The Core Failure criterion predicts failure of core materials in sandwich structures due to interlaminar shear (, ) and normal stresses . It is assumed that core failure is highly dominated by the out-of-plane stresses and therefore the in-plane terms are neglected. The normal stress is only considered in the 3D formulation of the criterion. By default, the 2D formulation is active.

The failure criterion distinguishes between isotropic (isotropic-homogeneous) and orthotropic (orthotropic homogeneous and honeycomb) core materials. For isotropic cores, a simplified formulation of the Tsai-Wu is used [ 44 ]. For orthotropic materials, the maximum stress approach is implemented [ 43 ]. An isotropic-homogeneous core has othotropic stress limits in order to support the core failure criterion as described below. R, Q, and Zt / Zc are the strength limits with respect to the corresponding stress component.

Isotropic Core

(5–112)

Orthotropic Core

(5–113)

In previous releases of ACP, the core failure criterion was implemented differently. The previous implementation can still be evaulated using custom failure criteria. An example implementing the previous core failure criterion is provided in Evaluating Custom Failure Criteria.