Characterization by fracture mechanics of intra and interlaminar damage in composite laminates

Composite materials present a complicated internal structure that may generate different mechanisms of damage associated with events of failure. The prediction of the onset and propagation of such events requires the knowledge of properties that may appear at different levels: micro (level of fibres and matrix), meso (homogenized version of a lamina) and macro (the total structure with properties of the whole laminate). Determining these properties requires special tests where it is difficult to replicate the conditions that appear in an actual composite component, and additionally, in a controlled manner. In this paper, experimental testing and numerical analysis are performed on a [0,90n,0] laminate. The experimental campaign aims to observe and measure the damage (both intralaminar and interlaminar) in the laminate subjected to tension. These experimental results are then used to define a Boundary Element Method (BEM) model to determine the stresses and displacements, enabling the energy release rates associated with the cracks existing in the model to be calculated. This approach requires the capacity of having damages under control, in such a way of having the properties that want to be determined involved in the mechanism of damage. The results clearly indicate the potential for conducting tests on cross-ply laminates that can produce controlled damage patterns for determining key properties of composites.