3.1.1 Composite material is, by its nature, non-isotropic. Mid-plane methods may be used
with good results for global evaluation of in-plane stress in cases with balanced
fibre layup. Any load transfer trough the thickness of the material is usually
carried by the matrix material only. The strength of the matrix material is usually
much less than the strength of the fibres, and the analysis must take this into
account.
3.1.2 The analysis shall be done accounting for the load factors with respect to potential
failures trough global buckling, shear stiffness of spar tubes, thin wall buckling
and other stability evaluations used in the design process.
3.1.3 When results of the computations for composite components are reported in the form of
a failure index such as Tsai Wu’s, the index value is to be calculated against the
permissible stresses, and the index value subsequently checked against unity. It is
not permitted to calculate the index value to compressive, tensile and shear
strength and then evaluate the safety factor on the index value.
3.1.4 More specific guidance on how to model composite elements and how to perform a
non-linear large displacement type calculation may be found in publications.