16-04-2012, 03:13 PM
FRACTURE MECHANICS
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Introduction:
Through the ages the application of materials in engineering design has posed difficult problems to mankind. In the Stone Age, the problem was mainly in shaping of the material. In the early days of the Bronze Age and the Iron Age the difficulties were both in production and shaping. For many centuries metal working was laborious and extremely costly. Estimates goes that the equipment price of a knight and horse in the 13th century was of the equivalent price of a centurion tank in Second World War.
What is crack?
Partial breaking of a material is called crack. Initiation of a crack begins due to repeated cyclic loading which causes localized changes in the structure of the material further leading to fracture.
What is fracture?
A fracture is the local separation of the body into two or more pieces under the action of stress. The word fracture is often applied to bones of living creatures, or to crystals or crystalline materials, such as gemstones or metal.
. Cleavage Fracture:
Cleavage fracture is the most brittle form of fracture that can occur in crystalline materials. Brittle cleavage fractures in ships, bridges and tanks have made it a notorious type of failure. Cleavage Fracture is encountered in cases like low temperatures and high strain rates. Cleavage Fracture of metals occurs by direct separation along crystallographic planes due to simple breaking of atomic bonds. Its main characteristics are that it occurs with a particular crystallographic plane.
Ductile Fracture:
Fracture occurring under the single application of continuously increasing load can be either brittle cleavage fracture or fracture associated with plastic deformation, which is essentially ductile the most familiar type of fractures by overload in tension, which produces the classic cup and cone fracture.
How does it happen?
We have seen cases in which fracture has occurred in static condition after prolonged loading conditions and stress. But here is another case where in the fracture has occurred in the dynamic state or in simple words the fracture has occurred during motion.
Conclusion:
Fracture is an unpredictable phenomena,the only solution to this is by proper design and using of modern manufacturing techniques. Quality of material plays an important role in robustness of the product.