A three-dimensional Finite Fracture Mechanics model to predict free edge delamination in angle-ply laminates

The layered structures exhibit a weakly singular stress state in the vicinity of free edges, attributable to the elastic mismatch of adjacent plies, thereby promoting delamination. In the present study, this so-called free edge effect is investigated for symmetric angle-ply laminates in the framework of the Finite Fracture Mechanics (FFM). For a given intrinsic properties, such as fracture toughness and strength, the computation of the interlaminar stresses and energy release rate is imperative for the evaluation of coupled FFM criterion. These quantities are determined in terms of non-dimensionalised functions employing a comprehensive three-dimensional Finite Element Method (FEM) model. Dimensional analysis facilitates finding these functions for all laminate configurations only once while preserving the generality of functions. A semi-elliptically shaped crack is presumed to nucleate at the dissimilar interface post-crack initiation. Given that, the considered crack has two dimensions, the solution of 3D FFM model leads to an optimisation problem. It is hypothesised that homothetic crack extensions occur, i.e., cracks extend only in a self-similar manner, maintaining a constant aspect ratio of semi-ellipse. For validation purposes, the prediction of the laminate fracture using proposed 3D FFM fracture criterion is compared with the experimental test results found in the literature for various laminate types (AS1/3501-6, T800/914, G947/M18) and layups ([±10_n]_s, [±15_n]_s, [±20_n]_s, [±30_n]_s). It is observed that close agreement can be achieved between prediction and experiments when intrinsic properties are known.