Simultaneous Measurement of Fiber-Matrix Interface Debonding and Tunneling Using a Dual-Vision Experimental Setup.

Background: Fiber-matrix debonding is a precursor for transverse cracking and several other types of damage in fiber composites. However, to date, there are limited experiment-based reports that study the fundamental mechanisms of fiber-matrix debonding. Objective: This work aims to uncover the governing mechanisms of fiber-matrix interface debonding by full-field measurements supplemented by numerical simulations. In particular, the application of a dual-vision image-based characterization approach on single glass macro fiber samples is discussed and proven useful in understanding the in-plane and out-of-plane debonding characteristics at the fiber-matrix interface. Methods: Full-field strain and displacement measurements based on digital image correlation are performed on model single-fiber composites. The use of a dual-vision system allows strain measurements in the vicinity of the fiber-matrix interface, also allowing for the identification of critical strain and stress values corresponding to the initiation and propagation of debonding damage. The experimental data are used to calibrate an inverse identification approach that outputs the shape of the debonded interface along the fiber length. Results: Full-field measurements allow for establishing correlations between local and global strain fields. Observation of debonding propagation along the fiber axis seems to be representative of the crack tunneling during the early stages of the failure process, i.e., when the crack tip is subjected to opening mode only. Conclusions: Side view measurements are useful as a first-order approximation of the debonding propagation velocity along the fiber axis but fail to provide accurate measurements for the debonding shape, esp. in areas where the crack is under a dominantly shear stress state. This issue can be resolved by full-field measurements coupled with computational simulations. [ABSTRACT FROM AUTHOR]