On the Accuracy of a Four Node Delaminated Composite Plate Element and Its Application to Damage Detection

Abstract

This paper presents a new fournode composite element, which incorporates nd delaminations through its thickness. Based on the extended finite element method (XFEM) technology, the element is particularized on a CLT (classical laminate theory). Delamination is considered in the kinematic equations with additional degrees of freedom. The result is a fournode quadrilateral element requiring only two single FEM (finite element method) formulations, a bending one and a membrane one. An important result is that this formulation has the same accuracy as when separate elements are considered (“four region approachâ€‌). It is furthermore proven that the delaminated element passes the “patch testâ€‌ if the selected FEM formulations to build the element pass the test in the pure single problems, making this methodology very attractive to develop other fractured elements. To illustrate this result, two benchmark problems were studied: first a complete delaminated cantilever plate, and second a complete delaminated circular plate. The element was tested in the context of SHM (structural health monitoring). Frequency shifts, damage indexes, and changes in mode shapes and frequency response functions (FRF) were obtained to quantify the severity of damage due to delamination.