Crystal defects - stress and strain

7 important questions on Crystal defects - stress and strain

Difference true stress-strain curve and engineering stress-strain curves

stress is calculated by dividing the applied force by the Original area of the test specimen

Some linear elastic materials and some non-linear elastic materials

linear=structural steel, glass, carbon fiber, aluminum alloy, polystyrene
nonlinear=concrete, cast iron, rubber, natural rocks, PVC

Volume expansion materials with poissons ratio under 0.5



is final volume
V0 is Original volume
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Yield point linear elastic materials

point where linear proportionality ends

Elastic recovery linear  elastic material

parallel line to the elastic deformation line in a diagram

Finding yield point non-linear elastic metals

construct line parallel to linear elastic portion of curve starting where it intersects a certain strain value( usually 0.002) the other end of the line is the yield point

Hall Petch relationship



is yield stress (MPa)
is a material specific constant (related to stress needed for dislocation movement MPa)
is the material specific constant (MPa)
d is the average grain diameter (m)

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