Material degradation assessment for stiffened composite shells using metamodelling approach.

The intense interest coming from the aerospace industry indicates the need of safe exploitation of composite materials in stiffened shell structures. Since stiffened shells are far most consumed structural component, it is important to study the behaviour of material degradation to evaluate the safe design guidelines. Moreover, current numerical procedures cannot simulate the collapse of stiffened shells with sufficient reliability and efficiency, leading to over-conservative designs. One can assume that great potential exist for future increase of effectiveness of stiffened composite structures by allowing of post-buckling of skin to occur during the exploitation [

1

].

An assessment of material degradation in terms of stiffness reduction in the skin stringer zone [

2

] is carried out to estimate the material degradation influence over post-buckling stiffness of the axially loaded stiffened shells. The presented procedure is based on the building of metamodels employing experimental design and response surface methodology. Metamodels are built using stiffened shell geometrical variables adding material degradation variables as: degradation region length and material elastic property reduction coefficient. The numerical responses, obtained from explicit finite element simulations of composite stiffened shells subjected to buckling and post-buckling, are used for the building of metamodels. The acquired metamodels are built both for approximation of the dependence of load-shortening curve on material degradation and for the inverse problem — the determination of material degradation degree from essential response parameters of the load shortening curve. The resulting design procedure provides an effective optimal design tool for the safe preliminary study of composite stiffened shells under axial compression [

3

].