Progressive Damage of Unidirectional Graphite/Epoxy Composites Containing a Circular Hole

Abstract

In this paper, experimental and finite element results are presented to describe the anisotropic states of stress, strain and damage of unidirectional graphite/epoxy composite plates containing a central hole subjected to off-axis uniaxial tension. The nonlinear stress analysis of the laminates is based on the finite element procedure formulated with a newly developed anisotropic damage model, in which the inelastic behavior of composite material is attributed to the irreversible thermodynamics processes involving energy dissipation and stiffness change primarily caused by the presence of micro-structural changes of the material. Moiré interferometry, a high sensitivity whole-field experimental technique, with a computer image processing system is used to determine and to interrogate the two-dimensional deformation field in the composites. Results from the tests and analysis clearly reveal the anisotropic damage characteristics and the influence of principal material direction on the deformation response of the composites. Failure of the composite material near the hole area takes the form of a damage zone and the damage mechanism involves redistribution of stress and strain. From the analysis, it may be concluded that macrocrack initiates at the material point near the hole boundary with high damage value and propagates along the direction of damage zone extension. Good agreement between the predicted and experimental results confirms that the current approach can provide a convenient and accurate means to interrogate the complicated damage behavior of notched unidirectional composites with a hole and can be readily extended to examine the damage response of unidirectional composite structures with different notch configurations.