# 4.4.5. Composite Material Properties

When using the composite boundary condition you must define a separate material to use for the composite. This will define the species in the composite, as well as its physical properties. The composite material will also define the chemistry mechanism to use in the composite and the ODE solver to use to solve it.

The properties in the composite material can be either constants, or functions of composition that will change as the composite decomposes.

    BEGIN PROPERTY SPECIFICATION FOR FUEGO MATERIAL new_composite
      REFERENCE temperature = 300.
      REFERENCE mass_fraction Carbon = 0.6724
      REFERENCE mass_fraction Epoxy  = 0.3276
      REFERENCE mass_fraction Char   = 0.0

      species_density Carbon = 1779.  # kg/m^3
      species_density Epoxy  = 1300.  # kg/m^3
      species_density Char   = 650.   # kg/m^3

      SUBROUTINE FOR density = density_inverse_mass_average
      INPUT VARIABLES FOR density_inverse_mass_average = species_density mass_fraction

      THERMAL_CONDUCTIVITY = "0.023*(temperature-273.15)^0.46"
      SPECIFIC_HEAT = "750 + 4.1*(temperature-273.15)"

      species_emissivity char = 0.95
      species_emissivity epoxy = 0.5
      species_emissivity carbon = 0.5

      SUBROUTINE FOR emissivity =  emissivity_mixture_average
      INPUT VARIABLES FOR emissivity_mixture_average = species_emissivity mass_fraction

      Begin ODE solver parameters
        ODE Solver = LSODE
        Absolute Tolerance = 1e-6
        Relative Tolerance = 1e-3
      End

      Begin Chemistry Description MyChem
        Begin Reaction R1
          Reaction is Epoxy -> 0.5Char + 0.5CH4
          Rate Function = Arrhenius A = 3.33e17  Ea = 2.2614e5 R = 8.314
          Concentration Function = Standard  mu = Automatic
          Heat of Reaction = 0.0
        End
      End
    END