Static/Fatigue Structural Behaviour of Damaged Stiffened Composite Plates for UAS Applications

Weight reduction in structural aerospace configuration is based both on specific material selection and on the selection of specific shape and sections. UAS structures need both the introduction of new advanced composites and the definition of light weight construction based on thin walled configuration. With this idea in mind, Stiffening concepts are frequently used to increase structural performance, i.e. buckling characteristics, of a thin plates. Manufacturing of composite stiffened structures can give rise to the presence specific damaged situations such as skin/stiffener de-bonding. Such kind of defect can cause buckling prior to the designed critical condition and can cause a reduction in global strength. The presence of cyclical loading and fatigue effect can have important consequence on damage propagation and structural integrity. The static structural behavior of a damaged stiffened composite panel is summarized from previous research investigation and presented. Uniaxial compression and biaxial test loading conditions are applied to the panel in order to point out the damage effects on static behavior. Significant strain distribution under critical and post-critical (local-global) static test condition are discussed. Cyclic compressive loading experimental results are updated and re-analyzed in order to point out the effect of damage under repetitive load. Specific results are presented and discussed.