FiniteDeformation context - OPM/IFEM-Elasticity GitHub Wiki

The <finitedeformation> context is for input specific for finite deformation applications (the NonLinEl app). It can have the following sub-contexts:

<formulation>

Use this to specify the nonlinear formulation to use.

Attributes: None

Value: Any of the following sub-contexts:

  • <planestrain> - Use a plane strain formulation in 2D
  • <axisymmetric> - Use an axi-symmetric formulation in 2D
  • <linear> - Use a linear formulation (no equilibrium iterations)
  • <totallagrange> - Use a Total Lagrange formulation
  • <updatedlagrange> - Use an Updated Lagrange formulation
  • <mixed> - Use a mixed formulation
    • Attribute: type - type of mixed formuation, (Qp/Pp-1, Qp/Qp-1, Fbar)
    • Value: Order of the internal pressure field for types Qp/Pp-1 and Fbar

<gravity>

Use this to specify the gravity vector to be used for calculation of gravitation forces.

Attributes:

  • x - Global X-component of the gravity vector.
  • x - Global Y-component of the gravity vector.
  • x - Global Z-component of the gravity vector.

Value: None

<isotropic>

Use this to define an isotropic material property.

Attributes:

  • set - The topology set to apply the material property to.

  • E - Youngs modulus. Ignored if the <stiffness> sub-context is used.

  • nu - Poisson's ratio. Ignored if the <poisson> sub-context is used.

  • rho - Mass density. Ignored if the <density> sub-context is used.

  • ver - Material version. The following values are recognized:

    • Negative or unspecified: Linear-elastic material model
    • 11 - 14 : Standard Neo-Hookean material model
    • 21 - 14 : Modified Neo-Hookean material model
    • Any other non-negative value is invalid

    The second digit of the ver value defines the volumetric energy function $U(J)$:

    • 1 : $U(J) = \frac{1}{4}\lambda (J^2 - 1 - 2\ln(J))$
    • 2 : $U(J) = \frac{1}{2}\lambda (J-1)^2$
    • 3 : $U(J) = \frac{1}{2}\lambda \ln(J)^2$
    • 4 : $U(J) = 2\lambda (J - 1 - \ln(J))$

    where λ is the bulk modulus (first Lame-parameter depending on E and nu) and J denotes the determinant of the deformation gradient.

Value: Any combination of the following sub-context:

  • <stiffness> - Function describing the Young's modulus
    • Attributes:
      • type - Function type
      • aging - If true, a function of time since element activation is specified, otherwise a spatial function is specified
    • Value: Function definition depending on the chosen type and aging
  • <poisson> - Spatial function describing the Poisson's ratio
    • Attribute: type - Function type
    • Value: Function definition depending on the chosen type
  • <density> - Spatial function describing the mass density
    • Attribute: type - Function type
    • Value: Function definition depending on the chosen type

See the expression functions page for the symbolic expression syntax.

<plastic>

Use this to define a plastic material property.

Attributes:

  • set - The topology set to apply the material property to.
  • Emod - Youngs modulus
  • nu - Poisson's ratio
  • rho - Mass density
  • Hiso - Isotropic hardening modulus
  • Hkin - Kinematic hardening modulus
  • yield - Which yield function to use:
    • 1 : von Mises
    • 2 : Drucker-Prager
    • 3 : Prager-Lode
    • 4 : Johnson-Cook
    • 5 : Isotropic hardening
    • 6 : Voce
  • Y0 - Initial yield stress
  • Yinf - Infinite yield stress
  • beta - (only for yield = 1, 4 and 6)
  • istrt - Start state (0: Elastic, 1: Last solution)
  • A - (only for yield = 4)
  • B - (only for yield = 4)
  • n - (only for yield = 4)
  • Q1 - (only for yield = 6)
  • C1 - (only for yield = 6)
  • Q2 - (only for yield = 6)
  • C2 - (only for yield = 6)

Value: The material parameters above can be listed the order shown (not recommended).

Example:

  <plastic set="mat1" E="206.9" nu="0.29" Hiso="0.12924" yield="1"
           Y0="0.45" Yinf="0.715" beta="16.93" istrt="1"/>

This is equivalent to:

  <!--                E     nu   n/a rho Hiso   Hkin yield Y0 Yinf  beta  istrt -->
  <plastic set="mat1">206.9 0.29 0.0 0.0 0.12924 0.0 1.0 0.45 0.715 16.93 1.0</plastic>

<contact>

Use this to define contact conditions in the model.

Attribute:

  • formulation - Which contact formulation to use (penalty or augmented lagrange)

Value: One of the following sub-contexts can be specified:

  • <sphere> - Defines a spherical rigid contact body
    • Attribute: R - Sphere radius
  • <cylinder> - Defines a cylindric rigid contact body
    • Attribute: R - Cylinder radius
  • <plane> - Defines a planar rigid contact body

Each of the three sub-contexts above can have the following sub-sub-contexts:

  • <point> - Defines the location of the master node of the contact body
    • Attributes: None
    • Value: spatial coordinates of the master node
  • <slave> - Defines the contact surface/edge on the flexible body
    • Attribute: set - Topology set defining the contact surface (or edge in 2D)
    • Value: None
  • <dirichlet> - Defines the Dirichlet properties for the rigid contact body
    • Attributes:
      • comp - The components to apply the boundary conditions to (one-indexed, string with 1, 2, 3 or combinations).
      • type - The type of the boundary condition specification (linear, expression).
    • Value: A constant number, the slope or a function expression, in accordance with the given type. A blank value gives a homogeneous Dirichlet condition.
  • <eps> - Defines the penalty parameter
    • Attribute: None
    • Value: The penalty parameter

Example:

    <contact formulation="augmented lagrange">
      <cylinder R="10.0">
        <point>10.0 -9.0</point>
        <slave set="lower"/>
        <dirichlet comp="12"/>
        <eps value="10.0"/>
      </cylinder>
    </contact>
⚠️ **GitHub.com Fallback** ⚠️