Influence of Frequency and Environmental Conditions on Dynamic Behavior of Graphite/Epoxy Composites

The purpose of this research is to experimentally determine the combined influence of frequency and environmental conditions on dynamic behavior of graphite/epoxy composites. The new additions to the data base on dynamic behavior facilitate confident use of these composites in applications.

This objective has been accomplished by performing flexural vibration tests on graphite/epoxy beams. Dynamic behavior in the dry room-temperature state of 25°C (77°F) is contrasted with four elevated-temperature states: (1) 82°C (180°F), dry; (2) 60°C (140°F), moisture saturated; (3) 82°C (180°F), moisture saturated; and (4) 93°C (200°F), moisture saturated. The properties determined are an effective flexural modulus and damping for frequencies from 10 to 1000 Hz. Specimens are of four distinct ply layups manufactured from Narmco 5208/T300 unidirectional tape.

Overall, the modulus and damping results indicate that frequency effects are quite small in all cases. They are a bit greater for matrix-controlled modes of response at the higher frequencies. At the same temperature, damping increases with moisture saturation. For dry specimens, however, damping decreases with temperature.