Python User Material Interface

See Also

• The Role of the Material Model in Continuum Mechanics
• Defining a Material Model
• Conventions
• Writing Messages to the Console and/or Log File

Overview

Material models written in Python are implemented as subclasses matmodlab.mmd.material.MaterialModel and are treated as builtin materials.

Invoking User Materials

User materials that subclass MaterialModel are invoked by assigning the model argument of the MaterialPointSimulator.Material factory method to the name of the material model.

Required Attributes

Material models that subclass MaterialModel must provide the following class attributes:

• name, as string defining the material’s name. Must be unique.

Required Methods

classmethod MaterialModel.param_names(n)

Class method that returns a list of parameter names. n is the number of parameters and is used to set the names of parameters for user defined materials at run time.

MaterialModel.setup(**kwargs)

Sets up the material model and return a list of state dependent variable names and initial values. By the time that setup is called, the model parameters have been

kwargs are optional keywords sent in to the model.

setup must return sdv_keys, sdv_vals, sdv_keys being the list of

state dependent variable names and sdv_vals being their initial values. Both should be consistent with the ordering expected by the material model.

MaterialModel.update_state(time, dtime, temp, dtemp, energy, density, F0, F1, strain, dstrain, elec_field, stress, statev, **kwargs)

Update the the material state

The following parameters are sent in for information and should not be updated:

• time, the time at the beginning of the time step
• dtime, Step time step size
• temp, the temperature at the beginning of the time step
• dtemp, step temperature increment
• energy, the energy at the beginning of the time step
• density, the material density
• F0, the deformation gradient at the beginning of the time step
• F1, the deformation gradient at the beginning of the time step
• strain, the strain at the beginning of the time step
• dstrain, the strain increment over the step
• elec_field, the electric field at the end of the step

The following parameter are sent in for information and should be updated to the end of the step:

• stress, the stress at the beginning of the step
• statev, the state dependent variables at the beginning of the step

The following variables are updated and returned

stiff, the 6x6 material stiffness

update_state must return stress, statev, stiff

Example

from numpy import zeros, dot
from mmd.material import MaterialModel
from utils.errors import MatModLabError

class MyElastic(MaterialModel):
    """Linear elastic material model"""
    name = 'my_elastic'

    @classmethod
    def param_names(cls, n):
        return ('K', 'G')

    def setup(self, **kwargs):
        K, Nu = self.parameters['E'], self.parameters['Nu']
        if E <= 0.:
            raise MatModLabError("negative Young's modulus")
        if -1. >= Nu < .5:
            raise MatModLabError("invalid Poisson's ratio")

    def update_state(self, time, dtime, temp, dtemp, energy, density,
                     F0, F1, strain, dstrain, elec_field,
                     stress, statev, **kwargs):
        # elastic properties
        E, Nu = self.parameters['E'], self.parameters['Nu']
        K = E / 3 / (1 - 2 * Nu)
        G = E / 2 / (1 + Nu)

        K3 = 3. * K
        G2 = 2. * G
        Lam = (K3 - G2) / 3.

        # elastic stiffness
        ddsdde = zeros((6,6))
        for i in range(3):
            for j in range(3):
                ddsdde[j,i] = Lam
            ddsdde[i,i] = G2 + Lam
        for i in range(4, 6):
            ddsdde[i,i] = G

        # stress update
        stress += dot(ddsdde, dstrain)

        return stress, statev, ddsdde