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Wednesday, 14 October 2015

METHODS OF PROTECTION AGAINST FRACTURE

               As per Griffin's theory surface cracks are more effective than internal cracks and causes brittle fracture. The surface crack of length C has the same effect as internal crack of length 2C. Fatigue cracks often propagate from the surface inwards. Protection against fracture or failure by crack propagation, in many cases, involves the following precautions and prevention steps:

  1. Use fine grained polycrystalline materials which offer good protection against brittle fracture.
  2. Avoid sharp corners and notches in the parts to eliminate points of stress concentration (one may take care of it at designing stage itself).
  3. Provide better finish to the surface, by polishing, it offers better protection as it removes some of the cracks from the surface.
  4. Avoid impurities in the base metal as well as during welding process.
  5. Introduce compressive stresses on the surface to counteract the tensile stress causing crack to propagate.
  6. Stress applied should be parallel to the direction of elongation.
  7. Use composite/reinforced materials to provide protection against brittle fracture.
  8. Ensure proper distribution of solute atoms in the metals to prevent the formation of brittle phase at grain boundaries.

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