| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 87 === The main purpose of this research is to investiage the chemical
stress induced by diffusion. There are tow general diffusion
processes of constant surface concentration source and
instantaneous surface concentration source are applied to
diffusion process. After the initial and boundary conditions
are obtained, we utilize the Laplace or Fourier-Lapalce
transform skill to solve the partial differential equation of
diffusion. The derivation of stress distribution arising from
the solute diffusion is similar to the thermal stresses arising
from the heat transfer. Some important results in this thesis
are concluded as following:
(1) If the concentration for instantaneous surface source is
equal to that for constant surface concentration, the chemical
stress for instantaneous is greater than that for constant
surface concentration.
(2) The concentration or chemical stress distributions are
similar to that of thin plate when the ratio of outer radius to
inner is near 1. For instantaneous surface source, the The
concentration or chemical stress distributions are similar to
that of solid cylinder when the outer radius of hollow cylinder
is much greater than that inner radius.
(3) There exists a time dependent function of surface
concentration which control the stress under the threshold value
to induce plastic deformation, i.e, it is the fast diffusion
process without plastic deformation.
(4) For composite hollow cylinder, only radial stress apply on
the surface of interface. The magnitude of the radial stress
depends on the diffusion time, Young''s modulus, the ratio of
diffusion coefficient, partial molal volume and chemical
potential of media.
(5) The chemical stress will enlarge the diffusion coefficient
and speed up the diffusion.
(6) In a grain boundary diffusion of thin film, the chemical
stress in grain boundary increase with increasing film
thickness. When the film thickness is large enough, the stress
or concentration distribution in the grain boundary can be
simplified as semi-infinite model.
(7) In the mass transport of glassy polymer, the maximum stress
occurs at the absorption surface and in the initial diffusion
time. The value of the maximum stress is $-E\overline{V}C_0/3(1-
\nu )$。 For given time and thickness of polymer, the
displacement of two side absoprtion is the same as the one side
absorption. Comparing the threotical and experimental
displacement curves, we can obtain the solvent of partial molal
volume in polymer.
(8) In the mass transport of glassy polymer, the chemical
stress for viscoelastic model is smaller than that for elastic
model. The same trend is also for the strain energy.
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