. A spherical inhomogeneity or void embedded in an infinite elastic medium under the application of nonhydrostatic loads represents a typical example. In this work, we consider the most fundamental loading of a far-field unidirectional tension. Analytical displacements and stresses are developed by the coupling of a Steigmann–Ogden surface mechanical model, the simple method of Boussinesq displacement potentials, the semi-inverse method of elasticity, and Legendre series representations of spherical harmonics. The problem is then solved by converting the equilibrium equations of displacement into a linear system with respect to the Legendre series coefficients. The developed solutions are general in the sense that they may reduce to their classical or Gurtin–Murdoch counterparts as special cases. Analytical expressions reveal that the derived solution depends on four dimensionless ratios from among surface material parameters, shear moduli ratio, and inhomogeneity or void radius. In particular, instead of depending on both flexural parameters in the moment–curvature relation, one fixed combination is sufficient to represent the surface flexural rigidity. This is in contrast with the influence of the in-plane elastic stiffness, in which both surface Lamé parameters matter. Parametric studies further demonstrate that, for metallic inhomogeneities or voids with radii between 10 nm and 100 nm, the effects of surface flexural rigidity on stress distributions and stress concentrations are significant.


Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. E65-E77 ◽  
Author(s):  
Bikash K. Sinha ◽  
Badarinadh Vissapragada ◽  
Lasse Renlie ◽  
Sveinung Tysse

Near-wellbore alteration in shear stiffnesses in the three orthogonal planes can be described in terms of radial variations of the three shear moduli or slownesses. The three shear moduli are different in formations exhibiting orthorhombic or lower degree of symmetry, as is the case in deviated wellbores in triaxially stressed formations. These shear moduli are affected by factors such as overbalanced drilling, borehole stress concentrations, shale swelling, near-wellbore mechanical damage, and supercharging of permeable formations. The two vertical shear moduli [Formula: see text] and [Formula: see text] in an anisotropic formation with a vertical [Formula: see text]-axis are obtained from crossed-dipole sonic data, whereas the horizontal shear modulus [Formula: see text] is estimated from borehole Stoneley data. The effective shear modulus [Formula: see text] is smaller than the vertical shear moduli [Formula: see text] or [Formula: see text] in a poroelastic formation exhibiting high horizontal fluid mobility. Consequently, analyses of radial profiling of the three shear moduli in a reasonably uniform lithology interval yield useful correlations, with mobility impaired by an increased amount of clay or by near-wellbore damage in a shaley sand reservoir interval in a North Sea vertical well. Radial profiling results help to identify suitable depths for fluid sampling and to complete a well for optimum production.


1997 ◽  
Vol 50 (11S) ◽  
pp. S204-S209 ◽  
Author(s):  
Wolfgang E. Seemann

In this paper, a thin piezoceramic element is considered which is bonded to an elastic or a rigid half-space. Such a model may be an approximation of the interaction between piezoceramic elements and elastic structures like beams and plates. For an elastic half-space, the determination of the shear stress in the bonding layer leads to a singular integral equation. A half-space which is very stiff may be modeled as a rigid substrate. For this case, displacement functions are introduced. Hamilton’s principle for electromechanical systems allows the use of Lagrange multipliers to incorporate the condition of a stress free upper surface of the piezoceramic element. The stresses in the bonding layer and in the piezoceramic element are estimated by this method and compared with Finite Element results. Though the singularity near the ends of the piezoceramic element cannot be modeled by both methods, stress concentrations can clearly be seen for the shear stress as well as for the normal stress. As infinite stresses due to the singularity do not occur in reality, the results allow an estimation of the bonding stresses except in the near vicinity of the edges. The knowledge of these stresses is important to prevent failure due to delamination.


