Preform Material Data

A preform is modeled as a porous medium, and the mathematical modeling uses Darcy's model. Hence, the preform is characterized using permeability tensor.

Draping computations play a crucial role in determining the tensor material properties. This data has to be transformed at each solution integration point using the local coordinate orientation. This is essential for the RTM process, and it is seen in the image below. The preform, which is characterized in a flat orientation, is draped to take the shape of the mold before the RTM process begins. To simulate the process, the material data is required in local orientation based on the mold shape.

Lay Flat and Draped Preform

Preforms are characterized in a flat orientation. That is, its material properties such as permeability tensor, conductivity tensor, specific heat, etc. are measured in this orientation. The process of shaping the preform to its final product shape is called the draping operation. Often what is measured as an orthotopic tensor in a flat orientation will be a full tensor in its draped position. This transformation has to be computed to perform the simulation.

Draping Computations

The draping computation has many internal steps, and HyperMesh is used for this analysis. The details of the process, shown in the figure below, are completely automated and hidden in Inspire. It is computed in batch mode. RTM Solver uses this exported ply orientation to compute material data in each integration point.

Known Limitations in Draping Computation

  1. For complex models, the automatic midsurface extraction may fail. The workaround is to create the midsurface manually and Inspire will use that interface and not try to create one automatically.
  2. Inspire does not support post-processing of draping results.


  • Units: kg/m3
  • Keyword: Density
  • Description: Density of the preform. This the density of the fiber (glass, carbon. kevlar, etc.)

Specific Heat

  • Units: J/(kg-K)
  • Keyword: SpecificHeat
  • Description: Specific heat of the preform

Thermal Conductivity Tensor

  • Units: W/(m-K)
  • Keyword: Conductivity_X, Conductivity_Y, Conductivity_Z
  • Description: Thermal conductivity is tensor data, and it is supported in the local coordinate systems.

Permeability Tensor

  • Units: m2
  • Keyword: Permeability_X, Permeability_Y, Permeability_Z
  • Description: Defined in Darcy's law for porous media. The oil mining industry uses a unit called Darcy which is physically more intuitive.
A medium with a permeability of 1 Darcy permits a flow of 1cm3/s of a fluid with viscosity 1 cP (0.001Pa⋅s) under a pressure gradient of 1atm/cm acting across an area of 1cm2. The permeability of sand is approximately 1 Darcy.
1 Darcy = 9.8692327×10−13 m2= 98.692327μm2
This is derived as

The GUI can show Permeability in Darcys, m2, or μm2.


  • Units: None
  • Keyword: Porosity
  • Description: (1.0 - Fiber Volume Fraction). Often the industry is more familiar with the term Fiber Volume Fraction, and it is easy to determine.


  • Units: 1/Pa
  • Keyword: Compressibility
  • Description: Used in VARTM analysis. This term has to be non-zero.

Pore Size (Diameter)

  • Units: m
  • Keyword: PoreSize
  • Description: This is the average pore size of the preform. Needs a special flag to use this experimental feature, and it is not exposed in the GUI.