1. Types of Fracture

2. Types of Fracture in metals
The concept of material strength and fracture has long been studied to overcome failures.
The separation or fragmentation of a solid body into two or more parts, under the action of stresses, is called fracture.
The introduction of malleable irons during the revolution of material construction led to the perception of brittle and ductile fractures as well as fatigue failure in metals.
Ductile Failure
Ductile fracture involves a large amount of plastic deformation and can be detected beforehand
Brittle Failure
Brittle fracture is more catastrophic and has been intensively studied
Failure in metallic materials

3. Ductile vs Brittle Failure

4. Example: Failure of a pipe

5. Factors affecting modes of fracture

6. Failure modes

7. Evaluation of Ductile and Brittle Failure
Ductile failure has extensive plastic deformation in the vicinity of the advancing crack. The process proceeds relatively slow (stable). The crack resists any further extension unless there is an increase in the applied stress.
In brittle failure, cracks may spread very rapidly, with little deformation. These cracks are more unstable and crack propagation will continue without an increase in the applied stress.

8. Brittle Failure
Arrows indicate points at which failure originated

9. Theories of brittle fracture
Griffith theory of brittle fracture The first analysis on cleavage fracture was initiated by Griffith using the concept of energy balance in order to explain discrepancy between the theoretical cohesive strength and observed fracture strength of ideally brittle material (glass).
Irwin and Orowan modified the Griffith theory to include plastic deformation at the crack tip.
Griffith reasoned that a preexisting crack could propagate under stress only if the release of elastic energy exceeded the work required to form the new fracture surfaces. However, his theory, based on energy release, predicted fracture strengths that were much lower than those measured experimentally.
Orowan realized that plastic work should be included in the term for the energy required to form a new fracture surface. With this correction, experiment and theory were finally brought into agreement. Irwin offered a new and entirely equivalent approach by concentrating on the stress states around the tip of a crack.

10. Griffith’s Fracture Theory

11. Griffith’s theory of brittle fracture

12. Modified Griffith equation

13. Thank you