(Unidirectional composites only, not available for woven composites)
The 6th argument activates or deactivates the pre-failure nonlinearity feature. A value of 1 activates the pre-failure nonlinearity feature, while a value of 0 deactivates the pre-failure nonlinearity feature.
The pre-failure nonlinearity feature is intended to account for the nonlinear longitudinal shear (softening) response that is commonly observed in fiber-reinforced composite materials prior to ultimate failure. This additional form of nonlinearity involves imposing a series of three discrete reductions in the longitudinal shear stiffness of the matrix constituent material ( 
and 
). This directly results in a corresponding series of three discrete reductions in the longitudinal shear stiffness of the composite material ( 
and 
). Imposition of these three discrete reductions in the longitudinal shear moduli are completed prior to matrix constituent failure. Thus it provides a longitudinal shear softening effect prior to matrix constituent failure.
The plot below shows a typical measured longitudinal stress/strain curve for a unidirectional carbon/epoxy lamina. The pre-failure nonlinearity feature approximates this type of nonlinear longitudinal shear response with a four-segment, piecewise linear representation. For further information on the pre-failure nonlinearity feature, refer to the Theory Manual.
