Wedge peel testing for automated fiber placement

The success of the automated manufacture of composites is generally measured by the interlaminar bond quality. The objective of this study is to establish a correlation between the simple wedge peel test and the DCB test for interlaminar fracture toughness. The demonstration of such a relationship will lend validity to the wedge peel test, and enable the development of optimal placement parameters more efficiently. Unidirectional composite specimens of both wedge peel and DCB configurations were fiber placed at various processing conditions using the NASA Langley Automated Fiber Placement Facility. The DCB interlaminar fracture toughness and the wedge peel strength were determined for each set of processing conditions. A clear trend in the data from the two test methods is shown. A rise in both the peel strength and the fracture toughness occurs with increasing processing temperature due to increasing resin flow. Peaks in both the wedge peel strength and DCB fracture toughness data are seen to occur at very similar processing conditions. Similarly, both peel strength and fracture toughness decrease with increasing processing temperatures beyond those which provide peak strength data. This decrease is due to possible thermal degradation of the resin. In view of these findings, it is suggested that the wedge peel test can be used for fast and efficient characterization/qualification of interlaminar bond quality.