Damage resistance property of stiffened composite panels under low-velocity impact

In order to study the effect of impact energy and structural geometry on damage resistance of stiffened composite panels under low-velocity impact, 3 groups of I-section stringer-stiffened composite panels were experimentally and numerically investigated. Drop weight low-velocity impact tests were conducted to capture the damage characteristics such as impact force histories, indentation depths and delamination areas. Finite element (FE) models were established based on an anisotropic elato-plastic theory incorporating fiber failure. Indentation depths of the specimens were simulated by the FE models. The simulated results are coordinated with the tested results very well. The results indicate that there is a knee point for the curve of impact energy and dent depth of stiffened composite panels. Some fiber breakage at the impact location on the surface of specimens can be found after the knee point occurs. The maximum impact force increases with the increasing impact energy, while the delamination initiation load and delamination area do not. The impact energy and the maximum impact force of specimens containing 1.5 mm indentation increase with the increasing thickness of skin or stiffener while the delamination initiation load only increases with the increasing thickness of skin.