The effect of geometric constraint on mixed mode crack paths

A study has been undertaken on the effect of geometry on mixed mode crack paths. In order to do this, a family of specimens were adapted from the common form of bend specimens used for mixed mode testing. Side grooves of different geometry and size relative to specimen width were expected to constrain the path of mixed mode cracks which would otherwise tend to a mode I crack, via a branch from the initial plane of the crack. A database of stress intensity factors were derived from finite element analyses of the specimens and used to quantify results from a testing programme. The geometry of the side grooves was shown to be an important factor on the influence through the thickness of the specimen. Although none of the specimens tested produced an effectively constrained mixed mode crack, it was supposed that there is an optimum size of side groove relative to the thickness of the specimen. The testing programme had not extended far enough in the time to cover the speculated optimum value. Angles of crack branching correlate well with a well-established criterion, even with side grooved specimens. Other factors that were considered were the through thickness variation in stress intensity factors compared with the final crack profiles, and the incident angles at the intersection of the crack front with the free edge of the specimen