(Unidirectional composites only, not available for woven composites)
(Abaqus/Standard only, not available for Abaqus/Explicit)
The 4th user material constant activates or deactivates the pre-failure nonlinearity feature. A value of 1 activates the pre-failure nonlinearity feature, while the default value of 0 deactivates the pre-failure nonlinearity feature.
The pre-failure nonlinearity feature accounts for the nonlinear longitudinal shear (softening) response 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 
) which 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 providing a longitudinal shear softening effect. 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 of the longitudinal shear response. For further information on the pre-failure nonlinearity feature, refer to the Theory Manual. Appendix C details the discrete values that SDV1 can assume during a progressive failure analysis where the pre-fail nonlinearity feature is activated.
