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Impact damage to composites has been identified as a major limiting factor in the wider use of composite materials as structural components. Graphite fiber is often selected as a structural fiber due to its low density and high strength, both desirable properties in rocket motorcase and launch tube design. An understanding of the damage mechanisms involved is critical in the determination of composite structural integrity and for the development of damage models and design codes. To this end, a test program was conducted to characterize the impact response of graphite/epoxy structures. Overall design of the test article utilized for this program was directed towards a generic thin-walled structure applicable for use as either a rocket motorcase or launch tube. Low-energy impacts between 1.25 and 7.75 J (0.9 and 5.6 ft-lb) were imparted to empty cylinders and to cylinders whose casewalls were strengthened to simulate launch tube and rocket motorcase configurations. Significant differences between the test configurations were identified with regard to visual damage, impact loads, absorbed energy, and casewall deflection. However, with all the readily apparent differences noted, the post-impact residual strength capability was quite similar. The data indicate that significant strength losses can be expected at impact energies as low as 1.3 J (0.94 ft-lb).
composites, low-energy impact, graphite/epoxy, residual strength, filament wound, rocket motor case, launch tube, impact damage
Aerospace engineer, U.S. Army Aviation and Missile Command, AMSMI-RD-PS-CM, Redstone Arsenal, AL