Notch (engineering)

A Notch in mechanical and materials engineering refers to a deliberately introduced v-shaped, u-shaped or circular defect in a planar material whereby stress is concentrated. Notch geometries play an important role in fracture mechanics and materials characterisation. Notches are most often found in impact testing of materials where the presence of a crack origin of controlled morphology in necessary in order to achieve standardised characterisation of fracture toughness. This is most commonly realized using the Charpy impact test , in which the impact of a pendulum hammer with a notched specimen and the height of its subsequent swing is used to infer the energy absorbed in fracture of the specimen. Impact testing of notched bars is also applied in the Izod impact strength test. Notched specimens find use in other characterization protocols, including tensile testing and fatigue.

Types of Notches

V-Notch

Sharp tipped V-shaped notches are often used in fracture toughness testing for materials of high ductility and for the characterisation of weld strength.

Crack Repair

Drilling a circular hole at the tip of a propagating crack can be used as a method for reducing crack tip stress concentration and preventing further propagation.