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Low Velocity Impact Damage and Response of Stringer Stiffened Composite Panel



Engineering applications with complex composite structures like hat stringer stiffened flat panels when subject to impact result in a varying degree of damage, damage behavior, and loading paths compared to traditional composite panels. These differences are investigated in a co-cured stiffened T800/3900-2 carbon/epoxy laminate by subjecting it to low velocity impacts with varying impactor tip radii (12.7 and 76.2 mm), impact location (edge and center of stringer flange), and impact type (metal versus rubber protected). For all cases, the damage response is quantified (force time history and delamination area) and the energy is held constant at nominally 90 J. Impact of the 5 kg pendulum head occurs at 5 m/s. It is shown that the onset of delamination and the delamination area are independent of the impactor radius in the stringer stiffened panels. Similarly, the force time histories at a given site are independent of the tip radii (e.g. both 12.7 and 76.2 mm striking the center of the stringer/panel interface had similar force response). The force time history results show that the contact force at the center of the stringer is higher than that at the edge due to the added stiffness of the stringer and panel interface. The impactors fitted with rubber tips reduces the contact force levels by up to 15% and 8% at the center and edge of the stinger, respectively. Finite element simulation of the 12.7 mm radius tip at the edge of the stringer/panel interface were validated with the experimental data using ABAQUS/Explicit.

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