Wedge peel testing for automated fiber placement

The success of the automated manufacture of composites is generally measure d by the interlaminar bond quality. The objective of this study is to estab lish a correlation between the simple wedge peel test and the DCB test for interlaminar fracture toughness. The demonstration of such a relationship w ill lend validity to the wedge peel test, and enable the development of opt imal placement parameters more efficiently. Unidirectional composite specim ens of both wedge peel and DCB configurations were fiber placed at various processing conditions using the NASA Langley Automated Fiber Placement Faci lity. The DCB interlaminar fracture toughness and the wedge peel strength w ere 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 a nd the fracture toughness occurs with increasing processing temperature due to increasing resin flow. Peaks in both the wedge peel strength and DCB fr acture toughness data are seen to occur at very similar processing conditio ns. Similarly, both peel strength and fracture toughness decrease with incr easing processing temperatures beyond those which provide peak strength dat a. This decrease is due to possible thermal degradation of the resin. In vi ew of these findings, it is suggested that the wedge peel test can be used for fast and efficient characterization/qualification of interlaminar bond quality.