An investigation was undertaken to determine the effects of hail damage on the fatigue strength of a graphite/epoxy composite laminate. Sixteen-ply coupons were subjected to simulated hail impact by iceballs of 25.4 or 38.1 mm in diameter. Upon impact, the 25.4 mm diameter iceball possessed 7.1 J of kinetic energy, while the 38.l mm diameter iceball possessed a kinetic energy of 27.4 J. For further comparison, additional coupons were impacted with a 12.7 mm diameter aluminum sphere with either 7.1 or 27.4 J of kinetic energy. Inspection revealed that neither iceball impact event caused any internal damage, while each aluminum sphere impact caused delaminations within each coupon. After being impacted and inspected, each coupon was subjected to constant amplitude tension--tension fatigue. It was determined that neither the 25.4 mm diameter iceball impact nor the 38.1 mm diameter iceball impact affected the fatigue performance of this particular laminate. The 7.1 J aluminum sphere impact also did not affect this laminate, while the 27.4 J aluminum impact did adversely affect the fatigue performance of this material.
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