The low-velocity impact response of graphite/epoxy laminates was investigated theoretically and experimentally. A nine-node isoparametric plate finite element in conjunction with an empirical contact law was used for the theoretical investigation. Theoretical results are in good agreement with strain-gage experimental data. The results of the investigation indicate that the present theoretical procedure describes the impact response of laminate for low-impact velocities.

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The effect of stitching on edge delamination and ultimate strength in graphite/epoxy laminates is investigated. Study is done on three different graphite/epoxy layups: [±30/0]s, [±30/90]s, and [±45/02/902]s. Progression of delamination is monitored using di-iodobutane enhanced X-radiography. Results show that stitching effectively arrests delamination, but has varying effects on tensile strength. A two-dimensional finite element is used to calculate interlaminar normal stress and strain energy release rate for stitched and unstitched laminates. The introduction of stitching causes little change in interlaminar normal stress. However, it reduces the strain energy release rate as the delamination crack approaches the stitch line.