A stiffness degradation model for cracked multidirectional laminates with cracks in multiple layers

In the present work the problem of the stiffness degradation of multidirectional symmetric laminates in the presence of off-axis cracks is studied. A new analytical model is presented, capable of estimating the elastic properties of a multidirectional symmetric laminate with an arbitrary lay-up and cracks in one or more plies. The model is based on the so called “optimal” shear lag analysis of a laminate with cracks in one layer (and its symmetric), coupled with an analytical procedure to account for the presence of cracks in multiple plies, considering also their mutual interaction. The model requires, as inputs, the geometric and elastic properties of the layers and the crack density only. A very satisfactory agreement is found between the present predictions and experimental and numerical results from the literature. It is also shown that accounting for the mutual interaction between cracks in different plies is fundamental for a reliable estimation of the stiffness drop.