FRACTURE BEHAVIOR OF CROSS-PLY FIBRE REINFORCED COMPOSITE LAMINATES WITH CRACKS UNDER BIAXIAL LOADING CONDITIONS

Composite structures are normally subjected to complex loading during operating processes that can generate multi-axial stress states at their surfaces. By using data from conventional uniaxial test of composite materials in the design processes, safety factors might be overestimated which lead to unnecessary enlargement of structure sizes. Compared to uniaxial testing method, biaxial testing approach provides more realistic data on the behaviours of composite structure under complex loading situations. Due to the lack of biaxial experimental data results of damaged fibre-reinforced composite laminates with geometrical discontinuities such as cracks or notches, this study is to investigate the effects of biaxial stress states on failure behaviours of composite laminates with cracks under static conditions. The cruciform type specimens with pre-crack in different sizes and orientation were tested under different in-plane biaxial loading ratio. Material system used in this study was glass fiber reinforced epoxy with layup [0/90]s. The crack initiation stresses are drawn on failure envelopes. Digital image correlation (DIC) technique was employed to generate strain field around the cracks during all tests. Full three-dimensional extended finite element method (XFEM) models with surface based cohesive behaviour approach or virtual crack closure technique were implemented by employing commercial ABAQUS code to simulate the initiation and propagation of the discrete cracks under biaxial loading conditions. The result showed that material attained higher load bearing capability under tensile-tensile conditions. The findings is useful in the design of composite structures with lower safety factor which decreases the weight of the composite structures.