Introduction to Fracture mechanics Definition of fracture Simple

Introduction to Fracture mechanics

Definition of fracture Simple fracture is the separation of a body into two or more pieces in response to an imposed stress that is static (i. e. , constant or slowly changing with time) and at temperatures that are low relative to the melting temperature of the material. The applied stress may be tensile, compressive, shear, or torsional.

Definition of fracture mechanics and toughness. The study of how materials fracture is known as “fracture mechanics” and the resistance of a material to fracture is known as its “toughness”. The theory of fracture mechanics assumes the pre-existence of cracks and develops criteria for the catastrophic growth of these cracks.

Accidents reported in 19 th century. � � � � Out of 2500 liberty ships built in world war II, 145 ships broke in two. Steam turbines 1950. Framed welded tankers 1954. Comet aircraft 1955. King bridge in Melbourne 1962. Pleasant bridge in Virginia 1967. Tank Barge vessel 1972

An oil tanker that fractured in a brittle manner by crack propagation around its girth. (Photography by Neal Boenzi. Reprinted with permission from The New York Times. )

A natural gas pipeline that failed during field testing. From E. Parker, Brittle Fracture of Engineering Structures, Wiley, 1957, p. 269.

A ship that fractured while in port From C. F. Tipper, The Brittle Fracture Story, Cambridge Univ. Press, 1963.

Crack modes: - I- Opening mode in tensile. II- In plane shear mode. III-Anti plane shear mode.

Photoelastic fringe pattern associated with a particular crack geometry.

Griffith crack theory � Griffith noted in 1921 that when a stressed plate of an elastic material containing a crack, the potential energy decreased and the surface energy increased.

Irwin theory

Stress intensity factor for different states: �

The End