On Low-Velocity Impact Testing of Composite Materials

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Abstract
The importance of understanding the response of structural composites to impact cannot be overstated. This understanding includes both the impact phenomena themselves and the influence of materials properties on the impact response. This paper presents the need for instrumented testing to optimize our understanding of the impact event, especially the response of the impacted material. The conclusion is drawn that the impact force history is a more relevant measure of a materials characteristics than is the total kinetic energy of the impactor. Static and dynamic impact phenomena are assessed to lay the foundation for the eventual development of a standardized test method focused on the lower velocity range impact response behavior of composites. In addition, a relatively inexpensive but very versatile low-velocity, instrumented pendulum impact tester is described and actual test data for both graphite fiber/thermoset matrix and graphite fiber/thermoplastic matrix are compared. Actual energy absorption curves are shown. A simple method is described to allow direct measurement of the total energy exchanged during the impact event, and the use of these data to permit the vital dynamic calibration of the load cell for every different impact event is illustrated. The different stages in the damage process are characterized, for the first time, for the two materials systems studied.

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