Chevron-Notched Specimens for Measuring Adhesive Fracture Toughness

Abstract

The Mode I fracture toughness of a nylon-modified epoxy adhesive joint has been measured using a chevron-notched specimen. Special data reduction techniques were developed for this bonded specimen. The fracture toughness KIc, and corresponding fracture energy GIc, for the adhesive were extracted from the Kc measured for the joint, and the toughness calibration (K-to-G) was shown to be insensitive to adhesive thickness. The measured KIc values were found to be reproducible and reasonable when compared to values reported for other toughened epoxies. Using this technique, we found that the toughness increased slightly with mouth opening rate (or crack velocity), decreased with adhesive thickness over the range 50 to 375 µm and remained fairly constant with temperature until Tg (glass transition temperature) was approached.