UC San Diego

As composites are increasingly used for primary structures in commercial aircrafts, it is necessary to understand damage initiation for composites subject to low velocity impacts from service conditions, maintenance, and other ground equipment mishaps. In particular, collisions with ground vehicles can present a wide area, blunt impact. Therefore, the effects of bluntness of an impactor are of interest as this is related to both the external visual detectability of an impact event, as well as the development of internal damage in the laminate. The objective of this investigation is to determine the effect of impactor radius on the initiation of damage to composite panels. A pendulum impactor was used to strike 200 mm square woven glass/epoxy composite plates of 3.18mm and 6.35mm thicknesses. Hemispherical steel tips with radius 12.7mm to 152.4mm were mounted to a piezoelectric force sensor which measures the contact force history. Impacts were conducted with and without rubber bumpers to mimic the bumpers used on ground vehicles. Strain gauges were mounted to select panels. Experimental data show distinct threshold energy for the onset of delamination and fiber breakage. These energy levels increase with increasing tip radius. Strain increases with decreasing tip radius. Strains at the panel center are less affected by the presence of rubber bumpers with increasing tip radius. Finite element simulations match the experimentally measured contact force and strain data. Curved FE panels show peak contact forces independent of impactor radius and incident angle. In-plane compressive stresses decrease with increasing radius tips and incident angle