ENERGY-RELEASE RATE DETERMINATION FOR EDGE DELAMINATION UNDER COMBINED INPLANE, BENDING AND HYGROTHERMAL LOADING .2. 2 SYMMETRICALLY LOCATED DELAMINATIONS

Edge delamination in composite laminates subjected to combined inplane, bending and hygrothermal loading is analyzed using a crack tip element approach. It is assumed that two delaminations exist which are symmetrically located with respect to the midplane of the laminate. It is shown that, under pure bending, a linear analysis indicates that one of the delaminations generally has a positive mode I stress intensity factor, whereas the other crack generally has a negative mode I stress intensity factor. This indicates that crack face compression exists and an analysis incorporating crack face contact constraints is required to accurately obtain energy release rates. However, for many cases of bending combined with in-plane loading or uniform temperature or moisture change, both cracks have a tendency to open. General expressions are derived for the total energy release rate and the individual mode I and mode II components under these conditions. Specific example problems and results are presented.