On the Use of Quasi-Static Testing to Assess Impact Damage Resistance of Composite Shell Structures

The response of various composite structures to transverse loading was studied through im-pact and quasi-static testing. The AS4/3501-6 graphtie/epoxy composite structures considered have a [±4.5n/0n]s, layup configuration and include convex and concave shell sections, plates, and full cylinders. The impact tests fall within the so-called large-mass, low-velocity regime, where previous findings for composite plates indicate that quasi-static tests represent the impact response accurately; i.e., impact and quasi-static tests can be considered equivalent. This equivalence includes damage if the same peak force is reached in both the impact and quasi-static tests. The present work extends the impact and quasi-static equivalence from composite plates to various composite (shell) structures, including shells with an instability. Over nearly the entire range of impact events and shell structures considered, impact and quasi-static responses (including damage extent and distribution) are found to be equivalent. A small number of the most flexible (large-span, thin) specimens displayed a large-amplitude oscillatory impact loading response that was not observed for the quasi-static tests. These few specimens indicate one regime where the equivalence is limited The general equivalence demonstrated here for a wide range of composite structures has important implications for testing and design of damage-tolerant aerospace components. The findings also suggest that quasi-static experimentation can often be used to simulate the impact response (particularly damage) of composite shell structures.