Difference between revisions of "Transversely Isotropic Material"
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== Transverse 1 == | == Transverse 1 == | ||
In this transversely isotropic [[Material Models|MPM material]] (or [[FEA Material Models|FEA material]], the isotropic plane is the x-y plane, which is the plane for 2D or axisymmetric analyses. The axial direction is along the z axis, which is in the thickness direction for 2D analyses or the hoop direction for axisymmetric anlayses. The stiffness and compliance tensors are: | In this transversely isotropic [[Material Models|MPM material]] (or [[FEA Material Models|FEA material]]), the isotropic plane is the x-y plane, which is the plane for 2D or axisymmetric analyses. The axial direction is along the z axis, which is in the thickness direction for 2D analyses or the hoop direction for axisymmetric anlayses. The stiffness and compliance tensors are: | ||
<math> | <math> |
Revision as of 13:27, 1 April 2013
Constitutive Law
This anisotropic MPM material (or FEA material) is a small strain, linear elastic material. The stress (σ) and strain (ε) are related by:
[math]\displaystyle{ \vec\varepsilon = \mathbf{S}\vec\sigma + \vec\alpha\Delta T + \vec\beta c }[/math]
[math]\displaystyle{ \vec\sigma = \mathbf{C}\vec\varepsilon + \vec M\Delta T + \vec M_\beta c }[/math]
where S and C are the compliance and stiffness tensors, [math]\displaystyle{ \vec\alpha }[/math] and [math]\displaystyle{ \vec\beta }[/math] are the thermal and solvent expansion tensors, and [math]\displaystyle{ \vec M }[/math] and [math]\displaystyle{ \vec M_\beta }[/math] are the stress-temperature and stress-concentraion tensors. ΔT is difference between current temperature and the stress free temperature and c is the weight fracture solvent concentration. These equations use contracted notation where stress and strain tensors contract to vectors:
[math]\displaystyle{ \vec\varepsilon = (\varepsilon_{xx},\varepsilon_{yy},\varepsilon_{zz},\varepsilon_{yz},\varepsilon_{xz},\varepsilon_{xy}) }[/math]
[math]\displaystyle{ \vec\sigma = (\sigma_{xx},\sigma_{yy},\sigma_{zz},\sigma_{yz},\sigma_{xz},\sigma_{xy}) }[/math]
and the order of the shear terms is by the standard convention. The stiffness and compliance tensors contract to 6X6 matrices while all thermal and moisture expansion tensors contract to a vector. When used as an FEA material, the solvent expansion and solvent concentration terms are not used.
In a transversely isotropic MPM material (or FEA material), one plane is isotropic while the direction normal to that plane defines a unique axis with different properties. Properties in the isotropic plane are subscripted "T" for transverse plane properties and properties along the unique axis are subscripted "A" for axial properties. You can pick from two types of transversely isotropic materials, which differ only by orientation on the unique axes.
Transverse 1
In this transversely isotropic MPM material (or FEA material), the isotropic plane is the x-y plane, which is the plane for 2D or axisymmetric analyses. The axial direction is along the z axis, which is in the thickness direction for 2D analyses or the hoop direction for axisymmetric anlayses. The stiffness and compliance tensors are:
[math]\displaystyle{ \mathbf{C}^{-1} = \mathbf{S} = \left(\begin{array}{cccccc} {1\over E_T} & -{\nu_T\over E_T}& -{\nu_A\over E_A} & 0 & 0 & 0 \\ -{\nu_T\over E_T} & {1\over E_T} & -{\nu_A\over E_A} & 0 & 0 & 0 \\ -{\nu_A\over E_A} & -{\nu_A\over E_A} & {1\over E_A} & 0 & 0 & 0 \\ 0 & 0 & 0 & {1\over G_A} & 0 & 0 \\ 0 & 0 & 0 & 0 & {1\over G_A} & 0 \\ 0 & 0 & 0 & 0 & 0 & {1\over G_T} \end{array}\right) }[/math]
where E and G are tensile and shear moduli, ν are Poisson's ratios, and A and T refer to axial and transverse properties. The thermal and solvent expansion tensors are
[math]\displaystyle{ \vec\alpha = (\alpha_T, \alpha_T,\alpha_A,0,0,0) }[/math]
[math]\displaystyle{ \vec\beta = (\beta_T, \beta_T,\beta_A,0,0,0) }[/math]
where again, A and T refer to axial and transverse properties. The stress-temperature and stress-concentration tensors are found from
[math]\displaystyle{ \vec M = -\mathbf{C}\vec\alpha \quad{\rm and}\quad \vec M_\beta = -\mathbf{C}\vec\beta }[/math]
All these properties are set as explained below. The solvent expansion terms for for MPM only.
