The derived SI unit of shear modulus is the pascal (Pa), although it is usually expressed in gigapascals (GPa) or in thousand pounds per square inch (ksi). Its dimensional form is M^{1}L^{−1}T^{−2}, replacing force by mass times acceleration.
The shear modulus is one of several quantities for measuring the stiffness of materials. All of them arise in the generalized Hooke's law:
Young's modulusE describes the material's strain response to uniaxial stress in the direction of this stress (like pulling on the ends of a wire or putting a weight on top of a column, with the wire getting longer and the column losing height),
the Poisson's ratioν describes the response in the directions orthogonal to this uniaxial stress (the wire getting thinner and the column thicker),
the bulk modulusK describes the material's response to (uniform) hydrostatic pressure (like the pressure at the bottom of the ocean or a deep swimming pool),
the shear modulusG describes the material's response to shear stress (like cutting it with dull scissors). These moduli are not independent, and for isotropic materials they are connected via the equations $2G(1+\nu )=E=3K(1-2\nu )$.^{[9]}
The shear modulus is concerned with the deformation of a solid when it experiences a force parallel to one of its surfaces while its opposite face experiences an opposing force (such as friction). In the case of an object shaped like a rectangular prism, it will deform into a parallelepiped. Anisotropic materials such as wood, paper and also essentially all single crystals exhibit differing material response to stress or strain when tested in different directions. In this case, one may need to use the full tensor-expression of the elastic constants, rather than a single scalar value.
One possible definition of a fluid would be a material with zero shear modulus.
Shear waves
Influences of selected glass component additions on the shear modulus of a specific base glass.^{[10]}
In homogeneous and isotropic solids, there are two kinds of waves, pressure waves and shear waves. The velocity of a shear wave, $(v_{s})$ is controlled by the shear modulus,
Shear modulus of copper as a function of temperature. The experimental data^{[11]}^{[12]} are shown with colored symbols.
The shear modulus of metals is usually observed to decrease with increasing temperature. At high pressures, the shear modulus also appears to increase with the applied pressure. Correlations between the melting temperature, vacancy formation energy, and the shear modulus have been observed in many metals.^{[13]}
Several models exist that attempt to predict the shear modulus of metals (and possibly that of alloys). Shear modulus models that have been used in plastic flow computations include:
the MTS shear modulus model developed by^{[14]} and used in conjunction with the Mechanical Threshold Stress (MTS) plastic flow stress model.^{[15]}^{[16]}
the Steinberg-Cochran-Guinan (SCG) shear modulus model developed by^{[17]} and used in conjunction with the Steinberg-Cochran-Guinan-Lund (SCGL) flow stress model.
the Nadal and LePoac (NP) shear modulus model^{[12]} that uses Lindemann theory to determine the temperature dependence and the SCG model for pressure dependence of the shear modulus.
MTS model
The MTS shear modulus model has the form:
$\mu (T)=\mu _{0}-{\frac {D}{\exp(T_{0}/T)-1}}$
where $\mu _{0}$ is the shear modulus at $T=0K$, and $D$ and $T_{0}$ are material constants.
SCG model
The Steinberg-Cochran-Guinan (SCG) shear modulus model is pressure dependent and has the form
where, μ_{0} is the shear modulus at the reference state (T = 300 K, p = 0, η = 1), p is the pressure, and T is the temperature.
NP model
The Nadal-Le Poac (NP) shear modulus model is a modified version of the SCG model. The empirical temperature dependence of the shear modulus in the SCG model is replaced with an equation based on Lindemann melting theory. The NP shear modulus model has the form:
and μ_{0} is the shear modulus at absolute zero and ambient pressure, ζ is a material parameter, m is the atomic mass, and f is the Lindemann constant.
^McSkimin, H.J.; Andreatch, P. (1972). "Elastic Moduli of Diamond as a Function of Pressure and Temperature". J. Appl. Phys. 43 (7): 2944–2948. Bibcode:1972JAP....43.2944M. doi:10.1063/1.1661636.
^ ^{a}^{b}^{c}^{d}^{e}Crandall, Dahl, Lardner (1959). An Introduction to the Mechanics of Solids. Boston: McGraw-Hill. ISBN0-07-013441-3.CS1 maint: multiple names: authors list (link)
^ ^{a}^{b}Nadal, Marie-Hélène; Le Poac, Philippe (2003). "Continuous model for the shear modulus as a function of pressure and temperature up to the melting point: Analysis and ultrasonic validation". Journal of Applied Physics. 93 (5): 2472. Bibcode:2003JAP....93.2472N. doi:10.1063/1.1539913.
