Based on the emerging theory of damage mechanics, a general form of constitutive equation of damaged composite ply and the associated damage evolution law has been established. With experimental observations, a damage criterion has been formulated by the decomposition of micro-failure mechanisms. Initial results obtained from the tests and analyses conducted on several graphite composite laminates with simple configurations show the fundamental behavior of damage initiation and development. It is also illustrated that the current approach provides a convenient and accurate means to examine the complicated damage behavior of the structures made of composite materials.