1980 ◽  
Vol 15 (4) ◽  
pp. 175-182 ◽  
Author(s):  
P Stanley ◽  
B V Day

The paper describes a three-dimensional photoelastic analysis of a series of Araldite models, each containing five or six different offset-oblique holes positioned in such a way that there were no ‘interaction’ effects between neighbouring holes. The geometric parameters defining a hole were varied systematically and the elastic stress distribution around the outer edge of each hole was obtained. The stress data are presented in non-dimensional form in terms of the shear stress in a plain cylinder. The dependence of the maximum stress on the geometric variables is discussed and it is shown that the stress concentrations for a wide range of hole/cylinder parameters can be reasonably well predicted from flat plate data. In some cases the predictions are unconservative.


A theory is presented for obtaining the effective elastic Green function G(k) of well-bonded fibre-reinforced materials at low volume-fractions of fibre in the presence of disorder. The centre of mass positions of the fibres are taken to be random. The theory is applied to the case where the alignment is also random, and comment is made on its suitability for less totally disordered geometries. The shear stress at the fibre-matrix interface is also calculated, and effective elastic moduli obtained by taking the low k limit. Finite frequency effects are considered; the damping of long wavelength acoustic modes by disorder is calculated. Results are given for general length distribution, Young modulus and number density of fibres in a matrix of arbitrary bulk and shear moduli. The fibre radius is taken to be small compared with the fibre length. In a limiting case, that of high overlap of fibres and high values of Young modulus for the fibres in an incompressible matrix, the results for the composite Young modulus and interface shear stress obtained by a full Green function treatment take forms similar to those first derived heuristically by shear-lag analysis (H. L. Cox, Br. J. appl. Phys. 3, 72 (1952)). The increment in shear modulus of an incompressible elastic medium when inflexible, inextensible random-flight wires or fibres are embedded in it is also calculated.


1970 ◽  
Vol 37 (1) ◽  
pp. 85-92 ◽  
Author(s):  
W. T. Chen

This paper presents an exact solution for the stress distribution around an elastic spheroidal inclusion in an infinite transversely isotropic elastic body which is otherwise under a pure shear stress. The stresses and displacements are expressed in terms of elementary functions. The technically important consideration of the stress concentrations around a spheroidal cavity is discussed. Numerical results are given for a number of hexagonal crystals.


Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. WA181-WA196 ◽  
Author(s):  
Ting Lei ◽  
Bikash K. Sinha ◽  
Michael Sanders

We described a nondestructive method to estimate the maximum and minimum horizontal stresses and formation nonlinear elastic constants using sonic data from a vertical wellbore. This method for the estimation of horizontal stress magnitudes consists of using radial profiles of the three shear moduli obtained from the Stoneley and cross-dipole sonic data in a vertical wellbore. These shear moduli change as a function of formation stresses, which in turn change as a function of the radial position away from the wellbore. Two difference equations were constructed from the three far-field shear moduli and the other two were constructed from differences in the shear moduli at radial positions with different stresses in the presence of near-wellbore stress concentrations. Outputs from this inversion algorithm included the maximum and minimum horizontal stress magnitudes, and two rock nonlinear constants referred to a local hydrostatically loaded reference state. The underlying acoustoelastic theory behind this inversion algorithm assumes that differences in the three shear moduli are caused by differences in the formation principal stresses. Additionally, the orientation of the maximum horizontal stress direction was identified from the fast-shear azimuth in the presence of a dipole dispersion crossover. Hence, the principal horizontal stress state was fully determined. Good agreement was obtained between the predicted minimum horizontal stress magnitude and that measured from an extended leak-off test in a vertical offshore wellbore in Malaysia. One of the nonlinear constants was obtained from differences between compressional velocity at two depths caused by differences in the overburden stress and the maximum and minimum horizontal stresses. Estimates were obtained for the stress coefficients of the compressional, fast-shear, and slow-shear velocities referred to a local reference state. These stress coefficients of velocities helped in the interpretation of observed time-lapse changes in seismic traveltimes caused by fluid saturation and reservoir stress changes.


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