Search results
Results from the WOW.Com Content Network
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 modulus E 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),
E i is the Young's modulus along axis i; G ij is the shear modulus in direction j on the plane whose normal is in direction i; ν ij is the Poisson ratio that corresponds to a contraction in direction j when an extension is applied in direction i. The Poisson ratio of an orthotropic material is different in each direction (x, y and z). However ...
The bulk modulus (which is usually positive) can be formally defined by the equation K = − V d P d V , {\displaystyle K=-V{\frac {dP}{dV}},} where P {\displaystyle P} is pressure, V {\displaystyle V} is the initial volume of the substance, and d P / d V {\displaystyle dP/dV} denotes the derivative of pressure with respect to volume.
Other names are sometimes employed for one or both parameters, depending on context. For example, the parameter μ is referred to in fluid dynamics as the dynamic viscosity of a fluid (not expressed in the same units); whereas in the context of elasticity, μ is called the shear modulus, [2]: p.333 and is sometimes denoted by G instead of μ.
Torsion of a square section bar Example of torsion mechanics. In the field of solid mechanics, torsion is the twisting of an object due to an applied torque [1] [2].Torsion could be defined as strain [3] [4] or angular deformation [5], and is measured by the angle a chosen section is rotated from its equilibrium position [6].
The governing formula for this mechanism is: Δ σ y = G b ρ {\displaystyle \Delta \sigma _{y}=Gb{\sqrt {\rho }}} where σ y {\displaystyle \sigma _{y}} is the yield stress, G is the shear elastic modulus, b is the magnitude of the Burgers vector , and ρ {\displaystyle \rho } is the dislocation density.
where is the shear modulus, which can be determined by experiments. From experiments it is known that for rubbery materials under moderate straining up to 30–70%, the Neo-Hookean model usually fits the material behaviour with sufficient accuracy.
The phenomenological equation which describes Harper–Dorn creep is = where ρ 0 is dislocation density (constant for Harper–Dorn creep), D v is the diffusivity through the volume of the material, G is the shear modulus and b is the Burgers vector, σ s, and n is the stress exponent which varies between 1 and 3.