Modelling delaminations in postbuckling stiffened composite shear panels

A method has been developed to predict the effect of delaminations in a pos tbuckling stiffened structure manufactured from laminated composite materia ls. The emphasis of the technique, driven by aircraft certification require ments, was towards establishing whether delamination growth would initiate under given loading conditions. A geometric nonlinear finite element analys is was used to calculate the strain energy release rate around the circumfe rence of a circular delamination using the virtual crack closure technique. In order to deal with the complex structural response in a computationally efficient manner, the structure was modelled using plate elements with two layers of plate elements used in the delaminated region. The effect of del amination size on the strength of postbuckling panels was shown to be a com plex phenomenon in which trends were difficult to predict. Large delaminati ons could significantly affect the global and sublaminate buckling modes an d therefore be less critical than smaller delaminations. It was concluded t hat the method could accurately predict the load and location at which dela mination growth would initiate, given suitable critical strain energy relea se rate data.