Material Science: Factors causing Brittleness in Materials

Below are the various factors/conditions under which material behave in brittle fashion:

  1.  Low temperature aiding stress increase to move dislocations. At, higher temperatures then the brittle-ductile temperature, the material yields plastically
  2. Surface Condition/Finishing free of defects results in limited plastic deformation caused by dislocation motion. Presence of surface flaws makes crystals prone to brittle failure
  3. Grain Size and the Stress Required to Move a Dislocation: the stress to nucleate a crack by slip intersection increases with decreasing grain size.  Thus, fine grained materials have a lower transition temperature compared to coarse grained materials
  4. In Polymeric Materials molecular motion is frozen below glass transition temperature causing viscous flow or high elasticity restricted.  Thus polymers behave brittle under these conditions and this behavior can be explained by Griffith theory.  
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