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Fundamentals of Fracture and Ductile Fracture and Brittle Fracture
Fundamentals of Fracture
Fracture is a form of failure, and is defined as the separation or fragmentation of a solid body into two or more parts under the action of stress. Fracture that occurs over a very short time period and under simple loading conditions (static i.e. constant or slowly changing) is considered here. Fracture under complex condition, for example alternating stress, is considered in later sections.
The process of fracture can be considered to be made up of two components, crack initiation followed by crack propagation. Fractures are classified w.r.t. several characteristics, for example, strain to fracture, crystallographic mode of fracture, appearance of fracture, etc. Table-8.1 gives a brief summary of different fracture modes.

Shear fracture, promoted by shear stresses, occurs as result of extensive slip on active slip plane. On the other hand, cleavage fracture is controlled by tensile stresses acting normal to cleavage plane. A shear fracture surface appears gray and fibrous, while a cleavage fracture surface appears bright or granular. Actual fracture surfaces often appear as mixture of fibrous and granular mode. Based on metallographic examination of fracture surfaces of polycrystalline materials, they are classified as either transgranular or intergranular. Transgranular fracture, as the