PREDICTION OF CRACK INITIATION IN LAMINATES WITH FIBER DISCONTINUITY: A VARIATIONAL APPROACH

Composite laminates with continuous fibre are strong and stiff but due to the presence of fibre discontinuity, the stress concentration may cause damage to occur and lower its mechanical properties. Therefore, it is necessary to evaluate the influence of fibre discontinuity on the mechanical properties of the laminates and its damage behaviour. This work extends the applicability of the variational approach method for analysing laminates with alternating materials in the longitudinal directions based on the original variational model of Hashin's analysis. The stress analysis considered an arbitrary number of regions with different material properties and herein we specifically used the analysis to evaluate laminates with fibre/ply discontinuity. For simplicity, we assumed a plane stress condition or stress distribution, we assumed that the normal stress in the loading direction was constant along the direction of thickness in each ply. The admissible stress state that satisfied both equilibrium and boundary/continuity conditions was constructed with unknown functions that were determined using the principle of minimum complementary energy. The finite fracture criterion was then used to describe the onset of matrix crack in the resin pocket. The critical energy release rate was calculated and used to predict the crack onset stress in the laminate with different numbers of discontinuous ply and length of the resin pocket. These results were compared with experimental results, which obtained good agreement.