The Tensile modulus, principle direction (fibre) result indicates how much stress is needed to cause a unit of movement.
For a Fiber and Dual Domain Fiber analysis, the Tensile modulus in first and second principal (fiber) results generate fiber-over-thickness (FOT) averaged values, which means that they are element-based values averaged over all the laminates of each element. For a 3D Fiber analysis, Tensile modulus, principal direction (fiber) results are recorded for each element in the model at the end of the analysis.
The first principal direction coincides with the fiber orientation first principal direction, and is determined by the Fiber orientation Fill+Pack analysis. The second principal direction is perpendicular to the first principal direction. If the first and second principal directions are X, and Y respectively, then Z is the third principal direction.
The thermo-mechanical property calculation for fiber-filled composites are based on the orthotropic assumption, that fiber-filled material properties are different in three orthogonal principal directions. Under this assumption, there are 9 independent mechanical constants and three independent thermal expansion coefficients. In Midplane/Dual Domain models, because of the plain stress assumption in the shell structure analysis in warp, only 4 mechanical constants (Tensile modulus in first/second principal directions, Poisson ratio v12, Shear modulus G12) are necessary.
The option selects the 9 mechanical constants (E1, E2, E3, v12, v23, v13, G12, G23, G13) and 3 CTE's (thermal expansion coefficient in first/second/third directions) all at once. In a Fiber analysis using 3D analysis technology, the complete set of thermo-mechanical properties with orthotropic assumption is necessary for a Warp analysis using 3D analysis technology. These properties are element-based, so each tetrahedral or beam element has its own orthotropic set of properties.