Experimental characterization of compression failure mechanism initiation and growth in notched carbon fiber reinforced composite specimens

This paper describes an experimental investigation to evaluate the compression failure mechanisms of kink banding, splitting, and delaminations under non-standard quasi-static loading of laminated carbon fiber reinforced composites. Tests were performed on double-edge notch compression (DENC) specimens to observe microscopic compressive damage initiation and progression. Acoustic emission results from specimens loaded to failure were used to define ranges of static stress associated with different forms of damage. Subsequent tests were interrupted at these stress intervals and results obtained from multiple inspection techniques provide quantified characterization of failure mechanism initiation and growth as a function of applied load level. Optical images of the exterior surfaces, micrographs of the laminate thickness generated via a grind/polish procedure, and postmortem X-ray computed tomographs provide detailed information on the 3D morphology and evolution of failure mechanisms in the laminate. Key failure characteristics include interior kink bands, surface ply splitting, and delaminations at two different types of interfaces. Kink bands are only present near ultimate failure while splitting and delamination initiate at approximately 50% lower stress levels. The experimental observations provide insight into the critical and subcritical nature of these failure mechanisms and their possible interactions in a multidirectional laminate under compression loading.