All numerical quantities in a finite element input file must be expressed in a consistent set of units. For example, if the geometry of the model is specified in centimeters and the force is specified in Newtons, the material moduli must be expressed in units of N/cm2.
All material properties in the composite material database are stored using the (N/m/K) system of units (i.e., force is expressed in Newtons, length is expressed in meters, and temperature is expressed in degrees Kelvin). Therefore, if a model is built using a different system of units, you must identify the appropriate system of units so that Simulation Composite Analysis can provide stiffness and stress to the Abaqus/Standard finite element code in the correct units. Simulation Composite Analysis has pre-programmed conversion factors that can be used to express constitutive information in several commonly used systems of units. In addition, it has the capability to provide constitutive information in a user-defined (or custom) system of units.
The system of units that will be used by the Simulation Composite Analysis User-Defined Material Subroutine is defined by the 1st user material constant listed on the data line that immediately follows the *USER MATERIAL statement. The table below shows the allowable range of integer values for the first user material constant and lists the system of units specified by each value.
If the 1st user material constant is assigned a value of 1, 2, 3, or 4, the software will automatically perform the appropriate unit conversions and provide the constitutive relations in the system of units shown in the table above. However, if the model is defined using a system of units that is not represented in the table, you must set the value of the first user material constant to 5, indicating that a 'custom' system of units will be used. In this case, you must specify the three conversion factors needed by Simulation Composite Analysis to convert from the default units of Newtons, meters, and Kelvin to the custom system of units. These three conversion factors for force, length, and temperature will be listed in the HIN file as discussed previously (The HIN File).