1- author predicts that the future will1- author predicts that the future will

1-     Linear Elastic Fracture Mechanics (LEFM) is a
theory which was first introduced by Griffith in 1924. LEFM is a theory of
fracture which deals with sharp cracks in elastic bodies. It is based on the
assumption that the material is isotropic and linearly elastic. With this assumption
in mind, LEFM has been developed using the stress intensity factor (K) which is
determined by the stress analysis and expressed as a function of stress and
crack size. There are three modes of fracture. Mode 1 is where crack surfaces
move opposite and perpendicular to each other, while modes 2 and 3 involve
sliding and lateral tearing. It is important to note that LEFM only works when
inelastic deformation is small compared to the crack size.

 

2-     The author predicts that the future will include
applications of fracture mechanics in tiny functional devices that need to have
structural integrity. While these applications are outside traditional
engineering problems, they can be solved using the current techniques.

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3-    Griffitth’s main discovery on
fracture mechanics was energy balance for cracked body. His motivation was to
understand the effect of scratches on fatigue. Previously it was thought that
it should be possible to estimate the fatigue limit of a scratched component by
using the maximum principal stress criterion or the maximum principal strain
criterion. Using the results of Inglis, Griffith showed that the scratches
could raise the maximum stress or strain by a factor from 2 to 6. However,
Griffith discovered that the maximum stress or strain would be the same on a
shaft of 1 in regardless of whether they were one ten thousand or one hundredth
of an inch deep which forced Griffith to reject the earlier belief. This led
Griffith to conclude that certain minimum work was needed to produce a fracture
and saw the fracture problem an extension of the elastic theory of minimum
potential energy. in addition, he was also able to realize the critical strength
depended on the crack length. Griffith performed his experiments on model glass
material. His experiment showed that the tensile strength of glass was lower
than the theoretical strength, thus making him believe that glass had internal
flaws.

 

4-    Orowan’s work led to believe that
Griffith’s work was for less brittle materials. Irvin, using Orowan’s work
noted that the energy expended in the plastic straining could be estimated.
Finding that the fracture energy was two thousand times the surface energy,
Irvin theorized that Griffith’s theory could be used if the plastic work were
to be substituted for the surface energy thus modifying Griffith’s theory.