Global-local plug-in for high-fidelity composite stress analysis in Femap/NX Nastran

The prediction of the actual stress fields in real structural applications is still not completely resolved, especially when dealing with composite structures. The geometrical complexity of laminate parts and the multiple length scales which are involved in the problem lead to a severe tradeoff between accuracy and computational costs. Consequently, to keep the size of the numerical problem below a certain limit, stress engineers tend to use classical laminate elements in their FEM simulations, which cannot provide the interlaminar stress solutions through the stack of plies with enough accuracy. To extend the capabilities of Nastran, this work proposes a global-local method to extract the 3D strain and stress fields from the 2D elements. The code, named MUL2@GL, has been developed as a user-friendly plug-in for Femap and requires a minimum training to be operated. By just selecting the critical elements in Femap, the code automatically generates a dedicated model for an advanced composite FEM code which is embedded in the plug-in. This solver provides the distribution of the 3D solutions across the thickness of the element. The proposed code is highly convenient for the evaluation of the failure onset in critical areas of the structure such as cutouts, corners or free edges, where the hypotheses of laminate plate elements no longer apply. As an example, we show the capabilities of the method in a benchmark composite wing and the free-edge stresses in a cutout.