^Guinan, M; Steinberg, D (1974). "Pressure and temperature derivatives of the isotropic polycrystalline shear modulus for 65 elements". Journal of Physics and Chemistry of Solids. 35 (11): 1501. Bibcode:1974JPCS...35.1501G. doi:10.1016/S0022-3697(74)80278-7.
^Rubinstein, Michael, 1956 December 20- (2003). Polymer physics. Colby, Ralph H. Oxford: Oxford University Press. p. 284. ISBN019852059X. OCLC50339757.CS1 maint: multiple names: authors list (link)
Homogeneous isotropic linear elastic materials have their elastic properties uniquely determined by any two moduli among these; thus, given any two, any other of the elastic moduli can be calculated according to these formulas.
$K=\,$
$E=\,$
$\lambda =\,$
$G=\,$
$\nu =\,$
$M=\,$
Notes
$(K,\,E)$
${\tfrac {3K(3K-E)}{9K-E}}$
${\tfrac {3KE}{9K-E}}$
${\tfrac {3K-E}{6K}}$
${\tfrac {3K(3K+E)}{9K-E}}$
$(K,\,\lambda )$
${\tfrac {9K(K-\lambda )}{3K-\lambda }}$
${\tfrac {3(K-\lambda )}{2}}$
${\tfrac {\lambda }{3K-\lambda }}$
$3K-2\lambda \,$
$(K,\,G)$
${\tfrac {9KG}{3K+G}}$
$K-{\tfrac {2G}{3}}$
${\tfrac {3K-2G}{2(3K+G)}}$
$K+{\tfrac {4G}{3}}$
$(K,\,\nu )$
$3K(1-2\nu )\,$
${\tfrac {3K\nu }{1+\nu }}$
${\tfrac {3K(1-2\nu )}{2(1+\nu )}}$
${\tfrac {3K(1-\nu )}{1+\nu }}$
$(K,\,M)$
${\tfrac {9K(M-K)}{3K+M}}$
${\tfrac {3K-M}{2}}$
${\tfrac {3(M-K)}{4}}$
${\tfrac {3K-M}{3K+M}}$
$(E,\,\lambda )$
${\tfrac {E+3\lambda +R}{6}}$
${\tfrac {E-3\lambda +R}{4}}$
${\tfrac {2\lambda }{E+\lambda +R}}$
${\tfrac {E-\lambda +R}{2}}$
$R={\sqrt {E^{2}+9\lambda ^{2}+2E\lambda }}$
$(E,\,G)$
${\tfrac {EG}{3(3G-E)}}$
${\tfrac {G(E-2G)}{3G-E}}$
${\tfrac {E}{2G}}-1$
${\tfrac {G(4G-E)}{3G-E}}$
$(E,\,\nu )$
${\tfrac {E}{3(1-2\nu )}}$
${\tfrac {E\nu }{(1+\nu )(1-2\nu )}}$
${\tfrac {E}{2(1+\nu )}}$
${\tfrac {E(1-\nu )}{(1+\nu )(1-2\nu )}}$
$(E,\,M)$
${\tfrac {3M-E+S}{6}}$
${\tfrac {M-E+S}{4}}$
${\tfrac {3M+E-S}{8}}$
${\tfrac {E-M+S}{4M}}$
$S=\pm {\sqrt {E^{2}+9M^{2}-10EM}}$
There are two valid solutions.
The plus sign leads to $\nu \geq 0$.
The minus sign leads to $\nu \leq 0$.
$(\lambda ,\,G)$
$\lambda +{\tfrac {2G}{3}}$
${\tfrac {G(3\lambda +2G)}{\lambda +G}}$
${\tfrac {\lambda }{2(\lambda +G)}}$
$\lambda +2G\,$
$(\lambda ,\,\nu )$
${\tfrac {\lambda (1+\nu )}{3\nu }}$
${\tfrac {\lambda (1+\nu )(1-2\nu )}{\nu }}$
${\tfrac {\lambda (1-2\nu )}{2\nu }}$
${\tfrac {\lambda (1-\nu )}{\nu }}$
Cannot be used when $\nu =0\Leftrightarrow \lambda =0$