Buckling-induced delamination analysis of composite laminates with soft-inclusion

In this paper, the effect of material impact damage on buckling-driven delamination growth in composite laminates under compression is studied using a finite element method. The initial material damage, e.g. fibre fracture and matrix cracking due to impact, is modeled through a so-called soft-inclusion, in which an area with reduced stiffness is introduced in the analysis of buckling-induced delamaination growth with an ADINA-based finite element program. Parametric studies are carried out through numerical tests with different inclusion sizes and stiffness reductions, and a comparison with experiments is made. It is found that for single delaminations of moderate size, even significant stiffness reductions in one haft of the delamination diameter have a fairly small influence on the initiation of delamination growth. Moreover, the experimentally measured local buckling load and deflection responses during delamination growth are lower than those predicted by the finite element model with severe stiffness reduction. It is concluded that such a soft-inclusion model is not sufficiently accurate to model the material damage, and more mathematically elaborated models which are capable to cope with material degradation, multiple delamination, crack closure and so on, should be developed.