Failure mechanisms of laminated composites subjected to static indentation

Quasi-static indentation tests on composite laminates have been performed. Thermal deply and C-scan techniques are used to observe the internal damage characteristics of laminates induced by static indentation. The results indicate that the dent depth increases slowly and almost linearly as the force is lower than its maximum. The observation shows that the damage induced at this loading stage includes matrix cracking and delamination only. Once the force exceeds the maximum, the dent depth increases sharply while the force remains almost unchanged. Deply test results demonstrate that the transition to rapid increase in dent depth is due to the fiber breakage produced at this loading stage. The results also indicate that the damage resistance of a composite laminate can be characterized by the maximum contact force. On the basis of this principle and test results, it is concluded that the damage resistance of toughened composite is much higher than that of brittle one.