محاضرة رقم 19

Fracture can take place in essentially two ways , either following macroscopic yield when the fracture is said to be ductile failure, or without macroscopic yield, when it is called brittle fracture.

Experimental studies of brittle fracture can be divided broadly into two types, those that are undertaken with a view to understanding the details of what happens during fracture and those that are aimed at providing engineering data about a polymer. Experiments of the former type are often designed to test the predictions of a theoretical model, whereas experiments of the latter type are performed in a way that accords with some recognized international standard.
The Griffith theory is concerned with the elastically stored energy near the crack, whereas the Irwin model is concerned with the distribution of stresses near the crack. Both theories apply strictly only for materials that are perfectly elastic for small strains and are therefore said to describe linear elastic fracture mechanics.