Transverse 2
In this transversely isotropic MPM material (or FEA material, the isotropic plane is the x-z plane. The axial direction is along the y axis, which is in the plane for 2D analyses. For axisymmetric analyses, the isotropic plane is the r-θ plane and the axial direction is along the z axis. The stiffness and compliance tensors are:
[math]\displaystyle{ \mathbf{C}^{-1} = \mathbf{S} = \left(\begin{array}{cccccc} {1\over E_T} & -{\nu_A\over E_A} & -{\nu_T\over E_T} & 0 & 0 & 0 \\ -{\nu_A\over E_A} & {1\over E_A} & -{\nu_A\over E_A} & 0 & 0 & 0 \\ -{\nu_T\over E_T} & -{\nu_A\over E_A} & {1\over E_T} & 0 & 0 & 0 \\ 0 & 0 & 0 & {1\over G_A} & 0 & 0 \\ 0 & 0 & 0 & 0 & {1\over G_T} & 0 \\ 0 & 0 & 0 & 0 & 0 & {1\over G_A} \end{array}\right) }[/math]
where E and G are tensile and shear moduli, ν are Poisson's ratios, and A and T refer to axial and transverse properties. The thermal and solvent expansion tensors are
[math]\displaystyle{ \vec\alpha = (\alpha_T, \alpha_A,\alpha_T,0,0,0) }[/math]
[math]\displaystyle{ \vec\beta = (\beta_T, \beta_A,\beta_T,0,0,0) }[/math]
where again, A and T refer to axial and transverse properties. The stress-temperature and stress-concentration tensors are found from
[math]\displaystyle{ \vec M = -\mathbf{C}\vec\alpha \quad{\rm and}\quad \vec M_\beta = -\mathbf{C}\vec\beta }[/math]
All these properties are set as explained below. The solvent expansion terms are for MPM only.
Material Properties
The properties for Transverse 1 and Transverse 2 are the same, although their initial orientations are different. The properties are
Property | Description | Units | Default |
---|---|---|---|
EA | Axial tensile modulus | MPa | none |
ET | Transverse tensile modulus | MPa | none |
GA | Axial shear modulus | MPa | none |
GT | Transverse shear modulus | MPa | none |
nuA | Axial Poisson's ratio | none | 0.33 |
nuT | Transverse Poisson's ratio | none | none |
alphaA | Axial thermal expansion coefficient | ppm/M | 40 |
alphaT | Transverse thermal expansion coefficient | ppm/M | 40 |
betaA | Axial solvent expansion coefficient | 1/(wt fraction) | 0 |
betaT | Transverse solvent expansion coefficient | 1/(wt fraction) | 0 |
DA | Axial solvent diffusion constant | mm2/sec | 0 |
DT | Transverse solvent diffusion constant | mm2/sec | 0 |
kCondA | Axial thermal conductivity | W/(m-K) | 0 |
kCondT | Transverse thermal conductivity | W/(m-K) | 0 |
(other) | Properties common to all materials | varies | varies |
In a transversely isotropic material, the three transverse properties are not independent; they are related by
[math]\displaystyle{ G_T = {E_T\over 2(1+\nu_T)} }[/math]
As a consequence, you can only specify two of these three properties
Transverse 1 and Transverse 2 give identical materials but with different initial orientations. You can change to any other orientation when defining material points by selecting rotations angles for particles. In 2D, the only rotation angle that is allowed is about the z axis. Because there is only one rotation angle, you need both material types to allow you to specify all possible orientations for 2D analysis of transversely isotropic materials. In other words, for 2D analysis, the axial direction has to either be in the x-y plane (Transverse 2) or normal to the x-y plane (Transverse 1). Any other orientation would induce out-of-plane shear that is not allowed in 2D calculations. To handle such material orientations, you need to use 3D calculations.
History Variables
None