Postbuckling behavior of composite laminates with two delaminations under uniaxial compression

Nonlinear buckling analysis using the finite element method is employed to study the buckling and postbuckling behavior of unidirectional composite materials with two delaminations under uniaxial compression. Strain energy release rates around the crack tips are calculated to assess the possible growth of the two delaminations in various positions and with different lengths. From the analysis, the results indicate that if the long delamination is close to the surface of the laminate, the inner, short delamination has no effect on the buckling stress. However, the presence of inner, short delamination may significantly change the behavior of delamination growth. If the short delamination is above the long delamination that is located on the middle surface, the presence of the short delamination may significantly reduce the buckling stress. But its effects on the behavior of delamination growth is minor.